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MG MGB Technical - Slipping clutch overdrive

Is there a separate clutch that operates the overdrive? I am certain the clutch that controls the usual engine, transmission, drive train is OK. I have tested it by reving engine with brakes engaged and releasing the clutch and engine stalls immediately.

If there is such a clutch, how can I adjust it so it will not slip?
Lee
1970 MGBGT
Overdrive did not come with this car originally.
LS Sheldon

Lee. The two best sources for such information are John Twist, in the US, and Chris Betson, in the UK. John operates as University Motors Ltd and Chris as Octarine Services. A web search under their trade names and their given names should allow you to contact them. There is some form of "cone clutch" within the overdrive unit which is not adjustable and does, over time, give out. The basic question is: What is your demonstrated problem? In my case, the system seemed to free wheel when the transmission had been in overdrive and I backed off on the gas after switching out of overdrive. Chris provided me some good insight into the problem. John offers (or used to) a class in rebuilding the overdrive transmission in his shop. The cost of the flight into Michigan, hotel, food, and the class were less than the cost of a rebuilt OD tranny. Something well worth considering. The transmission we rebuilt has served my daughter quite well for a number of years now.

Les
Les Bengtson

for a start I'd check the g/box oil level and if you don't know when the oil in the gearbox was last changed I'd give it a thorough drain by getting it hot and leaving it to drain as long as possible remove the o/d filter plate and clean that too

there are two John Twist videos on dismalting the o/d for service plus other videos on o/d amoug the 200+ posted (can't put links now as dinner is served)
Nigel Atkins

Quantumechanics (www.quantumechanics.com)is one of the best known trans.& OD rebuilders as well as a parts supplier in the US. The relined sliding member (cone clutch) sells for a paltry $225 exchange. The owner, John Esposito will probably help diagnose the problem over the phone.
Berry
BTP Price

The gearbox was completely rebuilt by a professional that has done many before. Unfortunately I drive the car so infrequently I did not discover the problem until about 3000 miles and three years later. I now live about 200 miles from the shop and it is really too late to go back.

I change the oil in both the engine and gearbox once a year even though the mileage would not warrant it.

Judging by the comments, it looks like there is no simple adjustment. The gearbox will have to be removed to be repaired.

Thanks,
Lee
LS Sheldon

Lee- The solonoid could be cycling in and out of stick due to low or dirty oil or low oil pressure. I'd screw a pressure gauge into the available threaded bung and see if you're pumping within the recommended range to engage and hold the sun gear. In the years I've driven the OD MGB, only the solonoid and dirt have caused failures. Really never heard of a mechanical failure or the cone gear wearing out. But then Les has a lot more experience in these things then I do.
Of Course a call to John Twist during his consult hours will answer your concerns on the spot, and my guess is save a yanking. Good Luck. Vem
vem myers

Sorry to bomb the list (again), but I remember the topic of clutch failures in LH ods being mentioned and how they are not usually replaced in rebuilds. Scroll down to the third topic.
http://www.quantumechanics.com/categories.php?op=newindex&catid=12
Berry
BTP Price

Lee,
as you use the car aso little changing the engine oil every year is a good idea

a thorough drain is more important than frequency

the resolution to yout o/d problem could be simple

the problem could be electrical, switch, wiring, solonoid

or

as lack of use can cause lots of problems you could try using the car regularly for a while to get all parts and components activating regularly - this will help the whole car and might solve your problem but I can't see how it would make matter worse
Nigel Atkins

This thread was discussed between 28/10/2012 and 30/10/2012

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