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MG MGB Technical - A better throwout bearing
|I am trying to find out if there is a bearing out there that is not made of carbon for the clutch throw out bearing. i have replaced it once a about four years ago. the car has not really been driven a lot since i have moved to fl. from ri.there is a noise coming from the peddle area and when you put a little pressure on the clutch peddle it stops. the clutch grabs fine. i don't like the noise and I'm waiting for the clutch to detonate. Thanks Don Baker|
|dab donald a baker|
|A rumbling noise that stops when you start to depress the clutch is more likely to be the transmission input shaft bearing, I had the same problem in my transmission and had to replace the bearing.|
|The stock carbon bearing is the best of the lot. We've seen more failures with the ones where people attempted to 'be modern' and put in ball bearings that subsequently dried out and seized.|
The carbon bearing (if properly made and not total crap - I understand there are some bad batches from the subcontinent out there) are very reliable - as long as the driver knows how to drive properly.
Nothing will withstand the incompetent driver (often used to American cars) who sits at the stoplight with the clutch held in all the time.
The Wiz is right - look to the input shaft bearing for the noise. The sound of a carbon bearing worn through is more a penetrating metal on metal shriek...
|There is no pull off spring for the throw out arm and bearing to pull the bearing (carbon block) off of the thrust surface of the pressure plate and as a result the bearing is in constant contact with the rotating surface. This is a very light contact and doesn't contribute wear on the carbon block, but it is sufficient to keep a modern, ball bearing spinning constantly which results in the lubricant drying out, causing premature failure of the bearing. Doug Johnson of British Automotive used to have a modification kit to add a pull off spring. This spring is mandatory if one is going to use a ball bearing type of throw out bearing. |
I purchased one of these modification kits for our MGB because we had experienced short life span of the carbon block throw out bearings (and even one ball bearing type). I finally realized that the problem of short throw out bearing life span on our car was the result of using the heavy duty clutch in our car (if a standard clutch is good, isn't a heavy duty clutch better? - Not!). Since replacing the clutch with a standard one, we have not had a failure of the carbon block throw out bearing in nearly ten years of daily driving.
The standard clutch and Bill's admonishment to only depress the clutch when shifting, should make the carbon block throw out bearing last as long as the clutch disk (the design criterion was that the wear on the carbon block is supposed to wear at approximately the same rate as the clutch disk, resulting in a elf adjusting clutch). Cheers - Dave
|Yep Dave D. I wish I had one of those 'elf' adjusting clutches. And then I want 'troll' adjusting rear brakes. hehhehehhehe|
|Kind of related to clutch use but do you guys in the US/UK find people don't stop properly at traffic lights and end up creeping forwards slowly while the light is red?|
Happens here all the time. I imagine it's the same everywhere? People in automatics. They stop several car lengths behind the car in front then slowly creep. In an MG (and my daily actually) I always take the car out of gear and foot off the clutch. I usually then end up with a huge gap in front of me due to all the creepers ahead! My general rule is not to move unless I can come totally off the clutch pedal to do so.
Ah well, gives me a nice gap to accelerate into when the lights go green!
Oddly enough these creepers are often the slowest people to start moving when the light DOES go green!
I've experienced similar symptoms recently. I discovered that one of the two release/thrust bearing retaining clips had rotated loose so that it was no longer holding that side of the bearing in place. When I replaced them, I made sure they had plenty of pre-bend tension in them. Done 1000 miles since and all OK. Naturally, I put a new thrust bearing in at the same time - the old one was showing signs of chipping around the edge, not surprisingly.
Best of luck
|Dave B. - It's not nice to make fun of old men (you are destined to be one yourself someday) :). Cheers - Dave|
|I was sitting at traffic lights on a dual carriageway recently with the window down and the car next to me had the window down as well. Her car was moving back and forth all the time cause she was holding the car on the clutch. I asked her "Do you go through clutches often?" She said "Not that its any of your business but Ive gone through 3 in this car alone" so I said "well if you use your handbrake, which is why the car has one, instead of riding the clutch to keep the car still, you might find they last a bit longer!" Bad driving like that really bugs me, and they'd be just the people who'd be moaning about other drivers all the time.|
|A comment on people at stoplights.|
So many of them have been brought up on automatics that they do not stop a distance behind the next car to allow them a slight roll-back when they engage the clutch to start off again, particularly uphill.
Although you can usually get away smartly without much roll-back, it is disconcerting to have someone a foor off your back bumper - you know who they will blame if you do roll back into them....
|Roll-back when they start off again? That's a driving test fail in the UK. A slight incline can be catered for by engaging the clutch slightly while still holding the car on the foot-brake, then driving off as normal. A steeper incline should have the handbrake applied and held on until you are taking the weight of the car on the clutch and throttle.|
I've had a roller-bearing release bearing in the roadster for some 30-40k now, without a pull-off spring, and whilst it started squeaking quite soon after fitting just as it starts to take any load, then stops squeaking when it takes a bit more, it hasn't changed how it works in that 30-40k. Roller bearings are standard on the V8, midget 1500 and other BL vehicles, again without pull-off springs. Other manufacturers may need them but the MGB doesn't. But the after-market bearing for the MGB hasn't been available for a long time, as far as I know. In any case they are waste of money, are you going to leave that bearing in there when changing the clutch? I think not.
There has been a problem with one type of MGB release bearing that has a roll-pin through the side of the casting to hold the carbon ring in, instead of being bonded, and this can cause the carbon ring to shatter. A friend has just had to have his clutch replaced after only about 4k miles. The old bearing was pinned, but the carbon ring in his case had been completely worn away, no evidence of broken pieces in the bell-housing, just tons of dust. Make sure you get the bonded type, the pin is very obvious (http://www.mgb-stuff.org.uk/wn_clutchframe.htm and click on 'Release Bearing') and easily avoided. Last wek I changed another clutch where the friction plate and cover plate were badly worn, so bad it was slipping in all gears, but the carbon release bearing was only about 1/3rd worn. The standard release bearing should easily outlast the clutch - unless you abuse it.
|Actually that is a fair point you make there, Paul. I never roll back when I'm doing a hill start. I did when I was a learner driver, but reasonable clutch control should allow you to move off on any hill without rolling back. When Im releasing the clutch Im also releasing the foot brake or holding the car on the handbrake and Im getting on the accelerator. Its a swift fluid movement and if done correctly should not allow for any rolling. I can do this in any car without practice.|
This thread was discussed between 14/06/2008 and 16/06/2008
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