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MG MGB Technical - Clutch Slave Cyl.

in my first attempt to drive my '70 GT, I noticed that my clutch was responding to the pedal about half the times I used it! when I bought the car the slave was frozen but worked it free. when I tried to drive it, the clutch would get stuck occasionaly either engaged or disengaged. there seemed to be no rhyme or reason, but my question pertains to whether or not it will get better the more I use it. The car sat for more than a few years, during which time it froze. I smacked it free with a hammer (hey, limited funds and I was getting desparate) and it started working (so I thought). if it's just gummed up and nasty from sitting over the years, will it eventually get better if I keep trying to drive it?
Chris

Slave cylinder heal thyself? I don't think so.

If the car were sitting around for as long as you
said, you'd be better served by rebuilding both
slave and master cylinders and flushing the
system.
Daniel Wong

Strip them down and - if the bores are not damaged - fit new rubbers.
Chris at Octarine Services

Chris,

Also make sure you inspect the internal condition of the hose connection between the master and slave. Internal deterioration can disrupt fluid flow either way.

Another thing to check is whether a PO has extended the length of the master cylinder push rod. If so there may be some disruption to the free flow of fluid through the feed holes round the head of the piston if it is prevented from returning the proper distance.
Regards
Roger
Roger

Ya gotta learn when to do it on the cheap and when to put some cash into the project. The hydraulics are one place you can't scrimp. A bad clutch cyl can damage a clutch or gearbox and cause you to spend many more dollars than the original fix would have cost. If the clutch cyl is bad--chances that the brake system isn't too healthy either. Failure there can cancel your whole project...or even your very existence.
R. L Carleen

I agree with all this advice - my clutch system seemed to be working fine until I took out the B of winter storage this year. However looking at the internals after I'd taken the cylinders to pieces it was a miracle that they had worked at all.

I was going to ask for help on a separate thread, but since this will be important for Chris if his repairs creep up as far as the master cylinder I'll ask here.

How does one replace the rubber bung in the porthole through the firewall ? After failing earlier in the year I put this down the the rubber being inflexible due to the cold. I tried again in the recent hot weather and found it equally impossible. My wife is surprisingly reluctant to curl up under the dash to help and I have proved that bad temper and foul language on their own don't work.
Before I give up and make a couple of metal sandwich plates with a captive bolt - am I missing a trick?

Thanks
Vic
V Todman

the master cylinder has been replaced with a working one from a different B. as far as I know, the slave on that B is working as well. How difficult is it to swap slaves?
Chris

Vic,

If I have the correct 'bung' in mind, when I rebuilt my master cylinder I removed/replaced that 'bung' to enable me to lock up the banjo bolt through the firewall. Mine refitted OK, without any undue pressure needed to fit it onto the opening. If memory serves correctly I had the seat out. That makes achieving anything behind the dash just that much easier.

I know it seems a silly question, but is the one you are trying to fit correct? You might try it against the one on the passenger side from inside the engine bay for a comparison.
Regards
Roger
Roger

Swapping a slave cylinder is relatively easy--just follow the shop manual, step, by step and it'll fall together.
R. L Carleen

Just yesterday I noticed that I was leaking a rather large amount of clutch fluid from the rubber boot at the slave cylinder of my 77 MGB. Please advise, is the fix as simple as just replacing the slave cylinder assembly or might this be a symptom of a larger problem..
Stephen (TN)

Stephen, it's as easy as replacing the slave cylinder and as hard as bleeding the air from the system after you have done so. Many people suggest if you are replacing the slave to replace/rebuld the clutch master and replace the rubber hose to the cylinder. They reason it's a matter of the next weakest link. Many good threads in the archives on how to do all of this. I recently rebuilt the slave in my 76 B with out doing the other but have the parts on hand -- I was doing the minimum work as I was working on the car at a local mini storage so I could drive it home.
Good luck and regards,
Dennis
D F Sexton

A tip on bleeding hydraulics, which I believe came from a british classic car magazine:
Attach a piece of plastic tube to the bleed nipple and put the other end in a jar with some hydraulic fluid in it (nothing new I hear you think), BUT plug the end of the hose with a screw/bolt and make a cut just above the plug lengthwise (+/- 1cm long).
You now have your own, free one-way valve.
I have used this method ever since I saw it and it has worked very well. You don't need an assistant anylonger to close the bleed nipple when the pedal is depressed.
HTH,
Rufus
R Pool

Roger - Correct Bung?
Hi Roger - Can't say if it is the correct bung but it was the one I removed from the hole earlier. In my case it's difficult to locate the groove into the periphery of the hole and keep it there, seems to be working just fine and then it pushes clean through. Most times it's gone too far to pull back and I have to get out from under the dash to retrieve it.
One day when I produce a real instruction manual; where all the operations are listed; I'll include taking the seat out before beginning the master cylinder replacement. Reminds me of the 2CV where replacing the points began with removing the front bumper.
Vic
V Todman

Isn't the slave rebuild kit like...five bucks or so?
Paul Hanley

This thread was discussed between 29/04/2004 and 05/05/2004

MG MGB Technical index

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