clutch questions

Seight-V8 · Post by **Seight-V8** » Sat May 28, 2016 8:52 pm

hello all,

So as they clutch plate wears and gets thinner....which way will the fingers of the clutch cover go?.....in towards the engine, or out towards the gearbox?

Any by how much?

I'm trying to work out how much clearance i'll need for a AP concentric slave bearing, between the bearing and the clutch fingers, but I also need to think about wear and how much the fingers will move over time.

i'm thinking I need about 3mm clearance, and the bearing moves 18mm total travel.

cheers

scott

SimpleSimon · Post by **SimpleSimon** » Sun May 29, 2016 11:33 am

Fingers move out towards release bearing with wear 5/7mm approx ballpark

Seight-V8 · Post by **Seight-V8** » Sun May 29, 2016 6:42 pm

Cheers,

Just wondering now how much travel the bearing moves to dis-engage this clutch plate.

The bearing has 18mm travel, and if I need 6mm clearance, doesn't leave much left to fully dis-engage the clutch....

Does all this sound about right?

cheers

scott

stevieturbo · Post by **stevieturbo** » Sun May 29, 2016 7:31 pm

18mm of travel is a lot, I'd doubt the clutch needs anywhere near that to release.

DEVONMAN · Post by **DEVONMAN** » Mon May 30, 2016 7:58 am

I'm not sure why you are considering 6mm clearance as a concentric bearing will take up all the clearance on first operation and then stay almost touching the fingers.

Unless you are using a 7.25" racing type clutch, the finger movement to release is about 10 to 12mm.

Whatever wear you get on the clutch plate in it's life, (say 2mm total) the fingers will move towards the gearbox by approx. times 6 this..

stevieturbo · Post by **stevieturbo** » Mon May 30, 2016 8:11 am

DEVONMAN wrote:I'm not sure why you are considering 6mm clearance as a concentric bearing will take up all the clearance on first operation and then stay almost touching the fingers.

Unless you are using a 7.25" racing type clutch, the finger movement to release is about 10 to 12mm.

Whatever wear you get on the clutch plate in it's life, (say 2mm total) the fingers will move towards the gearbox by approx. times 6 this..

yes, but if he builds it, with a new clutch and say only 1-2mm clearance from a fully retracted slave. As the clutch wears, fingers rise there will come a point where the slave/release bearing starts applying pressure to the fingers which can lead to premature slippage.

There needs to be some clearance built in....or better worded room for wear and tear built in.

In normal operation yes the slave/bearing will normally sit close to the clutch fingers though, but there needs to be slack behind that too.

Seight-V8 · Post by **Seight-V8** » Mon May 30, 2016 10:09 am

so here what ive worked out.

Clutch plate is 8.6mm thick....and this means 41.6mm finger height.

when clutch wears to AP info stated 6.9mm, then finger height is 47.6mm

So wear allowance in clutch system will be 6mm.

AP info states clutch needs 12.5mm travel.

So I have 18mm travel in slave bearing, (6mm wear, 12mm travel).....

So yes I need 6mm space from the clutch finger face to the bearing face....

Think I'm now happy, that I can make a spacer up for the slave bearing.

regards

scott

sidecar · Post by **sidecar** » Mon May 30, 2016 10:52 am

I've set a few concentric slaves up and it does take a bit to get you head around how things work, which is more or less backwards to 'common sense'!

The last one I setup was for a Ford 302 to with McLoed pressure plate, the plate needed 12mm of movement of the fingers to fully disengage the clutch. The ratio of the fingers to the actual pressure plate was 6:1 so 12mm movement of the fingers moved the plate 2mm. (I got this info from McLoed)

So when everything is new you need the slave cylinder to be right at the end of its travel (fully extended) when the clutch pedal is pressed, in other words at 18mm. Without the pedal pressed the slave should be at 6mm extension (18-12). This would also mean that the friction plate can wear 1mm (remember the 6:1 ratio) before the slave 'bottoms out' in its bore and is fully compressed. Once that happens you are at the point where the clutch could start to slip.

The other thing to be really careful of is that when everything is new and you are pushing the slave out fully to 18mm it could pop out of its bore which is a total pain in the ass! You need to get the master to slave ratio just right to avoid this and you still might have to fit a pedal stop.

The other interesting thing is that the fluid level in the reservoir will actually go up, not down as the friction plate wears!

The figures above are just an example and might not apply to your setup but they are correct for the Mcloed setup that I worked on.

One last thing, the release bearing in this sort of setup will always be in contact with the fingers, do not try to create clearance here as the slave will just move out to take up the slack. 18mm of total travel seems to be the norm with most slaves so you can not afford to waste any of this travel. You need all the spare travel to be there so that as the plate wears the slave can move back up its bore but set the system up so that when the clutch pedal is pressed the slave moves 12mm. Also don't use a huge master cylinder that would over extend the slave and then just restrict the clutch pedal movment, you will end up with a heavy clutch pedal that is hard to control. (It would have a vicious bite point!).

Seight-V8 · Post by **Seight-V8** » Mon May 30, 2016 11:34 am

thanks sidecar, that explains everything perfectly for me.

cheers

scott

DEVONMAN · Post by **DEVONMAN** » Mon May 30, 2016 7:57 pm

stevieturbo wrote:
DEVONMAN wrote:I'm not sure why you are considering 6mm clearance as a concentric bearing will take up all the clearance on first operation and then stay almost touching the fingers.

Unless you are using a 7.25" racing type clutch, the finger movement to release is about 10 to 12mm.

Whatever wear you get on the clutch plate in it's life, (say 2mm total) the fingers will move towards the gearbox by approx. times 6 this..
yes, but if he builds it, with a new clutch and say only 1-2mm clearance from a fully retracted slave. As the clutch wears, fingers rise there will come a point where the slave/release bearing starts applying pressure to the fingers which can lead to premature slippage.

There needs to be some clearance built in....or better worded room for wear and tear built in.

In normal operation yes the slave/bearing will normally sit close to the clutch fingers though, but there needs to be slack behind that too.

I wrongly assumed that the clearance Seight-v8 was talking about was a running clearance between the bearing and the fingers. Naturally there needs to be some clearance within the bearing /slave cylinder assembly to to allow for wear.

sidecar · Post by **sidecar** » Mon May 30, 2016 8:30 pm

Seight-V8 wrote:thanks sidecar, that explains everything perfectly for me.

cheers

scott

No probs!

I found that it took lots and lots of repeated taking of measurements and drawing it all out on paper to be sure that it all works correctly. I made a concentric slave support that was welded onto the front tube of the T5 gearbox, it all needed trueing up on my lathe, it took hours as I did not want to be at home to 'Mr Cockup'

seight · Post by **seight** » Tue May 31, 2016 5:19 pm

My John Eales bell housing had the mounting position for the Saab slave machined into it, I measured and measured before having it machined down to the right height and shape for the AP slave with 6mm clearance when fully retracted. I was a bit nervous I was about to f it all up.