Transmission, Manual

Clutch Bleeding Tips

Clutch Bleeding Tips

> I have been troubleshooting a problem with my hydraulic clutch on my
> car and have run into a problem. I found that the same flexible house was
> leaking fluid and needed replaced. Thinking that was the only problem I
> called up Dave Roberts at 928 Specialists and ordered the hose (thanks again
> for the prompt service Dave). But after getting the hose in place I ran
> into a problem bleeding the clutch. I found when I opened the bleeder valve
> and depressed the clutch that fluid squirted out like normal then I would
> tighten the bleeder value and release the clutch pedal. The problem is when
> I went to repeat the cycle opening the bleeder valve caused fluid to sucked
> back through the hose and into the system again. Has anyone seen this with
> their car? I am assuming that in the master cylinder that there is a valve
> that would allow the fluid to be sucked from the reservoir and therefore
> relieving the negative pressure that is suck the old fluid back into the
> system. If so am looking at a new master cylinder?
> Doug Burger
> 81 Euro S 5speed Gran Prix Weiss

Your pushrod on the pedal side is adjusted in too far in. There is a port in the Master that allows fluid to flow from the reservoir. If the piston can't come back far enough the port never opens. Be patient, bleeding the clutch is VERY tricky in our cars. There is a natural spot for a bubble of air at the top of the master cylinder. Most people suggest dettaching the slave cylinder and pushing the piston all the way in to dislodge the air in the master cylinder. You should leave the pushrod on the pedal side a tad loose until you get a firm pedal or you won't be able to bleed at all and it will drive you nuts (don't ask me why I know that!).


There are two mechanisms that allow the reservoir to replenish the master cylinder, one is that the seal is a one way affair, that should allow fluid to pass as the master cylinder piston is released, secondly, there is a small hole that connects the reservoir to the front side of the seals when the piston is all the way back (i.e. the hole is closed off when the piston has moved a small distance.) Check that there is free play at the push rod when the pedal is released (to make sure that the piston isn't being held forward). If that's OK, it sounds like the piston is sticking. As the fluid is not passing the seal freely, it could be that the seal has swollen, and that might also stop the piston returning fully.

I would suggest that you buy a master cylinder reconditioning kit (or whatever that translates to) which contains replacement seals. On my car (1980 "S" Euro RHD), the master cylinder can be dismantled from inside the car. I think that there is just a circlip holding the piston in. Prepare for a spring loaded piston, and some fluid before you release the circlip.

To get the car going in the mean time, I would suggest that you try bleeding again, but after the pedal is depressed, close the bled nipple, release the pedal (slowly), then depress the pedal again before opening the bleed nipple (slowly). this will prevent air (or old fluid) being sucked back in.

So you know what it should be like: when I had replaced the seal in my clutch slave cylinder, I bled the fluid through without even pressing the pedal. The fluid came through under gravity!

Paul Smith

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