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MG MGB Technical - clutch release bearing problem

To my mgbgt, I change the clutch release bearing, carbon type, the old are worn, I change the crankshaft oil seal also, all carefully, I donít change the uprated clutch, in good state, I have 1950 engine.
Now, at neutral, to the engine idle, there is a metallic noise in the release bearing and in the clutch fork, if I touch the clutch pedal the noise cease, but if I declutch the engine idle dip, the engine stall. The clutch work very well.
Incidentally, the OD donít work, I check all, really all, I change the solenoid, the OD harness, the switch, all the ďOĒ ring, the filter, the oil. Nothing. He work very well, all days, during sixteen years.
Goods ideas. Thank you.

Michel, it looks like your release bearing has worn down to the metal housing and needs replaced. This can be due to several factors. Tight fork pivots or the hydraulic system still maintaining some pressure although this would be unlikely. You may of course be into the very bad habit of driving with your foot covering the clutch pedal and this will result in very rapid wear of the thrust bearing.

The most likely cause is your heavy duty clutch which is known to be quite hard on release bearing life. If I were you I'd change the clutch and fit a standard Borg & Beck which is known to be well up to the job.
Iain MacKintosh

Thank you
Yesterday Iím going under the car, I push away the push rod in the slave cylinder, the clutch fork travel free, to the rest the release bearing touch lightly the clutch cover (diaphragm). I put a footrest for my left foot. Yes, I fix all again, I change all, the clutch and the OD, but the engine is balanced!

Michel - you don't say the year of your car but for a MkII of 1968 or later and if you have an ammeter check the circuit continuity.

If it has the manual switch on the dashboard or column stalk locate the connector where the yellow wire in the main harness joins the yellow red in the gearbox harness by the fusebox. Pull that connector apart, insert the ammeter, and with the ignition and manual switches on and the gearbox in an overdrive gear you should see about 800mA.

If the manual switch is on the gear lever then the connector will be joining two white wires in the main harness to a yellow or yellow/red in the gearbox harness, otherwise it is the same.

If you don't have an ammeter then with the ignition on, the manual switch on and the gearbox in an overdrive gear you should have 12v where the yellow or white wires in the main harness join the gearbox harness.

If it has the manual switch on the dashboard or column stalk then with the ignition and manual switches off push the meter probe in the side of the connector that has the main harness and check you have a resistance to ground of about 15 ohms.

If the manual switch is on the gear lever for the resistance test you will have to leave the manual switch on and pull apart the connector and test the wire in the gearbox loom and check the resistance is about 15 ohms.

If both those are OK electrically it is good then there must be a mechanical problem with the solenoid or elsewhere in the overdrive, but having changed the clutch I'd say it will be electrical. Did you get the reversing light and overdrive wires back on the correct switches? Do the reversing lights work? Or only in 3rd and 4th?

The earlier gearboxes have different resistance, but with these with the engine stopped but the ignition on, you should be able to hear the solenoid operating and releasing when you operate the manual switch or move the gear lever in and out of an overdrive gear.

Sounds like you have *already* changed the release bearing. The noise that goes when you touch the clutch pedal - do you mean just touching it or does it only stop when the pedal has been moved a little way? If it is just touching it then I'd expect the noise to come from the pedal itself, that wouldn't be enough to move anything in the bell-housing.

Does the idle drop as soon as you start disengaging the clutch? Or only when the pedal is nearly all the way down? If only when the pedal is nearly all the way down it sound to me like the release bearing may be being moved too far and is rubbing on something, possibly because it is too thick.
Paul Hunt 2

I have a slight problem with this argument as I have seen release bearings which make a noise when just touching the thrust face which would be the case with foot off the pedal and the only load being the slave cylinder piston spring and then be silent when the clutch is depressed. I cannot see what noise the pedal would make under idle conditions. Now if it is the proper uprated clutch the bearing throw should be the same as with the standard unit so it is worth checking the fork travel to see that it too is within limits and this should be approx 16mm. If the master and slave cylinders are standard then these dimensions should be met.

Finally and if it is the correct release bearing it cannot be too thick. Michel says that the fork is slack so even if it was too thick it has moved back to accommodate this extra thickness and will then go the prescribed 16mm to release the clutch.

Pull the rubber gaiter off Michel and shine a torch into towards the release bearing. Hopefully you'll be able to determine whether or not there is any useful life left in it.
Iain MacKintosh

Thank you very much for your input, super.
It's a 1972 mgbgt with a angled switch to the dashboard
I check all with a bulb, all work perfect, the reversing light also, I check the solenoid out of the OD, he work perfectly (the old and the new), I don't know in the OD, I will check with a ammeter.
Concerning the clutch, if I push the pedal 1 or 2mm the noise cease, the noise come from the clutch fork, the engine drop when the clutch is fully disengaged,
I think, I remove all.
Thank you,

Michel. The only way I know for the release bearing to make noise when the clutch pedal is not depressed and then, quiet when the pedal is depressed is if the retaining clips are not present or have broken. In that case, the throw out bearing can jiggle slightly in the clutch forks, making a small noise. When the pedal is depressed, the fork moves forwards, pushes the throw out bearing forwards and taking up any slack in the system.

As to engine rpm drop when the clutch is fully disengaged, does this mean when the pedal is pressed to the floor? If so, the problem would seem to be thrust washers inside the engine. If they are worn, it allows the pressure of the throw out bearing to move the crankshaft forwards causing it to bind. This is a common problem with the Triumph designed 1500 engine used in the later midgets, but, I have not seen such a problem with the older BMC designed engines except when badly worn.

Les Bengtson

Les, I agree that when the pedal is slack that the bearing can go out of line and then adopt a different angle when the load comes on and that's why I said to try to get a look into the housing. Yes Triumph engines have a problem with thrust washers in that they can even fall out but there is always a slight drop in RPM in most engines and the B series is no exception when the clutch pedal is depressed. It's not much, but will amount to 70 - 100 rpm. This is normal and inevitable and caused by the increased friction between the crank and the rear thrusts. Don't forget that we are talking about increased loads due to the heavy duty clutch. I'd still want a look inside first but I do fear that the clutch will have to be replaced.
Iain MacKintosh

Thank you very much.
The car is daily use since fifteen years, the engine and gearbox also. They are worn, but he work very well. Iím in the process to build a new engine, 1924cc, for the car, new gearbox also.
I will remove the engine/gearbox, I would say to you what is broken.

This clutch has obviously done a fair mileage along with the engine and transmission. I think you should examine the components on disassembly and probably replace the three piece clutch kit.
Iain MacKintosh

I changed my clutch and bearing a couple of months ago and found that the new Moss supplied B & B kit was way too tight in the fork to pivot properly. My wife took the fork to University Motors (Moss dist.) and checked several bearings and found that all were too tight...I had to file the fork inside dia. to get a proper smooth action in the throw out bearing...Tom
Thomas Koch


This is an old problem - the bearing housings were given an anti corrosion coating that made them too large.

This has since been rectified, Moss must have old stock.
Chris at Octarine Services

I remove my engine last saturday, concerning the clutch, nothing, all is perfect, I change the clutch and I fit a roller clutch release bearing, there are no noise. Concerning the O/D, big mistake by me, I put the relief valve plunger upside down. Now, the O/D work very well. Thank you

Where did you find a roller clutch release bearing? To the best of my knowledge, they are no longer available in the USA or the Repeblic of Texas.

I'll bet that when you replaced the release bearing it was a little tight in the yoke, not pivoting freely. When the fork was released it stayed in the same position, causing the inner part of the bearing to lightly rub the input shaft, which would explain the noise at idle. When you depressed the pedal even slightly the bearing would have moved off the shaft- of course everything in the clutch was working properly except the sticky bearing. The only reason the roller bearing solved the problem is probably because it pivots freely. (Don't you have to fit a return spring when you use these in the MGB?)

Anyway, that's my theory. Take a look at the bearing you took out and see if you can tell if it was rubbing the input shaft.


I think, the part to the diaphragm, pressed by the release bearing is twisted, buckled, causing the vibrations.
Glen, I bought my kit clutch to Moss in England.

This thread was discussed between 13/02/2006 and 23/02/2006

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