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?

 

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

Resolder or replace.

 

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.

 

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

 

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