Intermittant P0758/2-3 shift flare
#1
Intermittant P0758/2-3 shift flare
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.
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.
#2
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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.
#4
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.
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#8
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
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
#9
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
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
Thanks!
#11
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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.
#13
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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.