Clutch release bearing

[peters3103]

Hi gents,
Today I fitted my new Borg & Beck 10” clutch to the engine. No problems there. I also removed the old release bearing to find that my new item is slightly different. Although it fits perfectly the dimensions are a little different.
Old: OD of body 3”, ID of carbon brg 1 1/2”
New: OD of body 3 1/16”, ID of brg 1 5/8”
The measurement from the centre of the pivot to the face of the body: Old 11/16”, New 3/4”
Centre of pivot to face of bearing is obviously different as the old one is worn.
Old 7/8”, New 1”
I can’t see that the OD & ID should matter but wondering about depth from pivot point to face of bearing.

[mgcjag]

Hi...there are several different release bearings dependant on the depth of the clutch cover used haveing a different depth when measured from the face of the flywheel to the face where the release bearing touches...I dont know which you should be useing but sugest trial fitting gearbox to engine to ensure your slave cylinder/clutch fork has the movement required to operate the clutch....Im sure you could look up part numbers etc but i wouldnt just rely on that....here are two different ones i found....very different body shape even though one on left has worn carbon...the one on the right even deeper from pivot than yours....Steve
PS..there is a chart somewhere that shows the depth of coverplate and associated release bearing required..cant remember where iv seen it..but think it was manufacturers info rather than Jag

[peters3103]

Thanks Steve, I suppose if I fit the gearbox up as you suggest and there is some free play, ie the bearing isn’t touching the pressure plate, all should be ok? If there’s insufficient free play could that be an issue?

[mgcjag]

Just for info did your new release bearing come as part of a complete clutch kit from one if the usual suppliers..Steve

[mgcjag]

Yes insufficiant free play will be a problem and wear out the release bearing...you need to ensure you slave cylinder is correct for your set up....and ensure its set/ adjusted as per the Service manual ...Steve

[peters3103]

Yes it did come as a kit from SNG Steve. My car is a 3.8 with an all synchro box.

Pete

[mgcjag]

Hi Pete..if purchased as a kit i would expect it to be the correct part for the cover supplied.....always possible your original is wrong or matches the old cover plate...worth checking the depth of your 2 cover plates just for intetest..Steve

[peters3103]

Steve,
There IS a difference in the cover (pressure) plates.
Measurement from flywheel to face of ring that release bearing depresses:
Old 3 3/16”
New 2 9/16”
That’s a difference of 5/8” and the overall difference between the old and new release bearings is only 1/8” giving an increase between the release bearing and the cover plate of 1/2” which is of concern is it not? It probably won’t depress the cover plate enough if at all.
I’ll try fitting the gearbox and see what I end up with.

Pete

[peters3103]

Gearbox fitted today and I have approximately 3/8” for and aft movement of the fork (measured at the centre of the slave cylinder pushrod hole).
When the pushrod is fitted (which needed to be adjusted shorter to fit) the release bearing is held against the cover plate due to the spring tension of the slave cylinder. Should I fit an external spring to the fork to hold it off and prevent premature wear of the carbon bearing? Or can the spring be removed from the slave? I thought I’d read that somewhere.

[mgcjag]

Hi Pete...ok So you know see a differance between the old and replacement ....these measurements could be just down to different manufacturer...but you never know if the old clutch was the original or replacement...do you have a service maunal...have you looked at the slave cylinder setup in it....if you dont we have service manual in the knowledge base section....slave cylinders did change with different models some self adjusting and some haveing an extermal spring to hold the release bearing off the clutch cover by a set distance as per service manual....the 3.8 section shows the external spring type......ideally the fork should be positioned approx in the center of the bellhousing hole when the release bearing is touching the cover plate.....dont forget that scimming a flywheel will also affect this and position the clutch further forward......the pushrod needs approx 1/4 in to release the clutch...hope this helps...Steve

[peters3103]

Thanks again Steve, yes I have a factory manual and have discovered the later 3.8 cars had a hydrostatic slave cylinder which didn’t use a return spring. I did replace my slave cyl. some years back but wasn’t aware of any differences and just ordered one and fitted it without any obvious issue. The fork is now centred in the bellhousing opening when the bearing is touching the clutch cover plate as per my photo. Also there is sufficient room for the fork to travel at least 1/4” so feeling a little more confident now but want to be sure all is ok before the engine goes back in. I just measured the slave cylinder which is 80mm and that would suggest it’s non hydro would it not? Not sure whether the pushrod is the correct length for the slave as I don’t have that info. If it is non hydro then it should have a return spring fitted right?

Cheers,
Pete

[mgcjag]

Hi Pete..far as im aware the 80mm in the non hydrostatic and needs the external spring....either way personaly i would use the extermal spring set up....that way your sure the release bearing is always kept clear of the clutch cover and wont wear ..Steve

[peters3103]

Steve, my 3.8 factory manual has a section on “later cars”. No reference to 4.2
Thanks for advice. I’ll get a spring.

[mgcjag]

Hi Pete..was just editing my last post as you posted....My service manual..same as in the knowledge base section details the change to the Hydrostatic started with engine no 7E.4607 (4.2) then changed back to non hydro at 7E18356 (ots/fhc) & 7E5558 (2+2).... Steve