Transmission falls out of OD Plus more

mdybus

1995 Buick Century Special 3.2 liter 4T60E transmission

My car had a high speed (highway) vibration, after replacing the "Complete" suspension system" including tires and wheels I was advised to get a rebuilt transmission.
New rebuilt Trans:
When cold will not shift into overdrive @ 55 mph takes 1.5 to 2 miles with a slight surging I assume from trying to shift into Overdrive, then a drawn out shift into OD. When warm the transmission will shift gears and into OD smoothly at 40 - 45 mph. I did not try a lower speed.
When accelerating the transmission has a vibration in 3rd and drive. When driving above 40mph you feel a rhythmic vibration similar to a bent drive shaft.
Engine at normal temp and no traffic the car runs perfect! Shifting is smooth and the transmission stays in overdrive. I drove from Georgia to Pennsylvania at night with no traffic and had no problems with Overdrive. On the way home the first 100 miles with no traffic all was good..After 100 miles I hit normal day Interstate traffic. After driving in traffic for a bit I noticed that when giving a little gas the motor speeded up momentarily then catches (like a slipping clutch) after this the transmission would not go into overdrive and remained in drive. My gas mileage drops from 28mpg to 19mpg and my water temp was a bar to a bar and a half above normal. Every once in a while, when in reverse, from a stop the transmission slips a bit before engaging. Like when accelerating from a short coast at highway speed as noted. The car has a brand new radiator, water pump, and hoses.
When doing a moderate acceleration to pass at highway speed when the transmission down shifts the transmission every so often makes an extremely loud BANG and the car jumps from the shock wave. This happened a few times when cold but almost always when warm. This Very hard shift has happed a few times when accelerating quickly onto a highway.
The transmission has eaten 2 new cv axles both on the left side. I assume, since everything else in the drive train after the transmission has been replaced and as mentioned the complete suspension system is new.
I was told the tcc valve was bad and replaced. Since then the shifting into OD is a bit smoother but when cold still takes up to 2 miles to shift into OD at 55 mph.

I've been diagnosing the problem for more than a year and feel that this rebuilt transmission is unserviceable with an internal crack that is bypassing fluid when the temperature of the trans fluid climbs above normal when in traffic and is working hard shifting in and out of OD and gear.
I had thought I was working hand in hand with my mechanic but found out the hard way I'm on my own and the guarantee is new school guarantee. (new school guarantee) bring your car to the shop. the shop does nothing for three days and returns your car to you. The guarantee is you can do this as many times as you wish. lol

imidazol97

Is your thermostat in the engine bringing the engine temperature up to normal the way it should?
Is it running too warm and causing the transmission to disengage the TC lockup in 3 and/or 4th
in order to keep engine speed up to cool down coolant faster by pumping it through the radiator
faster?

Without checking one of my factory service manuals for my s leSabres with the 4T60E, I believe it
does not let the TC lockup until the engine temp is a certain temp. Also, it may, may, keep it from going into 4th until it's at a certain temperature.

This is where having a shop that has the proper computer diagnostic tools and knowing how to use
them can help. They attach a Tech tool and drive the car from when it's cold to see just what is happening
or not happening.

I had both drive axles replaced by my shadetree neighbor, who does this stuff all the time. One had
a leaking boot at 200K. And I was feeling uneven operation of the joint with the the wheel turned. But
I also felt some uneven operation after both had been replaced. He said that there was wear in the torque converter that was causing some vibration. I also wonder if there's wear in the differential within the transmission. He said the cure was to put in a rebuilt transmission. However, the question is was your rebuilt by a highly qualified rebuilder? Or did they rebuild just what they could get by with instead of remanufacturing the unit.

Were the motor mounts/transmission mounts replaced when the unit was put in? There may be movement there from lots of softening or wear.

The loud noise and rough shift may indicate problems with the valves inside the trans.

Needs a good transmission shop and technician to drive it with computer attached. But a small part of your problems might be related to a thermostat/engine temp. Remember, controlling the engine temp for rapid warmup was needed to minimize emissions, hence no shift into 4th or no lockup to keep engine revs up to effect a faster warmup to lowest emissions.

mdybus

Thanks for the well meaning advice. However not much use to me. When I said I had the complete suspension I meant Complete including all parts from the transmission to and including wheels and tires.All transmission and engine mounts replaced, struts, lower ball joints, using all MOOG parts. any part from the transmission to the wheel lug nuts has been replaced with new. there is nothing more to replace. As for the engine temp my engine is always on 2 bars from cold. This does not move until the transmission drops out of OD. Then the engine temp climbs 1.5 to 2.5 bars above the mentioned 2 bars. Also when in this out of overdrive mode when pulling off the highway to refuel the engine begins to boil over and has twice caused about 1 and a half quarts of coolant to piss out on the ground from the reservoir. I am just about certain that I have to get another transmission. But need some reassurance before doing this a second time. My guarantee on the rebuilt is the Corporate States of America guarantee: You can bring your auto to the shop 125 miles away have it sit in the lot for three days, pick up your car with nothing done to it and drive home with absolutely nothing done except wasting time and gas money. The guarantee is: you can do this as many times as you like.

thecardoc3

Nobody can just tell you what you need to do. All you have provided is information that describes potential problems and the conditions under which "they" occur. That's enough from which one could start a diagnostic routine, nothing more. You don't have enough here to just blame the transmission, even if it does in fact need to be repaired. Without confirming the inputs to the computer when the problems are occurring as well as the outputs from it both by serial command as well as actually proving that the computer made the commands with proper equipment (low amps probe and digital oscilloscope) nothing can be determined.

BTW, your temperature gage isn't accurate enough to judge the engine temperature especially in relation to how the PCM would operate under any specific conditions.

mdybus

Thanks thecardoc3 I know now what I must do