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4L60e problem after rebuild... **UPDATE IN OP**

crashandburn

crashandburn

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Update: fixed the servo, dropped the pan. The connector must not have been on all the way because it had fallen off. Reassembled.
No codes.
NO FIRST GEAR STILL!
Still whines, and only has 2nd and 3rd. No 1st, no 4th.


So I just rebuilt my first transmission ever. It's for a 99 S10 Blazer. Got it installed, went through the gears with it on the lift, it seemed good. Pulled out to the road, and it felt good, but I smelled ATF, so I quickly went back into the garage and put it on the lift. Turns out the snap ring for the servo wasn't in right, and the servo had backed out a little and was leaking. So I pop it back in and try again. Now the trans is making a whining noise. I thought it might be the front pump, but the pitch goes down and disappears as rpm goes up. Go to pull out and the truck has no power. Turns out its in second (or maybe even third) gear. Even if I pull the lever down to first, it will not go into first. So I'm bummed out, thinking my rebuild attempt was a massive failure.
Then it hits me...
The trans seemed to work perfectly with no noise before I fixed the servo leak, while the servo was popped out maybe 1/4".
When I pushed the servo in, problem started. So it seems like the servo has too much pressure? Maybe I put one of the parts in backwards and now it is pushing in harder than it is supposed to?
Anyone have any ideas?

The ironic thing is that if I hadn't screwed up the snap ring in the first place, I would not know that it was working properly and I would have probably went to the junkyard and got another trans.
 
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It's certainly worth pulling the servo out to look, since that is so easy. If you flipped a piston or something, it could push the pin in all the time, which will keep it in 2nd gear whenever the forward clutch is engaged (it seems feasible in that case it would go into 4th as soon as it tries for 3rd.). Are there any fault codes? Severe faults can cause 2nd/reverse only. This also happens if you unplug the connector to the transmission - you lose the solenoids, but still have the manual valve, so it runs in 2nd at full line pressure.
 
Great advice, nothing to add there, start with the disassembly of the servo and make sure you didn't mis-stab the band.
 
I'm gonna run it on the scanner tonight after work. The SES light is on anyways because of a skip in the motor, which I will address after the trans is finished. A guy on a the Buick forum said that if the computer saw the line pressure drop when the servo was leaking it would send the transmission into limp mode, so it may just need the codes cleared. So I'll try that first, then see if I can figure out the servo.
 
Update:
I cleared the codes, no change.
I grabbed the servo out of my other transmission and swapped it in, being careful to put it in exactly how it came out. No change.

BUT...
The computer is throwing a PO753 code, shift solenoid A.
Anybody know which one that is?
 
You know that pack of pressure switches that mounts on the valve body? The connector for that is right by the A (1-2) solenoid (basically right where the 1-2 shift valve was in the 700). It should be #5 in this picture:

2012-01-17_231738_pic1.jpg


If would be weird for this solenoid to fail at the exact time you were messing with the servo, unless it was weak and the high line pressure killed it. The servo is more likely to spit out on the road because you get higher pressure than on a lift. If the PCM commands 2nd gear and then the servo spits, the 2nd pressure switch will see this loss and the PCM sees a fault. In limp mode, the line pressure goes very high. This could be the whining noise you heard.

You could test the resistance of all solenoids from the connector before you even drop the pan. To log the code, the PCM will measure an open circuit or short on that solenoid. It's possible you just didn't get the solenoid connector clipped on properly or the transmission connector might not be properly seated. All worth checking.
 
Just trying to take some of the workload off you when I can, Greg. :)
 
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