clutch diaphragm set up

[wantafaster1]

I know this has been on the forum before but I wanted to show pics of what I have. No access to a press or anything so I screwed the diaphragm bolts down tight and then backed them off until the diaphragm spring is flat. Clearance is equal all round at 20 thou.
I imagine the amount to come off the spacers is the thickness of 2 straps minus the 20 thou?

Now, there is only just daylight between the strap and cover, they are only just nipped up so I can still pivot them. Is it right that I then have to take the thickness of a strap off the three horns on the backplate?

[Spider]

If you needed to back the screws off to get the Spring flat, then you need to add 0.020" of spacers.

[wantafaster1]

Sorry bloody phone won't add the pics! Will crank up real computer soon, garage is Baltic anyway.

Spider, the .0020" is without any straps, I couldn't get the spring flat otherwise.

[Spider]

Ah, OK, got ya now.

Yes, that would be right.

I prefer to do them with the straps in so it's all lined up as would be when fitted, but really it shouldn't make any difference.

Also, being a lazy sod, less maths,,,,,,,,

[ianh1968]

Is it right that I then have to take the thickness of a strap
off the three horns on the backplate?

If you want to test how it will be with the horns machined, you can emulate
this by putting some suitable additional packing in with the friction disk.

For example, if you estimate that 0.020" needs to come off the horns,
find yourself some suitable shim or spacers the same thickness.
Anything will do, as long as it will all clamp up flat whilst at the same
time not ruining the friction material. How thick are the straps? If they
are 20thou and you have some spares, you could use them...

From the bottom, working upwards, place:
1) Your backplate
2) The friction disk
3) The shims, spread evenly round the friction disk material
4) The flywheel
5) The straps
6) The diaphragm

Bolt it all up and see what you have. If the spring is now flat, you will
know that 20thou is the amount to come off the horns. Because the
friction disk is now "20thou thicker", you will be effectively pulling the
diaphragm downwards by the same amount... (Which would be exactly
the same as having shorter horns and no shims).

Do not even think about the spacers until this has been established.
Only once you have ended up with a "flat" spring should you check
what the thickness of the spacers needs to be.

If you use this shim method, you should be able to sort out the horns
AND work out the thickness for the spacers at the same time. When
you can see that the spring is flat, just measure the gap between the
underside of the strap and the flywheel outside surface.

Ian

[leonrjohnson]

If you needed to back the screws off to get the Spring flat, then you need to add 0.020" of spacers.

I used this info that I got from MiniSpares Forum, and it worked well for me:

If using a pressure plate of unknown history, it is IMPERATIVE the clutch drive straps are set at the correct height. Many get this wrong and end up with a slipping clutch for some seemingly unfathomable reason. The following should also be carried out if the flywheel has been machined, or of unknown history also: - Place the pressure plate 'horns' upper-most on something to hold it off of the work surface but not interfere with clutch plate of flywheel - Place the clutch plate in position, with the protruding primary gear spline boss on the underside facing the work surface - Place the flywheel in position - If the drive straps are holding the flywheel up, or are under tension pressing on the pressure plate 'horns', more spacer-washers/shims are needed between the drive straps and flywheel - If there's a gap between the drive straps and pressure plate horns, the spacing between the straps and flywheel needs reducing - If no drive straps are fitted, using a straight edge or drive strap fitted to one of the horns, measure the existing gap between flywheel surface and underside of straight edge/strap, and make suitable spacers to this measurement - Where extra drive straps are fitted, as in racing (3 on each location instead of the original two), it is essential to machine the thickness of the drive strap off of each pressure plate 'horn' and spacer to re-gain correct diaphragm clamping action to avoid clutch slip The idea is to set the straps so that when they are in their 'as assembled' position, they are not under tension, nor are well clear of the pressure plate horns. They should be JUST touching. Under tension the clutch will slip due to decreased clamping pressure. Too far clear may cause disengagement problems.

[ianh1968]

If using a pressure plate of unknown history, it is IMPERATIVE the clutch drive straps are set at the correct height. Many get this wrong and end up with a slipping clutch for some seemingly unfathomable reason. The following should also be carried out if the flywheel has been machined, or of unknown history also: - Place the pressure plate 'horns' upper-most on something to hold it off of the work surface but not interfere with clutch plate of flywheel - Place the clutch plate in position, with the protruding primary gear spline boss on the underside facing the work surface - Place the flywheel in position - If the drive straps are holding the flywheel up, or are under tension pressing on the pressure plate 'horns', more spacer-washers/shims are needed between the drive straps and flywheel - If there's a gap between the drive straps and pressure plate horns, the spacing between the straps and flywheel needs reducing - If no drive straps are fitted, using a straight edge or drive strap fitted to one of the horns, measure the existing gap between flywheel surface and underside of straight edge/strap, and make suitable spacers to this measurement - Where extra drive straps are fitted, as in racing (3 on each location instead of the original two), it is essential to machine the thickness of the drive strap off of each pressure plate 'horn' and spacer to re-gain correct diaphragm clamping action to avoid clutch slip The idea is to set the straps so that when they are in their 'as assembled' position, they are not under tension, nor are well clear of the pressure plate horns. They should be JUST touching. Under tension the clutch will slip due to decreased clamping pressure. Too far clear may cause disengagement problems.

MY PERSONAL VIEW: This article is seriously lacking....

The writer makes NO reference to getting the ACTUAL DIAPHRAGM SPRING flat.

The writer is under the impression that any bias on the drive straps will affect
the clamping pressure of the clutch. He assumes that a standard setup will
be correct and only mentions that machining of the horns is essential if three
straps are used instead of two.

The instructions do not state that the clutch assembly needs to be fully clamped up,
they suggest that literally placing the items in the correct order will suffice. At the
same time the writer states that:
"The idea is to set the straps so that when they are in their 'as assembled' position"

How can they possibly be in an 'as assembled position' if the actual diaphragm
is not bolted and clamped up?

Given that you can bend the straps with your little finger, I estimate that having them
out of alignment will change the power handling of the clutch by about 0.5Bmp.
(That's not a typo, it's "Brake Mouse Power").

The order I do a clutch is:
1) Get the DIAPHRAGM SPRING FLAT.
2) Worry about the straps afterwards.

Ian

[wantafaster1]

Thank you for that. Exactly what I was trying to do, get the diaphragm flat first. On shift atm so won't get back to it later in the week.
I must say that the old assembly was really badly set up on both spring and straps but somehow I got away with it. Didn't know about setting this up years ago.