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MG MGB Technical - clutch?? problems

My 1966 RD has had a problem ever since I have owned it (2 years) of 'crunching' shifting into 2d gear. I bought it believing the 2d gear synchro was bad. At any rate I got an opportunity to purchase a rebuilt 3 synchro O.D. box and installed it earlier this Spring. I installed a new clutch, slave cylinder, and flex line at the time.

I fought that b@*!!$ for days trying to get it bleed properly. The best I could manage was about equivalant to how it ran and shifted before the new gearbox. I finally came to the conclusion the master cylinder was not so good so bought a new 'replacement' cylinder from VB.

I put it in about a week ago, and fought the b**@#! awhile and added a few creative new words to the English language before taking it to a mechanic to get it bled. I picked it up today, and he explained he thought he had all the air out of it, but it would not quite release properly. After driving it home, I realize it is worse than before.

Coincidentally, I opened into the original 3 synchro box this afternoon looking for a serviceable set of gears for my 60 MGA project (another story). It was surprising how good condition the old box is in. It is not without issues, but the synchros look almost new, and it should not have 'crunched' going into second.

So now, 1. I don't think my guy got it bled completely, and 2., I wonder if there is another problem that I have not replaced yet. About the only part left would be the clutch pedal. I remember finding the upper hole a bit egg shaped when I was swapping the master. I am sure a small additional amount of movement could make a difference.

What are y'all's thoughts and experiences on this subject? I want to be able to drive this car!

Safety fast!

JMG
JM Greenlee

Fix the pedal (braze the hole up and redrill- it gives an excellent bearing surface for the clevis pin), and be sure any clevis pins have NO wear. A little wear here has a significant effect on total travel. It will also be worse with a new clutch as the driven plate is still "fuzzy", and you need more travel for a clean release than you will after it gets a few miles on it and it has worn smooth.
FRM
FR Millmore

FRM is correct about the clevis holes and pins, get all the wear out of them. Then crawl under the car and push the slave rod all the way back into the cylinder (or remove the rod and use a phillips screwdriver to do this). This will push any remaining air in the cylinder back into the line. Now reblead the clutch i the normal manner. You may need to repeat this a couple of times, but it will get every bit of air out of the system. Good luck - Dave
David DuBois

My thoughts are that it's a bleeding problem.

First, any wear, unless huge, will be taken up by the spring inside the slave cylinder which moves the piston out and makes the system self adjusting. This is regardless of bleeding.

Second, you can check for full movement easily by holding a steel rule alongside the clevis pin while someone presses the pedal down. Full travel should give a full 3/8" movement at the clevis. Any less and you may have air in, or there is so much wear that the slave has come to the end of its travel (which is unlikely and will also stop the pedal reaching the floor).

Rich

This is the first step as Rich says, check the fork travel. I would even say that 3/8 is too little !! It should therefore be an absolute minimum.

First things first though, tell us if you can select first or reverse silently from stationary.
Iain MacKintosh

My recommendation is based on years of experience on many cars, much of it in British only shops. If all the hydraulics are good, and all the air is out, a small amount of wear at the clevis joints at the pedal/MC can cause dragging, especially with a new driven plate. I have many times had dragging with a new plate, when there had been no trouble before and nothing in the hydraulics had been touched. Rarely, but more likely as cars get older, the pedal shaft bushing may be worn.
Dave's recommendation on bleeding is exactly right.
The other thing to check, and it is common, is whether there is carpet, mats, or padding bunched up under the pedal, limiting travel. Very common with crappy or badly installed carpets, especially if they have extra padding. Take all the carpet etc. out to be absolutely sure.
FRM
FR Millmore

Agree entirely with Dave and FRM about reeasons for lost movement but the first question must be "can a non synchro gear be selected quietly" and if not "what is the fork travel" Then we look for the reasons for shortage of travel i.e worn pins and bushes or excessively thick carpets and underfelt or trapped air. Agree that a new clutch can be difficult for a short time but that was two years ago.
Iain MacKintosh

Iain-
Agreed, but:
The rather nebulous "about 3/8" is difficult to interpret, especially for those who have not had a lot of experience. A well used good clutch can work fine with 1/4"
JM had a problem two years ago, but has since replaced almost everything, so he may well have a new and different problem, including a contributing "fuzzy" plate.
He has observed wear on the pedal clevis hole.
If he can get in 1 or R, the next question might be what oil is he using, since the problem appears to be common to two "good" gearboxes. Hypoid oil can cause this 2nd synch. trouble, especially on the early box. A lot of people report very good results from use of synthetic gear oil, but I've never tried it, engine oil as specified always worked for me. From my research, synthetic looks like a very good bet for both improved shifting and wear.
FRM
FR Millmore

We're all jumping to fix a problem when we don't know what the problem is.

Iain's first post is right;

Check if the clutch is dragging by selecting non-synchro gears at a standstill. See if they crunch going in. Find the clutch bite-point and check it is well off the floor before the car starts creeping forward. If it works well then the box has a problem. Could be oil type, synchro etc.

If the clutch is dragging, or you're not sure, check for enough movement at the arm as first step to finding the reason why. If there's not 3/8" it could be air in the hydraulics, worn pedal, master pushrod, carpet etc. If there is 3/8" it could be sticky splines, oiled plate, flywheel or cover runout, tight or misaligned spigot bush etc.

Rich

Spot on Rich. I can never agree however that the B clutch is difficult to bleed if strict guidelines are followed. Fit a ring spanner over the nipple then push a piece of TIGHTLY FITTING CLEAR plastic tube over this with the other end in a jar containing 1/2" of fluid. Fill the master cylinder. Get an assistant to sit in the car whilst you go underneath. Slacken the ring spanner 1/2 turn only, ask assistant to depress pedal. Tighten nipple with pedal on the floor. Lift pedal,, slacken nipple and carry on this sequence. After about five pumps top up the master.

This proceduce does not take more than about six or seven pumps before fluid can be seen to flow clean and have no bubbles.

Now the words in capitals are vital otherwise there is a risk of air entering the bleed tube and you will be unsure of where it came from.

I was also taken by Paul Hunt's suggestion of bleeding in reverse via the front NS brake bleed nipple, perhaps I'll try that one day.
Iain MacKintosh

Just like to add an extra:
When I beld my clutch a few weeks ago I could not get a decent pedal - despite doing it as above.
Gettign annoyed, the next time the pedal was fully depressed I also pushed the pushrod on the slave cylinder back. Cue, sputtering and lots of air. I did this about 3 times, in conjunction with the assistane pushing the brake and the pedal feel was spot on afterwards and worked fine.

Tony
T Crossley

Tony, take it you mean "pushing the clutch" and not the brake !!!
Iain MacKintosh

Update:

Today I spent most of the day driving the car down to a British car specialist down in Arlington. The car was marginally driveable, but as it was almost all freeway, I managed it with a minimum of shifts. The whole staff looked at it with the conclusion that it was moving the fork plenty far enough to operate.

Suggested problems are:

1. Defective clutch. (I installed a rebuilt clutch bought through O'Reilly's. My guy said he had a lot of problems with rebuilt MGB clutches and only fitted new Borg and Beck clutches.

and/or

2. Clutch disk installed backwards.

I guess I will have to pull the motor once more to get it going. I plan to install a NEW Borg and Beck clutch when I have it apart.

Safety fast!

JMG
JM Greenlee

Good, you're homing in now. It would be hard to fit the plate backwards, not impossible, but the centre would make horrible noises on the flywheel I think.

A new B&B with attention to other points will hopefully sort it, "sticky splines, oiled plate, flywheel or cover runout, tight or misaligned spigot bush etc".

I'd check the flywheel runs true on the shaft. It's also possible the cluch plate centre was bent during fitting the gearbox which would cause drag.

Rich

Just thinking on that last point, a recon might already have had a bent centre if it had just been relined without checking. When you get the new plate spin it on the gearbox shaft to be sure it's true.

Rich

I've never heard of a rebuilt clutch. I know we used to reface them and that they were at one time exchange but that must have stopped 40 years ago. Now I do remember fitting a disc the wrong way round but that was 40 years ago as well but it did make me very careful for future and I don't think you can fit a B disc reversed as the hub contacts the flywheel before the facing does. Frankly I'd take the whole car back to O'Reillys, demonstrate the problem and demand a Borg & Beck for free and make them pay the bill for fitting !!
Iain MacKintosh

This thread was discussed between 03/07/2005 and 11/07/2005

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