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MG MGB Technical - 1979 MGB GT Clutch Problems

Bought my MG a couple of months ago. Its in average condition and I drive it every day.

Drove it last night, and as i came to a stop, i couldnt get it out of gear, i had to stall the car to get it to stop.

The clutch pedal seemed to do nothing, or at least very little. I tried it a few times after, and to start it works (feels limp, with the biting point being really low down, but it works), but then over a period of minutes, it feels like there is no pressure in the pedal, and the gearbox acts as if you havent put your foot in the clutch.

So you can get in the car, depress the clutch, put it into gear, then keeping the clutch depressed, over time, the clutch will act as tho you have taken your foot off the pedal, even though you havent!

Is this a leak in the hydraulics system, or is it just an air bubble? Its the first time anything like that has happened. it didnt seem to be that gradual... within 1 ten minute journey i think.

Grateful for any advice given...

Many Thanks
Jono.
Jono

It's the clutch master cylinder seals leaking Jono. The fluid leaks back past the piston seal into the reservoir so no leaks show outside. New rubber seals are a cheap and fairly safe option for a clutch master if the piston and bore look OK when you (or your mechanic) strip it. Otherwise a new cylinder. Rich.
Rich

Thanks for that Rich. That seems to make sense, as i had a quick look last night, and i couldnt find any visible leaks arount the master cylinder or any of the lines...

Guess im gonna have fun re-bleeding it afterwards then. From what ive been reading, people say its a pain in the neck...
Jono

They say that, don't they? I must have been lucky, never had a problem. I have an assistant press the clutch pedal while I nip up the bleed screw in mid-stream on EVERY firm downstroke before they stop pressing or release the pedal. I have a clear tube attached into a jar and give a couple of pumps after the bubbles have gone. Rich.
Rich

Out of interest, if i took it to a garage, what sort of price would they charge to sort this out?

dont mind getting my hands dirty, and ive done brakes before, so it cant be much different, but if its cheaper than taking the day off work + whatever it costs to get a taxi, it might be worth it!!!
Jono

Well, I think there are 2 possible seal kits at 6 each depending on Lockheed or repro, or one cylinder at 48, plus labour at around 40/hour.
If I took it to a garage I'd go for the new cylinder as you'll save the labour for them to rebuild it and at least you'll know it's good. If you know someone sympathetic with classics you might get away 120 all done, or even less if they are willing to fiddle with seals, but get the price first.
If you do it yourself it could be just 6 for seals, plus fluid. It's not a job that needs any special tools or understanding nor is it very safety critical so in many ways it's ideal as an intro if you feel you will want to work on the car in future. That said, if it's a daily driver and you don't have the time or basic tools you'll view things differently. Rich.
Rich

Hmm, I live just down the road from THE MG BARN. think they'd be sympathetic, but i may as well give it a go myself!

Where is the best place to get the seals from? Im guessing somewhere like Halfords wouldnt keept them in stock. Maybe ill see if The MG Barn will sell me some...
Jono

Jono, is the fluid level dropping? You said you'd checked the lines - including underneath right up to the slave cylinder? If the slave seals are leaking you'd eventually get a puddle underneath as the fluid seeped into the boot and then on to the floor.....
Dave Smith

If the fluid level isn't dropping it is almost certainly the master seals leaking back instead of pressurising.

I didn't need to bleed mine at all by connecting a gunson's EeziBleed to the slave nipple instead of the master cap, and using very low pressure, to fill it from empty. Watched till I could see fluid rising in the master then stopped the EeziBleed and topped off as normal. Has the full 1/2" to 5/8" of slave piston travel without any bleeding.
Paul Hunt

I checked and there seems to be no drop in the level of the fluid, but having said that, it only stopped working yesterday.
Jono

I doubt Halfords can help these days. Ring Moss 02088672020 or MGOC 01954230928 with your credit card details and you'll get them usually next day by post. Rich.
Rich

Ok, so i finally managed to get the new seals, and get them in and bleed it all. was a fairly simple job, HOWEVER... the clutch still doesnt work!!!! When you put your foot on the pedal, there is no resistance. It pumped out the bleed nipple when i bleed them so the master cylinder must be doing something!

Im still not losing any fluid, does this mean that it is the slave cylinder!?!

Need my car back... Is it time to take it to a garage!?!
Jono

Or could I not have bled it properly? I did whaqt the haynes manual said...
Jono

Jono,

Try bleeding from below - undo the bleed nipple and push the clutch fork arm forward to expel air & fluid, tighten the nipple and pull the arm back, repeat until no more air comes out. Keep the master well topped up.

By squeezing the air out this way there is less chance of air being trapped in the top of the slave cylinder.

While you are down there, check that there is no fluid behind the slave cylinder boot - if there is then you need to replace at least the seals, but I would go for a new cylinder as the bore is often corroded.
Chris at Octarine Services

You could also try the method I mentioned earlier which is subtly different to the bleed method shown in the book. The clue to it maybe being better is that it is detailed as the method used to drain the master cylinder ie, you close the nipple at the bottom of every stroke to stop fluid being drawn back up. Whilst drawing this fluid back up will not introduce more air it will not get rid of the air that's in there either. Closing the nipple every stroke means the fluid can only go one way. Air can still get trapped in the slave though as Chris says so try all ways and others you'll find posted on the web inc pumping the pedal several times then jamming it down overnight. Rich.
Rich

Jono,
Chris's point is good. If you pull back the slave boot and get fluid, there's your problem. I had exactly the same symptoms on my A. Logic said it seemed like the master as described above. I rebuilt the master as you did and still no clutch. I bled the system every way I could and still no clutch. Then I rebuilt the slave and... voila! it worked like new. Sometimes the obvious is not so obvious.
Bill
Bill Boorse

Ok, just ordered myself a new slave cylinder, and the flexi hose that connects to it. even if its just my crap bleeding, id rather have them for this weekend so that iv got a chance of fixing it this weekend...

Heres hoping...!!!!

Just to mention, ordered it from www.mgpartsuk.com was 13 cheaper than MGOC. and they didnt charge me for postage as they will put it in first class for me. Cant be bad.
Jono

I reverse-filled mine from the slave bleed nipple and it didn't need any bleeding at all.
Paul Hunt

Just wanted to say thanks to everyone for the help.

Back on the road. Biting point seems very low, so ill probably try re-bleeding it again at some point, but for now, i can drive it again! Woohoo!

On to other problems to fix now... The overdrive has stopped working whilst its been off the road. typical. but from what ive been reading (http://www.mgcars.org.uk/news/news363.html), i recon its electrical... Anyway, that'll be for a different thread if i get stuck...


Thanks again...
Jono

Travel should be 1/2" to 5/8" at the slave piston. A low biting point, as well as being caused by air in the system, can also be caused by wear in the pedal, master cylinder push-rod, and the clevis pin that connects them. The wear in mine was adding up to about an inch of travel at the pedal pad. Welding up and redrilling the pedal hole, using a used but unworn master push-rod, and a new clevis pin made a big difference.
Paul Hunt

My experience just recently has still got me stumped,
My clutch stopped working so had a look and found the slave cylinder leaking so I had it resleeved in stainless and new rubbers, put it back in, bled the system as normal, definitly got all the air out, still no clutch. we rebuilt the master cylinder with new seals, still no clutch, but noticed that there was not enough travel on the slave cylinder so I made a new pin 10mm longer and now the clutch works fine,
is this wear in the clutch that makes more travel required?
Wayne Styles 1

If there is insufficient travel of the slave piston - it should be 1/2" to 5/8" - there is either air in the hydraulics or very worn linkages at the *pedal* end. Either can mean that the biting point is very near the floor, or may drag badly or not disengage at all. However the last two, particularly if it happened suddenly, are more likely to be hydraulic problems. 10mm is a huge amount to extend it, and there is obviously another problem present. You may have taken up all the free play that should be available in the system, i.e. you should be able to push the slave push-rod back further into the cylinder with your hand and create slop in the release arm. If you can't then the clutch is not fully engaged and may slip.

The clutch is self-adjusting which means it automatically takes account of any likely wear on the slave push-rod, clevis pin, release arm, release arm pivots, release bearing, cover plate, friction plate, flywheel, Uncle Tom Cobbley and all.

The clutch is a known pig to bleed so when I replaced my system I didin't even try but filled the system from the slave bleed nipple instead, which gave me full travel with no bleeding. I think you need to go back to the original push-rod and try again.
Paul Hunt

Wayne, there should never be a need to fit a longer pushrod because the clutch will self adjust and the bearing/arm and pushrod will follow the thrustpad on the clutch cover as the plate wears. That is on the assumption that the slave piston pushes it by means of the internal spring. Are you sure that you put the spring in place before you fitted the cup and piston ?
Iain MacKintosh

Think that my pedal/master cylinder push rod are worn, as i can feel 1/2" to an 1" of play just in the pedal.

Just out of interest, does anyone have the length of what the push rod should be, so that i can make a comparison?
Jono

Jono,
In case you've not seen it there's a page here about bleeding etc,
http://www.mgb.bc.ca/service/tips/clutch.html
Rich

This thread was discussed between 24/02/2005 and 10/03/2005

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