M46 OD sticks on

My friend's 740 GLE has an odd problem with the overdrive, you engage it and it clicks in immediatly, but when you press the button to disengage it the dash indicator goes out but the OD stays in gear, you can even downshift with it still in OD, eventually at a random time it disengages with a somewhat unhealthy sound. It never seems to slip though, is this something that can be fixed or should we grab a new tranny from a junkyard?

Reply to
James Sweet
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Sounds like the relay might be crapping out. Is there an audible click when trying to disengage the OD?

Resolder or replace.

--

-don

'81 242t '89 744ti

Reply to
don hodgdon

The relay works fine, it clicks and the dash indicator works fine, definitly something in the OD itself, as I said it makes an unhealthy grinding sound sometimes when it finally does disengage, obviously not an electrical problem.

Reply to
James Sweet

Perhaps the solenoid wich is mounted on the outside of the OD does not work propperly. You can also hear it click if you engage the OD. Also check/replace/fill the od's oil and clean the metal filter.

martijn

Reply to
Martijn

Four potential problems. Listed in ease of diagnoses. Most likey number two.

The relay is allowing power through even after you "turn it off". Remove the cover to access the fuses and relays. TWO people in auto. Drive the auto, engage the OD, when the OD is truned off, and the OD stays engaged, non driver reaches in and taps the relay sharply with handle of screwdriver or something similar. If OD drops out when relay hit, coil contacts or internal circuitry is the problem with the relay. Remove the relay, pop the cover and look at the coil contacts. claen or replace the relay if necessary.

Second is Solenoid on OD itself. It has two internal O-rings that after a hundred thousand miles or so, allow fluid past into the coil area. This fluid keeps an internal piston from moving and keeps the OD on until the fluid drains off. A temporary fix is to remove the internals of the solenoid and clena it out, which will last a few thousand miles if you are lucky. Replacing the O-rings is like getting a new solenoid without the Dealer cost. O-rings run $5.10 from me and come with instructions.

Third problem is much more difficult to repair since it indicates and internal problem with the OD. There is a small hole between the solenoid and the bottom of the dashpot where ALL the fluid to engage or disengage the OD must pass. IF, this hole gets blocked by a part of an O-ring, the OD will not disengage. To access and clean, the solenoid is removed, the pan on the bottom of the OD comes off and the far left plug and internal parts are removed. Th eprot is the blown clean from the solenoid side to the internal. Takes a right angle blow gun or can of air with a squirt tube and some contortions on your part. Replace the offending O-ring and put everything back in the correct order and your good to go.

Some 700's have a situation where one or both of the relief valve springs break and the valve gets hung up not allowing a release. There is usually some slippage that occurs with this situation. Repair is accessed like number three above since the springs are under that same plug.

For some detailed instructions for the soelnoid, contact me at ODGuru at kc dot rr dot com.

Duane ODGuru Laycock Only

Reply to
Duane Hoberg

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