Overdrive in 740 turbo

  • Thread starter Thread starter Ray Varella
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Ray Varella

I have a 740 turbo with an electric overdrive and it lurches under load
in much the way a car does when someone is learning to drive with a
manual transmission.
I have done a visual inspection on the wiring leading to the unit and
wiggling the wires and cleaning the connections remedied the problem
temporarily.

I can't get the car high enough to really get a good view and have room
to work.
Has anyone else had a similar problem, any suggestions on how to
pinpoint the problem?

Thank you

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

Ray
Click to expand...


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.
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?
Click to expand...

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

Duane
 
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