Overdrive in 740 turbo

This might help

If your electrical connections are tight and the fluid level is OK, under load could be the beginings of failing actuating piston seals or a broken high pressure control spring.

Testing while driving with a high pressure ( 600PSI or better) guage attached to test port of OD will tell much.

Actuating Piston O-rings require removal of OD from trans and antoher set of pistons to replace the bad style probably in the unit now.

Spring requires removal of OD pan, then the far left plug to access.

Duane

Thanks Duane, Is it possible to disable the overdrive unit and still get 1-4? It lurches under load in most gears.

Ray

Lurching under load in all gears is different than lurching only in OD mode which is what I deduced from your original post.

Two causes of OD induced lurching in all gears which is not caused by a damaged or worn engine to tranny clutch.

Power is getting past the various switches and relays to power the solenoid at all times. If removing the ground wire of the solenoid under the auto does not stop the lurching, the solenoid needs to be refurbished.

Fluid has gotten past two small O-rings on an internal solenoid piston into the coil body and has locked the OD on.

Duane

Duane, If I am understanding correctly then is it possible that while I had the car jacked up from the rear the fluid that had worked its way past the o-rings on the solenoid drained back into the case and that would have temporarily alleviated the symptom? Disconnecting the ground wire seems to have had no effect on the lurching.

I appreciate your help.

Ray

If it's lurching in all gears then it isn't an electrical problem with the overdrive, it sounds like either an internal mechanical failure or the clutch is slipping. You can't bypass the overdrive, it's separately removable for rebuild or replacement but it forms the rear section of the transmission.

Sorry for a late reply, I finally took some vacation time.

Possible, and probably helped for a while, but usually what happens is a portion of the fluid just drains out onto the ground. When you again use the OD, fluid again gets pushed past the internal O-rings and locks the OD on but only partially.

Cure for solenoid is remove from OD, remove internals via the front of the brass barrel, and replace the O-rings. Size here is important. Match at a hydraulics supply shop. Hardware or automotive rarely carry anything that small.

Difficulty is, if the OD is locked on, after a while you would not have any shudder since the fluid pressure would have built up to the pressures needed to maintain full contact internal to the OD. Usually around 25 to 30 MPH. SInce your shudder is in all gears, the actuating pistons are allowing fluid past and you are getting the shudder as the fluid is held and released past those O-rings.

If this is the case, your only "cure" is to remove the OD and change the O-rings and actuating pistons. I would surmise that you have the original Teflon type O-rings which if not heated to around 600 F will fail into many pieces after about 10,000 miles. Rubber tyep O-rings that fit the Teflon width groove do not have sufficient size to effectively prevent fluid blow by which erodes the rubber to ineffective after about 5000 OD miles.

Duane

Duane, That is excellent clear and concise information. I will work on the solenoid first and should that not remedy the problem do you sell parts for these units? If not can you recommend a source?

Thanks again for your help,

Ray

I sent a message to you off list. I hope it reaches you in a readable format.

Duane