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transmission overdrive switch[740-760/85] posted by Larry Ayres on
Sunday, 14 June 1998, at 10:46 p.m.
The overdrive on my 85 740 Turbo engages fine at around 40MPH but fails to
reliably disengage when decelerating. If I manually turn it off, at around 35mph
all is fine. If I don't it seems to disengage just as you come to a stop with
a loud clunk, sometimes. Usually this happens when it's hot outside. I have just changed the transmission fluid. There is little info in my Haynes manual, but I
undertand that there is a switch on the tranny that should make sure that the
overdrive is only engaged in top gear. Is this true, and could this be the problem ? What are the usual symptoms of this switch failing ?
Larry Ayres
Re: transmission overdrive switch[740-760/85] posted by George Swift on
Monday, 15 June 1998, at 2:09 a.m.
Larry,
The way you worded your post could get responses for a manual or automatic transmission. After re-reading, my guess is
that you have a manual transmission. Do you really shift into O.D. at 35mph? If so, everything may be normal, and your car is just refusing to cooperate with the inputs. The owners manual would agree.
I have experienced the same problem with J Type o'drives. The switch you referred to has nothing to do with disengagement. The first thing to check is the sealing washer between the solenoid and the housing. If the washer is too thick or too thin, the fluid pressure will not bleed off, allowing the hub and driven plate to stay engaged. This condition is often mis-diagnosed as something more complicated.
The more complicated items are : weak springs (on the driven plate), Weak or broken pressure relief valve spring(s), or damaged or worn actuator piston cylinders. A pressure test tells all. Guesswork may cost less, but an accurate evaulation takes less time, and can save money buy diverting serious problems.
--
George Swift / Volvo Car Care