Woody427

I have a bone stock 99 S10 blazer 2wd with a trans issue that's driving me nuts. Most of the time it will either flare up (go to neutral) on the 2-3 upshift OR throw a P0758 and go into limp mode. When it's in limp mode with full line pressure it makes the 2-3 shift just fine-quick and firm. Sometimes it's just a long slow shift into third and sometimes it shifts totally normal. It's never thrown any other code, and has no problems shifting into any other gear either up or down.

So far I have done all the following-

Swapped out both the A and B solenoids-all four of the ones I have bench tested good for resistance and operation.

Tested the internal wiring harness-passed

Swapped out the whole valve body-made no difference.

Adjusted the shift cable


For some reason it has trouble engaging the 3-4 clutch. Still not sure if it's mechanical or electrical. I've been studying the legend in the GM service manual and thinking I should look at the 3-4 accumulator, or the servo. Servo seems least likely because it moves with every shift, and the problem is only with third gear. I don't think I fully understand the role of the accumulator either.

Any ideas/suggestions would be greatly appreciated.

SixShooter1125

I am having a similar issue, if I am soft on the skinny peddle, the 2-3 free revs. If I let off and let it down shift to 1st and give it more gas it will shift all gears fine.

pancho toco loco

iTrader: (8)

sounds like your clutches are worn. Time for a rebuild...........

Woody427

Clutches hold fine once they're engaged. Something is delaying their engagement. If I don't lift when it flares up and goes to neutral it slams into third gear fairly hard.

joecar

Have a read thru the attached.

SixShooter1125

Identical problem.

Mine slams into third and if I get off the gas it goes back to free rev.

SixShooter1125

I'm sorry if this is a dumb question, but what computer is the article referring to?

Gilbert@Ace Racing

I have had the pleasure of diagnosing the wicked amperage draw situation that Joecar posted more than a few times in my career. It's not fun.

However, based on the symptoms that both the guys here have discussed I would have to say that in my experience I have seen the 3/4 clutches engage, slip, partially engage, weld together, set slip codes, not set slip codes and I could go on. And all the while the issue is the 3/4 clutches are smoked and the computer does a damned fine job of covering it up. Point is, 9 times out of ten guy overthink their issues for one reason or another. Bottom line is, the transmission has outlived it's usefulness. Whether it's a brand spanking new rebuild or a high mileage unit... If it has been slipping any at all, the 3/4 clutches are compromised and it needs to be rebuilt.

I honestly do hate to be the guy that beats that drum... But the reality is, unless it's a high end unit by a builder who has taken the time to understand that transmission at an extremely high level, it is wounded and all the subsystem diagnosis and parts replacement under the sun will not compensate for a smoked clutch pack.

Honestly guys... I have yet to open one up that didn't need 3/4 clutches. Ever.

g

Woody427

It's a bone stock one with 200K on it (has had fluid changed a couple times) I don't have a problem with pulling it out and having it rebuilt. My big concern was that I have an external electronic problem that would still be there after I went to the trouble and expense of a rebuild. I will get my hands on a better VOM and try the diagnostic that Joecar linked to first. I would really rather it was an internal problem. This car has anti theft and best I can tell I would have to replace BCM if I replace the PCM, or get a matched set with the tumbler and key off another car.

Thanks!

joecar

I'm saying that the diagnostic is simple enough to do easily (eliminate as many unknowns as can be eliminated).

Gen3Benz

iTrader: (4)

Thanks for the link to the TASC article.
I have a 2000 sonoma in the shop with the exact symptom.
Another way to check the PCM circuit is to unplug the transmission and probe each solenoid ground wire while commanding the solenoid on/off.
Does the exact same thing, 1/2 switches instantly and the 2/3 takes a few seconds to fully lose ground.
Have a PCM on the way.

Gen3Benz

iTrader: (4)

PCM installed and programmed.
Shifts perfect
Thanks joecar!

Monte4ever

iTrader: (2)

You described my issue exactly. If I start from a dead stop the trans shifts like it suppose to. However, if I come down in speed to make a turn or something, the trans free revs. But as soon as I gas it some it kicks into gear. This trans was rebuilt by a very good trans shop and has less than 300 miles on it so I hope I don't have to pull it back out.