Clutch Throwout bearing problem - need some advice

briankeithsmith · 05-06-2009, 04:31 AM

Background:
1. this is a race car, so clutch actuation has been modified in the following way:
a. No clutch cable
b. I have an aftermarket pedal set that implements a clutch master cylinder which drives a Wilwood slave cylinder that pulls on the clutch fork in the same manner that the clutch cable would.

With that out of the way:
I put the engine/tranny back in the car on Saturday. Fired it up. No issues until I got ready to put it into gear, and what I encountered was that I was pressing the pedal, but it was as if the clutch wasn't releasing enough. So when I'd try to put it into 1st gear for example, the car would try to inch forward as 1st gear started engaging, meaning that the clutch was still engaged to some degree.

So I bled the clutch system, tried again, no luck. So I pulled the engine out, separated tranny/engine to take a look. The TOB appeared fine, no apparent issues. The clutch fork appeared fine, nothing apparently wrong or visibly wrong.

I lined the TOB up with the clutch fork,mated engine/tranny, tried again. So last night I'm back to work on this thing and I bled the clutch system again. I had my wife press the clutch and I could see that the clutch arm was moving very little. So I figured maybe she wasn't pressing hard enough. So I got in, and pressed the pedal - I noticed pedal was pressure was normal to a point then it pedal pressure increased, and SNAP - POP - pedal goes to floor.

I get take off my inspection cover in the rear of the cabin and look down in the inspection hole of the bell housing and I see that the throw out bearing finger on the top has snapped off.

So I've said all of that to ask this:
1. It seems like something is preventing the clutch from totally disengaging - that's what I experienced on Sunday, and that's basically what I saw when my wife was pressing the pedal.
2. And obviously whatever it is, is a significant enough force that the finger on the TOB couldn't hold up to that force and gave way

So what should I be looking for?
Guide tube? Could that possibly be holding up the disengagement of the clutch?

Any ideas or suggestions appreciated. I ordered another TOB last night, but certainly don't want to break this one...

A930Rocket · 05-06-2009, 05:09 PM

Brian,

Just thoght of something. With your car sitting for some time, the clutch/PP/flywheel combo may be stuck together? Can you drive it around, maybe jarring it loose?

IIRC, someone else had the same issues and fixed it by driving it this way.

lucittm · lucittm's Garage

The clutch pressure plate has a big spring kind of like a belleville washer. The pressure plate is supported by metal rods and plates that keep it aligned with the pressure plate housing and the clutch disc. It is possible that there is an alignment problem between the TO bearing and the pressure plate. Pushing/pulling on the TO bearing with the alignment problem is not allowing the clutch to release and side loading the TO bearing.

When you started the engine were there any vibration issues?

Hard to imagine that the TO bearing would be siezed onto the guide tube...

Now if the screws holding the guide tube were loose and the guide tube was out of alignment, that could also cause the TO bearing to be cocked to one side and the clutch to not release properly.

Wow, I wonder how much force it takes to break that TO bearing finger?

Good Luck,
Mark

A930Rocket · 05-06-2009, 06:27 PM

I talked to Brain tonight. After 26 years, the guide tube has some wear and galling on it. The thought was that the TOB was sticking and/or getting cocked eyed on the guide tube. He's ordering a new one tomorrow.

cl8ton · 08:27 PM

Jim is correct I believe, the guide tube is the culprit.
I was having a "Crunchy Clutch" for a while when pressing the clutch pedal in.

Sometimes sticking in the down position. Dropped my motor this winter and found the issue.
I have a Sach's Sport clutch with the longer TO fork tube.

There were plenty of signs on the guide tube that something was rubbing against it shown in the pics.

I replaced the TO bearing and cleaned up the galling, then prepped it with Anti Seize. To date...no problems.

briankeithsmith · 05-07-2009, 04:59 AM

Anything I need to know that's special in regards to the replacement of the guide tube?

briankeithsmith · 05-07-2009, 05:04 AM

Here's the Guide tube:

Here's the broken TOB:

cl8ton · 05-07-2009, 06:52 PM

Brian I think if the guide tube is not disfigured, it should be OK.
Just clean it up with a belt sander and coat it with anti-seize.

Just remove the 2 Allen bolts and the guide falls off.

The weird thing with my clutch sticking issue was, the clearance between the
TO and the guide tube was close but certainly not tight yet there were sign of it sticking on the guide tube.

The only thing I can attribute the sticking too was the TO bearing replacement???

Good Luck!

briankeithsmith · 05-08-2009, 04:43 AM

One more question Rod : Is there a seal at all that needs to be replaced behind the guide tube? I bought the tube, but have been trying to determine if I pull the other one off, am I gonna have a seal issue to deal with (currently not leaking, don't want it to leak)...

My guess is NO based on the way it looks...

briankeithsmith · 05-09-2009, 06:34 PM

Yet another question:
1. How far does the TOB have to move generally to relive the pressure applied by the pressure plate. In other words , if someone is depressing the clutch, and I'm looking through the inspection port on the topside of the tranny, and I'm watching the fork pull the TOB, how far should I expect to see the TOB move in order to relieve the pressure to disengage the clutch?

FYI - what I'm seeing is about 1/16 of an inch... AND THEN.... The TOB snaps... (yep broke the 2nd one today, looks just like the pic I posted earlier this week)

lucittm · lucittm's Garage

There is a seal behind the guide tube for the transmission input shaft. It is a pain to remove, replacement is straightforward. I did mine when I was in there. Normally they will weep for awhile when they fail, then you can go in later and replace it.

I am thinking the TOB actuation arm might be bent. One arm bearing on the TOB only on one side and not the other.

Tough luck on the second TOB. Let us know what you find out.

Mark

A930Rocket · 05-09-2009, 07:53 PM

Good idea. Bent or cracked allowing for uneven pressure. What about play in the vertical shaft?

Quote:

Originally Posted by lucittm

I am thinking the TOB actuation arm might be bent. One arm bearing on the TOB only on one side and not the other.

Mark

briankeithsmith · 05-10-2009, 09:03 AM

I'm probably gonna pull that shaft out just to see what the deal is. But I gotta figure out which way is the proper way to drive the key-pin out that holds the fork on the shaft...

How can I tell from which direction I should drive the pin out - and I assume the pin is re-usable assuming I don't maul it up too bad?

briankeithsmith · 05-10-2009, 06:27 PM

Tonight I pulled the fork and clutch fork shaft out. Everything looks fine there. No apparent issues. I'm going to try to have them magnafluxed tomorrow to see if there are any cracks that could be causing it not to pull the TOB.

(I don't think there are any - everything looks pretty darn good....
Especially to be 26yrs old...

NathanUK · NathanUK's Garage

Did you find out what happened?