Once the snow clears I plan on digging into an odd problem with my clutch. Early last summer I had the clutch, master cyl and slave replaced... along with a resurface of the flywheel etc.

The clutch works fine, however it seems there is a leak somewhere. The fluid level doesn't go down in the reservoir, but it seems to be leaking from the 'pressure' side of the hydraulic system and into the 'non-pressure' side.

The symptom when driving is that while I am sitting at a stop with my foot on the clutch, the clutch will engage while my foot is on the pedal. Releasing the pedal and pressing it again restarts this 'process.'

I bought the DORMAN Part # CM39102 master cylinder from rock auto. Even though I feel like MSA buys from rock auto and resells at a huge markup, I'm wondering if the price difference ($30 RA vs $90 MSA) is perhaps getting what I paid for.

In any case, I cant seem to find rebuild kits for the master or the slave, so it seems like I will need to replace them again. Any advice for how to determine which cylinder is the culprit, or just replace both and call it a day.

A friend of mine suggested that I buy the identical parts from rock auto, then return the ones I have currently installed on the car. To me that is a bit on the wrong side of the karmic wheel. I would love to get some advice on determining where the leak is, as I would prefer to only replace one part.


76 280z L28 N42, 5 speed unknown transmission...

 

Hi Pez!

First of all, if your fluid isn't going down in the reservoir, I doubt there is a fluid leak in the system.

That said, it could be you have air in the system. Have you bled it? If not, you can do that just like you do brakes.

I have had only one issue (so far) with RA parts. Had one of their drum brake cylinders leak on me right out of the box. Took a week to get a replacement and the second unit worked fine.

I did get a brake master cylinder from RA and it seems to be working just fine.

I'll be keeping an eye on this thread. I'm almost ready to re-install the motor and transmission on my own restoration and that clutch system will be checked out when that happens.

------------

Another thought ...

If the system has been thoroughly bled and still does the same thing, I'd suspect the master cylinder. It's might have a slight internal leak and letting the fluid past the seal and back into the reservoir. So as you've already surmised, if you can't rebuild it, it is time for a new one ...

I can't see it being the slave, not with that symptom. If fluid got past the slave cylinder's seal, it would be leaking out and your level would go down.

 

It's leaking by the plunger seal in the slave or master cylinder. The drip will tell you which one is bad. That's why it creeps with your foot on the pedal. Buy a good new one not a rebuild.

 

@beg -

I had it installed at a Nissan dealer, but I supplied the parts. I would think if bleeding was the issue, I would need to pump the clutch to get it to actuate (like the brakes). It actuates fine, just doesn't stay that way. It takes about 15-20 seconds for the clutch to re-engage with the pedal down.

Guessing that if I had a helper or a complex system of mirrors, I would be able to see the fluid go down in the reservoir when I depress the clutch, then slowly fill back up as the fluid slips past the internal leak.

@ramz -
I think I will take that advice and spend the cash. Plus I will install it myself, I've gained a great deal more confidence than I had last summer. I will just start with the master and see if that solves it, then move on to the slave if it doesn't.


When it gets warmer.

Cheers

 

Pez - closely inspect both cylinders for a leak. Ramz is right (as usual) - if you can see ANY kind of a leak, even the smallest, that would be a dead giveaway. If nothing there, again, I'd go for the master first. It's harder to replace than the slave but is more likely to be the cause.

Hope it warms up for you soon. You don't want to know the weather here.

 

It doesn't have to leak at all to be defective. It's leaking by the piston seal back into the reservoir. It's a basic hydraulic system. I work on them all the time, same problem. If the master is leaking you will have a wet floor under the pedal.