Hi all…just starting up a new thread following a recent failure of a brand new standard carbon type bearing…so want to start a discussion on Roller type replacements…lets not go down the theory line of how they cant work in our cars as the clutch fork moves in an arc etc…lets just focus on do they work…have you fitted/used one…they are very popular in the race scene but they rebuild their engines frequently…so just for road car use…It is a real dilema fitting a new carbon type and not knowing if it will last a week…I will also post this on UK E type forum for wider coverage…please join in…ask your friends,… restorers …please chip in…thanks…Steve … link to same thread i posted in UK Roller release/throwout bearing - The 'E' Type Forum
I recently fitted a roller throwout/clutch release bearing to my 70 4.2 FHC. The last carbon bearing had worn completely away resulting in no clutch and the reason for beginning the restoration of this car - in 1985.
I went back and forth between fitting the standard carbon bearing or a roller bearing, initially fitting the carbon bearing, but before installing the engine into the car, I switched to the roller bearing.
The roller bearing is the same height as the carbon bearing and is a direct easy replacement. I was a little anxious that the bearing holder is made of a composite material - very light.
I’ve only got a few hundred miles on this engine and bearing thus far, but it seems to work well and I have no complaints. I believe I purchased this from XKS/Moss Motors.
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The carbon or graphite bearing is OK, and if that part remains free of oil, it should provide plenty of service before needing replacement. My preference would be the needle bearing unit, simply because the old idea of graphite for a wear surface is like thinking a pencil would never need to be sharpened Just one man’s opinion…
I think you missed the point. The discussion concerns the replacement carbon throwout bearings available today, rather than the technology discussion of carbon vs roller bearing - I think Steve made this clear in his original post. There have been multiple threads in recent years concerning catastrophic early failures of replacement carbon throwout bearings, and the various attempts by the suppliers to provide a more reliable product. In that context, can Steve (@MGCJAG) describe the latest failure he is refering to - in particular how did it fail, and where did it come from? I confess that I am now digging around in my replaced parts bin (yes, I rarely if ever throw anything away!) looking for old worn carbon throwout bearings that might have 10,000+ miles left in them, as a last resort should I need to replace one in the near future. Of course, since there are multiple variants of the carbon throwout (with different offset from pivot to bearing surface), I’ll have to make sure I match them with the appropriate style of pressure plate…
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Given the reportage of the higher rate of failures of modern carbon throwouts, I totally support your idea of using a good used one over a new one.
Were I ever to need to do this – and I never will, because the Rover doesn’t depend on a carbon throwout, and in fact, they almost always never wear out, being internal to the transmission – I would absolutely use the roller version over the carbon version.
Hi David…the link in my original post gives details from the forum member that had the problem. …brand new Borg and Beck clutch kit…car on a rolling road…20 mins use and the carbon broke up…Steve…PS the bearing is on its way back to B&B for investigation
Hi David, knew on here, I’m the guy with the Borg and Beck throw out bearing issue.
Steve nailed it really, the car was at Northampton motorsport having the final touch’s to a mapping for the ecu fuel injection and thus a rolling rd session.
20 mins in changing through the gears it fell apart.
I know 100% there were 3/16 clearance on that bearing to the clutch cover plate, and yes the spring was fitted in order to pull the arm back, etc.
I’ve opted this time after speaking to Rob Beere for a roller type bearing, simply and only because of the reliability to which I’ve already been on the wrong side of. The car is still at Northampton motorsport I tasked them with the job of fitting it, I was just about all in with it, at present it’s all back together and awaiting a slot to get it back on their rolling road….
I think what we are really after is how are any of you guys getting on with a roller bearing?
Or does anyone know of a decent reliable replacement carbon bearing?
Interesting the guy above who had a composite housing carbon bearing I have not seen that one before. Who makes that?
Thanks guys any help is gratefully received.
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Back when I was racing an E Type, and using a Centerforce clutch, that had no release ring, rather the bearing ran on the ends of the diaphragm spring (and would have torn a carbon bearing to shreds) my fabricator made up several roller bearing release bearings, pictured below. As indicated the bearing swipes across what ever it is pressing on, and if that is a stock clutch with a release ring that’s steel to steel contact. The bearing is on a 2.25" radius but only moves 3/8" in to completely release the disc. You could calculate how much it moves laterally, but I bet it’s not much. These bearings both worked but weren’t used for long as I went to a Quartermaster annular release bearing. You’ll note on the one sitting on the tape measure they machined the tangs out so the motion could be taken there. Did it work? Yes but how long would it last???
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I had a new graphite throwout bearing wear very quickly as the graphite came loose and rotated in the sleeve it was pressed into. Quality…
Replacements should be checked that they have a locating screw or rivet to stop this happening
Dennis
Hello Paul:
Welcome to the forum - I read your story posted on the E-Type UK forum. My understanding of the above post by @charltonowenby was that he installed a roller bearing with a composite bearing holder/body - not a carbon bearing. Don’t know who the manufacturer is but he indicates it was sourced from XKs Unlimited/Moss Motors. I believe I read on here somewhere in the past that they too had issues with their roller bearing offering but that needs to be clarified - although I don’t see a listing for it on their website now. Hopefully Charlton will chime about this a bit more and a time frame for when it was purchased. Here’s what he said in his post:
Good to hear Julian Barratt is directly involved with you dealing with Borg & Beck trying to get the technical aspects of their carbon release bearings sorted out - it’s been a problem for too long it seems. 
0.799mm (0.031") total, but the full affect would depend on how close to concentric with the centre line it started at. I think the Annular Throw Out system would be the way to go, the drawback being that if anything hydraulically went wrong with it, its an engine and gearbox out job to fix. However, all this type of device I’ve dealt with have been very reliable.
Regards,
Bill
Wow… what a wealth of information.
Thank you…
Apologies Gary I did read it correctly and then typed it in as a carbon bearing !!
It would seem at least to me that the sideways movement at 0.031” as mentioned by Bill above would be acceptable as long as the pedal had some kind of stop on it to limit the travel. as obviously the further you stroke the pedal the more that roller release is going to swipe across the fingers of the clutch plate thus causing a possible failure. That’s my view anyhow, happy to hear others views?
You know, you can stick with what came with the car originally and take your chances, or you can opt for the improved version of a device and not worry as much of a failure. It is a massive job to change out a throw out bearing, and if the new carbon based units are not as good as the old, originals, then where have I missed the point? The arc you mentioned in the travel of the release mechanism is still used to this day, and it is not much of a concern for standard applications. Of course, there are release bearings that ride on the front shaft of the transmission, and with a little ingenuity, one could be fabricated without too much effort if arc travel is an issue.
Gary … Julian barratt has been in touch and yes he definitely wants to get to the bottom of this issue, it’s going back to Borg n Beck via him.
Although after reading many others have had the same problem, i am not over optimistic of anything other in the way of compensation other than another carbon bearing…
Still lets see, credit where it’s due to SNG, they’ve picked it up and are going forwards with it .
all is well
If its a standard Jaguar Gearbox, dropping the drive train is not within a Bull’s Roar of not hard; small hand or not.
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all is well
As I understand it, there are/were two different roller type release bearings available. One is sold by Rob Beere racing in the UK, and the other was sold by both SNGB and Moss Motors and (I believe) sourced from Borg&Beck (B&B). From what I’ve read and seen in photos they differ significantly in design. The Rob Beere bearing is designed to work with a diaphragm clutch with no pad - that is, it bears directly on the diaphragm springs. The face of the release bearing is not flat (as the carbon bearing is), but is conical in shape. I presume that it is intended to roll on the tips of the diaphragm springs as it approaches them, rather than slide. I think I’ve read that it can be used with a conventional 9.5" diaphragm clutch pressure plate if you first remove the pad - not sure how easy that it to accomplish. In contrast, the design that was offered by Moss and SNGB was designed to work with a diaphragm clutch with a pad, just like the carbon release bearing. It had a flat face, not the taper of the Rob Beere design. The Moss/SNGB offering was discussed here on several occasions and appears to have features a re-enforced plastic carrier which caused some consternation. There is a report in the archives of someone fitting one and finding that it interfered with the bellhousing and required some trimming. I cannot find this product on the SNGB or Moss web sites any longer, which suggests that it had problems, at least in E-Type applications. A number of forum users including @politeperson (XK-120), @XK140MCOTS have reported fitting it. Maybe they can comment on their experience?
The Quartermaster release bearing I use has 2 O rings for seals, that’s it, and if properly set up is self adjusting as the disc wears. The transmission must have a tube that is attached to the transmission and covers the input shaft, as it rides on the tube and just butts up against the front of the transmission - no bolts or other devices hold it in.
David xk… you are correct with your description of the Rob Beere item, the pad is removed from the clutch cover …easy modification, and indeed the bearing is shaped to run within the ends of the said fingers of the clutch cover, it’s is not flat, as per the carbon item (as you previously said)
However these instruction MUST be adhered to or failure won’t be far away…
