Switching 10" Spring Clutch to 9.5" Diaphragm

[abowie]

Hi Andrew....the Starter motor holes are different between 3.8 and 4.2.......clutch fork mount position could be different unless you have measured them...Steve

I can drive the car so I suspect they are the same. I think that the release forks are all the same too. I do have a 3.8 starter fitted as the box is in my 3.8 coupe so that might explain why I've had no trouble there.

I've actually got a couple of different bell housings kicking around. For completeness I'll post some pictures if I can find them all.

[mgcjag]

Hi Andrew....the 3.8 and 4.2 flywheels have a different number of teeth.....and a different diameter....both models use different starter motors......the fixing holes on the bellhouseing are drilled in slightly different locations to accomodate this......you will notice that the 4.2 bell houseing has recessed fixing holes to accomodate the ring dowles for the spigot plate that the 4.2 starter uses....both starters use different diameter pinions..this becomes very apparent when trying to fit high torque starter motors.....you need one that matches your bellhouseing and flywheel combination....Steve

[mgcjag]

Hi Rory...re the clutch fork....i can clearly see a difference in the pivot position in your two forks..the rear one has the tube mounted slightly higher......they do not look the same

[288gto]

I'm not sure if that's just the angle of the photo Steve?

Rory you say you have a "Medatronics" gearbox and bellhousing. I know on the Elite set up and sometimes on the Broadsport box I have , it is necessary to relieve the hole in the bell housing to allow full travel when using a diaphragm clutch. Darren ( dal2.0lifrogeye ) has first hand experience of this on his own and works cars. Altering the release arm as you have done seems a better solution.

[rfs1957]

You're right Steve, here's one I made earlier.

Before heating :



After heating :



I agree they look different, but perhaps not as regards the actual position and heights of the pivots, centres, and cups for the release-bearing ears, which are what determines how the part works.

If Jaguar used the same part number for decades then one must be a substitute for the other, no ?

Unfortunately I didn't lay them on a surface plate and do any measurement, although I will jig-up the trial bent one before I bend the new one to the same shape.

The pronounced kink in the clevis-pin end should help it clear bellhousing windows.

Steve3.8's list of the Borg+Beck release-bearing references suggests that there were indeed many more references used than the two I had been told covered everything - I've since added a caveat to that post.

[tinworm]

This to Andrew - am I right in thinking you have a all synchro box in a 3.8 E ? Steve was correct in that the 3.8 and 4.2 bell housings are different and pointed out the starter motor mounting holes/housing. The 3.8 bell housing can with difficulty be made to fit with extensive machining. An easier way is to use the 2.8 XJ6 or the old 'S' type bell housing which is a blend of 3.8 and 4.2. It has the large machined hole on the back to accommodate the all synchro box but still uses the earlier inertia starter which can be used with the 3.8 104 toothed flywheel. The flywheel is available from '64 with dual drilling's for the spring type and diaphagm clutch which is what Rory has been engaged in configuring.
So I think Andrew you must have either a modified 3.8 bell housing or one of the two bell housings I mention above ?

cheers Barrie

ps 2.8 XJ6/ s type bell housings do turn up on fleabay usually misidentified as 4.2 units once you see the difference it is easy to tell them apart. I put this in for anyone else who may be contemplating a gearbox change

pps Andrew just re- read your earlier post - I see you have gone the modified 3.8 bell housing route !

[rfs1957]

Re-forging the shape of these is not as simple as it sounds.



Or rather, changing the shape of the original forged ones is easy, but repro - or maybe just later - ones are cast, so they fracture - this one broke whilst hot, as I thought it was steel, but in fact it is cast iron, as I proved by taking a file to it.

Thought these pictures might help someone identify the two versions.











So I'm now looking for an original New-Old-Stock, failing which I'll refit the one seen here which will do fine, it's just got a bit of wear in the ears.

[Richardhealey]

Bad luck Rory

Whilst you are making your modifications, it was suggested to me by Angus ( and I have taken the advice!) to fit an ‘upgraded’ release bearing. I am sure like me, you dread the thought of a bearing failure and the enormous work it would entail...

Denis Welch Motorsport, part number CCLU112M.

Haven’t fitted yet, no affiliation. Blah blah blah

Best wishes,
Rich

[1954Etype]

Rich, send it back. Sincere apologies but we have fitted 2 now and both have clutch judder. (Ones in my car and is being swapped out this winter).

We have decided to go for the short slave cylinder with external return spring and carbon release bearings now.

[Richardhealey]

Eek! Thanks Angus!

[1954Etype]

Hate for you to fit it and have a problem!

[Richardhealey]

Thanks Very much Angus. Engine out having installed it is my Room 101....

[rfs1957]

But carbon release bearings worked for generations with no issues didn't they ?

And a roller race won't cure the issue of the thrust plate becoming detached from the diaphragm fingers, so two unconnected issues here.

Can't help feeling this is leading us up the garden path.

PS However, long chat with a certain Pat Callis this afternoon, whilst conducting my research into release bearing sizes - he was recommended to me by someone else in the trade as the authority on Jag clutches, albeit from a racing perspective ............... he uses a Bedford CF van (circa 1960 - 1980 ?) roller-bearing release, and hates the carbon release bearings !

Where's that garden path ?

[tinworm]

Personally I prefer carbon release, the thing to do is don't ride it - knock the car out of gear at junctions etc.

Barrie

[1954Etype]

Rory, you remove the contact plate so the roller bearing operates directly onto the fingers. Unfortunately, we introduced judder when pulling away on 2 cars despite carefully setting up the arm etc.

[rfs1957]

This is how things were explained to me by Simon at Precision Clutch near Yeovil.

precisionclutch@aol.com - 01963 362 484

AP clutches are now made in China, maybe India ?, and there have been several instances of the thrust pads coming loose, this is in no way specific to Jaguar clutches.



The one I had from him is a "reconditioned" original Borg and Beck, of which he has no more cores, but if you send him your old housing he can fettle it up as per the one he sold me.

You can see mine isn't new if you look at the roots of the spring fingers where there are some traces of the past in an area that the blasting process didn't reach ........... however their reconditioning does NOT involve a new diaphragm spring.

I think this is a service that's widely available.

I also spoke to Christopher's suggested supplier (for which I never thanked him, my apologies)

viewtopic.php?f=3&t=11948&p=106936&hilit=clutch#p106936

of Bonding and Reline in Leicester, one very helpful Larry Street on 0116 260 1717, who confirmed that nine times out of ten the diaphragm spring is not changed in a reconditioned assembly.