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MG MGB Technical - Clutch problem

Hello,

I bought a B having a clutch problem. First I believed it was faulty hydraulics. I rebuilt master and slave wich were not leaking and I replace the bottom hose. I repaired the play at two forks and it does not solve the problem. The car doesn't was to engage in 1st, 2nd and reverse; with some effort it engage in 3rd and 4th. I measured the lower arm travel as mentioned in Moss catalog and it appears to be 3/8" as stated. What could be the problem, is it really the clutch? What else should I do to be sure I will not remove the engine for nothing.

Thanks.
Jean Guy Catford

When I pulled the engine out of my A--I found that the bushings on the clutch fork pivot had worn to such an extent that the bushings were completely worn through and the holes that they were pressed into were now egg shaped. Pivot bolt was worn to about 3/4 of its original diameter as well. This can definitely cause some serious clutch efficiency issues. Had to junk that fork, fortunately I had another from another engine that only needed new bushings, as those too were showing wear. I believe that, with a bit of perserverence, you should be able to remove the rubber boot from the clutch fork and,. with an inspection mirror, check for play.
R. L Carleen

On some cars, installing the clutch plate backwards will cause this. I don't know if it's the case in an MGB.

I'd guess that if the pilot bushing (spigot bushing) is turning the input shaft then that might cause these symptoms. That would probably be caused by incorrect installation, not wear.
Matt Kulka

Just thinking out loud --

If the release, or throw-out bearingwas worn too much, i'd think you'd get some grinding of the transmission gears.

First thing that comes to mind is, perhaps a air bubble within the hydraulics -- that slave unit can be a bear to bleed completly.

Perhaps excessive play on the withdrawl lever ---Moss part # 330-240.

Just for the heck of it, try a new clutch pedal return spring -- this brings the pedal back to "home" and is connected to the clutch pedal.

Just some thoughts-ideas.
glg

A precision, the lady that owned the MGB told me she used her car as a daily driver and one day used the clutch ceased functionnning. I found a lot of paly at the 2 forks(push rod). I was surprised that the clutch was operationable with such a bad status. The clutch does not seem to have air bubble in hydraulics but its like a 1/8" is missing at lower push rod
Jean Guy Catford

Jean, Do your geras grind trying to select reverse, in that case the clutch if at fault. If as you say all travels are correct and we must assume that it is properly bled then you will unfortunately have to have the engine out. Check the fork pivots at the same time. I feel that the diaphragm spring is collapsing so you should fit a three part kit, disc, cover and bearing. At the same time you must check for presence of oil on the friction faces or leaks which may just be starting at the engine rear main bearing or gearbox input shaft and rectify before putting the engine back in again.
Iain MacKintosh

Jean,
You could also check the transmission oil. Does is it have any or is it too heavy? Otherwise it appears you've tried all the easy things.

Doug
D. Cook

You can remove the transmission without removing the engine but it is not for the faint of heart.
Disconnect battery.
Undo four drive flange bolts to drive line and push drive line backward (compress slip joint) and then remove the two rear tranny x-member bolts and loosen the front two. dis-connect the speedo cable, reverse wire and OD wireing (if you have it).
Remove transmission input lever (shifter). Disconnect clutch slave cylinder from tranny bell-housing.
Remove starter. Dis-connect muffler strap from tranny x-member (if you still have it), dis-connect all tail-pipe hangers and dis-connect ground strap. Loosen front engine mount nuts several turns. Place jack with suitable blocking under oil pan, just in front of back mounting plate. Take tension off x-member and remove bolts.
Loosen transmission mount bolts a little. Remove all but two top ones. Lower tranny onto blocking (or tranny lift) such that the shift tower is well below the bulge in the tunnel. Remove upper bolts. Carefully slide tranny back and off. It can be done lying under car but it requires a considerable amount of grunt. better to have a separate floor jack with appropriate adaptor installed.

After repairing clutch stuff, installation is, as they say, reverse of removal.

Mike!
mike!

Oh heck, is it really worth all the effort.
Iain MacKintosh

Jean,
1. Can you select all gears esily with the engine off? IF not its in hte transmission.

2. How does the pedle feel. Should be little free play. With out the return spring the pedal should rest lightly on the master. There should be about 1/2 to 1 inch free movement in the pedal. Then press the pedal to the floor. Should be a firm, smooth, and even travel all the way down.

A spungy pedal indicates bad hydralics.
excess freeplay could be caused by worn fork/piviot or an improperly installation.

Hope this helps
Doug Gordon

Mike, I'm curious if you have removed a four synchro transmission using your method? I have been told it isn't possible without removing the shifter tower and rotating the transmission. Two of the NC MG car club members removed one from a 79 and had to rotate the transmission after removing the shifter tower. I don't know if their car had an overdrive.
http://www.ncmgcc.org/Newsletter/0402/page5.html
Clifton
Clifton Gordon

Hi,

Thanks all and I will definitely have a look inside wich is a promise of a fun" week-end.

Cheers
JGC
Jean Guy Catford

I don't know squat about MG trannies but I have rebuilt several other types of trannies and basically they are all the same. After checking the clutch fork for play I think you should check your shifter rods and the balls that hold the shifter rods in place - usually called detent balls - they can hang up and make shifting hard if not impossible. Worn shifter rods can cause the problem and worn shifter forks don't help either. The shifter forks are pegged to the shift rods using roll pins and I have seen trannies where the roll pin broke causing a shiftless condition. When rebuilding trannies for myself I drill out the rod and fork holes so I can use 2 roll pins together.

Just a thought.
Mike MaGee

Jean,
You still haven't answered the point as to whether you can select reverse silently. If it is impossible to select reverse without grinding then it IS a clutch problem but it selection of reverse is sil;ent then Mikes point is very valid except for the fact that the selectors are fixed by pinch bolts instead of roll pins.

I still have a feeling that it is the clutch that's at fault but you must clarify the point to be sure.
Iain MacKintosh

Sorry Iain,

To answer your question: definitely if I tried to place it in reverse it exhibits an unpleasant grinding noise. My basic problem was to discriminate between hydraulics missing a bit of more displacement or may be a warp clutch. I wished that it was faulty hydraulic but a clutch problem is nearer the truth.
Regards,
Jean Guy Catford

Jean,

That's hit the nail on the head now. There can be now doubt that it's the clutch that's wrong and provided that you are confident that the hysraulics are OK then you will have to fit a three piece clutch kit as my earlier post.
Hope it goes well.

Never fear.
Iain MacKintosh

Clutch piston travel should be 1/2" to 5/8", not 3.8". Wear in the clutch slave pushrod, forks etc. will not affect clutch travel as it is taken up by the hydraulics in exactly the same way as wear in the friction plate and release bearing. Wear on the linkage at the pedal end *does* affect clutch travel though. And grinding in reverse *is* a symptom of insufficient clutch travel as well as a warped plate.
Paul Hunt

Also, if you sometimes hear growling noises when the pedal is depressed to the floor, this is indicative of the clutch rather than the hydraulics. I had this going on for years and was always worried that something bad would soon happen.

Last year I started off and the growling became intense. I also lost the ability to disengage. I made it back to the house and just as I was parking, there was a loud bang and the engine stopped.

Upon removal, the clutch fork was bent into a new form and the clutch was in pieces.

What happened was that the carbon ring in the throw out bearing wore down to the metal supporting it. When the metal comes in contact with the bearing plate on the clutch (which has 3 flats on the edges and for the life of me I have never been able to figure out why) the whole thing comes apart rather violently.
Richard Smith 1

I have what appearsto be an identical problem. While out driving a few weks ago I started to lose the ability to shift cleanly (clutch not disengaging entirely). I ordered a replacement kit from Victoria Briish that included everything but the metal tubing and the fluid (master cylinder is a new plastic reservior type, Taiwan), and after bleeding nearly a quart of fluid through it (repeated bleedings) the pedal still does not fully disengage the clutch. Travel on my slave cylinder is 3/8". I haven't been able to determine what the correct travel should be.

The clutch has about 20,000 miles since I replaced it, and when I replaced I used a ball bearing throw out bearing, not the originally supplied carbon.

I removed the rubber bellows seal from the crank arem that operates the throw out bearing, I can see no problems. When I actuated the crank arm by hand (using a lever) I can feel the pressure plate releasing properly.

Any thoughts?

I am really not looking forward to pulling the tranny or the engine yet again.
Bruce

Hello,
Paul in reply to my post you wrote that travel of lower arm should be 1/2" to 5/8" not 3/8" as stated in Moss catalog. As I rebuilt both cylinder and replaced bottom hose, what could be responsible for a shorter travel and what should I do to regain a normal travel. I bleed extensively and no bubble is coming out. Also I blocked lower arm from moving with welding vise to check if a spongy pedal is present. The result is a not spongy at all.

Cheers,

JGC
Jean Guy Catford

Pauls point is a very valid one and I think the only lifeline that you have left before taking the box out. He advises removing the clutch pedal and master cyl pushrod and checking for wear. Gradually welding up the holes and then dressing, drilling and reaming the holes for a new clevis pin. Apparently this gave nearly an inch difference in engagement point at the pedal but I don't know what this would relate to an the fork. If you have jammed the fork you can check pedal free play quickly by depressing it gently by hand. The hose has nothing to do with travel unless of course it was balooning which it isn't as your pedal is solid. I think its time to bite the bullet.
Iain MacKintosh

JGC

I recently had my gearbox out and had trouble bleeding the clutch. I tried a bout five times with no bubbles and still had problems shifting gears. I took the B to a clutch & brake shop and asked them to power bleed. They didn't have the correct fitting so did a manual bleed twice and I'll be damned if it didn't work. Shift fine now. They are just tricky things to bleed.
I did read an article on one of the MG website that talked about using a gunson Exi-bleed in reverse. Connect it to the slave cylinder nipple and bleed up to the master cylinder. Advice was that this worked well.
Cheers
Ray
RM Taylor

My best bleeding of the clutch was by letting the fool thing sit for a day and night.
I was frustrated by the lack of "pedal" after numerous attempts at bleeding so I walked away for a day.
Picking up again the next day I noticed that the fluid was down and the pedal was hard. Topped up then bled once more to remove last stubborn bubble and all was well.

I am suspicious of the assembly when I hear that the car was just purchased... Perhaps the PO did it wrong (wrong part or installed backward) or the shop he/she took it to messed it up.

mike!
mike!

I only wish the "let it sit" idea worked. I let the car sit overnight and tried it,no dice. I then let it sit for a few days with no luck. Tough to believe it still needs bleeding. I have pumped a lot of fluid through it already.
Bruce

Jean When a clutch pressure plate packs up the throw out fingers vary in hight (distance from the thrust)so in the case of a self adjusting clutch like the B the high one adjusts the clearence but the clutch does not disingage untill all three are down. In the B its a diaphram which is a series of fingers but it does the same thing. It usually means a cracked diaphram and used to be common in early dia.type clutches.
As for bleeding the clutch it can be done by clamping the slave piston hard in, displacing any air while bleeding. I think the first part is what Lain meant.
Denis
DENIS

Jean, you've already said that the pedal is solid when you tie the fork so the bleeding is OK. Provided that the pushrod holes and clevis pin are not completely shot and I doubt if they are then Denis is absolutely correct. That's what happens to the diaphragm spring and you just have to have the whole thing out.
Iain MacKintosh

Bruce,

Regarding the "let it sit" idea. It works best if you let it sit with the clutch pedal held to the floor by a piece of lumber wedged against the seat frame. The sitting gives the air in the system time to rise to the high point (a few inches from the master cylinder). When you let the pedal up the fluid rushing back into the master cylinder carries the air bubble with it.

However, I've heard more than one say what RM does about pushing fluid up through the system from the bleed nipple. All seem to agree it's a good method. Someone recently claimed they did it with a pump type oil can. Didn't even use the EZ-Bleed.
Matt Kulka

Hi,

Now it is evident that the is faulty. I bleed it from the bottom with a fluid toward the master and it didn,t change nothing. And to be sure I measured the displacement of the lower arm on my B-GT and it is the same observed on the B. I will definitely replace the clutch. My only concern is at the exhaust manifold stud which are pretty rusted.

Cheers,
JGC
Jean Guy Catford

Well, it has set with the clutch pinned to the foot well with a board, released and reset again several times, no luck. I tried another trick from another sites bulletin board (forgive me) and tried pumping a lot of fluisd through with just my thumb on thje bleed port, no luck.
The most travel I have seen from the slave is just under 7/16". I am unhappy to say the least, as well as covered in DOT 3. I have a tough time beliving the clutch itself is bad, my shifting gave out gradualy over the course of a half hour or so, as if it were a hydraulic problem.

I did have a clutch flex line (hose) failure, so replacing the whole shootin match made sense. This ain't rocket science, what the hell am I missing?
Bruce

Bruce,

I believe a travel of lower arm of 3/8" is adequate as written in Moss cat. ( I think that extremly rarely Paul is in the field with a longer displ.) My both MG have a 3/8" at the lower arm and one is functionning perfectly and the other not. You are facing the same problem I do. It is at the clutch level...
Cheers,

JGC
Jean Guy Catford

Check the pushrod going from the clutch pedal to the clutch master cylinder. They are often worn and are not a part of the rebuild kit. Moss supplies them as a seperate item. My daughter's car had exactly the problem described, which came on as she was driving in city traffic down in Tucson. Ernie, at Ernie's Brit Cars, checked out the system, replaced the MC pushrod and the car has worked fine since. Old pushrod had its clevis pin hole worn to twice the original diameter. Now, I replace the MC pushrod as a part of clutch MC rebuild. Les
Les Bengtson

Jean,

I talked with an aquaintance here in town that worlks pretty much exclusively on British cars. He was pretty sure that the slave cylinder travel should be 1/2" at a minimum. He did note that the arm travel inside at the throw out bearing was less, presumably due to the shorter distance from the pivot point.

Is it possible that the Moss catalog is talking about the arm travel on the opposite side of the pivot (fulcrum) from the slave cylinder?

There was no grinding or slipping of the clutch, no unusual noise from the clutch prior to the failure.
Bruce

To further Les' comment (and as noted on the other clutch thread): You can get an incredible amount of wear on the clevis pins or the holes they're mounted in up at the clutch pedal and down at the slave cylinder. I had a clevis pin that was literally worn halfway through the shaft. That coupled with the hole in the clutch pedal starting to oval eventually made it so the clutch was barely releasing.
Matt Kulka

Paul Hunt pointed this out about 15 comments back. This thread is going round in circles folks. I'll try to measure fork travel on one of my cars tonight and post it tomorrow.
Iain MacKintosh

I have come to the conclusion that the NEW master is crap, and Victoria British is sending me a replacement. To be on the safe side I am also getting a set of seals to rebuild the original master cylinder in case the second Tiawanese unit is also a dud.

I put a 24" crescent wrench (spanner) on the clutch lever and measured the actual stroke required to release the clutch after contact of the throwout bearing to the pressure plate fingers. 1/2" is the required travel I measured at the point where the slave cylinder push rod is pinned to the clutch lever arm..

I unbolted the slave cylinder (hung loose on the hose)and I had my wife press the clutch pedal to the floor with just my thumb providing a small amount of resistance at the slave piston, and the slave only traveled 7/16". That is the maximum travel I had observed at any time. I had achieved that same 7/16" of travel with the system fully assembled. It is definitely NOT enough to do the trick. I do not believe that there is any air left to be bled from the system.

When I recieve the parts and install them I will post the results.
Bruce

I just replaced the clutch master cylinder in my car. It was an original design from Moss. It was manufactured in England in June. Who says the only available units are the cheapo Twaiwanese? Ray
ray

Victoria British is claiming that is all they can get. I didn't put much stock in the statement, I just know that is their position. I am stuck cause I already spent the money on the stuff. I wasn't going to put it in at first, but I didn't want to wait any longer to fix the car, and the shipping charges from Vic Brit are very high, so eating that wasn't appealing either.
Bruce

Jean,
Just crawled under my car and took the measurements. Pushrod moves 7/16" exactly and this is sufficient to provide full release of clutch. However I must stress that any less is definitely not acceptable as I rekon that I have some play at pedal clevis and that if I rectified this I would get a bit more. Your 3/8 IS NOT ENOUGH and you should rectify this before going any further.
Iain MacKintosh

Epilogue,

Well it was like that: Once upon a time a nice little B having ...
Seriously,I removed the engine-trans last W.E. and the clutch disk was discombabulated with 3 rivets at the center broken and two springs missing. It was an easy task to do and I must admit the advice concerning derusting seized bolts and nuts by heating and using a candle as penetrating oil worked fine. It appears it is an "old yankee farmer's" trick. I removed the 6 exhaust nuts easily in opposition to the ordinary assle.

Thanks all for your advice.

JGCatford
Jean Guy Catford

Thanks Iain,

I have the new master cylinder in hand and I will install it tonight or tomorrow. I also have a rebuild kit for the original master. The answer will be forth coming.

Hey Jean,

When your clutch started to fail to disengage, was the failure abrupt, or did it fde out slowly like mine did? I would like to know how they failures would comparison. My clutch just started to shift hard slowly (over about 1/2hr.), then pretty much not at all, but the failure was pretty progressive. I imagine that broken rivets and popped springs would be a pretty fast and noisy failure. Let me know if you would,thanks.
Bruce

Hello,


It fade out slowly and one morning nothing was functionning. This trouble was not noisy at all and this was the part of the puzzle, it was hard to believe that the problem reside at clutch level without any suspicious noise.

Cheers.

JGC
Jean Guy Catford

Also be aware that whilst wear in the mechanical linkages at the pedal end will contribute to insufficient clutch travel and difficulty in gear selection, the design of the system takes up all 'normal' wear in the mechanical linkages at the clutch end, as well as wear in the friction plate itself. You would have to have massive amounts of wear to defeat this, like a broken release bearing (BT, DT), needing succesive pumps of the pedal before the slave piston reaches the end of the cylinder and pops out with the fluid.
Paul Hunt

This thread was discussed between 14/06/2004 and 08/07/2004

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