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MG MGB Technical - clutch or overdrive slip???

Hi folks. I have a '71 BGT over here in france. The clutch or overdrive has started to slip under heavy acceleration in 3rd and 4th gears only. it also becomes more noticable once the engine has warmed up. Spoke to MGOC on the phone who said there is no way to tell if it is the clutch or overdrive that is slipping. Spoke to a friend who mentioned adjusting the solenoids on the overdrive untit. Anyone know how to tell if its the clutch or o/drive unit? (the slippage occurs with or without o/drive selected)
John

I have had this happen on our 74 GT with overdrive. Overdrive only slips when overdrive is engaged and hot. The clutch will slip all of the time whether in od or not.

Good luck,
Mark
M Whitt

John
The engine (at least) will have to come out for a clutch inspection, so you'll see if the clutch is badly worn. If there's any doubt at all, get the OD rebuilt. This will save lifting the engine and box a second time.
D Wellings

If there is any possibility that it IS the overdrive, before you do anything major:

1. check your transmission oil level. If it is not 20-50 (or if you don't know), change it.

2. replace the "O" rings on your overdrive solonoid. While you're at it -

3. clean the filter screen.

This little service operation will take about an hour; the "O" rings will cost you about $2 US. It just might solve your problem as it has for me. If it doesn't, get some excellent advice for the cost of a phone call from John Twist at University Motors in Ada Michigan, US. http://www.universitymotorsltd.com/
John maintains that most overdrive problems can be solved from under the car.

FWIW,
Allen
Allen Bachelder

The solenoid isn't adjustable on the later LH OD fitted from late 67.

The OD is 'in circuit' whether OD itself is switched in or out of course, but switched out drive is through the locked one-way clutch in which slipping is nigh-on impossible. Switched in slippage can occure if there is insufficient hydraulic pressure or worn brake bands, so that should be the arbiter.

Clutch slip is more likely to happen in 4th than 3rd, OD slip is more likely to happen in 3rd than 4th, due to the relative differences in torque each side of the gearbox.
Paul Hunt 2

I second that. The gearbox multiplies engine torque - since the OD comes after the gearbox, if it were the OD it would slip worst in First and Second, because that's when the torque across the OD is greatest. Here, it slips in 4th, where engine torque is Not multiplied, so torque across the OD is low, and torque across the clutch is high (the "road" has its greatest mechanical advantage over the engine when you're in high gear) - this strongly indicates that it's the clutch, not the overdrive, that is slipping.
Sam

...but - don't remove anything until you've ascertained that this isn't caused by some electrical leak causing the solenoid to partially engage in 3rd/4th. Disconnect the wire at the solenoid, to make sure the solenoid has absolutely no possible source of electricity, and test drive again before you decide that the problem is mechanical.
Sam

If it is the sliding member in the overdrive you will likely have slipage in reverse rather than forward.
John H

Don't put it in reverse with the O/D on. And its your clutch, not the O/D (though the O/D might have issues as well). Replace the pressure plate with a OEM one, Replace the disk with one from a TR7, and use a graphite or roller T/O bearing (don't forget to check your pilot bushing as well.
D.A. Abbott

D.A. I wasn't suggesting that he put it in reverse in OD. If the lining on the sliding member in the OD is worn out the transmission will slip in reverse.
John H

Putting the gearbox into reverse with OD switched on should have no effect as the gearbox lockout switch is there precisely to prevent OD being engaged in reverse, regardless of the position of the manual switch. If the lockout switch is faulty (and I have never heard of one being closed whrn it should be open, only the other way round which is 'fail-safe') you will have OD in 1st and 2nd as well, and this is easy to check by driving gently in either of those gears and operating the manual switch on and off and seeing if the revs change as you do so - they shouldn't.

I would advise againt fitting a roller bearing release bearing. I installed one the last time I changed my clutch thinking it was a Good Idea. After a few hundred miles it started squeaking just as it starts taking up the load of the clutch. Then I started reading about 'pull-off spring kits' to pull the bearing *away* from the cover plate (there is a spring in the slave cylinder pushing it into contact with the cover plate so as to give a consistent biting point), otherwise it is rotating all the time. Then I though forward to the next time I change the clutch - would I really leave that old roller bearing in there? Of course not! And as carbon bearings last more than the life of the clutch if driven correctly the significant extra expense of the roller bearing is a complete waste of money.
Paul Hunt 2

Also....the solonoid either works or it doesn't. There is no adjustment, it just pushes the ball bearing across the flow and stops it, forcing the sun to rear it's ugly head . . That pressure-to the sun- is adjustable by very expensive, and exclusive mech-gurus lurking in the yellow pages . Luck, it's prolly your clutch.Cheetos Vic
vem myers

This thread was discussed between 08/02/2007 and 17/02/2007

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