Restoration & Modification Projects > Modification Projects
My Black Bitza
wabco40:
--- Quote from: Scott on September 16, 2015, 08:18:22 AM ---According to the instructions for the hydraulic throwout bearing, I need 150-200 thou clearance between the bearing face and the clutch fingers. It also stated that chev bellhousings are shallow, so you may not have that much. Sure enough I measure it all up and I have around 20 thou clearance.
Apparently It's OK to space the bellhousing out a little from the block using washers.... No thanks. Or I can buy a 250 thou spacer from the supplier and then shim the throwout bearing up to the correct clearance. It's from a US company, so wouldn't be a fast turnaround time, of cheap. I figured I'd have to make my own up instead.
Of course no decent aluminium place is open on a saturday arvo, so I went to masters/bunnings for a look. Sure enough, masters sell sheets of 3mm plate aluminium.
3mm is around 120 thou, which gets me pretty close. The instructions say 100 thou is still OK, so 140 though should be fine. Plus there's more spiggot engagement that if I used a thicker spacer, which I like the idea of.
I've gotten as far as marking the plate up with a scribe and hopefully I get some time tonight to cut something out.
--- End quote ---
Hi Scott,
The clearance you need is not between the bearing face and clutch fingers. The bearing on a Concentric Slave Cylinder runs on the pressure plate fingers and is designed to be compressed by more then 0.5" when at rest.
Its the compressed clearance of the CSC that you need to measure, to make sure it does not bottom out.
Measure from the clutch fingers to the gearbox mounting face on the bellhousing. Then measure from the front of the gearbox case the surface of the fully collapsed bearing.
Subtract the first measurement from the second to give you how much clearance or cushion you have. Anywhere between 1/8" (0.125") to 3/8" (0.375") is ok. Anywhere in this range is ok and there is no advantage/disadvantage being in the upper or lower end of the range.
If the clearance is more then 3/8" then a CSC spacer will need to go between the bearing and gearbox to move the CSC closer to the engine.
If its less the 1/8" then you will need a bellhousing to gearbox spacer to move the gearbox and CSC further away from the engine/bellhouing.
Scott:
Yep, that's exactly what I have measured.
Clutch fingers to outside bellhousing face was 64.7mm
Gearbox mounting face to collapsed bearing face was 64.2mm.
Difference is 0.5mm, or 20 thou clearance when compressed.
As the clutch wears, the fingers will stick out more. I figure the clearance is to allow for that, so that the bearing isn't fully collapsed and under load when the clutch is towards the end of it's life.
I guess I was assuming the CSC returns to fully compressed once you take your foot off the pedal, hence referring to the gap as the clearance between the two. Either way, a 3mm spacer between the gearbox and engine will sort it out.
wabco40:
Hi Scott,
I read your post as clearance between the clutch fingers and bearing face and spacing the bellhousing away from the block, where its cushion clearance and spacing the gearbox away from the bellhousing. Anyway glad you have got it sorted :thumb:
I am going to be setting up my clutch and CSC this weekend. Looking at your post it looks like I might be in for a 1/8" gearbox to bellhousing spacer as well :grr:
Scott:
I just re-read my instructions and they refer to the clearance as an air-gap between the bearing and fingers. Sounds like your instructions explain it differently. I was going to make a spacer for between the bellhousing and engine, but between the bell and gearbox is probably a better idea. I skimmed over reading that part obviously :bouncesmile: I'll have a look at the box when I get home.
Hopefully your clutch package is slightly shorter than mine and it all works out, or you only need to throw a shim under the CSC.
--- Quote from: American Powertrain ---IMPORTANT for GM Customers: Your GM bell housing is very shallow. Due to the variances in flywheel and clutch stack-up height you may find that you do not have enough room for the release bearing. If you cannot achieve a minimum of .080” of air gap between the bearing at rest and the clutch fingers, use a small washer or spacer at each of the bolts between the bell housing and the transmission to move the transmission back as much as .200”. A turnkey .250” CNC machined aluminum spacer is available for $49 if you prefer.
NOTE: Do not pry pull the HRB apart when removing for shimming. Your HRB is sealed and prefilled with fluid. Use a small prybar to gently push the assembly away from the front of the gearbox if needed.
If this is not sufficient American Powertrain stocks several low profile clutch pressure plates that will reduce stack-up height on the clutch by as much as ½”. This should be considered as a final option and is not generally necessary.
--- End quote ---
Scott:
On a side note, I also considered removing the bearing retainer from the front of the box to see if I could machine the front face down slightly. I could have gained around 40 thou quite easily doing that by the look of it, but I doubt I would have gotten all I needed.
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