93 Tranny Low Pressure problem

The 4t60E Transaxle will not engage in any gear until engine runs several minutes. Line pressures at idle measures low - about 50 psi in all gear ranges except low which reads 120 psi. Spec at idle is 74-85 in D4, D3, D2, 79-95 in P,R, and N, and 158-170 in low. After several minutes, car will move and drive even with these low pressures. With the vacuum modulator vacuum hose removed, the line pressures are at the specified maximums. This seems to tell me the transaxle pump is OK but maybe the vacuum modulator is not allowing proper pressure at idle (high vacuum) conditions. The measured vacuum idle at the modulator hose is a good steady 15 inches.

Am I on the right track? I did try replacing modulator with a universal Autozone adjustable one but I did not solve the problem even after trying several different adjustments. Am I on the right track? Do I need to get an OEM vacuum modulator? The fluid condition and level seem OK.

Thanks,
Tom

I would say you have an internal pressure leak. i.e. cracked clutch hub or some other internal problem

I have a 94 Lesabre with similar problem. Won't go into gear until
engine has run for a short while. Runs and drives fine after warmup.
Appear to be overfilled with fluid. What is the easiest way to get
excess out to proper level. Would appreciate any information you
can pass on if you have solved your problem. THANKS and GOOD
LUCK!

I haven't solved the problem yet. I do have some info that may be useful. I connected a pressure gauge and found that the pressure was low at idle. This may be due to an internal leak in the transmission which probably means I will need an overhaul to completely fix the problem.

There is a thermal element in the transmission that keeps transmission oil in the transmission from draining to the pan when the transmission is hot. This keeps more transmission oil available to run the transmission. When the fluid is cold, this thermal element allows transmssion oil to drain back to the pan. So when you read the dipstick, it will read fuller when cold than when hot (more transmission oil in the pan). So be sure to read the dipstick with engine running and transmission in Park after the transmission has warmed up. This thermal element may also explain why the transmission works better when hot. More transmission oil is available to run the transmission.

As I mentioned I have not solved the problem. These are my current theories. Something else you may want to do if you do not have a pressure gauge. Disconnect the vacuum line from the vacuum modulator. Plug up the disconnected line so you do not mess up the engine vacuum. Then start the engine. The transmission pressure will now be higher and you may find the car moves right away. Again this is just a test to confirm that the problem is pressure related.

If the transmission is really overfull, you have two choices - try to remove oil by sucking it out the dipstick tube using a long thin hose with suction bulb or loosen 4 or 5 screws on the pan and let it slowly drip out into a drain pan - messy!

Thanks for Response! Found a reply posted by avatar307 can't relocate in posts but he had found
in Factory Service Manual for 4T60-E Tranny the following:
Under Condition: Delayed Engagement, it lists Inspect
Componet: "Cooler Checkball (28)" For cause:
"Not seating, allowing converter drain back 7A-5A-34.) Cooler Checkball is located where the transmission cooler line attaches to the transmission
body. There are two lines the one that bends and
connects vertically into transmission has the checkball. The other line attaches in a horizontal
manner. Ordered a new checkball from GM dealer
cost $6. haven't received yet but will let you know
if any help.. Also added new modulator with little
improvement. Fluid level was ok when I checked
it properly after running to temp and checking out
in park. May have to change fluid if I am unable to
syphon out of filler tube. Thanks for the help will
try the blocking of vac line and disconnect from
modulator. I did remove restrictor valve in vac
line before modulator and seemed to help.


Got the checkball valve and installed with NO improvement.
Went ahead and blocked the vac line to the modulator and
everthing works fine. I'm sure this is not the right cure for
the problem but transmission engages instantally, shifts
smooth and seems to work fine sitting still or on the road.
Do you know if there are any problems to operating this
way? Thanks for your help.