Clutch Slave or Clutch master failure

[Blitzed]

Hi All,

73 240Z with L28 transplant. Recently purchase a clutch pedal kit from a supplier (new clutch master, slave and rubber line). Also replaced the stainless line from the master to the rubber line. Using  DOT 3 brake fluid in the master. Car shifts smoothly until 30 -45 mins driving. Once car is at temp, loose engagement from the slave (assume it's the slave and not the clutch). I can engage forward gears with a clunk 1st -4th, but will not shift into reverse (grind). 73 clutch slave, no spring from the bearing lever to the slave, single pedal adjustment on the master shaft to the pedal. 

First time it happened bleed the system, issue gone, shifting smoothly again. Next hour drive issue came back. I'm not sure this is an air or bleed issue, when the temp is down will shift smoothly again without bleeding or adjustment at the pedal. 

Where do I start? try a different fluid, replace the mater (valve expansion at temp), replace the slave? 

Any advise would be appreciated. 

[AK260]

Gosh this is a toughie!

 

What brand kit are you using?

 

So the easy thing is: don’t worry about the fluid as dot 3 or 4 have boiling points in excess of 200c (400F). If you can get your clutch fluid that hot then you really have other problems ! ;) But on that note I trust you are using fresh fluid and not old stuff that’s been sitting for a while? Being hydroscopic these fluids absorbs moister.

 

I thought my synchros were done for until I bled the slave cyl. Then realised how sweet my ‘box is. Based on that I would say your clutch is just on the edge of disengaging enough.

 

The obvious:

 

When this happens, how hot does the master feel to the touch? Is it significantly hot?

 

Have you bled both master and Slave cyls?

 

Are all your joints fully torqued up? And the nipples too? (The latter sounds painful[emoji1787])

 

Do you have any twists in the flexible pipe going to the slave?

 

Are you seeing any fluid leaks? Anywhere!?

 

 

 

 

[Mark Maras]

 Assuming there was no problem before the line change and no adjustments made at that time, it sounds like air in the line.

[zKars]

Since the problem goes away after a bleed and returns after a certain amount of use, I'm thinking it's bad seals in either the slave or master. Time to remove and inspect the bores and seals in both. If they are rebuilds of old castings, expect to find pitted bores. 

[Zed Head]

17 hours ago, Blitzed said:

when the temp is down will shift smoothly again without bleeding or adjustment at the pedal. 

Sounds like you might have one of your hydraulic lines next to a heat source.  The exhaust manifold or headers.

[Blitzed]

Hi All,

Thanks for the feedback. Spent the past 8 months knocking the ugly off the car. Car sat for 23 years in a garage so have no idea the performance / functionality of any part prior to storage. It's all a discovery process. 

Went through the entire braking and drive train. Just replaced the sub axle bearing so I'm sure the drive shaft and trans axle u-joint bolts are torqued. This is the only on-going issue. 

Purchased the slave attached from Z car parts of AZ. New master is straight forward, zero bleeder on the master. Single bleeder on the slave. Previous maintenance on the compression fitting (at the flex/rubber hose) was vise grip stripped so i replaced both hard (to the master) and flex or rubber to the slave to ensure no air leaks.

Will double check all connections for torque and leaking and bleed again. Keep you posted. Could this be clutch failure? 

https://zcarsource.com/clutch-slave-cylinder-240z-260z-280z-7-72-78-oem-new 

[Blitzed]

Sounds like you might have one of your hydraulic lines next to a heat source.  The exhaust manifold or headers.

All lines are in stock position, hard line runs along the firewall above the stock manifold and exhaust. flex line come off the body rail passenger side and slave is bolted to trans. It's all exposed to heat. 

[Zed Head]

17 hours ago, Blitzed said:

Once car is at temp, loose engagement from the slave

when the temp is down will shift smoothly again without bleeding or adjustment at the pedal. 

This is a big clue.  More bleeding probably won't help.  Something is getting hot.  Could be fluid, could be seals, Not likely mechanical, there's not much to the pressure plate and disc.

[Zed Head]

Have you popped the slave cylinder dust cover to check for fluid?

[AK260]

You’re right, no bleed nipple on the master but the trick is to have someone with their foot on the clutch pedal all the way down, then get a rag and undo the nut that tightens the outlet bolt exactly as you do a bleed nipple and do it up quickly before the fluid stops coming out. Repeat x3 (like the Irish, to be sure to be sure to be sure)!

[siteunseen]

Or get a big syringe and stick it down into the reservoir and pull the air out. Done it this way for many years because it works.

Syringes can be bought from a veterinarian's office.

Edit: not necessarily big but with a long tube.

Edited July 14, 2019 by siteunseen

[w3wilkes]

Or go to WalMart or UK equivalent and get a Farberware Soft Grips Black Stainless Steel Flavor Injector Set for less than $8

https://www.walmart.com/ip/Farberware-Soft-Grips-Black-Stainless-Steel-Flavor-Injector-Set/17813046

Edited July 15, 2019 by w3wilkes