With what appears to be a major failure of throwout bearings in new 9.5” clutch kits (been reported on another board). I was wondering if anyone has replaced the 9.5” with a 10” (3.8L) clutch kit in a 420 Jaguar (small) saloon? I’m not so worried about the efforts and feel. But want something I won’t have to redo in a 100 miles due to a failed throwout bearing.

A car I am looking at needs a new clutch and I have 2 NOS 10” clutch kits sitting in my basement. From looking at SNG Barratt’s website and comparing the 3.8S/MK II/420, it appears that the clutch fork is the same part number, the long slave cylinder are the same. So the questions that I have left are :
1) Will the 10” clutch clear the inside of the 420 bell housing?
2) Will the flywheel be drilled for both clutches?
3) Are the bell housings for the late 3.8S and 420 the same part number?
4) Should the 3.8L short or long slave cylinder be used with the 10" clutch kit?

Thanks in advance.

 

If you stick to Genuine Borg & Beck diaphragm clutch kits there should be no failure of thrust/throwout bearings. Are people fitting the correct bearing? I would stick to the diaphragm clutch. It's a better unit.







This is not going to be comprehensive. There were some bell housing differences. There were throwout bearing thickness differences. There were yolk differences over time. There were also ring gear number of teeth changes. What I have been told is that if you wish to switch full synchro boxes between 3.8 engines & 4.2 you should keep flywheel, bellhousing & starter motor sets together. Can't confirm the veracity of this. Hopefully someone else could advise. Plenty of people have put 4.2 engines in 3.8 S Types etc. but I don't know what issues they encountered other than Tacho etc.



2) Will the flywheel be drilled for both clutches? ~~~~ MANY FLYWHEELS ARE DRILLED TO ACCEPT BOTH BUT NOT GUARANTEED (mine is)

4) Should the 3.8L short or long slave cylinder be used with the 10" clutch kit? ~~~~ THERE WERE 3 SLAVE CYLINDERS P/Ns FITTED ~ I"M USING THE LONG (95mm) HYDROSTATIC CYLINDER PLUS THE EXTERNAL SPRING AND ADJUSTING TO PREFERRED TAKE POINT WITH ZERO ISSUES ON MY DIAPHRAGM CLUTCH on my 3.8S. THE SHORT CYLINDER IS 80mm & typically used with the 10" coil spring pressure plate. I find neither of the Service Manual adjustment procedures ideal. I suffer no heavy clutch pedal complaints that were common with the coil spring pressure plates.

If you start messing with different slave cylinders then rod length from the yolk clevis pin to slave cylinder has to be considered.


Mine.

 

Hi Glyn,
Thanks for your reply!
At least one of the throwout bearing failures was from a Borg & Beck clutch kit. The failure mode is that the carbon bearing separates from the metal holder/support. The carbon bearing doesn't breakup into pieces.

Are people fitting the correct bearing?
From what I have read they installed the bearing that came with the clutch kit.

There were throwout bearing thickness differences.
How do you determine the thickness of bearing that is needed?

Thanks Again!

 

Hi Bob.
I'm disturbed to hear that a B&B carbon thrust separated from it's carrier. Even if it was only one that is one too many. Never seen that ever & I've seen some horrors.

Regarding thickness of thrust/throwout bearing. The reason it is better to buy the kits. The coil spring pressure plate cover presents the thrust facing that the throwout bearing engages at a different height from the flywheel facing than the diaphragm unit does. Diaphragm throwout bearings are not interchangeable with coil spring pressure plate throwout bearings.

People that just purchase the bearing sometimes don't realise this. They are different part numbers. Even though they look very similar

 

I remember the 420 as the car that I drove with the hardest clutch pedal. I liked it. Do you happen to know what pressure has to be applied on the pedal?
Are there any other Jaguars with such a stiff clutch pedal?
Asking not out of pure curiosity: I'd like to build a driving simulator for my kids, and have them train on the most realistic system possible. And the 420 represents an
upper bound that my system should be able to reach.
The Renault 30 was hard too (and very unreliable).

 

The coil spring pressure plate gives the hardest pedal. The diaphragm pressure plate requires less pressure but is still a firm shove. Road testers at the time tended to complain about pressure required in traffic. Have no measure of that pressure. The 420 had the 9.5 diaphragm clutch.

Back to your original post it is plain that the bonding of the carbon bearing to it's carrier has failed. I'm pretty sure that would have been corrected quickly in production.

Part Number for 9.5" diaphragm clutch release bearing = C235752

Part Number for 10"spring clutch release bearing = HD3306