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Discussion Starter #1
My 96 C3500 has what my trans mechanic calls morning sickness. No matter if it the truck is hot or cold, it always takes about 5 miles for the trans to shift into OD. But only after a restart. You can leave the truck running all day and it will work great, until you hit that rest stop and shut off the truck. Then it takes a solid 5 miles to "release" OD.

The truck has a bad ABS module and is very difficult to get a scan tool to work on it. Even with the ABS unplugged. So I don't have any codes.

I have recently serviced the trans with new fluid and filter. This helped improve the other shifts.

What I did this morning with no avail was to swap the speed sensors for known good ones. All the ones I removed looked good and metered out at around 1400 ohms. The ones I installed metered out the same. No metal present on the sensors. I also cleaned the plug to the wiring harness. The harness is leaking from the plug. I cleaned up everything really good in the hopes that I could get the problem to go away until the ATF leaked out and shorted the connector. But this made no change. If it fixed it, I was going to replace the internal harness.

Any suggestions or tips on how to proceed?
 

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When you say OD do you mean 4th gear (OD). Or the torque convertor locking up?
Re the ABS. If you cant get a scanner that reads ABS codes to communicate. Then the module is usually bad.
 

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Discussion Starter #3
When you say OD do you mean 4th gear (OD). Or the torque convertor locking up?
Re the ABS. If you cant get a scanner that reads ABS codes to communicate. Then the module is usually bad.
I meant OD as in 4th gear but I don't get lockup until the 5 miles either. After that it will shift into 4th and if I downshift to 3rd it will have lockup.
 

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Off the top of my head I read something a few years back that a worn bore in the valve body for tcc lockup might be the culprit.The 4L80 was prone to this on transmissions with high mileage.Sonnax sells a kit to ream the bore/hole oversize and a replacement valve/spool is put into place but a bit of research into this might clarify things a little better.
 
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I had a similar problem on my '93 and it was the ignition switch. TCC wouldn't lock up, hard shifts, and if I'd shut if off and move the ign. sw. from off to run a few times, then restart, it would all work fine. You might try doing that.
 

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Discussion Starter #6
I had a similar problem on my '93 and it was the ignition switch. TCC wouldn't lock up, hard shifts, and if I'd shut if off and move the ign. sw. from off to run a few times, then restart, it would all work fine. You might try doing that.
It is not the ignition switch. I had the same problem on my 93. This is a different set of symptoms. The trans shifts fine for having almost 200K on it. The truck always stays in 3rd until about 5 miles. Then it will work fine. I have used it for several 4+ hour trips and it works fine other than the initial 5 miles.

An other issue/symptom is that the speedo is not reading accurately. It reads 70 when you are going 60. That is why I checked the speed sensors. Could the VSSB be going bad and throwing off the computer?
 

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Yeah, with your symptoms, probably not an ign. sw. After the 5 miles and the problem clears up, does the speedometer then read correctly?
 

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Discussion Starter #8
Yeah, with your symptoms, probably not an ign. sw. After the 5 miles and the problem clears up, does the speedometer then read correctly?
Speedo is still 10 mph off at 70 after the 5 miles.
 

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1995 Chevrolet Silverado Z71 6.5 TD
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My 96 C3500 has what my trans mechanic calls morning sickness. No matter if it the truck is hot or cold, it always takes about 5 miles for the trans to shift into OD. But only after a restart. You can leave the truck running all day and it will work great, until you hit that rest stop and shut off the truck. Then it takes a solid 5 miles to "release" OD.

The truck has a bad ABS module and is very difficult to get a scan tool to work on it. Even with the ABS unplugged. So I don't have any codes.

I have recently serviced the trans with new fluid and filter. This helped improve the other shifts.

What I did this morning with no avail was to swap the speed sensors for known good ones. All the ones I removed looked good and metered out at around 1400 ohms. The ones I installed metered out the same. No metal present on the sensors. I also cleaned the plug to the wiring harness. The harness is leaking from the plug. I cleaned up everything really good in the hopes that I could get the problem to go away until the ATF leaked out and shorted the connector. But this made no change. If it fixed it, I was going to replace the internal harness.

Any suggestions or tips on how to proceed?
I had a similar problem on my 1999 Yukon Denali it was a 5.7 though. It started out not shifting into OD for a few miles and eventually only reverse would work. The prognosis was the sun gear had failed and had to either get it rubilt or a GM reman that had all the updates that had been rolled out for the 4L80E. that's my two cents...Do the GM REMAN if your going to keep the TRUCK
 

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If the speedometer doesn't change at the 5 mile point, I've got no clue. If you have to go with a reman. trans. like Daddyoh said, I put a Jasper in my truck. Lasted just over 40,000 m. and the TCC completely failed. Right out of warranty. And I'm anal about trans. fluid/filter changes. No more Jasper anything for me.
 

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Discussion Starter #11
My trans mechanic told me it would need a rebuild in the near future but to drive it until I can't. He said it could be years before it is undrivable. The worn valve bore is probably it. I was hoping to fix this issue before I sell it. I don't want to sell it but I just bought a 99 K2500 suburban and I could use the money and the parking.

Also, my trans mechanic, says that the sonnax kit is no good. It causes other issues that will lead to premature transmission failure. He recommends a new valve body if they are worn that badly. He has built me several 4L80Es over the years and they always take a beating. His last rebuild was really overkill and it kicks ass. I also really torture my 93. I drive it like a race car and his transmission build takes it.
 

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Two thoughts. 1 - you mentioned speed sensor, but what about TPS? Also, adjustment of TPS?

2 - check big wiring plug going to trans. Clean and secure?
 

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My trans mechanic told me it would need a rebuild in the near future but to drive it until I can't. He said it could be years before it is undrivable. The worn valve bore is probably it. I was hoping to fix this issue before I sell it. I don't want to sell it but I just bought a 99 K2500 suburban and I could use the money and the parking.

Also, my trans mechanic, says that the sonnax kit is no good. It causes other issues that will lead to premature transmission failure. He recommends a new valve body if they are worn that badly. He has built me several 4L80Es over the years and they always take a beating. His last rebuild was really overkill and it kicks ass. I also really torture my 93. I drive it like a race car and his transmission build takes it.
I think you have answered your own question?
 

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Discussion Starter #14
I think you have answered your own question?
That is what I was afraid of. I was hoping that it would have been an easy electrical fix.
 
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