1985 740GLE overdrive woes

Good day,

I have a 1985 740 GLE with an M46 manual transmission with overdrive.

Overdrive acts flakey.

At normal to high temps, the overdrive can be engaged shortly after
hitting the road. The warme it is, the quicker it engages.

At low temps, it takes quite a while but it does eventually engage.

I have eliminated the switch on the gear selector (shifter).

I have opened up the relay and cleaned the coil contacts.

I have checked the terminations at the solenoid.

I addition, if I move the gear selector to the left a bit, the
overdrive will disengage leading me to believe that there are 2
problems; one with the 4th gear switch and something somewhere else.

I see on the schematic, that the EGR solenoid is in the same circuit
but I figure that it's just drawing power from the same place as the
relay circuit.

Where exactly is the 4th gear switch? Under the console? Can it be
adjusted? Can I reach it without pulling the console?

I have pulled the top cover of the console off, but never the shifter
boot.

Any ideas on the overall problem?

I don't really want to "diagnose by replacement" the solenoid as it is
pricey.

Could this be a problem with the transmission oil? Drain and change?

TIA

regards


jimB

 

Oh I forgot, relay does not click until the overdrive is ready to
engage. That is, until car warms up, no relay noise.

jimB

 

replace the OD switch on the gearbox. I think they can get contaminated
with oil which makes them sluggish with cold.

 

My 240 has this exact same set of problems, it's the 4th gear switch on
the side of the transmission housing. It gets worn and will prevent the
overdrive from engaging until it warms up because it thinks the car is
not in 4th gear.

 

Is that the 4th gear switch? It's on the gearbox?

I am glad I didn't rip out the console.

jimB

 

rh side of the gearboxcover (the other one is for reversing lights).
Resist the temptation to bypass the switch, as it will then be possible
to engage first gear and reverse with the OD switched on, which is
not_a_good_thing

 

no it would not.

thanks much

jimB