MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Clutch Failure?

Returning home yesterday in my newly aquired MGA, whilst changing gear I felt a distinct release of pressure on the clutch pedal, followed by an inability to select gear. Pressing down the clutch pedal resulted in fluid coming out of the slave cylinder. Got towed home, thinking the cylinder seal had gone. A easy fix. Pulling out the slave cylinder, showed that the piston had almost ejected itself from the cylinder, and become wedged. I am now starting to believe the clutch has gone. A very badly worn thrust bearing would allow this to happen perhaps. Or a broken spring? The current clutch has done say 10,000 miles so its not a new restro incorrectly done. There does not appear to be any slack in the pushrod pivot hole/pin. Can someone confirm its a clutch failure of some sort.
Having read many threads, and different views, on what you need to remove to get the engine out, can someone summarise the easiest procedure.
thanks.
Henry

This will be interesting to see what people have to say as with fluid comming out, it seems to me that the problem is not the clutch but your hydralic system or adjustment at the master cyliner on the control rod
JEFF BECKER

If the rod between the slave and the throwout arm is the correct length, the piston should not come out the end of the bore. Don't think this is a hydraulic or adjustment problem. About the only thing you could fix without pulling the engine is if some DPO had shortened the rod, or if the pin was extremely worn.


I have always pulled the engine separatly and would recommend that way especially since you probably won't need to remove the gearbox to fix the clutch.

I just disconnect everything, support with a hoist, and then remove all except for the bottom bolts holding engine to gearbox. I then lift until the gearbox hits the top of the firewall and put a support under the front of the gearbox. Then remove the bottom bolts and slide the engine forward.

You probably want to remove the crankshaft pulley. You may be able to remove the engine with the pulley attached, but by the time you figure out if it needs to be removed it will be much tougher to remove.

If you have to remove the clutch, you will need a clutch centering tool or an old input shaft to get the clutch centered. To re-install the engine, first eyeball the splines in the shaft to get them close to alignment with the clutch. Make sure the engine is hanging at the right angle, then gently slide it onto the gearbox shaft rocking the engine from side to side if necessary to line up the splines in the shaft.
Jeff Schultz

If the car still drives when in gear, the clutch is still working at least in part.

I would check the length of the pushrod at the slave. If it is too short for some reason, then the piston will pop out.

If your sort it out at the slave with a rod of the correct length and try to operate the clutch again, you will son find out of the clutch is working still or not. Then you can decide to pull the engine.

I saw this once when the bolt through the operating rod to the release fork was not tight and the bolt fell out. It did appear that the clutch had gone, but a quick inspection under the car revealed a slave cylinder piston that was out at an agle like yours and a missing nut on the end of the bolt, and everything loose and out of alignment. 20 mins work under the car and a rebleed was required. Car was back on the road 40 minutes after breaking down.
dominic clancy

At least seems a chance it is not the clutch. Any idea how long a correct pushrod should be. Is there only 1 part. I have the standard slave cylinder setup.
Still can't get my head round why it has happened now, although I have no way of knowing if it has happened before.
Henry

Before pulling the engine, I would fix the slave and try it again checking carefully to see if the piston is in danger of coming out of the bore. By watching it work, you should be able to see if it is some kind of external problem. Don't know the length for sure, but in the archives, this thread says the rod is about 2.5".

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=6&subjectar=6&thread=200401251507389579

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=10179730800099&mode=archiveth&subject=6&subjectar=6&thread=2002110212450420098

Jeff Schultz

Clutch pushrod is 2-3/8-inches from eye to end. Pushrod motion should be 5/8" total with full pedal travel.
Barney Gaylord

Henry,
I had this happen to me twice on my roadster. I found out that the slave cylinder push rod was 5/16" too short (compared to a friends spare rod) and this allowed the piston to move too far out in the cylinder bore and get cocked to one side. This allowed the seal to also get cocked to one side and leak. With the piston cocked in the end of the bore it had the clutch pushed in and the car would shift gears ok but obviously not move. Hope this helps and have a good day!

John
John Progess

I had a similar experience once. It turned out that the clutch release fork was badly worn at the hole that the pivot bolt fits through and also where the throwout bearing fits. Finally enough slop occurred to let the clutch slave cylinder travel beyond the point where it could still seal.
Tom Heath

Just measured the length of the pushrod in-situ, its no less than 2 3/8". But there seems to be a lot of wear in the eye, anything up to 1/8". Its possible a new pushrod may save the day, if I can get the pin out.
With it all set up, should the piston protrude beyond the cylinder at full pedal stroke. To me commonsense says about 1/8" is permissable.
Henry

The piston should not protrude beyond the end of the cylinder at full stroke. It needs full contact on the OD for maximum bearing surface to keep the piston straight and minimize wear. If the piston protrudes a little, and the cylinder wall wears a bit, the piston could stick in the extended position. When that happens the next pedal stroke will push the piston completely out of the cylinder.

If you notice that you have a worn clevis pin and/or worn eye in the pushrod you should change these parts immediately. These are common wear points. The release arm pivot bolt and bushing are also common wear points, as well as the release bearing, but you have to R&R the engine to replace those parts.

When you have substantial wear on the pushrod eye, clevis pin, pivot bolt, pivot bushing and release bearing, that's when it may be possible to pop the piston out of the cylinder.
Barney Gaylord

Also, if the hose is dead, then it is possible to have it act as a check valve in varying degrees. The cylinder doesn't return all the way, which will wear the release bearing. It will also mean that if you depress the pedal more than once, without enough time for the blocked hose to let all the fluid back, the piston can be ejected. This situation would normally cause clutch slip under hard driving, but if you drive gently it might not slip.

FRM
FR Millmore

Here is a picture of a new rod. It is 2 3/8" tip to center of hole.


R J Brown

The condition FRM describes will also make you think your clutch is slipping (it is). When you let the pedal out, it doesn't engage the clutch as fast as you do, making you think the clutch is worn out. Simple fix, wouldn't hurt to replace the hose.
Tom

Thanks for all this advise. Contemplating my options at the moment. It seems to me that the amount of slop required in the linkages to force the piston out, is more than I can see. Therefore any quick fix is only a temporary measure. Whilst I would prefer to use the car in the summer, an engine out may be best long term. Will miss driving to MGCC Silverstone International.
Henry

Henry. You tell us the pushrod is worn about 1/8". If the clevis pin has worn in a similar manner, you would have 1/4" of excessive movement. My experience is that the clevis pin actually wears more than the pushrod and requires replacement on a more frequent basis.

Thus, I would recommend you make no firm decision until you have both the pushrod and the clevis pin in hand and can inspect them. At that time, the pressure will be off the clutch bearing fork and you can obtain an idea of how loose it might be. Holding the end that projects from the transmission and trying to move it back and forth along the center line of the car will tell you how much the bushing is worn. If there is no movement, or very little, simply replacing the pushrod and clevis pin should allow you to drive the car during the summer and strip the system for inspection during the winter months.

Les
Les Bengtson

Interesting....I had a similar issue with my 61 MGA a few months ago and just got around to rebuilding slave cylinder. Back then, when in first gear, depressing clutch pedal to floor wouldn't disengage clutch, and, slave cyl leaked lots of fluid. Today, after rebuilt slave, with new pushrod installed, and first bled, the car ran fine, but, when coasting to a stop in first gear with clutch pedal fully depressed, the car remained in gear and couldn't change gear to neutral (or any other gear). Re-bled clutch at slave cyl and tried again. Worked better, but after a few mins, had the same problem. This was the exact same problem I had when I first decided to do the slave cyl rebuild, but, the slave cyl is not leaking.

Is this a matter of not bleeding all the air out, or, something more complicated?

steve
Steve Nyman

Steve,
Might still be a bleeding problem, but it sounds more like a problem with the master. If the clutch disengages when you first depress the pedal, but reengages if you hold the pedal down for a while, and fluid is not leaking out of the slave, the master probably needs rebuilding. You can have master problems without external leaking, because fluid can be leaking past the seals and back into the reservoir

Jeff
Jeff Schultz

Steve,

I had exactly the same symptoms with my Jag. The master cylinder inner seal was damaged so fluid was leaking slowly past causing the clutch to disengage when held for longer periods. Normal driving was fine. The secondary seal (or primary, not sure what each is called!) worked fine so there was no leak. New seals fixed the problem.

I had a similar problem on the brakes of my MGA. The pedal was firm and the brakes worked fine (apart from stuck pistons, but that's another story and not relevant to this) but the pedal moved slowly down when the brakes were held on.

It turned out to be exactly the same problem. The inner seal was in a terrible state, but the outer seal was fine, so no leaks.

If the bores are OK new seals will fix the problem. If the seal is damaged due to the bore being pitted, or if the bore is so pitted as to prevent a proper seal then it's new or sleeved master cylinder time.

Neil

Neil McGurk

Jeff and Neil,
Makes sense. Will re-bleed some more, but if that doesn't do it, will pull master cyl and go from there. I noticed yesterday when I had some help and could have someone hold clutch pedal to floor for a minute or so that the slave rod began to retract and no leaks. So, it's either air or the master as per your messages. Thanks!

steve
Steve Nyman

Steve,

From that, it's the inner seal, not air. The clutch bleeds really easily.

Neil
Neil McGurk

Seals in a master can be easily changed in car. If it has silicon fluid you cant damage paint. If you are still running paint thinner/dot 3,4,5 fluid nows the time to get it right and go purple.
R J Brown

Without getting back to the old silicon debate, it seems quite difficult to get hold of here. I got some from Moss and their price seems fair.

Local motor factors were pretty useless. "used to be popular in the '90s, but I don't think anyone sells that anymore mate"

More frighteningly one guy claimed that dot 5.1 could be used to top up dot 5! "you can use a higher number with a lower number, but not the other way round!"

Where do other UK silicon devotees get their fluid?

Interesting reading:

http://www.xs11.com/tips/maintenance/maint1.shtml

A quick web search shows that this is a hot topic on almost every auto BBS!

Neil
Neil McGurk

I use silicone now, but long ago when I was using glycol, I did change the master seals without removing the master from the car. You just have to make sure you drain all the fluid first, then use a lot of rags to catch any drips.

Jeff Schultz

I have never had a problem getting Si Fluid: MG Car Club in Cabridge was cheapest, Brown and Gammons quite expensive, Moto-Build OK, Bob West etc....
dominic clancy

This thread was discussed between 10/06/2007 and 14/06/2007

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.