MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Reverse slips when car is hot

I have a 74 MGB convertible, all stock, never modified, with 99,000 miles on the clock. It runs great when cold, but ONLY WHEN CAR IS FULLY WARMED UP, reverse slips so badly that it can barely back up an incline. The ONLY occurs in reverse, and ONLY if the car is at operating temperature. There are no leaks, and no low fluid levels. Car shifts just fine (not sluggish or stiff) in all gears, and has no slippage at all so long as the engine has not reached operating temperature. (The car does not over heat.) When it gets hot, it ONLY slips in reverse, the forward gears all work fine and don't slip.

What's up? I can't understand why slippage is limited to reverse gear, and limited to a hot motor. Seems to me if a clutch is bad or fluids are low or leaking, it should slip in all gears, and if the reverse gears are worn, there should be some other signs, such as whining--which in fact doesn't occur. Anybody with any answers or suggestions???

Thanks!!

THOMAS
GHT Thomas

Thomas,
Does the car have overdrive?
David
David Overington

If the car has an overdrive you have a problem.
DENIS4

Most likely the clutch lining on the sliding member in the overdrive is worn out. Chances are that when hot it will also slip going forward in 4th gear with the overdrive on.
John H

Less chance of slipping when going forwards as the helical forces tend to push the clutch together with more force. There is also only a fraction of the torque on the *overdrive* clutches in the higher gears i.e. 3rd or 4th compared to 1st or reverse. It's the foot-operated clutch that slips in 4th gear first when it is on the way out, because that side of the gearbox it is the *higher* gears that exert the greatest torque.
Paul Hunt 2

The O/D sliding mem,ber lining has become glazed. On the over-run (foot off throttle) or in reverse the drive is through the O/D lining but in forwards it is through a sprag clutch inside the annulus. I believe the springs engaging the sliding member are too light for the job & when rebuilding O/D's I always use V8 springs 37H1928. These are no loger available from Moss but can be got from O/D spares Ltd -ODSPARES@aol.com If the O/D has not been overworked & the lining is still good it can be deglazed - very coarse sand paper. & reassembled with the V8 springs & will work satisfactorily - I have done it many times.
Garth
Garth Bagnall

If you have a late (likely) OD, before going for a rebuilt or opening the Over drive, change all the gaskets and the ball bearing (part of the hydrolic valve) by opening the bottom plate accessable for the oil filter.
werner haussmann

And replace the "O" rings - or maybe Werner intended to include them. ' Can't remember if there are two or three - but you'll find replacements at your local hardware store.

Also clean the oil filter screen while you're at it.

FWIW,
Allen
Allen Bachelder

Yes, that is what I should have said, replace the "O" rings. Thanks Allen, .
werner haussmann

This thread was discussed between 12/09/2007 and 16/09/2007

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now