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MG Midget and Sprite Technical - long brake pedal

Update on my MG recomissioning. It doesn't leak fuel anymore, it starts and I've driven it round the yard of the lockup it currently lives it.

So progress, but still a few bits to sort, first of which is the brake pedal which doesn't appear to do much until it's within about an inch of the floor.

Front calipers + rear cylinders are new, originals having siezed while in storage. Brake pipes are also new in copper, originals being steel and rusted. System has been filled with new fluid and bled through using both pressure bleed and conventional method with an assistant. No air comes out. Rear brakes adjusted.

Only bit that is not new is the master cylinder (tin can type) which was just cleaned as it appeared to be working fine.

Ideas?

AdrianR

The two obvious possibilities are air, which you've discounted, or an issue with the master cylinder.

When bleeding manually, is fluid expelled as soon as the pedal starts to move, or does it not come out until the pedal is near the floor - as per your 'long' pedal?
Dave O'Neill 2

reckon your cylinder is the culprit then Adrian, lack of use takes its toll on these things if my experience is anything to go by
P Bentley

Especially on a newly set up system, I would adjust the rear brakes up fairly close - so there is some drag, but not so they overheat! They will quickly centre and adjust themselves, but this will give less travel at the pedal. If the rears are adjusted too slack it has a very significant effect on how well the front brakes work!

The other thing is to use it for a bit, then re-bleed the brakes. My belief is that however well you bleed them, with a newly filled system there will be air bubbles trapped in odd corners. Driving will shake these up and they will rise and coalesce into air bubbles that can then be bled out properly. Part of the "shake down" process.
GuyW

Dave - hard to tell as I can't be at both ends at once. Fluid seems to flow out readily when bleeding but perhaps not as much as I expected per stroke.

Guy - yes, will cross my fingers, turn around 3 times backwards and perhaps it will have magically fixed itself when i go back!

Failing that looks like I will have to get a M/C rebuild kit.
AdrianR

Adrian,
as you've got to use the car to properly bed the brakes in and iron out the wrinkles and shake it down all three may well prove Guy's point correct about the bubbles rising (like an over fizzed imitation lager or over prized grape drink).

It'll take a long time of course if you're just driving it round the lock up yard, as soon as you can you want to go for regular reasonable length drives and then things will start to drop in place more (or drop off :)
- or highlight what's wrong). :)

Don't forget tyres are a big part of braking I'm sure you'll have added new tyres rather than storage tyres but the new tyres may also need scrubbing in so as not to add to the low pedal.

Talking of which one of my initial thoughts was whether an oval to the pedal hole and/or worn pedal bush and/or bolt might be contributing to the problem.

Have a look in the Archives or even recent threads before ordering a M/C rebuild kit.
Nigel Atkins

ETA: Believe me I know how annoying it is when things don't go well with the car and it's tempting to replace parts to put an end to the issue but patience and more time and testing can work out better and less expensive than replacing parts - not that I don't think it's the number thing on a car to have the brakes in good condition so if in real continuing doubt then perhaps spend to get things sorted.
Nigel Atkins

Not sure if previously discussed but have you checked the run out on the brake discs?


GN Rowles

No hocus-pocus in my suggestions, Adrian. Just practical and logical principles.

Of course they won't work for pessimists.
GuyW

Hi
Not sure what model you have but my frogeye has a tandem master cylinder with push rods. If they are not adjusted correctly, I think that may give the symptoms you are suffering.
Hope you get it sorted
Graham
Graham V

Guy, I agree, bubbles may move or coalesce with use, or more probably a bit of use and then a bit of non-use.

I went and had another drive this evening. Pedal improves with pumping, but then goes long again almost immediately. Doesn't feel like I think a duff master cylinder ought to - if the piston was sticky and not going full travel then I'd expect the first part of the pedal to feel slack. Pivot has only very minor play, enough to account for 1/2" not 1/2 travel.

So perhaps there is still air, or there is some other spring force acting to push shoes/pads back such that they need half a pedals worth of fluid to take effect again.

So maybe get a very patient assistant and bleed it again before pulling anything else to bits.


AdrianR

It does sound like there is still air in the system.

My "use it for a bit and then re-bleed" would usually involve a 20 mile journey, which is sufficient to shake out the bubbles, then park up overnight and re-bleed the following day.

Another bit of "trickery" is to press the brake pedal right down and wedge it there with a length of wood, propped against the front of the seat, or against the floor cross member. Leave it wedged like that overnight after which you may find the brakes behave themselves. I don't know why this works, but it does on some occasions.
GuyW

Adrian,
as it's so easy why not give the wedged pedal trick a try and if that doesn't work then as it's quick and easy give Guy's other idea a try, have the brake shoes dragging a bit and see what difference that makes to the pedal and that might give you more direction to where the fault might be.
Nigel Atkins

No MOT so I'm limited to private land for now. I haven't come across the wedged pedal trick before, but sounds easy enough to be worth a try.

Any experiences with reverse bleeding? Seems to be possible on bikes just using a syringe but do cars need specific kit to do it reliably?

(might as well have a picture of the state of play)


AdrianR

Adrian,
there's stuff about reverse fill in the Archive, I'd try the wedged pedal first.

A quick look at your car shows it to be, like mine and many others, not quite factory standard so I'll put something I thought but didn't put earlier, are all your brake components matching each other and as an overall system (I had better words for what I meant earlier but can't think of them now).
Nigel Atkins

ETA: I've also seen that using the conventional method with an assistant on an existing M/C could introduce air, as you pump the piston rod passed its normal movement point of wear, so might not help but hinder in your case.
Nigel Atkins

Adrian. to diagnose your problem, and prove this fault, if you clamp off all the flexible brake pipes, and then try the pedal, if you get a good pedal with all the clamps on, you will know the problem is on the other side of the clamps, get an assistant to remove them one at a time while you check the pedal travel, if on removing one, the pedal drops, then you will no where the fault is, if with all the clamps in place you still have a bad pedal, then you will know the fault is between the master cyl and the clamps, I have had a number of new calipers in the past that have had very tight fitting seals, causing the pistons to retract to far, and this has caused excessive pedal travel, if this is the case remove the pads and pump the pistons out, (BUT NOT RIGHT OUT) then push them back in, do this a few times, until they free off, clamping off the front flexibles, will help prove if this is happening, this will cut out all this guess work and save you a fortune in brake fluid, and can be done without going out the workshop and save running into the back of someone while your trying them,
Andy Tilney

That is an embarrassingly good idea and good info.

But personally I'd still do the wedged pedal trick first as it doesn't require the availability of a glamorous assistant and the need to jack and support the car again (and rubber flexi-hoses?).
Nigel Atkins

Nigel there's nowt clever about that, its standard practice,and has been used to test for brake faults as long as cars have had hydraulic brakes,
Andy Tilney

Andy,
idea was the wrong word, I really meant it had yet to be suggested.

Sectioning to problem solve is obvious - after it has been thought of or suggested. :)

Can Goodridge metal braided hoses be clamped without spoiling?
Nigel Atkins

Goodridge braided hoses cant be clamped off, which is another reason, to add to the list of why not to buy them.
Andy Tilney

OK Andy, you've dangled the bait so I'll bite = what don't you like about Goodridge braided hoses?
Jeremy MkIII

I am of the opinion, that the main reason people fit these hoses to standard production vehicles, is so that they can bore people to death in the pub about how much better their brakes are since they fitted these hoses
Andy Tilney

I have them fitted, but rarely go to pubs these days.

The real problem with them is that you cannot check the condition of the inner pipe encased in the outer SS braid.
There are records of them bursting under heavy braking, because the connection to the tubing to the metal ends has deteriorated. Originals are well made and probably last a lot longer than copies which will surely be offered for sale. As they cannot be properly checked, the only safe thing would be to treat them as a service item and routinely replace them every 3 or 4 years.
GuyW

Clamping off sounds like a useful diagnostic technique. Fortunately I don't have braided hoses so I can try that.

I do have new calipers, so pull-back from the seals on those is a possibility. I also have some springy anti-squeal shims now which I didn't previously. They came with the fitting kit and were on the parts diagram so I installed them.

There should be a tinkering opportunity sometime over the weekend, I will report back after that.
AdrianR

Andy,
I'm a bit disappointing with just the main reason I was expecting a list

. . . I'm joking, I do understand about the pub bore sort but what if the braking is better for them despite the many other possible reasons for it. My beef is with not trusting modern rubber after having numerous problems with piss-poor rubber on fuel lines, gaiters, coolant hoses, seals, suspension bushes and wiper blades.

Are modern made rubber brakes hoses well made and trustworthy do you know?
Nigel Atkins

Thanks Andy,
I was expecting you to say what Guy picked up on i.e. checking their condition.
I too have them fitted plus silicone brake fluid - sorry can't stay, just off for a pint :)

Nigel,
100% agree especially fuel hose, even the R9 type can be poor quality, hence only using Esso super unleaded as it doesn't contain ethanol.
Jeremy MkIII

Nigel, I understand your concern over inferior brake pipes,and yes I am sure you are right, but if you buy them from an unknown source, or the ones made in someone's garden shed in China,then what do you expect, if you stick to a reputable make i.e Delphi, then you are fine, I always chuckle to myself when someone tells me they have goodridge brake hoses,electronic ignition, silicon brake fluid, cross drilled discs, brake pads made of the same stuff as they use on the space shuttle,if our type of cars are looked after correctly and serviced correctly, and not messed about with, they are very reliable and safe,and don't need any of this stuff, my car is as it left the factory 48 years ago, I am driving to Vienna in it in a couple of weeks
Andy Tilney

Guilty as charged!
I have 3 of the 5 items on your list and several others to boot.
Each to their own Andy.
Have a good trip.
Jeremy MkIII

I guess I am like others that look to fit the best or what we perceive to be the best quality parts we can afford to our cars in an effort to make them 'better' and by that I include safer, more reliable etc.
I agree that properly serviced and maintained the original spec is probably good enough, but to me a marginal increase in theory alone that something may decrease the chances of me being stuck on the side of the road, is tempting enough.
I have electronic ignition, I have SS brake hoses and I have four pot calipers on standard discs . . . but as has been said before none of this will work any better than standard if there is air or a fault with the system as appears to be with the OP's car.
P Bentley

Update. I left the pedal wedged for a week while I was away. When I got back it seemed a bit better initially but then started to go long again.

When I get some enthusiasm back I think I'll try removing pads and working the pistons a few times as suggested earlier. I haven't tried the clamping off yet.
AdrianR

Adrian,
thanks for reporting back even if it wasn't good news at this point.

It's good that you have some enthusiasm to return with, I just return to doing stuff on the car more often than not because I have to rather than want to - and brakes are always a have to.
Nigel Atkins

Since it was I who suggested wedging the brake pedal I should apologise that it hasn't worked on this occasion. A pity.

Does your car use an adjustable push rod between the pedal lever and the m/c - if so, is this set correctly?

Have you checked that the pedal pivot point hasn't worn oval?

Is there debris/sediment visible in the M/C showing from damaged or rotted m/c seals?
GuyW

Hi Adrian I was interested to see how you got on . I replaced most parts on mine as you have with similar symptoms, put through more than a litre of fluid with three attempts going round the car with a gunson eezibleed and was just about to give up when I got some pedal . It is still better (harder ) on the second press hoping it will be ok for MOT . As well as using the eezibleed I got a better fitting flexible tube for the nipple and submerged the end in fluid . I was surprised with 20psi how slow the fluid moves at the rear when the nipple is opened . My advice , try one last time
Mike Fairclough

Gday
"Only bit that is not new is the master cylinder (tin can type) which was just cleaned as it appeared to be working fine"
My apologies if I have missed in all the above that you have rebuilt or replaced the MC.
IMHO the MC is the culprit, at the moment you are just chasing your tail until you eliminate it from the equation.
HTH
Rod
R W Bowers

MC has not been rebuilt yet. Seal kit is sitting on the bench, but as I say enthusiasm currently lacking for going through all the messy stuff again. Give me a couple of weeks.
AdrianR

Adrian,et al, I had a similar issue with my 79 B. I would lose fluid with no sign of a leak and got a long pedal as well. It turned out the O-ring seal on the M/C failed and the fluid was being drawn into the intake manifold and was mixed and burned with the fuel.

Replaced the M/C also adjusted up the rear brakes. I would be a bit concerned about clamping the flex hoses for fear of internal damage regardless of its manufactured material.

Keep us posted as to your progress.

Cheers

Gary
79 MGB

PS Where in Bucks are you?
gary hansen

Gary clamping flexible rubber brake hoses is standard practice, providing you use proper hose clamps, and don't go mad when you tighten them up it is no problem, the only way you will damage them is if you don't use proper hose clamps, and if you do overtighten them,
Andy Tilney

Worth bearing in mind that with new unbedded brakes you'll tend to get a longer and slightly springy pedal. This will improve once all the surfaces match one to another. Also try hooking up the eesibleed with about 20 psi and see if the pedal improves - often a sign of duff M/C seals.
f pollock

Update - removed and rebuilt the M/C over the Bank Holiday. Didn't look too bad, just a bit of gunge at the linkage end. Not refitted yet. Ordered some hose clamps as well just in case.

@Gary - a few miles from Aylesbury if you know the area.
AdrianR

Refitted, seems much better so seems that yes, there was some lost travel in the master cylinder. Hopefully that's the last of it and I can now think about presenting it for an MOT.
AdrianR

This thread was discussed between 17/07/2017 and 03/09/2017

MG Midget and Sprite Technical index

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