My transmission was recently rebuilt, a few months ago, but it is acting strangely. By that I mean that it sometimes seems to slip before it downshifts at cruising speeds (like when I am driving up a significant incline). Interesting, if I downshift with the gear shift, the shift is crisp, but sometimes when downshifting when the transmission is in drive it seems to slip before or while shifting into the lower gear. Adding accelerator (firm) commands a quick downshift.

Also, I noticed the other day when accellerating, it did not want to upshift under power when the RPMs maxed out. When I let off the accellerator, it immediately upshifted.

So, does this sound like a soleniod issue, computer issue, ???

Anyone experience anything similar?

 

Without looking in the ATSG books or doing pressure testing. My first thought is you may need a longer accumulator pin. If it is slipping there most likely is a pressure loss. Is your problem a 1-2 or 2-3 shift issue?

 

Thanks for the comments and question/direction!
A buddy of mine has the rebuild book(s) - I believe that they are ATSG, and he/we are in the process of reviewing the trouble shooting section (good suggestion!).

If I recall correctly, I think that there may have been a large washer or spacer (between 1 and 2 inches in diameter) that we did not put back in (maybe the accumulator) - does that sound at all familiar - and if so, could that be the problem, making the accumulator pin "appear" shorter?

As for when and under what conditions it "slips" - it occurs when I am cruising upwards of 45 mph and going up a grade - so I would assume that it is a 2-3 (down) shift, but I will see if I can verify.

The other "thing" that it does, is that under power (pedal floored) it does not (up) shift into the next gear even at 5-6k RPM, until I remove my foot from the throttle.

This is the second time we rebuilt the transmission. When I purchased the car, the tranmission needed to be rebuilt (burned clutches) - it was an awesome rebuild, very quick/tight shifting. You could "break" the tires at each shift. Then, about a year later, the clutches went again - due to a clip that "came off" internally (forget which one). This is after the second rebuild. Needless to say, we replaced the "clip" with a new one (this time). But the trans never did shift the same after this "second rebuild" - but I cannot say that this "strange behaviour" was there when it was rebuilt back in December 2010. This car is a "driver" - not that it looks bad or anything, but it has 130k miles on it, and I purchased it to drive it (not park it only to drive on sunny days...).

 

If the washer not put in was the shim used for the front to back spacing that may be your prob. Did the washer have some numbers on it?

 

Not sure... Looks like my "task" for this evening will be to "FIND THE WASHER"!

I am guessing that the obvious answer is that it is NOT GOOD to drive the car with the trans in this shape (particularly when/if I feel that it is slipping --- otherwise, it may soon again be time to rebuild the transmission - replace the clutch packs)...

The other bit of information is that if I do feel it slipping, and I downshift by changing the gear shift, then it shifts crisp - immediately.

I'll report back tonight or early tomorrow about the washer...

Thank you very much for your insights!!!

 

............ The no up-shift with pedal floored issue sounds like you need a governor adjustment ... B&M makes a spring and weight kit for the governor ... it takes some trial and error tuning to get the shift points where you want them ..............

 

He has a 4L60E
no governor used like a 700R4 trans has.

I think you may have a fluid leak present in the 1-2 or 3-4 accumulator pistons- seals.

That would cause low line pressure between gear shifts.

Damage may be done allready to the forward clutch and 3-4 clutches.

4L60E & 700R4's don't tolerate low line pressures for too long.
Fail quickly.

Remove the trans oil pan and take a better look.
Garbage or debris in the bottom of the trans pan will tell all.

If no debris, clean yet, try and make repairs yet in the car.

Brian

 

Correct, it is a 4L60E.

Thanks for the suggestions!

Sadly (or perhaps a good thing) - I know what it should feel like (it was awesome after the first rebuild!) - I can tell that something is not right (thought so from the beginning when I first drove it after the second rebuild). If failed the second time (requiring a second rebuild) due to a clip that came off - after running strong for a year ~15k miles.

Thanks again for the comments (also welcome any other comments or suggestions). Looks like time to troubleshoot with the trans rebuild manual or other.

 

Don't feel bad.
I have failed successfully putting together a 4L60E transmission back in March of 2007 for a friend of mine's older brother.
He had a 9-second 87 GNX Buick Grand National.
They paid me very good for any custom work I ever did for them.
Some nights I went home $800.00 cash richer in pocket.

Anyhow at that same time in March of 2007, my best friend of over 20 years was dieing of lung cancer and a brain tumor.
He often hacked up blood out his mouth when trying to speak to you.
And he dropped from 185lbs to about 90lbs in 2-1/2 months.

So to no end this tore me up inside and drove me crazy.

I was called on to overhaul this Chevy 4L60E transmission.
I did the rebuild correctly 100% other than installing the input sprag correctly.
I installed it upside down.
So the trans only had Park, Reverse, 1st and 2nd gears.
the truck had monster 44" inch tall tires and the owner liked driving in 2nd gear anyway.
So they let me come back later to correct my mistake.

Moral of the story is never take on any complicated repair task unless your mind is 100% clear.
Otherwise mistakes will be made.
Even by among the best like me.

BR

 

Update... Ok, so I believe that I have found the "washer" - it does not have any part numbers on it... just appears to be a "standard washer" or perhaps a shim.

I have not yet dropped the pan to see what the fluid looks like (to see if there is any evidence of burned clutches) - but hopefully plan to do that in the near future, and will add another post at that time.

 

Ok, so I got some other feedback on the "problem" that directed me to look at two of the solenoids, I believe that they are the 1-2 and 3-4 solenoids - side by side on the back of the valve body (only ~$12 each - the replacement gasket and fluid were more expensive!).

Immediately after changing the solenoids, the car shifted much crisper; however, it was short lived. At the moment, the car does not shift into fourth. If I put the car in OD (4th), at speeds above ~40 MPH, it will shift up through the gears; however, it seems to "disengage" in 4th and then the engine will "rev" (freely) until the RPM's match the speed for 3rd gear, then 3rd re-engages.

I did attempt to read the computer codes (OBD II, I believe), but neither a newer code reader (only listed codes back to 1996) nor an older one could "communicate" with the car computer.

We then checked, and it appears that the car is running in "limp mode" - so I guess I've got to figure out why the computer is not functioning properly... planning to check all fuses first.

Thoughts, suggestions? (HELP!)

 

By the way, the fluid looked fine when we changed the solenoids... we did however, replace the fluid, gasket, and trans filter - since we were that far into the transmission.

So, it appears atleast so far, all of the clutches are in good shape!