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MG MGB Technical - Brakes 'Hanging on'

First of all my MG is a factory V8 with remote servo. But there are no fundamental differences in the systems.
I rebuilt the car 18months ago. Rebuilt M/C, new flexibles, odd new brake lines and new rear wheel cylinders. Perfect for 12 months then brakes hanging on, sometimes full on for an age. Assumed servo! Rebuilt it, no change!! Replaced air valve several times, no change!! Replaced servo with SS sleeved unit, no change!! Thinking it might be M/C return valve, rebuilt the M/C, no change!! Can't reproduce the problem in the garage. Have observes the air valve working perfectly, but as soon as you are on the move, dreadful again. With vacuum pipe clamped, apart from dreadful brakes, the effect is reduced. Apart from callipers i'm at a loss. Help!!!
Allan Reeling

Allan - You don't say if it's all four brakes.

If it is all four, shouldn't that narrow it down, meaning that the problem is at the pedal end. If it's just front or rear the problem is more localised.

Just a thought.
John Bilham

Hi Allan, John is right.Have you tried cracking open the bleed nipple/s when it happens. Does your car have the stoplight switch that fits on the pedal box, if so the problem maybe that the switch is screwed in too far and stopping the master cylinder from recuperating. Keep us informed.

regards John
john wright

John W, been down the road of the switch which was another false dawn!!
John B, Have been trying to recreate the problem in the workshop, to no avail. It's difficult to tell when driving whether it is front or rear, or both, which would suggest pressure in the system.
I do keep returning, like a moth to a flame, to the servo air valve, but changing everything has produced no improvement.
Decided, after 3 days of changing bits and bleeding till I'm blue in the face, to resort to alcohol, as a less drastic alternative to a sharp knife or rope and stair well!!!!
Allan Reeling

To be 100% certain that it isn't servo related, have you tried by-passing it completely?
Dave O'Neill 2

Allan have you checked if there is any pressure in the system when the brakes hang up.Dave has a good point about bypassing the servo, its worth a try, a pressure gauge plumbed into the system would be a massive help.
john wright

No Dave. Not a simple task, will have to work myself up for that!! Good thought though!
Allan Reeling

Alan is there free travel at the pedal. Does the return spring on the pedal give you a small clearance between the pushrod and the master cylinder at rest.
There must be clearance to allow the M/cyl piston to uncover the return passage.Even the pedal return spring missing can cause the brakes to hang. Denis
Denis4

You mentioned that you replaced the servo with a stainless sleeved unit-
Was that the whole servo replaced or just the hydraulic section
Why I ask is--I had a servo once that had rusted the shaft up a bit between the vac diaphram and the piston and it would hang on after using the brakes, sometimes bad enough to come to a grinding halt in traffic---not a nice feeling
willy
William Revit

Denis4, Thanks for that, one assumes that's what the brass shim between the M/c and the pedal box is for. But as the problem developed one would assume it's not the problem, but will check.
William, Yes the slave replaced together with the air valve piston, SS shim, diaphragm, spring and seals. Everything else in perfect condition. Can agree about "the feeling"!
John, I have always assumed that there must be hydraulic pressure in the system, only because that what it feels like, i.e., all 4 corners ON. The why is what's defeating me. Thanks to all.
Al
Allan Reeling

Further to last post I have checked M/c piston to pedal clearance. Plenty there!
Will check front to rear line in case it has been crushed and flexible for kinking.
Allan Reeling

How long after starting to drive before this happens?

Is it every time? Or only under certain conditions i.e. temperature, particular usage, etc.

How soon after dragging or being locked on do they free up? Do you have to do anything to free them? Or does it happen by itself?

When they are locked on have you tried jacking it and seeing which wheels are locked?

Can you push fluid into the reservoir by pressing the caliper pistons back both sides? How far does the pedal need to be operated before you can't do this? The push-rod may be too long.

When the dragging happens does it pull to one side or straight? One side implies a flex hose acting as a one-way valve, or a stuck caliper.

How does the level of retardation compare with the effectiveness of the handbrake when you are moving? More retardation than pulling on the handle does imply pressure in the calipers.

My roadster servo tends to lock on in hot weather, and the symptom of that is a very hard and high pedal compared to normal. I'm assuming that's because there is hydraulic pressure taking up all the normal 'free play' in the system. A pal's V8 had it so badly on a tour we disconnected the vacuum hose from the servo and plugged it with the pointy end of a spare spark plug. Have you tried doing that?

If it still does it then as suggested I would try hydraulically bypassing the servo altogether.

If it still does it then you may need to drive it until they lock on, then open a bleed nipple as suggested and see if fluid spurts out and they free up.

Another possibility is to keep driving when they are dragging then see which wheel or wheels are hot.
Paul Hunt

Paul,
1 There is no constant time elapse. It can happen reversing out of the drive or 3 miles down the road.
2 Every time but to varying degrees. i.e., anything from hesitation to release to, "bloody hell can't move"
3. As is the nature of the beast, tends to happen when there is a queue behind you, so "gun" the engine and drag the brakes till they release, usually only a few yards. So diving underneath or jacking up is not an option! I've been trying to recreate the effect in the garage and haven't succeeded yet so that I can tell how many are locking/dragging.
4 But pulls up straight, at least suggesting it's the whole system, or at least the callipers, and it's better than handbrake!!
5. Can't see the push rod or the piston being a problem, since they are original and I haven't always had the problem. Pedal free play is fine also.
6. Have blanked off the vacuum pipe. The last time it was bad I was going to Buxton, it was the only way I could get there and back but needed two feet on the pedal, even then the braking was dreadful.

A couple of weeks ago I was timing the engine dynamically and as the engine warmed up the air valve started "whistling", as if the fluid was expanding and opening the air valve. The main reason why I started suspecting the M/c return valve.
You last point might be a goer, watch this space.
Al
Allan Reeling

Allan the servo sounds to be the problem, you need to take the servo out of the circuit and see if that helps.
There should be no M/C return valve, the M/C piston and seal at the pedal end uncovers the recuperation port when the pedal is released, this allows all the pressure in the system to fall to zero, except when other issues occur.If the seal in the M/C has swollen then that could cause your problem, but it would happen all the time.
john wright

John,
There is a valve, held at the outlet end by the return spring. I have one in my hand, there may also be a pic!!! Not entirely sure what it does or indeed how it does it. But lockheed call it a return valve!
Have checked the front to rear line for damage and also the rear flexible for kinks............no problems.

Allan Reeling

I should also add that the current servo is the third one I have fitted since the problem started!
Al
Allan Reeling

Might not be convenient with traffic behind you, but have you tried reversing when they lock to see what happens?
John Bilham

Hello Allan, does that return valve fit against the main cup seal with a spring that rests against the end of the M/C. When the brakes are working normally, then I don't think that valve has any great effect during normal braking, I believe that it only come into use when you bleeding the brake system. The valve and spring will hold the main cup seal in place, otherwise the main cup seal will stay at the bottom end of the M/C.
John B asks if you can reverse when the brakes hang up. Have you looked at the rear brakes to make sure everything is in order.

regards John
john wright

John,
The valve sits over the outlet port. i.e., the other end of the return spring.
I'm putting on hold crawling about the garage floor. Instead I'm going off to find a quiet bit of road???? with my trolly jack, old clothes and a groundsheet and see if I can at least determine just which wheels are locking up.
Will let you know,,,,,,,if I survive that is!!!!

On a related tack, thought I would show my mod to the latest servo installation. To make bleeding easier with the air valve still in it's original 2 0'clock position. Just a double banjo with a bleed nipple in the end of the bolt.





Allan Reeling

"Have blanked off the vacuum pipe. The last time it was bad I was going to Buxton, it was the only way I could get there and back but needed two feet on the pedal, even then the braking was dreadful."

Interesting, with that vacuum hose disconnected on my pals V8 the change in braking effort was barely noticeable, neither was it that different to mine - on which the servo does work.

That valve looks like a residual pressure valve which as its name implies maintains some pressure in the hydraulic system when the pedal is released. Just watched a Wheeler Dealer on the VW Thing where he converted from drum to disc, and specifically mentioned that valve needs to be removed. However I understand that the non-servo dual system used in North America did have those valves. Was it part of the new servo? Did you find one in the original? I'm not aware that the factory servo has one, I'd be inclined to remove it.

" with my trolly jack, old clothes and a groundsheet and see if I can at least determine just which wheels are locking up."

Just walk round and feel the wheels.
Paul Hunt

PAUL, Yes the valve was in the original, which WAS original! It's a strange arrangement, can't really see how it works! In itself a rare thing!! Talking to Peter at North West Automotive Hydraulics and looking at his Lockheed literature on line, it is a definite part of that M/c. Presumably it keeps some pressure in the system to reduce pedal travel? Big question is how much?
When they don't release it usually only lasts for 10yards, not sure you would be able differentiate, as there will be heat there from the initial stop.
A couple of days ago I talked two mechanics I work with, about other things, but both of them, that day, had experience shoes delaminating.
I suppose that could lock up a drum? I would check but I'm ashamed to say my wheel nut key has gone AWOL!!
Interesting about the unservo'd braking. You would have thought lack of 2.3 : 1 assistance would be noticable. Perhaps that indicates something wrong in the system.
Are you aware of any problems with Goodridge Flexibles?
My first 1800 B was servo-less and I quite liked that.
Allan Reeling

When the cap on the non-return valve on my '77B fell off and I was left with no servo, the braking effort was exactly as Allan says. The brakes were as good as useless, and I had a very slow 30kms journey home.
John Bilham

You don't say whether the pedal feel is different when they are locked on to when they are not. If the pedal is higher and harder then it almost certainly is hydraulic pressure causing the problem. If not then probably not.

And your previous comment about reversing reminded me of a problem I had with the rear brakes. Does it lock up in reverse as well as forwards? Or only when going forwards. Mine had a spell of the rears jamming on when braking in reverse such that I simply could not move backwards, only forwards. I've no idea why, I hadn't changed anything, and it hadn't done it for the first 20 years or so. Couldn't see anything wrong inside the drums, but backing the adjuster off one click 'cured' it and it has never happened again.

Which leads me on to shoe orientation. The shoes have the lining material offset on the backing plate, such that there is a section of 'empty' backing plate at one end, but not at the other. All shoes should be orientated such that, when going forwards, a point on the drum will pass over the 'empty' portion of the backing plate first.

John - if yours has the dual braking system with integral master then I understand that this does offer a lot more assistance than before as the master bore also changed.

The earlier remote servo on single line systems was optional on UK cars until 1973, and some non-North American export models until 1976, with the remainder of the brake system being the same in both cases. This type of servo only offered light assistance, as the brakes had to be acceptable when the servo wasn't fitted. Which makes me question the 2.3:1 ratio on Allan's V8.
Paul Hunt

PS. Several sources talk about 1.65:1 and 1.9:1 for the MGB. Clausager does say an 'improved' servo with a bigger bore (5/8" to 7/8") was fitted in May 1970, which tallies with the Parts Catalogue. However in a master cylinder a bigger bore would require greater effort to get the same retardation at the wheels. Is the physics different in a servo?
Paul Hunt

PPS: Browsing the parts numbers has as many claims for the later servo being the lower ratio as the higher.
Paul Hunt

Paul,
Pedal is harder and higher!! And does happen in reverse.
Have a look at this, particularly the chart at the end. My V8 slave is 5/8" bore with a 5/16" air valve piston which on a type 6 equates to 2.3 : 1. Going up in diameter, the boost is reduced as one would assume.
Shoes are correct orientation but I will back the adjustment!
Currently exploring another theory, namely the liner on the Goodridge rear flex has collapsed and is acting like a "duck bill" valve. Easy job just replace it!! Waiting on the new one.
Allan Reeling

PPPS: More browsing indicates that the 'residual pressure valve' is in fact a 'slow return valve' in that a large orifice opens to allow the maximum fluid through when you push on the pedal, but that closes when you release the pedal, and a small orifice is left which allows the pressure to bleed away more slowly. The purpose of this is apparently to allow the driver to 'pump up' the brakes in the event of a long pedal. I have noticed that effect when there is air in the system, but not normally. So locking on could be caused by the small orifice being blocked some of the time.

If the problem is excess hydraulic pressure causing all four wheels to be braked.
Paul Hunt

Paul, That valve was replaced on M/c re-build.The "small oriface is a slot, approx 5mm x 2mm sealed at rest with a strip of thin copper. You can see how it allows fluid through under pressure but not how fluid gets back through it.
Evidently it is also necessary to maintain some residual pressure in the system to keep the rear cup seals under slight pressure, to prevent seepage losses. Obviously not necessary for the callipers. But I'm led to wonder why the RPV wasn't just put in the rear line as opposed to the M/c.
Allan Reeling

You're not by any chance using silicon fluid are you? I had the same problem in my GT and changed to dot 5 fluid which cured the problem. At the end of the day I reckoned that the lubricity of the silicon fluid was not sufficient to permit proper operation of the servo and the problem was cured
Iain MacKintosh

You're not by any chance using silicon fluid are you? I had the same problem in my GT and changed to dot 5 fluid which cured the problem. At the end of the day I reckoned that the lubricity of the silicon fluid was not sufficient to permit proper operation of the servo and the problem was cured
Iain MacKintosh

"it is also necessary to maintain some residual pressure in the system to keep the rear cup seals under slight pressure, to prevent seepage losses."

That doesn't tally with anything else I have read, and I have only been able to identify the valve - on the rear circuit only - for the early North American dual circuit master. What component is it in the single-circuit master and where does it fit?

I've replaced my V8 brake master and didn't find anything like that in the old one.

"the lubricity of the silicon fluid was not sufficient to permit proper operation"

That's exactly why it's not used in ABS systems.
Paul Hunt

Ian, Lack of lubricity is only one of the failings of Silicone, would never entertain the stuff.
Paul, See my post and image above, starts "John", that's the creature!! As I said above I have a spare one and can't for the life of me see how fluid "returns' through it.
Allan Reeling

I saw the picture, and subsequently realised it was similar to the drawings of one of the components in a seal repair kit. Googling that number came up with photos of the part, and it is the same. That led me to look through my old bits from when I changed masters (binned the cans as they were perforated but kept the inners) and found two, fitted to springs.

If you look on the flat face you should see a groove, arrowed in the attached. It's this groove that lets the fluid out of the lines back into the master cylinder.

That makes it the 'slow return' valve that I mentioned, i.e. rapid pumps of the pedal will allow pressure to build up in the case of badly adjusted brakes, but it shouldn't hold any lasting pressure. If that groove is not there, too small or partially blocked by something, then it will affect how the brakes release, particularly in the last circumstance. At the very least I'd replace that valve.

But having said that because this valve is only pressed against the output port by the master piston return spring, then any pressure in the line greater than the strength of the spring will simply push the valve away from the port allowing fluid to escape past the valve flange, which has three protections on it.

Maybe a faulty valve is retaining enough pressure to keep the servo activated.

Incidentally "Have a look at this, particularly the chart at the end." did not include a link, should it?

Paul Hunt

Paul,
Answer YES there should have been a link, poised but not pasted, here it is; http://www.triumph-spitfire.nl/servoimages.htm.
Yep I see the small groove. The valve which is in now is the third one used!!! Thanks for taking the trouble.
Have changed the rear flex. Haven't driven it yet, but not confident!!
Thoroughly fed up with bleeding!
Allan Reeling

Useful site!

Both mine have got the ally tags, which have very similar numbers, but nothing like the 'LR' numbers in that table. Is that reference number on it anywhere? Or any number indicating the size of the slave and reaction piston bore? I note that Spitfire unit only has one concentric groove by the outlet, whereas mine have three.
Paul Hunt

Paul,
The Aly tags do seem to convey something about the structure of the servo. Mine is numbered 4257-792/5 N42 L34 77. As far as I can make out 4257-792 at least gives a reference for spares.
I'm told the rings on the outlet actually do mean something. Neither of my V8 units have any rings, which I'm reliably informed equates to 2.3 : 1. Which having measured the two bores at 5/8" and 5/16", matches the info on that chart.
3 rings looks like normal MGB servo. Which seems to be born out by the photo of the servo in Clausager, page 94.
Have look at this site. http://www.northwestautomotivehydraulics.co.uk/LOCKHEED%20SERVO%20PART%20LISTS.%20KITS.%20SEALS.%20&%20ILLUSTRATIONS..pdf
Allan Reeling

Hi Allan - that link didn't work for me, but in case anyone else is interested I found the page here http://www.northwestautomotivehydraulics.co.uk/lockheedcatalouges.html

Both mine are 4257 812, and it does seem to be the 3-digit code after the 4257 that indicates the type-6 assistance. The Parts Catalogue shows that the V8 had the same servo as the 4-cylinder had since August 1970, so I'mm not surprised both mine are the same. Unless you have changed the ratio of the master to the calipers and cylinders I wouldn't have though you would need the assistance to be increased from 1.9 to 2.3.

Not that that would explain the locking-on, though. I'd still be inclined to disable the servo and see what happens - carefully if necessary!
Paul Hunt

Paul, My V8 was original in all respects, I have known it since it was purchased direct from Longbridge, having been a press car. Number 13 off the production line!! Who knows what Leyland did or used though. Steve and I are doing a re-shell of a R/b factory V8 owned from new. I shall look at the servo rings, or lack of them!!
I had a play yesterday, engine running the air valve is tight shut as it should be and pops up and down with gay abandon as pedal is operated. Checked with a vacuum pump and the canister holds a vacuum, and all the usual tests involving starting and stopping the engine with pedal down etc., it does to script!
Next to check, when new wheel nut key arrives, are drums and callipers.
Allan Reeling

That early it could have had anything, and it may well have been a deliberate ploy to kid the press the brakes were really light and sensitive, such skulduggery was not unknown. I can see why you want to keep it as it was.
Paul Hunt

Have replacement wheel nut key from McGard (excellent service!), Removed rear drums,stripped, cleaned and replaced. Apart from a leaking half shaft seal (8000 miles!!!***) nothing else of issue and problem still with me. Callipers next, only thing left!!
Allan Reeling

Can't see it being calipers, if it doesn't pull to one side when it happens then both of them would have to stick at the same instant, and release at the same instant.

You can't confirm it is from hydraulic pressure with the mechanical switch on the V8, but the the servo sticks in hot weather on my 73 roadster and that causes the brake lights to stick on as well as that has a hydraulic switch. I'd be inclined to replace the 3-way union with one that takes a switch, and connect that up to a test-lamp or meter in the cabin, to prove it one way or the other i.e. hydraulic problem or not.
Paul Hunt

Interesting idea Paul. But the callipers have to be examined, then everything is checked, Probably back to square one after that!! Hey Ho!!
Allan Reeling

Yep, back to square one. Callipers functioning perfectly. Am going to swap the servo, yet again, but erring on the side of M/c.
Paul.........The '76 V8 we are rebuilding has been owned from new, servo never replaced, and it is a 2.3 : 1, i.e., no rings on outlet!
So my servo was probably not a Leyland conspiracy to hoodwink press hacks!!!
Allan Reeling

Alan

have you tried bypassing the servo yet?
Dave O'Neill 2

Dave, don't know where that would get me. The current servo is the third one fitted, all to no avail! I have acquired a known working V8 servo, that will be my last throw of the dice on the servo front, before I return to the M/c.
There is obviously hydraulic pressure in the system, which isn't releasing. That pressure will put the brakes on and will also open the air valve, but cart and horse spring to mind. Since the pedal goes hard my logic suggests the line TO the servo is not depressurising, i.e., the m/c piston is not recovering. But this M/c is the second one used and the line is new!!!***
Allan Reeling

"Since the pedal goes hard my logic suggests the line TO the servo is not depressurising"

But with the servo pressurising the system there will be negligible fluid flow from the master which will make the pedal higher and harder. The servo push-rod closes off the hole in the servo piston, and it is the servo piston that is sending pressure to the brakes, not the master. The only thing the master is pressurising then is the air valve. When my servo sticks the pedal goes high and hard, and tapping the pedal usually releases it. When my pals got so bad that we plugged his vacuum it stopped the jamming on.

I would definitely disconnect the vacuum from the servo, if not bypass it altogether. Unless your master and calipers are a significantly different ratio to those that came later, the brakes shouldn't end up any harder than the one I drove with it disabled.

The oddity - in comparison to mine and my pals at any rate - is the 76. I've had three sets of calipers on mine and a replacement master and I really don't notice any difference in pedal effort between my V8 and my roadster (both three-ring servos), nor between my roadster with and my pals without.
Paul Hunt

I say again Paul, the brakes are useless without the servo. What are you using as pad material? green stuff, for example, has a better initial bite, other makes might be different also.
The pedal can feel normal then go rock solid, but it can be rock solid on first application!! I will try the, "known to work", servo and see what transpires.
Allan Reeling

Also disconnecting the vacuum pipe, obviously only removes the vacuum from the equation. If the problem stems from the air valve remaining open, It fails to tell you why. Is it sticking or is it being kept open by non recovering hydraulic pressure? If, as I suspect, the latter, WHY???
Allan Reeling

My pads have always been bog-standard, but I can't see pad material alone making that much difference to retardation, other than racing pads needing to be hot before they work properly.

Pedal rock solid on first application i.e. when the brakes weren't hanging is a symptom I don't remember from this thread.

If you disconnect the vacuum it doesn't matter if the air valve sticks open or not, as the diaphragm won't be moving the push-rod to block the hole in the servo piston, therefore the pressure at the corners will always be released back through the master regardless.

And that brings me on to another thought. Have you always used the same push-rod with the three masters? Or different push-rods? It occurred to me that perhaps the push-rod is too long and the pedal when on its stop is preventing the master pressure seal from fully clearing the bypass hole into the reservoir. I'd remove the pedal clevis pin, and see where the push-rod hole is in relation to the pedal hole when it has come back as far as it can, and the pedal is on it's stop. If the push-rod has come back further, that could be the cause.

And FWIW I've just disconnected and plugged the vacuum port on my V8 manifold, emptied the servo till the pedal was high and hard, and driving up and down the road I couldn't really feel any difference, I was able to lock the fronts from 20mph, by steadily increasing the pressure not banging them on.
Paul Hunt

Paul......"push rod", already been there! Exactly as you describe, no problem.
Anyway the next V8 servo is on...........i.e., the "known to be working" one!!i Have still to bleed up then drive..............watch this space!!!***
Modern cars, because they are nearly always servo'd, use harder pad material, i.e., less prone to fade. But the harder material does wear out the discs faster. Changing disc as almost become as frequent as changing the pads.
Allan Reeling

"Changing disc as almost become as frequent as changing the pads."

How true. Not impressed with having to change front and rear discs with the first change of pads on my ZS. By contrast the V8 is probably on its original discs after 220k.
Paul Hunt

WELL!!!!!
The "known to work", does what it says on the tin!!! Brakes now working perfectly!!! So one has to assume the re-sleeved and re-built servo has a fault.
Are the bores too tight? Will have to investigate because "I HAVE TO KNOW"!
Allan Reeling

Well done, you need to get hold of a 120 bar pressure gauge and some fitting, that would have sorted the job out much sooner. Have a beer or 3 to celebrate.

regards John
john wright

Thanks John, will have a beer or three, Sam Smiths would do, but not available down here! Still don't think it's the air valve piston sticking, but rather the slave piston itself. Anyway it's coming apart, will see. Thanks to everybody for their input!
Allan Reeling

I take it you don't have the larger piston in the smaller bore!?

I don't think it can be the piston though, because when the air valve releases, the diaphragm and its push-rod retracts and opens the hole in the middle of the piston, through which the fluid will escape.
Paul Hunt

Allan
If that is a resleeved hydraulic unit, it would pay to check that the fluid supply holes are drilled into the sleeve in the correct size
I had a master cylinder done once and the hole was drilled too small and the cup wouldn't clear the hole in the retracted position-blocking fluid flow
Also check that the bore has been polished after the hole has been drilled,-I have seen them drilled and left sharp inside causing the edge of the hole to cut pieces off the cup and blocking the hole
Have a good look at the pushrod in the booster and make sure it's smooth and free/not rusty as mentioned back in posting no.9
willy
William Revit

Good thought Willy but the problem was a re-sleeved servo slave, not the M/c. But will check the drillings. One assumes the SS sleeves are bought honed to size. The firm I used sleeved all 3 bores. But I still keep getting "floored" by the fact that I could see the air valve working perfectly, even with the filter cap and spring removed!!
Allan Reeling

Well, on disassembly, the air valve piston was as tight as a tick! The bore of the cylinder accepts an accurate piece of ground 5/16" stock, so it's oversize, the piston itself is 0.0025" under 5/16" and is a nice running fit, but put the rubber seals on and the thing is hellish tight.
COULD IT BE MORE BAD RUBBER PRODUCT!!
Allan Reeling

OR

Remind me,it's a while since I've had one apart
Do these O rings seal brake fluid or air
If it's air only you could try some rubber grease in there
If it's brake fluid the O rings may have been handled with dirty hands during assembly , which is a well known cause of rubber brake seals swelling

There would still be drillings into the bores of the cylinder the same as a m/cylinder which I would be checking, especially for smoothness in the bore

willy

William Revit

WILLY,
The seals are hydraulic. Drillings etc all look fine. The main piston and rod move freely. You have to assume since Lockheed refer to the air valve piston as dia 5/16", that is the size. Except on the identification strap of my M/c it refers to it as 19mm, when measuring it is actually 3/4"!!!
Not knowing Lockheed's tolerances it's difficult to know exactly what size the air valve bore and piston should be.
As for dirty hands, I assembled the Servo with clean hands and clean fluid!! On clean card on my dining table no less!!!
Allan Reeling

Alan
Interesting with the metric/imperial thing
19mm--.748"
maybe it got honed a couple of though or they used imperial tubing to resleave it
Either way all that means is you have an extra two thou clearance--can't see a problem there really--better than too tight
Don't know what to suggest with the pushrod side of things, except that if they are normal shaped O rings,maybe you could get some seperate somewhere and replace them
Be carefull getting O rings from an industrial supply shop as not all O rings are compatible with brake fluid

Maybe that's the problem -

willy
William Revit

Also
Do you always use the same brake fluid
You have to be very carefull selecting the correct Dot No. fluid to match what you are using
The Dot Nos. don't run in order, they are mixed up a bit just to trick us
Check on this chart- sorry about the giant link

willy

https://www.google.com.au/search?q=brake+fluid+Dot+No.+chart&biw=1348&bih=617&tbm=isch&tbo=u&source=univ&sa=X&ei=hYZlVbXZMIHr8AX7qYDwAg&ved=0CBwQsAQ#imgrc=BDKFvamdKnQDZM%253A%3BurcVB5t7en5PtM%3Bhttp%253A%252F%252Fwww.epicbleedsolutions.com%252Fblog%252Fdot-brake-fluid-vs-mineral-oil%252Fimages%252Fbrake-fluid-compatibility-chart.png%3Bhttp%253A%252F%252Fwww.epicbleedsolutions.com%252Fblog%252Fdot-brake-fluid-vs-mineral-oil%252F%3B418%3B552

William Revit

Willy, Always Dot 4.
Have been examining the bores of this servo slave. Bore gauges show the bore of the air valve cylinder has 3 different diameters!!! Presumably the piston is jamming on the smaller ones. Need to find out what, exactly, the bore should be. Anyone out there?
Allan Reeling

Allan
I've been thinking what you could do to straighten out your air valve piston bore
Being perfectly consistent in size along it's length would be more important than the actual finished size I reckon
Could it be possible that they pressed the ss sleeve in a bit tight and bulged it in the middle when it bottomed out

I'm thinking a trip to an engine reco place would be the go and poke a valve guide reamer through it till it's straight--Luckily, being of a 5/16" bore they should have a good selection of reamers that size stepping up in minor increments till you get it straight

cheers
willy
William Revit

WILLY,
Don't think the bore should be 5/16", the piston would be tight then never mind the seals. The largest bore is in the middle, about half way down, so makes measuring fairly impossible. We had a "play" with it yesterday with various reamers, seems like it should be more like 8mm!! The big question is whether the firm buy in SS tube ground to size or not. If so then one would expect, as you and I both thought, that the size they bore out the slave cylinder is critical as the walls are fairly thin and therefore fragile,
Allan Reeling

Allan
I know this is probably not the case BUT
Earlier back in the postings you mentioned that the Id. strap on your cyl. was marked 19mm
You don't suppose that this booster is an odd-bod metric unit that has emerged from somewhere and the actuator bore is in fact supposed to be metric also, at 8mm
I realise they don't appear to list metric specs but you just never know-That Id band could just be a clew worth chasing up------or not
willy
William Revit

Allan
Been poking around and found this--if you roll down to the specs
Couldn't believe my eyes
-8mm actuator piston
Looks as though there are metric units
8mm could well be your required bore size

http://www.ebay.com.au/itm/Lockheed-Type-Brake-Servo-Booster-Remote-Major-Repair-Kit-FULL-7-7-inch-/271440604397

Hope I'm not annoying you, - too much spare time I guess

Cheers
willy
William Revit

Willy,
Annoying, you must be joking!
That's very interesting. I talked to the firm who did the re-sleeve yesterday. Surprisingly they couldn't, wouldn't, tell be the bore but did say the sleeve is made by them and honed to size. However, whether before or after installation the chap i spoke to didn't know. Either way to get a variable diameter they are doing something wrong.
I'm afraid servo play is having to take a back seat for a few days, my suffix B LT77 has given up the unequal struggle to cope with the output of my 3.9 litre V8. Suffix H going in it's place!!
Thanks for your input, will turn an accurate 8mm bar and test the other servo air valve bore.
Allan Reeling

Willy,
Been in touch with Nelsons, as per your link, they only supply the service kits, and the guy I spoke to hadn't any idea whether any of the bores were imperial or metric!!!***
I warned him that his site information could be very misleading, which he took on board.
Al
Allan Reeling

Aaahh
Thought we were onto something there--oh well
Still makes me think yours' probably should be 8mm, but it sure would be nice to know for sure
cheers
willy
William Revit

Willy,
Just a surprise, really, that you can't find out this piece of info.
On the plus side this new gearbox is a rare LT77S, super strong out of a TVR!!
Allan Reeling

Allan
So this TVR box
Does that have the same ratios as the SD1 box or is it a bit unique
Is this going in your MG or something else
Cheers
willy
William Revit

The box is to replace the one I originally mated to my 3.9, which, in turn, i had put in my factory V8 to replace the 3.5. Don't think the original early LT77 was up to handling the power and torque. 220bhp and 313 ft lbs
Not sure about the ratios, but I think the intermediate gears are the same, not sure about 5th though.
Allan Reeling

Ahh--very good
I'm a bit of a V8 junky
Did my first v8 conversion back in 1976 and have done a few since then
Mostly using the Terrior 4.4 litre engines, They are a bit of a squeeze to get in being higher in the block which makes them wider as well--Mostly use the BorgWarner single rail c/r box--It's a four speed with 2.54 first gear and direct 4th - They are a fairly bullet proof box in a small car like a B
Here's a pic of the engine during fitting in the last car I did, You can see the taller/wider block

willy

William Revit

Looks good but 1:1 top gear!!! The LT77 is 3.3 first and 0.792 5th. so much lower than yours, that's Land Rover for you. Up the side of a mountain, pulling up tree stumps!!
Allan Reeling

What have you got as a final drive? Mines a 3.07.
Allan Reeling

Tried everything
3.5
3.36
3.08
2.77
Tried 3.5 but it's too spinny, all you do is change gears all the time and go nowhere
Put a 2.77 in a mate's car and he loves it,a real cruiser
but I reckon it knocked the performance down a bit, but cruise it will
Mostly have run 3.08
IF I were building another car now I'd go 3.36 for sure and probably a T5 5 speed box,should give about 2.8 overall in 5th, but I do like the big tall 1st gear in these 4 speeds
Here's a pic of the first v8 I did back in 1976
I don't like posting pics of other peoples cars but the second pic is of the same car painted green and fitted with a shortened Jag. indapendant rear after he rebuilt the car around 1979-80

willy


William Revit

and

William Revit

Like the "eyebrows" Willy. My 3.5 started out with an MGC 3.3 final drive with the LT77, I found that a bit"spinny"and it rendered 1st gear useless, 3.07 is a good compromise of decent acceleration, enough to surprise the boy racers, and economical cruising................40mph is 1500rpm. The 3.9 has the same final drive and a better cam and it's stunning! But it can wreck gearboxes as I've found. T5's are like hens teeth over here, RPI sell them with bell housing and clutch for 4,000! We'll see how the "S" does!!
Allan Reeling

Crikey
T5s are fairly common here
Both Ford and GM have had them since about 1986
The GM unit has a very long input shaft
The Ford one is the go
Parts for them are a tiddle on the expensive side, but around here you can pick up a good useable box for under $400 if you hunt around
They are a different mounting bolt pattern to the 4spd B/W box but with a few minor mods to the bellhousing the 4spd b/housing can still be used
The B/W bellhousing is the thing that is getting a bit scarce here
There is also a Tremec version of the T5 here and is supposed to be heavier duty- I havn't had one of those apart yet so couldn't really say
cheers
willy
William Revit

This thread was discussed between 03/05/2015 and 08/06/2015

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