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MG Midget and Sprite Technical - 3e Clutch in 15.000 km

This is the 3 clutch failure; they went all identical. I felt a judder in the clutch pedal and the clutch starts to pick up uneven. One of the three internal forks are broken.(photo). I have used the original Borg & Beck and the non-original witch is identical to the B & B but half the price.
I have a lightened flywheel, a Peter May roller release bearing, a ribcase gearbox and a mildly tweaked 948 cc A motor. I never had problems with the smoothcase and the same configuration. What can it be?


Flip Brühl

another picture

Flip Brühl

Flip,
What combination of master and slave cylinder are you using? If you get a mis-match of parts then the distance travelled by the release bearing can be too great, it "overthrows" the clutch putting excessive strain on the release forks (or clutch fingers if using the later style pressure plate)which then eventually fail. I cannot be sure, but think this may be your problem.

Guy
GuyW

If the clutch is being over-thrown then making a shorter master to pedal rod ensures it can no longer be overthrown. Or but an adjustable stop on the floor under the pedal. To establish if the clutch is being overthrown see where the bite point is on the clutch then go just beyond to see where the clutch is fully disengaged and then see how far the clutch pedal is from the floor.
Daniel Stapleton

Flip
isn't the Peter May roller thrust designed to work with a 1275 Diaphragm clutch where the Clutch cover plate diaphragm is modified by having its pressure pad removed so that the release bearing bears upon the diaphragm fingers? Although the Peter May roller uses a 948 carbon thrust release casting I don't think it is meant for a 948 spring clutch. Correct me if I am wrong.
Alan
Alan Anstead

Check the clutch fork bush, if the fork can be thrust out of square you might get a juddering pattern of wear on the pressure plate.
Fergus

Check the clutch fork bush, if the fork can be thrust out of square you might get a juddering pattern of wear on the pressure plate.
Fergus

What you need for the 948 with a stock clutch cover is something like the attached picture.
Alan

Alan Anstead

Thank you gentlemen,
I use a 3/4 master and 7/8 slave. I did not control the fork yet. Yes the release forks are overstressed. I can see the scars of it (photo). I control the depression of the pedal with the bolt in the pedal box. There is 1 cm of free play and although there is very few depression after disengagement of the clutch it should be less.
questions:
1 Where can I buy a diafragma pressure group for the 945? I know I have to fit 3 dowels.
2 How can I repair the scars on the flywheel?
3Do I have to replace the clutch plate?

Flip Brühl

It is probably not your problem since the friction disc is not failing, but I saw a Spitfire repeatedly loose the clutch because the engine back plate was bent, which mis-aligned the engine to transmission. It's worth checking while it is apart anyway.

Charley
C R Huff

Flip,

You can use the 1275 diaphragm clutch cover on the 948 flywheel, IIRC the bolt pattern is the same, but as you say you will have to have it machined to fit 2 new dowel pins.

I did so on my 1420cc build with a 1098 10CC (big mains) crank and a 948 flywheel using a heavy duty 1275 clutch cover and all was fine. I did all the machining myself and it was checked for balance by the engine machinist while doing some his specialised bits. I can't help with the clutch arm or release bearing details as I was using a Ford 4 speed box with the Ford release arm and bearing.
David Billington

1)Charley. How can I see if the backplate is bent? I use the original iron backplate. I did try a thicker aluminium one before, but than the clutch did not disengage as the clutch fork touched te edge of the hole in the bellhousing.
2)Marton. The clutch fork bush was ok but the bolt and nut were to loose!
3)As the flywheel is skimmed. the clutch fork almost touches the edge of the hole in the bellhousing when I press the clutch. The roller release bearing, at that moment is out of centre! and that can give the judder. (foto)
4)David, I ll buy a diaphragm clutch. what is a good one? Daniel Stapleton you recommend the AP Racing. Do you still do so?



Flip Brühl

Flip,
Check also that the clutch fork isn't bent. Its a fairly common fault which can cause the fork arm to contact the bellhousing before the clutch is fully disengaged.
GuyW

Flip,

I would think you could check for a bent back plate with a straight edge, but I don't know if you can get enough access with the flywheel in place. If you can't maybe offering the trans up to the engine would show a gap if the plate is bent. When we had the problem with the Spitfire, it was fatiguing the center of the friction disc until it failed and quit pulling.

I don't know if it relates to your problem, but I have read of some problems with roller bearings used on the "swinging arm" fork because the fork does not necessarily center the bearing on the pressure plate the way a tube-type guide would.

Charley
C R Huff

Fork is staight. Could it be that my flywheel has been lightened the wrong way? What are the normal dimensions of a 945 flywheel? I saw a picture with 148'' = 37.6 mm, mine is 30 mm= 1.18 or do I see the wrong number

Flip

Flip Brühl

Flip,

From memory the 1.18" (30mm) sounds about right but the drawing does look like 1.48" (37.6mm) in the scan but I have seen better images of that detail as I used it to lighten my 948 flywheel years ago. If no one else responds I'll go out in the morning and check the flywheel thickness on the engine in my shed, it's currently dark, late, and cold so it can wait till morning.
David Billington

Flip,

Hope this helps it's a scan from an old original C-AKD 1021-C the special Tuning booklet for Sprite and midget 948cc.

richard boobier

1 3/16 = 30.16 mm I am very happy with this!
Flip Brühl

This thread was discussed between 04/11/2016 and 08/11/2016

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