On one of my cars (its a clio 172) Ive fitted a more modern engine and box (from a clio 197) and to do the clutch Ive used a wilwood master cylinder.

Works MINT, lovely feel and all that, BUT when it gets hot on track, it ends up slipping, im 99.9% sure the reason is that when the clutch fluid (superblue brake fluid) is getting hot its expanding, and that expansion is then keeping the slave cylinder slightly pressurised and hence effectively its ending up like im riding the clutch.

So I need some way to relieve the pressure out of the line when its getting hot or something like that.


Any suggestions PFers?



CheeRS


Chip

 

Lower the level so you have a larger airchamber for when the fluid gets hot and expands?

 

I would have thought massive amounts of heat shielding is needed too. I do not know if it gets more flammable the hotter it gets but the fluid does burn a bit too well for my liking.

 

you can fit an inline device as fitted to most VW 6 speed setup which has regulated chamber, haven't got a picture to hand but you will find them on mk4 golfs, boras, fabia's all with 6 speed gearboxes

 

The problem is that its the fluid between the cylinders expanding, not whats in the reservoir, that would just overflow if that expanded.

 

Yes I was thinking of something along those lines as that is what the 197 has, but was hoping for an aftermarket one thats nice and simple to fit as most of them seem to be built into lines or on weird connectors not normal M10 or 3/8 UNF etc

You got a link to what you mean on the VWs?

 

Is the master cylinder backing of enough to release pressure out of the circuit?
Might just need a rod shortening a little.
Just a thought.

 

If the pedal/master is set up correctly...ie the orifice from master body to reservoir is uncovered, then there should never be a scenario where the system can pressurise pushing against the slave/release bearing.

And is there any chance the slave/release simply doesnt have enough clearance/travel from the fingers when fully retracted ?

 

Stevie/Wishy, thats a good point actually, it should just release the pressure back to the reservoir when not pressed, it must just be incorrectly adjusted!

Thanks mate, cant believe I missed that one! shame on me!

 

I had a slight problem years ago when I had the RV8/R154

Car drove fine, clutch always gripped, but over time the pedal feel would just change.

Releasing the bleed nipple and out squirted fluid because the system was pressurised.

Whilst fluid was able to return, clearly the pedal/master was adjusted slightly wrong and it was able to retain some pressure in the line.

So a quick test for you...when the hot slippage occurs, open the bleed nipple to see if there actually is any pressure in there, if so, look to adjusting the master rod.

it's always tempting to adjust this so there is no play...sometimes a little free play isnt a bad thing.

 

Yeah I was going to do the pressure thing next time it happened anyway (mainly just so that it works again) so will do that as a check.

annoyingly its fine on the road, I think it must be compression heating the fluid not heat transfer (and on the road you arent continunally changing gear like on track), so I guess I could just sit there and pump the fuck for 5 mins straight and see what occurs!

 

Ps

The problem I might have is that I have used a cable still and it goes into an adaptor that in turn pulls the master cylinder, and the pedal has an auto ratchet, so I probably cant trivially adjust it as its self adjusting when its cold then over adjusted when hot.

On another car Ive moved the master cylinder right over to the pedal and used it directly though, so i guess I will have to take the pedal box out and do the same, huge ballache though and this car is only meant to be a cheap and cheerful backup car for when the proper one isnt ready, dont want to waste too much time on it, might just get in habbit of releasing the pressure between sessions for now!

Or I could just do not quite as good a job of bleeding it actually, and then there would be some air to compress, I think thats why it used to be fine before I had engine out and back in as I was a lot more thorough bleeding it this time!

 

Larger bore feed pipe/hose?

 

There is no feed pipe. It's integral

 

Is your setup just to complicated?
Of you are using the 197 gearbox end can you not simply use the same end on the end of your leg?
Or is that too much effort for the limited reward?

 

Its not complicated particuarly no, its just a cable pulling a master cylinder, as it meant I could do it that way and not have to remove the pedal box and crack out the welder like I did on my cup as this car gets VERY little of my time, its only my "backup track hack" its got not love in it at all, lol.

 

Ditch the auto adjuster then.

 

Would be a real pain to do that, would still have to have the pedal box out and if doing that I may as well just move the master cylinder and get new lines made TBH.

(just trying to keep my time costs to an utter minimum as Im desperate to get my proper car finished and this is just to allow me to do a few trackdays in between and im REALLY short of time at the moment as working away from home so much and got loads of other stuff on)

 

I mean just drill, pin, bolt, whatever. Just to disable it from moving somehow, even if just for a test

 

I think I would still need to have the pedal box out even to do that, its a right ballache for space down there!

I do agree with what you are saying though, will have to have a look when am next near the car, although I think im going to try the "unbleed it slightly" approach first!

 

I would say it's feasible.

My ex had an old clio 16v (bonnet bulge one) She was at the county show on a red hot day, she was leaving the ground, in traffic for hours. She rang me to say the brakes were getting stuck on and she couldn't hardly move the car. By the time I got there (after she'd parked up with the engine off) the brakes had free'd off. They should have a metal heat sheild which was missing and it was heating up the brake lines at the back of the engine bay. Took a while to get home as she had to make another stop and let it cool before she could get going. Once moving properly it was fine.

I would say it's possible with a hydraulic clutch too. You still have a master and slave, the fluid between the two expanding would act on the slave if it was hot enough.

 

Again, if the master is adjusted properly it is impossible for the above scenario.

Either pedal would need to be depressed slightly, or master rod adjusted properly. Either way it's the same thing, the hole in the master is partially covered.