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MG MGB Technical - Overdrive Slip in Reverse

Hi All
What is the cause of a slight slip in the overdrive in reverse gear? and is it home repairable.
Ron
R. Algie

Hello,

The problem is not the OD as control switch will turn it off when in reverse. Otherwise it will slip. It is not suppose to function in reverse. Your problem is with that safety switch which is on all the time.

cheers,
JGC
Jean Guy Catford

Ron. The overdrive should not function in reverse gear as Jean Guy mentions. Chris Betson, of Octarine Services, has a website which has a technical questions area. He has always been very helpful when I have had overdrive related questions.

Les
Les Bengtson

The overdrive isn't engaging in reverse but the drive through it is slipping, if that makes sense.
Ron
R. Algie

Ron,

This is typical of worn clutch cone in the inner workings of the OD. Does it slip in 3rd and 4th when the car is hot as well? (when OD not engaged). If it is the clutch cone then really you are looking at a reconned or 2nd hand unit as self repair will cost more than a 2nd hand unit at least. Your sure it is not the main clutch that is causing the slipping?

Cheers
Iain
67 BGT
I D Cameron

You could try dropping the little OD filter plate and see if there is a lot of crap in there. When mine did this there were some small amber like pieces that I was advised were part of the OD cone clutch. I cleaned the filter and replaced all the O rings etc on the OD, as well as renewing the gearbox oil, and it did improve thing greatly. Lasted for another few months until I was breaking the car anyway.

Iain
I D Cameron

If you are getting slippage in reverse and it is not in the standard clutch then the overdrive cone clutch is worn out or the springs in the overdrive are broken or weak resulting in the cone clutch slipping. You should also notice slippage in 4th gear in overdrive. Going forward with the OD off you will not get slippage as the roller clutch in the overdrive will carry the load.
John H

As the others said, slipping cone clutch in the OD. BTDT. You will probably notice that it's temperature dependant (does it worse when hot), and you're also probably getting slippage in forward gears in overrun (i.e. if you're coasting to a light, you're not getting engine braking).

Like Iain, mine had little amber flakes in the screen. Cleaning didn't help. So mine is awaiting rebuilding..... :-(
Rob Edwards

Thanks for the replies I had a feeling that's what was wrong!
Ron
R. Algie

Isnt there a sprag clutch which causes this? this came up before and will be in archives.
Stan Best

It doesn't *slip* in reverse if the OD is energised (which it should never be of course), it jams because the overdrive gearing is trying to force the sprague clutch (one-way clutch) further into its locked position which knackers it.

With OD disengaged forward motion turns the sprague clutch in its locking direction to give a positive drive i.e. *not* via the friction linings. In reverse the sprague clutch is turned in its free direction and so movement of the vehicle is dependant upon the friction linings. Because of the direction of thrust on these in reverse it tends to push them harder together to resist slipping. But if the linings are worn or glazed they slip (and you get a tendency to free-wheel on the overrun), but it can also be caused by a broken circlip on the sun-wheel.

Gunge in the hydraulics could also be preventing the linings from fully engaging, so the first step is usually to drain the oil, clean the filters, and refill with ATF which tends to act as a cleaning agent. If that does the trick then use it a hit longer, then drain, clean and refill with the proper engine oil. Some say their's *only* works with ATF, but in those case I suspect there are still problems in the OD that the use of ATF is helping to mask. Still cheaper than a rebuild, though.
Paul Hunt 2

This thread was discussed between 15/05/2007 and 17/05/2007

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This thread is from the archive. The Live MG MGB Technical BBS is active now.