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MG MGB Technical - Is my clutch working?

I just rebuilt and reinstalled the engine in my '68 MGB GT. I also installed a new Borg and Beck clutch and the throwout bearing that came with it. I put a new bushing and pivot bolt in the clutch fork. I put a new spigot bushing in the crankshaft because the old one was somewhat damaged by the machine shop when they polished the crank journals (not surprising). I bled the clutch hydraulics using every method ever suggested on this bbs; but still the clutch APPARENTLY does not disengage. So, I replaced the slave cylinder (the old one was really old), bled again, and still the clutch APPARENTLY does not disengage.
Is there any visual or other method of determining if the clutch is actually disengaging (or not)??
The only other problem that I can think of that would cause this symptom is the input shaft of the transmission binding in the new spigot bushing in the crankshaft. If that is the case, what is the cure??
John Hubbard

Are you sure the driven plate is fitted against the flywheel with the shorter end of the hub facing the it? It should have flywheel side marked on it somewhere
Malcolm Adamson

Malcolm, I was pretty careful to put the marked side toward the flywheel. I distinctly recall having read the marking and orienting it that way.
John Hubbard

OK then if you can see the slave operating, it must sureley be something going on inside and there is only one way to find out unfortunately
Malcolm

John - if someone else pumps the clutch pedal can you see the slave piston moving? It should move 1/2" to 5/8" when fully bled. If it is not moving, or barely, try emptying the system and refilling from the slave nipple with a gunsons Eezi Bleed on very low pressure. Filled mine that way and didn't have to bleed at all.

But it is only the cover-plate diaphragm spring that pushes the piston back into the cylinder when you release the pedal. If you don't have that spring pressure you only need two or three pumps on the pedal to push the piston right out of the bore and dump your hydraulic fluid on the floor. So either it still needs bleeding or you are operating the cover-plate but it is still not releasing for some other reason.
Paul Hunt

In the archives, someone mentioned re-aligning
the gearbox and engine because the input
shaft, as you suggested, was binding in the
spigot bushing. They loosened the bellhousing
to rear plate bolts and moved the gearbox slightly
with a trolley jack, with everything still in
the car.

I'm interested in the outcome of your problem -
as Paul mentioned, do you see the slave pushrod
moving when the clutch pedal is pressed?

I have a much less severe problem with apparent
clutch spin with a new Borg and Beck clutch.
I noticed that the diaphram and clutch disk
material were different on the clutch kit,
compared with one I bought a few years back.
I wonder if incorrect clutches are being shipped
for Bs?
Ronald

Ronald, that sounds like a possible action. Certainly easier than pulling the engine and tranny to check. Yes, the slave pushrod moves - about 1/2", but maybe not quite enough...
John Hubbard

One more obvious question -- can you shift
into gear with the engine off? I would imagine
the transmission is ok, but you never know.

Another idea, jack up the rear of the car, put
the transmission into gear, and rotate the rear
tires by hand. Have someone step on the clutch pedal
and see if you can tell if something's binding
or not engaging that way, see if you can feel
a difference with the clutch pedal down or not.
Ronald

John - You said that you tried bleeding the clutch by every method suggested on the BBS. May I suggest, that if you have not done this already, you manually push the piston all the way to the back of the slave cylinder (I removed the rod from the slave cylinder and used a phillips screwdriver to do this). After this is done and the rod reinstalled, have a helper step on the clutch pedal while you open the bleeder screw a couple of times. This procedure will get rid of any air that might be trapped in the slave cylinder. Good luck - Dave
David DuBois

Well, we spent the afternoon trying various things, including most of your suggestions. The last thing we tried was attaching a come-along to the clutch fork to pull it back to ensure that we were getting the required travel. Even with that, we still had the problem. So, about 4:30, we started to pull the engine again. We must have a mechanical problem in the clutch/bellhousing area. I'll report more later.
John Hubbard

Just wanted you all to know the outcome. We pulled the engine and tranny tonight and found that the new clutch would not slide freely on the splines of the input shaft. So, no matter how much we pushed on the throwout bearing, the clutch plate could not move away from the flywheel. In fact, there was a distinct wear pattern on the very inner edge of the clutch plate friction material on the side toward the flywheel. Obviously, the clutch was pressed forward at the center because it could not slide back on the splines and we had it deflected back rather severely.
Tonight, we wire brushed and scraped the splines, plus used the old clutch plate to polish them up some. Then the new clutch plate slid freely. When we bolted the tranny back to the engine, it went together very easily, unlike the first time. We didn't put the engine back in the car; but I am pretty confident that this solved the problem.
John Hubbard

Thanks for your post, John. I've been following this thread and it's nice to have an update and apparent solution. Good luck.
Rick
Rick Jaskowiak

John,

The clutch should have come with a little sachet of red grease to put on the splines.
Chris Betson

This thread was discussed between 10/02/2002 and 13/02/2002

MG MGB Technical index

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