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MG Midget and Sprite Technical - Still struggling with 1275 clutch

Seems like I only visit when I'm at the end of my wits. And here I am again.

This spring after working on the gearbox over the winter, I backed the car out of the garage, drove a few yards, decided the clutch wasn't disengaging well enough, backed it up and drove it back in the garage.

Bled the clutch, but ended up with no clutch at all. Replaced all the hydraulics: master, metal line, rubber line, slave, and pushrod. No change in my situation.

The pushrod lines up with the lever without pushing the pushrod into the slave much at all. That's not right. So I pulled the engine and gearbox again. The clutch release lever does not appear to be bent, but I haven't yet removed it to lay it on a flat surface. The release bearing still has 10 mm of carbon thickness, and is well proud of its holder. The bushing on the release lever seems fine.

I should mention the clutch, pressure plate, release bearing, and other parts were all replaced in 2002, but only 26,000 miles ago.

There are probably mistakes I could make that no one would think of, but I did have a competent, mechanically knowledgeable friend over this evening and it's not something obvious. I've got the release bearing the right way round, the lever is right, the slave is right.

I was hoping that maybe we would find the clutch itself was somehow stuck in the wrong place, but it doesn't seem to be. The part that mates with the release bearing is about flush with the back of the pressure plate when it's mounted on the flywheel. When it's removed from the flywheel, that part stands proud about the thickness of the part. The clutch is not worn out.

I'm ready and willing to replace the clutch, pressure plate and release bearing. Probably will no matter what.

The weather here is great in New England, and this is the first time in driving season that I've been sidelined.

I'm hoping for ideas. Thank you.



Mark 1275

Mark
To me the pressure plate looks about the right height
but if the pushrod was only just into the slave, it nearly has to have a bent release lever or realy badly worn lever pivot
If the new pushrod is the exact length of the old one and slave is identical to the old one as far as offset from the boltholes etc it's about all it can be
Did the original pushrod enter further into the original slave cyl---

There is the posibility that all this part of it was working ok but maybe by accident the clutch plate itself got bent while removing / replacing the gearbox during the winter overhaul job--if it's bent the pedal feels normal but the clutch won't clear with the pedal down and it will crunch into the gears at standstill, sometimes that bad that you won't be able to select a gear at all---might be worth pulling it off and give it a spin on the gearbox shaft to check, it should run straight but probably 1/16" runout is ok but if it's got say 1/8" or more there is an issue

willy
William Revit

Have you checked the driven plate is fitted the right way round? One side is marked 'flywheel side' but it can be hard to see.
Other than that I agree it's likely to be a bent release arm. If you need one and have difficulty finding a good one over there, I have plenty of spares.
David Smith

David's suggestion would certainly fit the symptoms, including the fact that the clutch didn't seem to fully disengage when you first backed out of the garage.

The clutch centre has a longer "nose" on one side of the plate. This goes away from the flywheel. If you fit it the wrong way around this part touches the flywheel, holding the friction surface of the plate slightly clear of the flywheel face. The pressure plate will bolt up but this has a similar effect to an over thick friction surface and the diaphragm spring fingers don't then protrude out as far as normal. The result, via lever arm and pushrod, is that the slave cylinder is right at the outer end of its travel. The hydraulics, if bled properly, will still work, but the pressure plate won't pull back far enough to properly disengage the clutch.

GuyW

A worn out clevis hole in the clutch pedal arm will add to the problem. Check there is no excessive play in that area.
C MADGE

Thank you for the responses.

The pushrod is within a couple of thousandths, old vs new. I did modify the old by threading in a bolt to experiment with a longer length, but I did take measurements before.

Before last night, I'd not removed the clutch since new in 2002, so although it might be an issue, it wasn't subjected to any stress I know of over the winter. I may have distorted it last night, but I don't think I could have before then. The engine was pretty well protected, sitting on an engine stand out of the way.

I did make certain when I removed the clutch last night to reassemble with the "nose" pointed away from the flywheel.

I was really hoping to find a bent release lever when I removed it tonight. It looks pretty straight to me. The photo angle shows the gap from the flat surface as best I can. And there isn't more than a few thousandths play in the bushing the lever pivots on. Just the slightest movement.

It just doesn't make sense to me. I appreciate the ideas, and I hope there's something more for me to check.

Frustrating.



Mark 1275

Sorry for this rather obvious one Mark, but the lever arm is fitted the right way round? The open side of the claw ends facing forwards towards the clutch?
GuyW

Yes, the lever arm has been the right way round. It does seem it has to be something major and obvious like this, but this isn't it.
Mark 1275

Have you recently replaced the thrust bearing? There are 3 different ones depending on engine size, and a lot of the shallower 1098cc ones are sold as being for the 1275 which is wrong, they don't work properly.
David Smith

If the engine is still out, it is worth bench testing the clutch action to confirm it is free.
(remove clutch and flywheel, assemble as a unit and us drill press to push on the thrust pad of the pressure plate). That way you can confirm there is nothing odd going on there and know for sure the problem is elsewhere.
I suspect it's not relevant here, but we did once find a clutch plate with slighty thicker linings causing the problem. The position of the centre of the diaphragm was further in as a result, and by the time it was pushed in far enough to release the linings it was touching the centre of the plate, causing it to drag.
We have had a couple of other plates with oversize linings but not quite as thick. They resulted in a sweet spot where the clutch would release fine, but more pedal would cause drag.
I suspect they were all relined plates rather than new ones, using incorrect linings.
Paul Walbran

The other measurement that is useful is the stroke at the slave cylinder. If less than normal then the problem is in the hydraulics. If normal then the problem is in the bellhousing.
If greater than normal the hydraulics are wrong, a common mistake to be fitment of the 1100 slave cylinder which is only 7/8 rather than the 1" of the 1275. (This can result in over stroke of the diaphragm and contact with the plate as per last example in my previous post.)
It is a simple and very useful diagnostic step.
My only problem is that the normal figure has escaped my memory! Perhaps someone could help?
Paul Walbran

I know it is 11mm for MGB. I think 8 for 1275 but not sure.
Paul Walbran

Thank you for the responses, David and Paul.

I hope to get out to the garage tomorrow.

I'd say thrust bearings have not been changed.

I'll check the clutch operation on the bench. When I put the gearbox back on the engine to see if we could operate the clutch using a pipe on the lever, we couldn't make it work. I don't remember if it was because there wasn't enough travel in the lever after it touches the clutch, or if we couldn't bring enough force to it, which implied something else was wrong.

I had notes about the movement of the slave, and IIRC it was 8 mm. The master was 30 mm.
Mark 1275

When I converted my 1275 clutch to a concentric slave I measured the movement at the release bearing as a maximum of 11mm. I wanted to be sure that the new slave arrangement didn't overthrow the diaphragm so this was a maximum allowable amount. The concentric slave bearing remains in constant contact with the clutch when at rest so there is no lost movement and less than this 11mm max will disengage the clutch when in actual use.

Given the positioning of the lever arm pivot at around 1/3rd of the way along the arm, this would suggest more than 11mm at the external slave, not less.
GuyW

Hi Mark, just a thought for you,have you checked the spigot bearing bush in the back of the crank. If this has disintegrated or fallen out ,the first motion shaft could be moving causing a problem.
TONY GRIFFITHS

Hi, Tony. I do know the spigot bush is present, and was replaced back in 2002. I'll check it for play and see if it's worn.

Didn't get to the garage this weekend, but hope to early this week.
Mark 1275

I will be traveling to Foxboro, MA next week. Not exactly in your backyard but I can make a side trip to put another set of eyes on the situation. I would like to see it out of the car depending on how quickly you plan on getting it together. You have my contact info, let me know if I can help. John
J Bubela

Thank you for your offer, John. Email sent.
Mark 1275

The clutch is painful to bleed, are you sure that you don't have air left in it? Any air at all and the clutch won't work properly. A small master cylinder reservoir and in innacesible bleed nipple much lower down combine to make it very tricky. Takes me about 3 attempts every time to get a clutch pedal.
R Cohen

Appreciate your comment, and it's time for an update.

Although I haven't had insurmountable problems bleeding in the past, I did put a lot of effort into the bleeding this time. Did the process several times, and even with the slave cylinder in my hand with the piston pushed all the way in and fastened in place. I can't be certain I've got all the air out, but I've sure given it my best effort.

The visit from John from Connecticut was very helpful. He knows a LOT about midgets, and he was very generous with his time. I'd say we didn't find a smoking gun - something broken or installed backwards - but he opened my eyes to many small problems.

The two areas that seemed to most get his attention were the throwout bearing, and the play in the pedal at the clutch clevis pin. I'll post pictures when I'm home this evening, but I've now got a new throwout bearing, and I restored the hole in the pedal with the welder and a file.

The lever is definitely straight, even though I know a lot of my information points to that being the problem.

I appreciate that I haven't been forgotten, and I sure hope the latest batch of new parts will give me a working clutch. This is the first summer in 17 years I haven't been able to ride around with the top down, and I miss it.
Mark 1275

Here's what the hole in the pedal looked like to start with. Compared to an old one I received in a lot on eBay, it looks good, but the elongation does cause noticeable play.



Mark 1275

Added some weld with the MIG on both sides.


Mark 1275

Ground flat and filed to the original 5/16" hole. It's now a good fit to the clevis for the clutch master cylinder.


Mark 1275

David Smith (see above) makes a valid point about the release bearing. I have had two complaints where people have, allegedly, had 1098 release bearings supplied in 1275 clutch kits. The 1098 release will work but due to the different offsets is like fitting a part worn 1275. Then when viewed after time you may be led to believe that it is but a barely worn 1275.
Worth checking your offset!

I seem to be one of the few that has no trouble bleeding a 1275 clutch but what do I I do, or have, that is different to others. 3/4" master cylinder; 1" slave; stock Quinton Hazel 1275 clutch cover, hybrid clutch plate (I have a T9 5 speed gearbox) and, of course, one of my own roller release bearings.
I don't believe that I do anything strange?
I do use silicone fluid, and have done so for circa thirty years, on all of my cars.

I do have a remote bleed, fitted with a Goodridge automatic bleed valve, that sits under the bonnet. To bleed I just undo the valve which, apart from being automatic has a sealant on the threads to stop fluid leakage / air ingress, and then I just pump the master cylinder by hand watching fluid egress at the valve whilst topping up at the master cylinder. Simples!

Below is an article submitted to Midget & Sprite Magazine about getting rid of the air bubble.



In his article ‘On bleeding the clutch’ Dr John Davies explains how it is possible to trap a small pocket of air in the clutch slave cylinder that, seemingly, no amount of bleeding will shift.

When it comes to component castings it appears that they can vary manufacturer to manufacturer and even type to type so what applies to the slave cylinder that I have modified may or may not apply to every type. The casting that I have modified is from an unknown manufacturer and supplier and is of one inch bore as fitted to 1275 A-Series engine cars. At some point in the ‘mists of time’ I have had a stainless steel liner fitted. It is of the type that carries it’s seal ‘piggy back’ upon the piston. The piston is designed, stepped at its rear face, for loose attachment / alignment of the return spring. There is no piston retaining circlip on ‘my’ clutch slave cylinder.
The other type of slave cylinder generally has a piston then seal, a seal spreader, and a smaller diameter return spring.

The modification is only applicable to those that have already fitted, or are willing to fit, a remote bleed system as described in my June 2018 Mascot article using a flexible hose. That is because the drilling removes the bleed nipple seating that would also be necessary to support a remote bleed with a brake pipe instead of a flexible hose.

Simply I used an 8.5mm (3/8” UNF tapping) drill to drill down through the bleed nipple port and remove the seating for use with a nipple or hard line pipe. In this case the the remaining hole removes the cavity where the air bubble previously hid. Any slight burring around the hole, that cannot be removed, where it breaks into the operational bore of the slave cylinder, is well away from any contact with the piston and rubber seal.

The enlarged hole can just be seen, at the top of the cylinder, at the far end of the bore in the picture.

As an addition to the remote bleed I also use a Goodridge automatic bleed valve.

Bleeding should be possible as a one man operation not from within the vehicle’s cockpit but under the bonnet just by applying pressure, on and off, to the clutch slave cylinder pushrod where everything is within sight and reach.
Alan Anstead

Maybe not pertinent to this discussion but I'll mention it anyway as a heads up in case it is of use in the future. A neighbour has a FIAT X1/9 and needed a new slave cylinder due to the original leaking, once the new aftermarket cylinder was fitted no amount of normal manual bleeding, vacuum bleeding or pressure bleeding could shift any fluid through the system so they were about to try and change the master cylinder which can be a PITA but they pulled the new slave and examined it and the original and sorted the problem. The OE cylinder had a shoulder at the inner end of the bore to stop the piston, the new one did not and so the piston had gone to the extreme end of the cylinder and blocked the fluid port, once repositioned away from the end it all worked and bled fine.
David Billington

Trying to think of possible causes for this-
just by chance, your slave cylinder bleeder is in the top hole and not the end like it comes new in the box-------? It"ll never bleed properly with it in the end

willy
William Revit

A couple of videos which may help.

https://www.youtube.com/watch?v=_1vz-8Q_Qpg
https://www.youtube.com/watch?v=SRHUsCaK3LE

f pollock

Thank you for the ideas.

The first thing John said during his visit was that the release bearing looked like it might be for a 1098 cc. A new 1275 one looked almost 1/8" taller. The new one will likely be installed this weekend, along with the new clutch.

The bleed hole on the slave is definitely at the top, and I'll bleed it holding it in my hand at the angle that lets the air bubble come to the top, and then install it on the gearbox. This shows the old and new, and I'm sure I'll appreciate the few minutes it took to slot the mounting ear to make that top bolt a lot easier.



Mark 1275

Any advice for replacing the bushing in the clutch release lever? Does it push out pretty easily? Maybe using my drill press?

There is a noticeable difference in the play with the new bushing.

I have a little arbor press, but don't have a fitting of the right size to match up with the bushing.


Mark 1275

The old one came out pretty easily, just tapping with a makeshift drift. But the new one is all of 0.008" bigger OD. Is it meant to be altered by the installer?
Mark 1275

I’ve never replaced one, but .008” is quite a difference. I can’t see it going in very easily.
Dave O'Neill 2

Warm the arm up in he oven and chill the bearing in the freezer perhaps?
Although I thought they were just a simple press fit.
GuyW

I’ve just partially removed one to measure and it comes in at .433” with two different digital calipers, but .436” with a micrometer.

What measurements are you getting?

You might be able to fit it using Guy’s method, but you may well need to ream it to size, afterwards.


Dave O'Neill 2

The old is 0.432”, the new is 0.440”. The opening in the lever is 0.433”.

Wonder if Moss would have a suggestion.
Mark 1275

The last one I got was from AH Spares and it was a simple push fit. The bush you have may be bad batch.
Bob Beaumont

Thread it onto a nut and bolt, fasten in a drill chuck and use a flat file againt the outter surface as it rotates in the drill to take 3 or 4 thou off it?

Anyone can tell I am not an engineer but in this application that is what I would try.
GuyW

From the dimensions mentioned I would assume this is a standard 7/16" OD oilite which come in 1/4" and 5/16" ID, 7/16" is 0.4375" so from one source online the 0.440" seems about right for the dimension prior to fitting, see https://www.hpcgears.com/pdf_c33/4.8-4.13.pdf for one source. I wouldn't rely on the OD of a previously fitted oilite as they do compress slightly and it seems from the measurement variations mentioned the instruments could do with being verified against a suitable standard to give an indication of their accuracy and possibly re-zeroed.

Mark,

As you're in Massachusetts any chance anyone you know has a set of slip gauges. I lived for a few years in Manchester Connecticut and plenty of stuff around due to the industry in the area. My slip gauges are on the wrong side of the pond.
David Billington

For reference the H8 housing tolerance mentioned in the HPC page would give a permissible hole size in the clutch release arm of 0.4375" to 0.4385".
David Billington

I've fitted quite a few of these bushes over the years and have always removed and fitted new ones with no special tools. Always a gentle press fit. I put the old bolt through first, get them started with a light pin hammer. Remove the bolt and finish them in a vice. Use a new bolt on reassembly.
David Smith

Dave, thank you for checking with the one you have.

Guy, you and I think alike - hot and cold, and taking a bit off the OD with the drill press or the lathe. I'll see what Moss says in the morning before I try altering the bushing.

David, I'm not sure what I should be doing with slip gauges. My father-in-law has many tools and may have them. Would they provide a more accurate measurement of the ID of the opening in the lever?

Not that it will help me with the fitting, but am I supposed to soak the part in oil before installation?

Thank you for the ideas. I was hoping to make real progress on the reassembly today, but this kind of sidetracked me. The improvement in the amount of play with the bolt makes replacing the bushing worthwhile. I'm looking for all the thousandths improvements I can gather.
Mark 1275

David's on the right track as you would expect.
First run a 7/16" drill gently through the pivot hole to clean it up, then lightly countersink one side, if you have a countersink cutter.
Yes - oil the oilite bush, even if it's pre-oiled. Use the Willie Revit process. Place the bush on the palm of your hand and fill with gear oil. Press hard with your other thumb on the open end. Repeat until you can see oil sweating out of the bush.
Press the bush into place using your drill press or a vice. I doubt you'll need to do any further machining, except possibly a light countersink either end of the Bush just to eliminate any possible burrs.
If the new bolt feels too tight gently run a suitable drill through the bush. We're not talking about high precision work here!
Greybeard

Mark,

The idea with slip gauges is to use them to verify the accuracy of your measuring instrument and potentially your technique https://en.wikipedia.org/wiki/Gauge_block . Slip gauges will be far more accurate than a micrometer or caliper so can be used as a standard to verify their accuracy and repeatability. My workshop grade set has the calibration chart and shows the deviation from the specified length in millionths of an inch.
David Billington

Mark, I think the bush is likely to be oversized.

As David Smith noted, I've also lightly pressed/tapped quite a few out over the years and had no issues.
I'm not sure they are oilite as the couple i've got look more like plain brass/bronze bar.

I've measured two up with Mitoyo and Moore and Wright calipers and micrometers and they come out about 0.434 average as they are not quite round.
richard b

Mark
David and Greyfella are onto it, but I can't help myself, I have to have a little say as well
Although the new bush is a larger size (tighter press fit)than you think it should be it's not really-
Being sintered bronze it is porous and when it's pushed in the outside surface will smooth out to a smaller dia.
If you look at it through a magnifying glass the surface is only partially metal and very porous and looks like a pile of sawdust- As you push it in all the peaks fold over into the crevices
Compare your old one to your new one under the magnifying glass and you will see the diff.
Just push it in it'll go--Main thing is to make sure the hole you're pushing it into doesn't have a sharp edge, just run a scraper around the edge of the hole, oil the bush up and push it in in the vice,or press if you have one, I don't think your drill press will be anywhere near strong enough to do it ,
done

Your measurements aren't quite acurate anyway

"The old is 0.432”, the new is 0.440”. The opening in the lever is 0.433”

Going by that the old bush should have just fell out at .001" smaller than the hole
William Revit

Sounds like I should be good to go. I do appreciate you taking the time to explain it, William. I've got a good vise for the task, and can set up the small arbor press if needed.

I agree my measurements probably aren't spot on using an inexpensive dial caliper.

For what it's worth, I did talk with Moss this morning. It very well may have been Guy I talked with, disguising his voice with an American accent. The advice was to take the OD down a bit with emery cloth and a drill, and then put the bushing in the freezer and warm the lever, maybe even just in the sun.

I hope to get the bushing in tonight.
Mark 1275

Got the bushing in. Took more force with the vise than I expected. I won't be losing any thousandths here now.

I did abrade the OD with 600 grit in the drill press, but it didn't take more than 0.001" off. Then put the bushing in the freezer for a while, and warmed the lever with a heat gun.

Thank you for all the advice.
Mark 1275

Back on the road!

Drove this morning to get an inspection sticker, and all went fine. I have a clutch.

I learned that even though I think parts are new because I replaced them, it's been 17 years and they can wear. I'd say the biggest improvement was the new release bearing, but replacing the bolt and bushing on the lever helped.

I also think the clutch was on its last legs last year. When shifting into first this morning, I was very cautious and it's because I've gotten used to getting a little bit of grinding going into first or reverse. Now there's no grinding at all.

Thank you for all the advice, and thank you John for making a house call.
Mark 1275

This thread was discussed between 13/06/2019 and 24/07/2019

MG Midget and Sprite Technical index

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