Clutch - Throwout Bearing Problem (I think?)

[andrewb70]

James, while the thought of manual adjustment of the TOB air gap sounds like a pain in the ass, at least you get direct control of that. And while it seems like you wouldn't want to deal with continual maintenance of it over time, I think it isn't that bad. Our cars get such few miles that adjusting something every 10,000 miles means we adjust every 3 years or so.

Just a thought, since it seems that the auto-adjust OEM bearing is taking matters into its own hands.

jp

All good points John, but using OEM parts can definitely be more reliable. I personally think that the problem is insufficient travel at the TOB to release the clutch. If James is using an LS F-body MC, then it is 3/4" bore. One possible solution is to use the early LT F-body MC which mounts the same way but has a bigger 7/8" bore.



Andrew

[James OLC]

It's a Tilton 77 Series MC with a 3/4 bore. I'm going to try to check how much stroke it is getting tonight. I agree that upsizing to 7/8 might be neccessary (darn).

One other advantage to the OEM slave-TOB is that should there be an issue, replacement parts are plentyful.

[andrewb70]

It's a Tilton 77 Series MC with a 3/4 bore. I'm going to try to check how much stroke it is getting tonight. I agree that upsizing to 7/8 might be neccessary (darn).

One other advantage to the OEM slave-TOB is that should there be an issue, replacement parts are plentyful.

James,

Double check how much stroke your pedal arrangement allows at the MC. You can try increasing the stroke or just get a bigger bore MC.

Andrew

[CarlC]

James,

I agree with Andrew, nothing ugly in the pics.

The first, and easiest, thing to check would be the amount of stroke at the MC. For reference, I used the guidelines that an LS7 clutch setup using a stock MC required 15/16" of MC stroke for proper release. Depress the pedal, mark the shaft with a Sharpie at some convenient reference point, release the pedal, and measure the distance from the mark to the reference point. For me, I could use face of the MC boot as a reference surface.

If the MC you are using has the same bore as the stock LS, and the clutch requires the same throw as a stock LS, then getting the 15/16" dialed in should work. As always, we're assuming that the scattershield depth, with or without block plate, is similar to stock. If the MC has a different diameter than stock a simple volume calculation can be done to get the same volume for another sized MC. For example:

Fluid volume ASSuME-ing that the stock GM MC is 3/4" bore: V = piD^2L/4 = 3.14259 x .75^2 x 15/(16" x 4) = 0.414in^3

If your MC is 7/8: 0.414in^3 = (3.14159 x .875^2)/4 x stroke, stroke = 1.656/pi x .875^2 = 0.688in.

So the stroke will be 11/16" but will have a higher pedal effort ASSuMe-ing similar pedal ratios.

The GM bearing does use a spring preload to keep the bearing against the fingers as Andrew states, but it's still just a hydraulic cylinder. It must expand and contract, so air is your enemy. Though some have had problems bleeding these, I did not. I did bench-bleed the MC and line before installation. It will not be possible to bench bleed the MC and line if you change both ends to AN. If you change only the MC side to AN it should make bleeding much easier. After bench bleeding I just plugged the line into a new GM bearing, and it worked. It was bled using four pedal strokes just for giggles, but the pedal feel did not change and no air was observed coming out.

The bearing and MC were new (modified ATS parts,) but I disassembled the MC to do the "drill mod." Is that necessary? I don't know for sure, but it can't hurt. I spent at least 30 minutes cleaning the MC and hose thoroughly and bleeding both as an assembly.

I believe that some of the troubles with the stock GM bearing is that one must be absolutely fanatical about getting all of the air out of the MC and the feed line. If this is done properly, and the new TOB is not extended during assembly, then it should be plug-and-play since I believe the bearing was bench bled as well from the factory. GM does not want to spend hours bleeding a clutch, they want the line workers and mechanics to be able to jab it together and work. Some have had problems with the hydraulics after a clutch repair. However, since the TOB is self-adjusting, just like the pistons in a disk brake caliper, if the mechanic opens the bleeder to release excess fluid the chances of introducing air into the hydraulic cylinder is very high. It is not easy to depress the TOB cylinder with the bleeder open, especially if the TOB is left on the transmission during a clutch change. It is better to remove the bearing from the transmission and bench bleed.

Since we're out of the Emergency stage I'm also going to move the thread to the Manual Transmission section.

[parsonsj]

One other advantage to the OEM slave-TOB is that should there be an issue, replacement parts are plentyful.

Fair enough, though I bought my TOB at the local speed shop for $109.

Good luck and keep us informed.

jp

[andrewb70]

Fair enough, though I bought my TOB at the local speed shop for $109.

Good luck and keep us informed.

jp

John,

The other problem for James is that he has a T56 without the bearing retainer. In order for him to use a bearing like yours he would need to do some custom fabrication.

Andrew

[parsonsj]

he would need to do some custom fabrication.

So what's the problem? Have you seen his car?

jp

[andrewb70]

So what's the problem? Have you seen his car?

jp

LOL...yes I have...and sometimes things just need to be simple!

I really believe he is having a simple hydraulic issue. Not enough fluid moving through the system to fully release the clutch.

Andrew

[James OLC]

Thanks for the advice guys. For the record John I really miss the good old days when I could just go to Automotive Engineering and walk out with just about anything I could dream up. Back here in the great white north we measure parts availability in weeks, not hours... at least the parts that I am looking for.

Anyways, with respect to the MC stroke, I measured it at approximately 1" this evening and I think that I can get a bit more if I need to. I'll shoot to get a better measurement when everything goes back together. As it is I think that I may have killed this slave (it that's possible) by overextending it (until it puked brake fluid).

I am tending to agree with the hydraulic issue at this point. I've got a new slave coming and when it goes back together I'm going to tweak the plumbing a bit. In addition to doing the drill bit mod on what is left of the factory line, I am going to see if I can replace the new line that I added with true 4AN.

New TOB should be here early next week so I'll focus on getting the rest of the car ready until then and will have an update when it's back together.

In the mean time - any other thoughts or advice is appreciated.

Thanks everyone,

[rq375]

[quote=James OLC;485984]I am tending to agree with the hydraulic issue at this point. I've got a new slave coming and when it goes back together I'm going to tweak the plumbing a bit. In addition to doing the drill bit mod on what is left of the factory line, I am going to see if I can replace the new line that I added with true 4AN.quote]

I bet $1 that the restriction in the factory line is your problem, it's at the master cylinder end and about 1" long inside the line. Drill it out to .125

[vp23271]

James,

I saw you at the OC Goodguys Auto Cross, but forgot to ask how you fixed your throwout bearing issue. Your 67 seemed to be running great and you got yourself a trophy too! Congrats!

So how did you fix the issue?

[KEISLER]

I measured the distance from the clutch fingers to the bellhousing mounting surface - 2.25".

I measured the distance from the compressed TOB bearing surface to the plane of the transmission mounting surface - 2.4"
,snip,
Does anyone have any suggestions, ideas, or recommendations on what these measurement mean and what remedy there may be?

James, I have not read all of these post replies, but I can tell you that if your numbers are correct then you are constantly engaging the clutch fingers and it would be a wonder the clutch is not burned up.

If the 2.25inch number is correct, you need to reshim the bearing to 2.10 - 2.0inch compressed and not any more. You can see my comments about why on the other thread mentioned with the Pontiac guy with the Weir bellhousing.

If you hit a wall on this, PM me and we'll help you further.

[thomasmoto]

I have a Centerforce DF and used their TOB worked fine and not expensive, but it's not a hydraulic type.

[andrewb70]

I have a Centerforce DF and used their TOB worked fine and not expensive, but it's not a hydraulic type.

So how is that relevant to the price of tea in China?

Andrew

[chicane67]

On a side note, it's a good thing that you are utilizing a Tilton 900 series asembly... as the pedal ratio is adjustable.

[James OLC]

I changed too many things to be able to point to any single thing as being the solution. I wound up replacing the TOB with a new GM piece, changed fluid types, bled the things like a maniac repeatedly, added heat sheilding to the hydraulic line over the headers and adjusted/extended the clutch rod out about 3/16" at the pedal.

I also put some more effort in rev matching on downshifts.

I only put a couple of hundred miles on it so far but it seems to be better.

[AJSZR2326]

i remember when i upgraded my clutch on a 02 z06 there was something you had to drill out to increase flow for the hydraulic set up.sorry its been like 5 yrs since i saw it. i think lingenfelter gave me the info. found the link:

http://www.torcavettes.com/tech/ClutchHydraulics.htm

[MCMLXIX]

I changed too many things to be able to point to any single thing as being the solution. I wound up replacing the TOB with a new GM piece, changed fluid types, bled the things like a maniac repeatedly, added heat sheilding to the hydraulic line over the headers and adjusted/extended the clutch rod out about 3/16" at the pedal.

I also put some more effort in rev matching on downshifts.

I only put a couple of hundred miles on it so far but it seems to be better.

James,
What was your final setup?
MC?
TOB?
Etc?

Here is my plan -
* have motor and trans
LS3 crate motor
T56 from 2002 Camaro
* will get
LS7 clutch kit
Wilwood pedal assembly -
*will try and fit reverse mount
http://www.summitracing.com/parts/WIL-340-3342/
*may end up with forward mount
http://www.summitracing.com/parts/WIL-340-3950/

Wilwood MC (not sure on size)
http://www.summitracing.com/parts/WIL-260-10372/