Clutch - machining backplate (pressure plate) lugs
Turbo Mini Forums

After a while searching I decided the grey diaphragm and the AP (CP2084-41) plate were right for me so ordered them - arrived today, nice...

But the more I read about machining the lugs, the more confused I get.

I can see why they would need machining when additional straps are added but I've also seen threads that say machine 1.5mm off them anyway and another that says machine them so the spring is "flat" when compressed.

In this thread http://www.turbominis.co.uk/forums/index.php?p=vt&tid=10837 there is a reference in the table to "Set up height (nominal) mm 52.55" Is it something to do with this?
If so, where is this height measured?

Rod.

Schrödinger's cat - so which one am I ???

Its so that there is less gap between the backlpate and flywheel thus squeezing the clutch harder.

1/4 Mile 14.3secs 96Mph Terminal 10psi of boost.


Fibreglass Parts? - http://www.tdkracing.co.uk/
Split Rims? - http://www.force-racing.co.uk/

52.55 inches, its a very tall clutch pack,lol

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Schrödinger's cat - so which one am I ???

The 1.5mm - i think - came from me a long time ago. I had a grey diaphram, that was not holding the torque. I studied it, and with the aid of a machine at work, deduced that i needed to remove around 1.5mm of material from the backplate lugs to optimise the clamping force.
The spring didn't neccesarilly sit flat actually - I recall it was just under 1mm off being flat, but it worked and was as good as it could be.

One aspect i do know, is that the diaphram 'body' flexes an awful lot - and it is likelly that this deformation is why it benefits from the tweak.

What is strange though, is that when i measured a double Grey, this was closer to optimal out of the box; it needed only around 0.5mm off the backplate lugs for optimal clamping.

Thanks Dave,

When you were doing your testing, did you measure the load at various compressions to come up with your figure because load vs compression can't be linear with that kind of spring (a large bellville washer at the end of the day!) or where you just looking for the specified load from Fab's table.
If you found 1mm off flat was best,
1- was that with a new or used plate (AP give only 1mm of wear anyway and looking at how close the rivets are to the surface, it will be lucky to get that!)
2- how much does the clutch disengagement travel add to that, ie, any risk of pushing it past flat?
Cheers,
Rod.

Schrödinger's cat - so which one am I ???

I did these tests in 1999/2000. Long before TurboMinis.com and Fabs table LOL

I was taking readings on a special machine designed for testing synchonisers. It was on an auto cycle that measure load every 0.05mm and logged it, then creating a graph.

I wanted to find the 'peak zone' that i could then use to set up my compression, such that with a brand-new friction plate, i'd get the maximum life out if before it went too thin and lost sufficient clamping force.

I don't have any of my data from that time, not even notes. All I do know is that it worked, and it's worked for others since.

Can't help any more than that... :(

Schrödinger's cat - so which one am I ???

IIRC, all Grey diaphrams (or is it GG) have the extra 'tangs'...

grey and double grey have those

Holy thread revival attempting to address my clutch slip issue.

With a new paddle plate, and an orange diaphragm the spring is some way off flat.

I appreciate they should not be completely flat, but what would be regarded as optimum for maximum clamping efficiency.

Running 3 drive straps so that adds a little height.

Need to measure, and get the lugs machined.

Thanks

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Edited by minimole23 on 18th Aug, 2021.

Using a new clutch plate they should be as close to flat as you can get, without them being over-centre at rest.
This is where they are exerting the most force and hence clamping pressure.
This is also better for the crank thrust loadings when operating the clutch.

Mine needed 1.5mm off in the end, but to keep things slightly conservative have had 1.2mm off. Picking it up tomorrow.

Be interesting to see if the clutch is lighter to save heaving up to and over centre.

Edited by minimole23 on 24th Aug, 2021.

https://www.youtube.com/watch?v=C3c5EcpYiP8

https://www.youtube.com/watch?v=4lEbKGpZ4xw&t=997s

One of the best explanations I saw, especially the torque wrench to check.

Bravo sir

Own the day

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

With the paddle plate, less oil and chunk off the backplate it now bites hard. Time to pull it to replace the 300 mile oil seal, as it’s buggered.