Transmission Shifting Slow/Funny

[dmperfection]

Trans started acting funny yesterday on my '02 Tahoe; reverse and drive shifting seems fine, but when in drive and taking off from a dead stop, it seems to hold on to 1st gear for a long time - up toward 4k rpm, then it'll jerk into next gear - oil level checked out good, no excessive odor that I could tell. What I did try was manually shifting beginning with 1st, when I shifted to 2nd it still wouldn't go into second without really increasing the rpm's. I drove around the block a few times playing with the trans and found that if I let off the gas a little around the 2k rpm range, it will slowly shift into the next gear - I say slowly because if I let the gas off the first time, it's a 50/50 chance it shifts into next gear - if it didn't shift, I increased rpm's again to 2k - 3k, let off the gas, sometimes a few tries, then it shifts.

I don't really know which trans I have; I'll check tonight when I get home from work.

I'd appreciate any advice or guidance on this problem.

Thanks everyone!
Steve

 

[blueflamed03]

Steve, same indication I had when my tranny went out. Sounds like time for a rebuild

 

[dmperfection]

Not quite the response I wanted to hear......

Any help you can offer on the quest to find a good Trans shop? I'm out in Los Angeles, CA.

I've poked around online and reviews are pretty sketchy on a lot of places - some are happy, most aren't.

 

[scottg918514]

If just the 1 to 2 problem and not 2 to 3 to 3 to 4. Then I'd suspect a 1-2 shift servo problem. If so, a relatively cheap fix, in fact a lot of DIYer's put in the Corvette 1-2 shift servo themselves. Unlike the other servos, it is external to the tranny and easier to replace for you or mechanic.

 

[DTAILS]

If just the 1 to 2 problem and not 2 to 3 to 3 to 4. Then I'd suspect a 1-2 shift servo problem. If so, a relatively cheap fix, in fact a lot of DIYer's put in the Corvette 1-2 shift servo themselves. Unlike the other servos, it is external to the tranny and easier to replace for you or mechanic.

+1

 

[dmperfection]

Thanks for the input; here's the update to my limited testing last night.

I borrowed a friend's Snap-On MODIS scanner and hooked it up; too bad she didn't give me all the connectors - I was only able to do OBD scanning, and not able to do any of the diagnostics at the trans to test servos. Anway, I was able to hook up for live feed while drivng and found that I do have good 1-2 shifting, the problem is 2-3 shifting - there's a really long lag but eventually gets into 3; 3-4 seems fine, but I'm missing one last gear - maybe overdrive? Once I get to 4, rpms hit toward 3k rpm at 65 mph.

I'll keep you posted on my progress...

Thanks again everyone.

 

[Jay]

Usually when I've run across a situation like this it was either a leaky boost valve, cracked 1-2 or 3-4 accumulator piston, leaking/worn converter PWM valve, or bad o-ring on the 2nd or 4th servo. Any of these can bleed off line pressure and cause a delayed shift... the computer only commands shifts, the hydraulics perform the shift in this transmission. If the line pressure isn't adequate for the shift it won't happen even with a command. Raising engine rpm will raise line pressure since you are spinning the pump faster and the extra fluid volume from higher rpm can overcome some bleeding to complete a shift. But, as you are very likely seeing, the side effect is delayed shifts and eventually a burned up band or clutch.

How many miles on the trans? There could be some quick/cheap fixes with a simple pan drop... but I don't want to lead you down a path of parts swapping on an old trans (usually means throwing good money after bad).

If you don't mind spending a little money (~$50-100), you could replace the o-rings on the servo pistons, replace the 1-2 accumulator piston, and replace the boost valve. This may fix the issue. If the 3-4 accumulator piston has cracked, the valvebody will have to come down. Which will make replacing the PWM valve much easier also.

What makes me hesitant is that there could be an issue with the forward clutch or direct clutch pistons which are inside the rotating assembly. If these are bleeding off pressure from either cracks or o-rings then the trans has to be torn down.

It's your call.

 

[dmperfection]

Thanks for all the suggestions and comments. It's been a little while since my post, and but here's the update and resolution.

I ran it over to the dealer for diagnosis; they determined there was no 2nd and 4th gear, and gave me the bad new.....needed new trans (their estimate was pushing $3,200 - installed).

I did plenty of digging around for good rebuilders, and went out and visited several shops. I settled on a rebuilder near me, and ran me just over $2k for the complete job with 3 year/50k mile warranty. Rebuilder told me that 2nd and 4th gear bands were completely broken. I've put about 4k miles on the trans since the rebuild, even took an 800 mile trip to Vegas, and she's solid....so far.