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Q & A: MGB Overdrive and Reverse Failure

This may be strange getting asked a question from so far away.. Sydney , AUSTRALIA, but I feel you would be the best person to ask as I purchased an American MGB LE and imported back to Australia and converted back to right hand drive.. This was a Californian car..( Los Angeles )

I am not 100% happy with the answers I am getting here as to the problem I am experiencing with the overdrive on my car as most B's here are 3rd and 4th gears whereas mine is only 4th gear...

I purchased the car 20 years ago at 105,000 miles and is now 116,000 miles.. AT 101,000 The car had an engine short block replacement and the clutch was renewed.

Once about three years ago after a long and fast run I experienced the problem first time and has not appeard again till recently, when this happens almost all the time now..

The problem is that when the car is cold the overdrive behaves quite normal, but when the car has warmed up after 10 - 15 minutes I cant engage reverse gear..
the gear will shitf into gear but the clutch wont engage.. I can turn the engine off and come back a few minutes and all is fine, the reverse gear engages.. the other problem is that I also the overdrive unit sometimes wont engage in top gear.. this is spasmotic.. something that happens very occasionally is that when accellerating hard in 1st or 2nd the clutch appears to slip for a second or two.. another thing that may be related or not is that when coming down a hill in thrd gear the clutch seams to have trouble engaging.. now all this happens when the engine is hot and whether engaged in overdrive or not...

When cold and in any gear the normal clutch checks out, by not slipping and will stall the engine..

I have just drained the gearbox and cleaned the filters and relaced the oil with a CASTROL GTX 2 ..20W -- 50 which CASTROL recommend for older vechicles,
and this did not improve the situation at all , if any thing may have made worse..

I have had such a vast range of opinions from o rings need replacing and the engine/gearbox needs to come out, to the solenoid needs replacing, and a range of other hints.

Thats why I have come to you as I feel you will put your finger on it right away.. If need be I am happy to phone and discuss if cant be answsered in a few words..
I would prefer something in writing if you have time so I can give to the person who will be doing the repairs..

My feeling is that is something electrical, that I hope can be tackled from the outside of the overdrive..

If the car is driven as is will any damage be done to the overdrive.?? ...

The Federal, Canadian, and I believe the Canadian specification MGBs, 77-80, had a TCSA circuit (transmission controlled spark advance) which allowed manifold vacuum to the distributor advance unit only in 4th gear. All a bunch of emissions junk... read more