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MG MGB Technical - Co-axial clutch release mechanism
|Does anyone have any experience of fitting a co-axial clutch release mechanism to the B. Our rally GT has just got through its 3rd carbon release bearing averaging 3,000 miles each bearing. Cambridge Motorpsort offer a co-axial release mechanism with a roller bearing and this looks attractive. Has anyone tried it? Are other people experiencing the same wear rate with the carbon bearing?|
i did not try it on the B but had it on my Mondeo V6. It is really State of Art and never failed within more than 200000 kilometers, although you will need to modyfy the bellhousing of the B for routing the hydraulic line to the bearing and have a second line installed for bleeding it.
I have one to my 1840 much modified engine, it's not a Cambridgemotorsport product, but a APracing fitted by me, I have also special steel flywheel with 7.25" clutch and a small clutch master cylinder, the gearbox is sccr. I don't have problem with anything. I use the car, mgbgt 72, essentially for track day.
|The carbon bearing should last at least as long as the clutch lining. (Caveat: That assumes you're not holding the pedal down at stops, riding the clutch, etc). If yours are only lasting 3000 mi, something is wrong. Make sure that everything on the control path (all the hydraulic/mechanical bits between you and the bearing) are free to move & working properly. Especially check the release fork bush and pivot bolt -- these often wear and when worn will allow the fork to sag and no longer hold the bearing concentric with the clutch cover.|
Let us know what you find!
|I think Graham may be using his GT for rally competition, that could account for the short release bearing wear. I believe thier rally competition is much different than the all paved road TSD rally's run by our local clubs. Many circle track race cars use a conical release bearing.|
The basic idea behind the roller type throw-out bearing is the reduction of friction so that shifts can be made more quickly and more accurately under extreme conditions, as in racing with a lightened flywheel and crankshaft. On a street machine, it has little practical advantage, but has the disadvantage of requiring frequent removal and relubrication in order to prevent it from self-destructing. This is due to the fact that the MGB has a clutch throw-out mechanism that has no provision for keeping the throw-out bearing from remaining in constant contact with its pressure surface on the clutch cover. Without modification, the roller bearing will be constantly spinning as there is no provision in the original design to disengage it. The Original Equipment carbon throw-out bearing can withstand this constant contact. In addition, as Rob pointed out, worn throw-out fork lever bushings can allow the roller bearing to misalign relative to the clutch cover, rapidly increasing wear. While this increased maintenance need is not a problem on a race car, on a street machine it is a big hassle that is just not worth the trouble
|Excess wear of the throwout bearing can be as simple as the return spring missing on the pedal. If the pedal does not return fully there is a small amount of pressure holding the bearing a little harder against the pressure plate than normal.|
|The other thing that will cause excessive wear on the carbon throw out bearing is the use of a heavy duty clutch. Cheers - Dave|
|There is a spring in the slave that is designed to press the release bearing against the diaphragm, to take up any wear and give a consistent biting point. The pedal spring stops it bouncing up and down and wearing the master linkages, and gives a consistent pedal height.|
The MGB V8 has a roller bearing release bearing as standard and it doesn't need lubricating. This was also used on Sherpa vans which get a much harder life, with again no lubrication.
Do what the Flying Finns did and don't bother with the clutch after pulling away.
|Paul Hunt 2|
|I have now completed the installation of the co-axial release bearing and can report that it appears to be working very well. The installation was fairly straight forward.|
The old carbon release bearing had broken up with quite large chunks lying in the bottom of the bell housing which was coated in carbon dust. Hoepfully that is the end of taking the gearbox out for a good few thousand miles.........
Please keep us posted on the long term record of your conversion. If it's practical for street machines, a lot of people will be grateful to you.
This thread was discussed between 21/08/2007 and 02/09/2007
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