Hydraulic Throwout Bearing Issues (maybe) - help!
 

I am going to be the first to admit that clutches (et al) are not my strong suit to begin with and the T56 and hydraulic TOB in the '67 is the first one that I have ever done (besides servicing in my old WS6).

That said, as a lot of you know I was having issues downshifting the car car at the Optima challenge - the car would upsift fine but when I tried to do higher speed/rpm downshifts the transmission wouldn't slip into gear. Heck, it wouldn't be forced into gear either... some times it would go with a little more aggressive blip but not always.

Opinions at the time ranged from transmission (doubtful - new by Rockland), to fluid (it was full), to clutch/TOB engaugement (possible), and hardware issues (but after inspection nothing is loose, backed out or missing).

So, out comes the transmission. At first look everything appears to be ok - nothing is loose or appears unusual. So, following some instructions I found on the RAM site I take some measurements to see if maybe the TOB needs a shim (which was one of the more common suggestions up front).

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"

It would seem to be (and as admitted, I am a far cry from an expert here) that the TOB isn't compressing enough and that based on these measurements there is pressure on the clutch fingers all the time.

so...

Does anyone have any suggestions, ideas, or recommendations on what these measurement mean and what remedy there may be?

My first thought was maybe bad TOB?

Any help would be appreciated.

Thanks,
James

what clutch master are you using?

Jody

McLeod SFI LS bellhousing
McLeod RST dual disc clutch
McLeod aluminim LS flywheel
Stock GM hydraulic throwout bearing (new but maybe refurbished)
Rockland Standard T-56 - Son of Tranzilla

0.75" Tilton 77-series Master Cylinder with CV remote reservoir

does the stock GM throwout bearing have enough travel to disengage the dual disc clutch? I didn't think it did, but not positive. I thought the McLeod dual discs had their own bearing to use, mine did.

Jody

I don't know if this has anything to do with it, but when I looked at the car on Tylers lift I was a little concerned with how close your hydraulic line was to your header pipe. Does it get worse with heat?

Jody,

I spoke to McLeod earlier today... it hurts even thinking about the conversation...

It's the same thing every time I call them... "a clutch either works or it does not work, if you can upshift you can downshift... you have a transmission problem." After convincing them that I was looking the the throwout bearing as a possible issue and specifically bringing up your point, they said that "the stock GM TOB with a stock GM 3/4 master just barely releases properly and they have two solutions to ensure full release - their 13/16 master or their TOB." But again, if it upshifts it downshifts so that can't be it anyways. Man, are they defensive (to be polite).

I did also ask them about the apparent preload on the clutch fingers. Their response was that it is "perfectly normal and acceptable and all clutches have that preload. As long as the bearing does not bottom out it's not a problem." Now, that seems contrary to what most other clutch manufactures say (and when I mentioned that and the word shim he didn't seem to know that there were other clutch manufacturers) so I don't know.

Definately losing my mind here...

I guess that it's possible. I can't say for certain that I notice a worsening with heat - but that is because I tend to make sure that everything is warm before proceeding to hammer on it. I have considered a fluid issue (with respect to volume not temperature) but since one of my off season projects is heat shielding everything that even looks like it will bite me, I'll definately be covering that when it goes back together.

On the fluid volume side of things, the Tilton MC's come out of the master with a -3AN line and the factory disconnect is a -4an line. I am wondering if the couple feet of -3 vs -4 is an issue and I'm not getting proper fluid flow down to the slave. I'm going to look into that as well...

I am also going to double check runout after I pull the clutch tonight. I haven't encountered anyone who has even found an issue there with the LS engine and the McLeod stuff but it's easy enough to check again.

Jason at Katech mentioned that he has seen disengagement issues related to a bend clutch disk so that will get some attention as well.


Anything else anyone can think of looking at? Without seeing a definative problem I am at a bit of a loss for what to do next...

Reading through your comments I don't like the barely sufficient explanation for the stock throw out bearing. Sure doesn't seem like it gives you much room for error in regards to master cylinder stroke. Any variation in your bellhousing depth or pressure plate springs could easily make barely not work. If it was me I would take barely out of the equation and call Rockland. I assume it's in every gear?

I have an email in to Rockland now and am waiting to hear back. I agree that it seems that 'barely' is not the word that you want to come to mind in this case but I am taking everything that I heard in that conversation with a grain of salt...

I hear ya...I know how that goes. You call in twice and get two different answers. If you can verify enough disengagment it has to be internal tranny. Can you put the bellhousing back on and simulate the tranny with a bracket and measure the clutch disengament? Did it every creep in gear with the clutch in?