Radial compliance of clutch release

[Peter Carmichael]

[duplicated from the Se7ens List but I am desperate]

 

In case you think I might be enjoying myself, let it be

known that the engine is out of the car and on a stand

at the moment while I have a little think about a bijou

problemette.

 

I have a concentric hydraulic clutch release slave

cylinder of my own design. It isn't quite concentric and I

haven't built any compliance into it. I want to fix this

before it all goes back together and hopefully cure the

squeal from the clutch which was heralding a premature

wear pattern.

 

My only idea is to shave the external diameter on the

piston so it is a loose fit on the bearing and then refit

the bearing on some blobs of silicone sealant. Does

anybody think this has a chance of working?

 

 

Edited by - Peter Carmichael on 11 Oct 2000 00:56:24

[I.Mupferit]

Err.... Just run that by me one more time!

[PACR]

Sounds like a bodge....

 

Law of tempory bodges: If you know how to do a better fix, and buy / make the parts to do it the bodge will last for ever.

If you can't figure out a lasting fix the bodge will hold long enough for you to think it's worked and bolt everything together, and then fail in the most inconvenient location - in your case Peter outside your neighbours drive...

 

If you are just after the silicon to give some compliance then it should be OK. But if it has to resist any shearing forces then it will be useless.

 

Piers

[elie boone]

Dear Peter,

I am building a live axle car with a Borg-Warner gearbox, fitted also with a concentric release slave cilinder.This cilinder was thaken from a Saab 900 (complete unit) as it is also used in Posches on circiut racing.To get this fitted i had to cut the original release bearing support tube to accomodate the slave cilinder and had a aluminium ring made up to bring the release bearing just 2 mm from the release plate it is not tested yet but i am 100% confident this work.i have a picture of this set up but i do not have the means to put it on this website (sorry)if you need more info i will give my tel.nr off line.

 

 

[Peter Carmichael]

Thanks for the responses. I knew it was a somewhat esoteric issue.

 

The piston I am using comes from the Saab release. I have made a new housing for it - this was necessary because the space involved is so small because the bellhousing doubles as a dry sump tank. The release bearing is a matched item for the clutch, but has no radial compliance built into it. If the gearbox, bellhousing, and engine aren't perfectly aligned then you get the squeal that I have. You can't measure the assembled alignment because it is all enclosed. The clutch came with a long list of tolerances which I am obviously outside. It all works pretty well, except for the squeal.

 

If I use windscreen bonding agent instead of straightforward silicone I am fairly sure it will cope with the shear forces (rotational drag in the bearing).

 

I've looked at all the bits and I have looked at all my original drawings. There is very little space for any sort of mechanical fix. Most release bearings have some compliance built into their mounting. The Saab one mounts on some barbs which provide frictional location. The bearing I have is a very small diameter and radius faced; both are features that are necessary for the clutch.

 

Elie,

 

Are you sure 2mm is enough? The diaphragm fingers will proceed outwards as the clutch wears. My miniscule race clutch will have 3.5mm movement to full wear. You might like to think about thinning out your aluminium spacer.

[Nick]

Peter, I'm afraid the quote below is the best answer I got when I reposted - note the last line about being in good humour!

 

OK folks, I'll attempt a translation

 

"I have a concentric hydraulic clutch release slave

cylinder of my own design."...

 

I know I can buy these things, but I've got a lathe and the ones you can buy are a complete rip off, so I thought I'd make my own...

 

"It isn't quite concentric and I

haven't built any compliance into it."

 

I'm not very good with my lathe and the bits I've made don't really fit together because at least one bit is oval and it doesn't fit into a round hole...

 

"I want to fix this

before it all goes back together and hopefully cure the

squeal from the clutch which was heralding a premature

wear pattern."...

 

I have to fix this as otherwise my clutch won't work and I'll end up buying the bits I was trying to avoid buying in the first place.

 

"My only idea is to shave the external diameter on the

piston so it is a loose fit on the bearing and then refit

the bearing on some blobs of silicone sealant. Does

anybody think this has a chance of working?"...

 

In addition to a lathe, I also have a file. Does anyone think that, if I file off the lobes on the oval bit I knocked up, then gum it all together to compensate for my dodgy metalwork, I'll end up with a working clutch?

 

To which I think the answer is no.

 

There comes a point where the concept of a kit car is taken beyond some people's ability to make it a reality. I think that the questioner has reached that boundary.

 

All in good humour"

[elie boone]

Peter,

I did not messure the distance between release plate and bearing i guesed it was 2 mm this may be 3 or 4 mm but i dit used the original Saab bearing.The aluminium ring whas made up by a profesional moulds maker,my brother did the drawings (his day job at the Volvo factory).

If you have a cintered clutch i dont think you will ever use it the full 3.5 mm before a engine rebuild? in my opinion the best thing to do is make a drawing with all the mesurements and find a company ho can make the support for the release bearing.if the release bearing is in diameter to small or to big it is possible to have a additional ring made up whitch is bigger or smaller but then you have to bring the release bearing further back in to the gearbox.beware use the correct material for this ring.Nick is missing the point,because bying parts and assemble them is just to easy and not satisfying.

 

 

[Nick]

Nick is not missing the point! I posted Peter's request on another forum but unfortunately nobody was able to help. However, the post I quoted was sarcastic.

 

All the best, Nick

[elie boone]

Nick, i now it whas sarcastic sorry![:0]

 

 

[Peter Carmichael]

The "quote" is disconcertingly accurate. smile.gif

 

Elie,

 

I am way ahead of you. I have accurate drawings. I was posting my drawings to QED to get them to redesign their flywheel in the right place. The only thing that is causing problems is the inability of every component supplier to make perfect components (engine, gearbox, bellhousing, gearbox front cover). There is no space to move anything anywhere. This is inside the dry sump bellhousing and spare millimetres do not exist.

 

Tony Tewson from Super Clutch (used to work at AP) said that car manufacturers spend ages trying to eliminate clutch squeal. He also tipped me off that with a little reprofiling to the piston the Saab release bearing would fit and be suitable for the clutch, and its mounting has provision for some radial compliance.

 

I reprofiled the piston tonight and I will be buying a Saab bearing tomorrow. I think I am there.

[Peter Carmichael]

There is a further option. The Saab bearing is radially located on a natty rubber anulus with squidgy bits. It is the wrong diamter for the Quarter Master release bearing, but I could split it, cut out a section and then have my all steel release bearing mounted on a production spec squidgy mounting.

 

With two options I am now confident I have this sorted.

[elie boone]

Succes Peter but remember the tale of the turtle and......