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September 29th, 2008

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Q & A: Transmission

Monday March 18th, 2002
Q & A, MGA, MGB, MGC, MG T-Type, Midget
John,

I have a problem with a 72 BGT with the Laycock O/D tranny.

The car is a 1972 MGBGT, 220,000 miles on the car; engine has about 9,000 miles since rebuild. The transmission was taken from a 1971 GT parts car showing 87,000 on the clock, and has done about 25,000 in its present venue.

The unit works very well, with crisp up and down shifts, no slippage either in or out of o/d. UNTIL..... Until the road speed reaches between 50-55 mph, at which point the unit downshifts out of o/d. No matter whether in 3rd or 4th, if the o/d is on, when the road speed reaches the "critical" point, the o/d shifts out.

I have checked the usual suspects: fluid level is full; no obvious external leaks; all electrical connections are sound and tight, and all the electrical components test "OK."

Could it be somewhere in the hydraulic operating system? The pump is the only o/d component who's operation would vary directly with road speed, the pump operating off the output shaft. Or possibly a bad check valve?

Frankly I'm at a loss as to where to begin. Any help you could offer would be greatly appreciated.

Rick Morrison

RICK!

The same Rick Morrison who was treasurer of the MGCC NA experience?

The rule is that ALL overdrive problems can be fixed IN PLACE. So, I would first double check the fluid level -- use Castrol 20W/50 GT... read more