Moss Motors, Ltd

When my engine heats up past 80 degrees centigrade(c temp gauge in car) my clutch peddle will bite high and she will show signs of slipping ,  I feel that he fluid is exanding but cant get back in to clutch master thereby puting pressure  on fork causing slip. I feel confident this is the case as during the winter cold  my clutch  never    slips only when engine gets above 80 degrees  c, which does not happen in cold winter . I want to replace the clutch master I understand this can be done with unit in car,moss sells internal as one unit has this been done by anyone? In addition has anybody experienced my problem with expanding clutch fluid? any help will be appreciatted  car is 70 b

 

Bob J

The first thing I think of when a hydraulic system builds up pressure when operated is that the return hole is blocked in the MC, either by crud or the piston is not returning all of the way and the most common cause of that is someone improperly adjusting the pedal pushrod to MC clearance.  Some ppl tighten them up so there is negative clearance and this will always cause a problem but since there is no pedal stop in the B it just about has to be a clogged return hole, or a crudded up piston preventing return because you can't adjust the pushrod.  I think I saw your post about no pedal at start up in the forum earlier today.  A clogged return hole would make the system difficult to bleed too. 

I had a similar problem to this with a Celica.  The clutch worked fine, until I got in it in the morning (50F)  then no pedal, I could bleed it and it was good for days, until the next cold morning.  It was the slave cyl and the master working together.  The vent on the cap on the master was gooped up and the slave was worn so it would suck in a bunch of air at night past the slave seal as the MC vent sealed itself and cooled and then it would push the fluid back into the reservoir as it warmed a bit, opening the reservoir vent in the process.  The air was always at the master, but the source was the slave.  There was no visible sign of leakage.  It drove me nuts for a few weeks.

Try this, completely replace the clutch fluid, and be sure you bleed it well and see it it still does it. A good test it to stop the car, have a bleeder wrench handy and crack the bleeder valve.  If it spits fluid just sitting there, its building pressure in the system (return hole) Either way, you probably need to do both MC and slave at the same time..

If the hydraulics are old, consider just replacing vs rebuilding them since they're iron and quite likely pitted on the inside

Hope this helps

 

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-Michael

Mike:

Thanks for the responce and no I didn't post about no peddle I have to much pedal, but it sounds like a mc is in future will drain system and bleed the old stuff out first maybe some of the crap will go out the slave is brand new along with the flex hose.

thanks again

Bob J

OK, here comes the voice of potential doom.

Many clutches, as they age and weaken, will start slipping when hot, but will be fine when cold. I have experienced this personally. Of course you should check out the possibility that you have a minor problem, but generally speaking, when the clutch on a B starts slipping, a new clutch is indicated. Clutch springs are quite strong, and unlike brake return springs, they are capable of pushing the hydraulic components "out of the way" with some authority when they are healthy. Anything's possible, but I'd start pricing a clutch...

Try this. The next time it starts slippiing under accelleration while hot, downshift to third. Does the slipping go away? If so, the clutch is a gonner. If not, try second. If it slips in all gears you may indeed have a release mechanical or hydraulic problem, but if it only does this in higher gears, you've gone through a clutch, my friend.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

I live in s. Fla . so it's always warm. I had a similar problem .Turned to to be the slave hose.Looked normal but was explained to me that if the old rubber hose is still in use it will contract when cold and expand when hot ,makes sense. I would try the less expensive route first. I replaced with a stainless one and have had no more troubles. good luck.

Mike thanks for info wiil change out hose and fluid and see where that gets me, yesterday was a much cooler day and was not a problem after a 20 mintute run at all speeds.

thanks

 bob j