PUZZLER - Hydraulic Clutch.

[Apollo 62C20]

Need some help folks!

Background: I have replaced the master cylinder, clutch slave cylinder and hydraulic clutch hose on my 1962 C20. When the clutch pedal is depressed the slave cylinder extends and pushes the clutch fork perfectly but after 2-3 seconds the slave cylinder begins to slowly retract and let the clutch engage. When you are watching it happen it looks as if a bleeder valve has been opened and fluid is slowly leaking out. If you pump the clutch it pumps right back up but it is a real pain while doing things like parking, waiting at a light or launching a boat. The entire system is new, fluid was from sealed containers and the brakes are functioning beautifully. I have bled the clutch 6-8 times over the last two weeks and nothing has changed. Suspecting a leak I peeled back the dust covers and checked both the slave and master for fluid but found them bone dry. The system doesn't seem to be losing any fluid as the reservoir has remained full.

Following the advice of forum threads I have also tried "blocking" the clutch fork while I bled. No change. I have also checked the line for bulges that may be allowing expansion. Nothin'. I "bench bled" the master again. Same. I have even bled all of the connection points. Same issue.

Am I crazy? In a sealed, non-leaking hydraulic system the slave cylinder has to track the movement of the master cylinder right?

Anyways, I need some ideas! I am close to taking it to a (gasp) mechanic.
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[jocko]

could you have a bad slave cylinder? i.e. fluid leaking back/forth past the internal seals in the "closed" system - and therefore, producing no visible leaks?

I agree - sounds like a very odd problem, and I'm not being much help. If no obvious leaks, and it sounds like a "bleed-down" sorta thing, that's all I could think of.

[Apollo 62C20]

I got the slave from LMC. No disrespect to those guys but I have gotten a few items that were low quality before....

I'm not sure how I could check that. I guess I could pull the piston out for any weird stuff.
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[markeb01]

I'm with Jocko, this might be an internal bleed problem. I suppose this could be in the master cylinder as easily as the slave. One other thought being - do you have any loops in any portion of the hard line or rubber hose going to the slave cylinder. If so air could be trapped in the top of a loop, similar to what happens when a disc brake caliper is incorrectly mounted upside down.

[fixit-p]

Your master cylinder is bypassing internally, if it were bypassing at the slave cylinder you would see an external leak but when it bypasses at the master cyl. it just leaks back into the reservoir.

[Apollo 62C20]

Thanks for the input. @Markeb01 I don't have a loop but there is a hump as the line crests the firewall. I may try detaching the slave and holding it in the air to allow air flow upwards. I'm also gonna call and see if I can get my master cylinder warrantied. I will keep you updated. Thanks again. I was thinking it may be a defective part. We will see!
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[Heater63]

I'm with fixit-p. It sounds like leaky MASTER is not holding the pressure

[Heater63]

oh, and I love the byline fixit! if anybody shoots straight about the internet it is Pres. Lincoln! LOL

[maxwoof]

I can tell you that when I was experiencing the same problem - clutch slowly engaging, replacing the master cylinder was the fix for me - 62 k-20. Master from RockAuto.

[61_FL_Apache]

One of the two have to be leaking internally. Go with the cheapest one first..

[jocko]

Originally Posted by 61_FL_Apache

One of the two have to be leaking internally. Go with the cheapest one first..

Excellent point...

[fixit-p]

Originally Posted by Heater63

oh, and I love the byline fixit! if anybody shoots straight about the internet it is Pres. Lincoln! LOL

Honest Abe wouldn't lie..................would he??

Originally Posted by 61_FL_Apache

One of the two have to be leaking internally. Go with the cheapest one first..

I disagree, troubleshoot and change out only what is bad. If the slave cylinder is bypassing it will leak externally because the rubber boot is designed keep crud out and not to hold pressure (that's the piston seals job). The master cylinder on the other hand if it leaks internally it just goes into the reservoir, no external leak. Same with a bad wheel cylinder if it bypasses you have brake fluid all over your brakes and if the master cylinder bypasses it goes into the reservoir and while at a stop the vehicle may start to creep forward same symptoms just different circuits.

[Apollo 62C20]

UPDATE:

Problem-Clutch slowly 'bleeds off' and engages when pedal remains depressed, No signs of fluid in dust covers, slight airy noise coming from master cylinder when clutch is engaged.

Solution - Replace Bad Master Cylinder. Although I had just recently purchased the master it was defective. After installing the new one everything works great! Strangely my brake pedal is higher and harder than ever.

On a side note: the old master looked new when I installed it but was horribly rusted when I removed it (5 months later) so I coated the new one with a light coat of grease to see if I can keep it from happening again. I'll let you know.


Thanks for helping me out with this one guys, I really appreciate it!

[maxwoof]

Congrats on fixing your problem. My master was rusting up quikly too - I painted it with some rustoleum smoke grey. Probably should have done that before I mounted it to be able to get at the back. Looks ok - not too far away from the natural cast iron look.