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 MGB Technical - Difficult sifting

Can not engage transmission with engine running. I've replaced the clutch master, hose, and slave. Have had some difficultly bleeding the system. Repeated pumping up of clutch only slightly improves the situation.

If the car is started in gear with clutch pedal depressed, the clutch is capable of holding the engine against the brake. Therefore, I don't believe this is the clutch itself.

Questions
1. What is the approximate distance the slave cylinder rod should move?

2. Could this be the throwout bearing instead?
steve m

Steve, The slave push rod should move around 3/8" to 1/2". It should also remained extended with no movement until the pedal is rleased. I doubt if it is caused by the throwout bearing. Look for air in the clutch hydraulics or defective/leaking cylinders or clutch hose. Clifton
Clifton Gordon

Steve - Give this procedure a try with your clutch hydraulics. Crawl under the car and push the rod from the slave cylinder and by extension, the piston all the way to the back of the cylinder, then reblead the system. You may have to repeat this a couple of times to get all the air out of the slave cylinder, but it works great.
Good luck - Dave
David DuBois

Try reverse bleeding the system. Connect a "gunson Easy Bleed" to the bleeder screw on the slave cylinder, push the rod in to expel any air in it, then use the easy bleed to reverse fill the system. All the air will be push up and out the clutch master. Several people swear by this method.
william fox

Thanks everybody,

I believe I'm facing two problems; cheap aftermarket components (not lockheed)and what I'm coming to believe is a bad throw-out bearing. I replaced the cheap master with a new lockheed which helped quite a bit. I think the hydraulics are now correcting reasonably well.

Could someone please describe the symtoms of a bad throw -out bearing. What were your experiences?
Steve M

William, using the Easy Bleed to move fluid up from the slave cylinder to the master cylinder? Do you do this with the reservoir cap on? Doesn't this pump fluid out the reservoir and make a mess? I use the Easy Bleed on the break system and seams to invaribly make a mess if the cap on the reservoir leaks.
Geoff Kimler

Steve, Bad throw-out bearings usually make a noise. I guess they could cause a shifting problem if worn very thin. Clifton
Clifton Gordon

Steve. Normally, the bad throwout bearing is indicated by noise. The bearing has a graphite inner ring which wears in use. Eventually, if not replaced, the graphite will wear to the point where you are getting metal to metal contact between the throwout bearing and the pressure plate release mechanism. The metal to metal contact will, normally, cause a grinding sound when the clutch pedal is depressed and the engine running. (There are exceptions to every rule.) As others have noted, the first thing to do is to inspect the pushrods associated with the slave and master cylinders and the clevis pins which connect the pushrod to the brake pedal and the clutch fork. Wear in these areas can cause the symptoms you describe, particularly wear in the MC pushrod/clevis pin. When you have checked those areas, recruit and assistant and check the actual movement of the pushrod when depressed. It should be about 3/8", minimum, for the system to work properly. Then, bleed the system again. There is a reverse bleeding system which uses a pump, attached to a bottle of brake fluid, to pump from the slightly opened bleed nipple to the partly drained MC. There is a vacuum bleeding system which uses a slight suction on the bleed nipple to draw fluid through the system. Finally, there is the old "recruit an assistant and do the pump the pedal/hold/bleed process". All of the systems work. All take more time than you would expect if you have not done it before. Les
Les Bengtson

Two things;
if all else fails bleeding. Run a hose from the slave back into the master. Open the bleeder and pump the fluid in a circle. This will get all the air out. On the down side you will not get dirt out of the system. #2 I have in rare cases had pressure plates go bad causing a problem of not releasing. Even replaced them under warranty back in my dealer days. Bob Blm sure didn't pay much for warranty work!
Bob Thompson

Les has some good advice.

I recently (about 3 weeks ago) had the good(?) fortune of having my clutch catastrophically fail. It made quite a racket. I was able to drive the car home while the failure was in progress with it giving up the ghost as I pulled into my garage (really good fortune).

For about three years the clutch had been making strange noises off and on when depressing the pedal. I thought it might be the throwout bearing but, since changing the bearing is such a pain, I just continued to drive it. It would go for weeks at a time without making noise.

When it was in its death throws, the shifting effort became VERY high - same symptoms as bad hydraulics.

Mine did finally fail completely. To the extent that I tried to start the car a couple of days later and when I depressed the clutch, it pushed the slave piston completely out.

Just thought I would pass this recent experience on.
Richard Smith

This thread was discussed between 20/03/2003 and 22/03/2003

MG MGB Technical index

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