HYDRAULIC THROWOUT/RELEASE BEARING NOT ENGAGING FULLY

Hello friends,

Before I dive into this, here are some of my stats:

-LS1 5.7 w/ a 2-piece C5 bellhousing (from TPC)
-Bellhousing adapter for 2-piece bellhousing (from TPC)
-Spec clutch (from TPC)
-Spec pressure plate (from TPC)
-OEM LS flywheel (from TPC)
-Tilton 7/8 clutch master cylinder (from TPC)
-LS1 OEM style hydraulic slave throwout/release bearing (from TPC)

I have a few bugs I'm trying to work on with my recent LS1 swap, but my largest problem seems to be with the hydraulic throwout (T.O.) bearing.

Problem #1 - as a general rule of thumb, there should be between .100 and .200 inches of 'play' designed into the installation of the T.O. bearing. This allows for future clutch wear. From my understanding, nearly all TPC installs simply bolt together and work amazing. Some, may need a shim behind the T.O. bearing to get just the right amount of 'play'. My scenario is the opposite. When I bolt everything together my T.O. bearing is just beginning to engage the pressure plate fins. Does anyone have any ideas on something I may have installed wrong causing this problem? Or if everything is installed correctly, any ideas on how I can obtain that .100 to .200 of 'play'?

Problem #2 - using rounded measurements, my T.O. bearing appears to have a total potential travel of .750 inches. I have the clutch pedal adjusted to it starts engaging the clutch almost immediately upon applying pressure. However, my T.O. bearing is only traveling about .500 inches. Leaving nearly 1/3 of the potential travel unused. I believe this is why my car is difficult to get into gear, grinds into reverse, and spins the back tire when in gear with the clutch pressed. I have bled the lines off my pneumatic vacuum bleeder for about 30 mins continuously. I don't see any bubbles in the lines. Does anyone have any idea why I cannot get more travel out of my T.O. bearing?

Any input would so very helpful. I am totally stumped and so close to being able to enjoy driving this car!

-Aaron

I believe that it sounds like your clutch installation is correct. Hydraulic throw out bearings are designed to contact the pressure plate fingers all the time. A hydraulic throw out bearing is like a disc brake so it will follow the pressure plate fingers as the clutch wears. I could check my car to see how far the fingers move if you would like but I think your measurement of .500" is good.

I put a Coyote 5.0 engine with a Tremic 5 speed transmission and hydraulic clutch in a '67 Mustang and it experienced the same problem initially. I was going to bleed the system again but the problem went away on its own after I drove it a few times. Something must have seated or aligned itself after a few releases and standing starts. Maybe you could get lucky?
Gil

UPDATE. The reason my clutch wasn't disengaging was because the pilot bearing aluminum reducer had start to disengage from the crankshaft. This permanently pressed the pilot bearing up against the clutch so it never stopped spinning. All fixed now.

Aaron,

Just saw your last post on this subject.  While I'm glad you found the problem, I'm curious what measures you took to prevent it from happening again.

When I built my motor, the pilot bushing adapter was also loose in the crank housing.  I had it knurled to increase it's OD 0.001 inches and then used Loctite 609 retaining compound for insurance.

Details in link below if you need them.

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