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MG MGA - My clutch saga continues...!

Today I was able to get my transmission back in to my car -- fairly smoothly. After reattaching the clutch slave and bleeding the system, I tried the clutch. It worked and disengaged the clutch disc. But...!!! I observed the clutch slave piston forced back into the slave by the clutch assembly springs. The brake fluid was forced out of the master cylinder cap!!!

What the heck is wrong now?!
gerard hutchinson

There may be nothing wrong. The clutch assembly springs are suppposed to push the slave piston back into the slave cylinder. This is how the hydraulic clutch is self adjusting. The overflow at the master cylinder cap should be a once only happening as the slave piston finds the proper position.
You only have a problem if it does it again.

Mick
Mick Anderson

Gerard,

My first thought is that you may still have had air in the system. How did you bleed the clutch? I've always found the two person technique (*) for bleeding the MGA clutch to work effectively.

(* Person A: clutch pedal UP; Person B: run clear hose from bleed screw into a container to catch the expelled brake fluid then slightly OPEN bleed screw on slave cylinder; Person A: smoothly press clutch pedal DOWN to the floor and hold; Person B: CLOSE the bleed screw; Person A: let clutch pedal UP. Repeat UP/OPEN/DOWN/CLOSE cycle until no more air bubbles exit with the brake fluid. Be sure to check/replenish master cylinder after several bleed cycles before continuing to bleed.)

If this doesn't solve the problem, consider disassembling the slave cylinder to ensure the piston is free moving and the seal and spring are installed/oriented correctly.

If the problem still persists, consider removing the piston from the master cylinder and similarly inspect for free movement and to ensure seal, etc. is installed/oriented correctly. While you are there, also check to be sure the brakes are working properly! (If in slight doubt about the orientation of the seal, but wishing not to remove the piston, then peel back the outer dust boot on the slave - and master - cylinder to check that no brake fluid is bypassing the internal seal.)

Steve
Steve K

As Mick pointed out, if - after operating the clutch several times - you refill the master cylinder and the clutch works, and brake fluid ceases to be expelled out the cap, then you don't have a problem.
Steve K

Gerald. I agree with Mic and Steve K. If the system is properly bled, and the clutch disegages, the system is working properly. You do not need to fill it to the brim when the clutch pedal as on the floor. To do so would over fill the system. The reservoir should be about 1/4" to 1/2" below the top of the reservoir when properly filled.

Les
Les Bengtson

Watching the clutch slave piston get pushed back in several times. Is it possible for the clutch springs to over power the hydraulic system?

NOTE: In a previous thread I asked if the clutch assembly could be adjusted to reduce the "slack" between the throw-out fork and the pressure plate. I was able to do it by turning the three 3/4" nuts on the top of the clutch assembly. Can anyone tell me more about these "adjuster nuts?"
gerard hutchinson

Gerard,

I think that you are just getting yourself into more trouble the more you do.
The nuts on the top of the clutch assembly do not reduce "slack" in the system. There is no slack. The rearward movement of the thrust bearing surface of the clutch assembly pushes back the operating fork which pushes back the slave piston. There is no clearance.
The adjusting nuts on the clutch assembly set the pressure plate friction surface parallel to the flywheel surface.
If you have moved those nuts without setting up the clutch assembly with the proper gauges then you are going to be in all sorts of trouble.
I suggest that you take the clutch assembly to a qualified mechanic with the correct gauges and have the assembly set up correctly.

MIck
Mick Anderson

Gerard,

I agree with Mick that there is no reason why you should be tinkering with the adjustment screws on the clutch pressure plate, and if you have done so then you should remove it and have it checked.

In the meanwhile, perhaps you can still sort out your problem. When you say you watch the piston in the slave cylinder get pushed back in, what are the conditions when that occurs? Is someone holding the clutch pedal to the floor and the piston returns, or does the piston return when the clutch pedal is returned to its rest position. The latter is normal, the former is not and would occur if there is air in the system - just as with the brakes. Please summarize again what you believe the problem is.

Note, there is only one "adjustment" in the clutch system, and that is the free play adjustment on the rod that pushes the piston in the master cylinder. That adjustment is NOT to take slack out of the system, but to ensure that there IS some slack between the resting position of the clutch pedal and when it first engages the rod in the master cylinder. The clutch pedal should move about an inch from its resting position before you feel the resistance of the clutch system. If there is NO free travel in the clutch pedal before the master cylinder piston is engaged, that is equivalent to "riding" the clutch, i.e. the slave cylinder piston would not be permitted to return to its rest position when the clutch pedal is fully up, and so the throw-out bearing would still be engaging the friction surface.

By the way, do you have a copy of the original MG Shop Manual to refer to?

Steve
Steve K

Gerard

Download a copy of the relevant section of the workshop manual from here. It will help you a lot....


http://www.clancy.ch/Workshop_Manual.html
dominic clancy

Mick,
The piston in the slave returns WHILE the pedal is held to the floor. I agree that it seems like air may be in the system.

When I first attached the clutch to the flywheel there was NO way to depress the thrust bearing any further. Said another way, the thrust ring had no chance of disengaging the clutch plate. Prior to removing the gearbox I could move the throw-out lever back and forth freely by hand. The lever movement was limited only by the size of the opening in the gear box.

However, as I turned those top nuts, while the clutch assembly was attached to the flywheel, I watched the thrust bearing move outward. As a result the lever no longer moves freely. According to the manual section provided by Mr. Clancy the thrust bearing is attached to levers that are moved into the correct position by the adjusting nuts(I do have a manual but thanks for the link). Perhaps I adjusted too far outward but I don't understand how the mechanism can work without adjust those nuts at all.

Question: Based on the Figure E.1. on page E3 of the manual, where should (H) the release plate be positioned?
gerard hutchinson

Gerard, can you explain what you mean by there being no way to depress the thrust bearing further? You're talking about clutch fork movement before the gearbox was removed, and then you're also talking about installing the new clutch on the flywheel sans gearbox in the same explanation, and I think we should break it down a little.

Why did you replace the clutch in the first place? If you had free movement of the clutch fork all the way back and forth by hand, this doesn't seem right at all. I've never worn a bearing down to the metal housing, but I understand that it will still make contact with the pressure plate bearing surface and do bad things. So if your new pressure plate allows the same kind of movement with the clutch fork, your problem is not with the pressure plate but possibly your throwout bearing, clutch fork, and connecting linkage. If the clevis pins and bushings have all worn they can cause excessive play in the system, have you checked those?

It seems to me that by moving the adjusting nuts so that the diaphram springs move the bearing surface away from the flywheel, you're upsetting the natural order of the diaphram clutch. The centers of the springs are supposed to be pushed in, so that the outer edges are in turn pushed out and pull the pressure plate off the clutch plate. If you've changed the angle of the springs from this:




to this:

/
/

now you're making it awfully hard for them to achieve this:

/
/

and I'm not surprised that your hydraulic system is unhappy about it.

Anybody, am I totally wrong in my guess as to what's going on here?
Mark J Michalak

OK, my goofy pictures of diaphram springs didn't work. It should be more like....

from this:

}


to this:

>

now you're making it awfully hard for them to achieve this:

{

Clear as mud, right?
Mark J Michalak

Gerard,

It does not sound like air in the system if the clutch operating arm returns while the pedal is depressed to the floor. If there was air present you would not be able to move the arm at all. It sounds like fluid escaping back into the master cylinder. This assumes that you are not rapidly pumping the pedal to get the arm to move, and fluid it not obviously leaking from the slave cylinder.

As for the clutch mechanical parts not operating properly, one or more parts must have been incorrect. Slave pushrod wrong length, pushrod clevis pin hole worn oval, clutch operating arm bent or incorrect item, clutch operating arm pivot worn, operating arm thrust bearing wrong type or worn.
Or most likely, based on your results, the clutch operating levers not set correctly.

Unfortunately I do not have the measurement from H to the friction surface of P. Maybe another member may have it.
You can only hope that when adjusting the levers without a gauge plate, or the spacer type gauge, that you finish up with the correct H to friction surface of P distance and the pressure plate parallel to the flywheel.

Mick
Mick Anderson

Gerard,

From what you have said I assumed that you are replacing a coil spring clutch with another coil spring clutch. A diaphragm clutch is not involved, before or after?

Mick
Mick Anderson

If the clutch slave piston (and push rod and release arm) move back to rest position while the pedal is being held down, you have internal leakage in the clutch master cylinder allowing fluid to get past the piston main seal back into the reservoir. This requires installation of a new packing kit for the master cylinder at the minimum, assuming the bore is in good condition. If the bore is scratched or pitted so badly that it cannot be honed out smooth, then it would need to be sleeved (which is much cheaper than a new master cylinder).

As to the 3/4" lock nuts on the clutch cover assembly, you should never be tinkering with those. This is for initial assembly alignment setup and should never be touched again except for a professional rebuild of the clutch cover assembly, as it requires special fixturing for correct adjustment (see notes in the workshop manual). If you have moved these nuts you may now be in for replacing the assembly or having it rebuilt.
Barney Gaylord

In the past it may have been the case that re-sleeving was a lot cheaper than a new cylinder. It is not the case any more, it's just a bit cheaper, so do check out the price of a new cylinder from various sources before you go to the expense of having one rebuilt. Bear in mind that if you rebuild, you have to pay postage in two directions, so the "saving" is even less than first glance.




dominic clancy

I have come to the painful conclusion that it is best for my sanity to buy a brand friggin new clutch and throw this POS in the friggin river!!!

gerard hutchinson

Gerard,

Before you give up, you need to do close inspections, otherwise with a new clutch you may have the same problems. Start at one end and work you way along.
When you depress the pedal and hold it down, the slave pushrod moves back to the rest position. You need to observe whether the master cylinder pushrod moves back while the pedal is held down. If it does, the master cylinder needs repair before you proceed with a new clutch.
When the master cylinder is OK check the master cylinder pushrod clearance.
Check that the flexible hydraulic hose does not bulge under pressure.
When that is OK check the slave pushrod clevis pin hole for ovality and the pin for wear.
Ensure there is no fluid leak from the slave cylinder.

After all external checks are OK you will have to remove the clutch. Check for wear of the bush in the pivot of the operating arm and the bolt. Check that the operating arm is not bent and is the correct item. You may need to take measurements and check with other owners. Check the condition of the thrust bearing and that it is the correct type. Again measurements may be necessary.

Only now would you get a new clutch.
Before fitting you need to check that distance mentioned earlier (see image).

Can anyone give the correct measurement for the horizontal red line in the attached image?

Mick


Mick Anderson

This thread was discussed between 01/06/2008 and 04/06/2008

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