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2000 Suburban Tranny issues after replacement

Michael Litzner

By Michael Litzner
in Ask A GM Technician

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Michael Litzner New Member

Michael Litzner

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Posted (edited)

I just dropped a rebuilt transmission from Rockauto into my 2000 Suburban and I am having two problems with the new unit. I was wondering if anyone here could point me in the right direction for troubleshooting.

 

1. The gear indicators on the tree on are not lining up with the transmission. The indicator usually skips N, and doesn't always indicate park. I have messed with the shift cable adjustment quite a but and it doesn't seem to make much of a difference. At the moment I am thinking the problem may be the Neutral\Park Sensor on the side of the tranny? The tranny didn't come with a new one, bit the old one wasn't having any indicator issues before replacement either.

2. The truck doesn't want to stay in overdrive unless you are heavy on the gas. As soon as you let your foot off the gas once you get to speed (55) the tranny will drop to 3, or maybe the torque converter is unlocking, it will be at about 2200rpm at 55mph. I am wondering if this could be a line pressure issue? There is a spot to adjust line pressure on these correct?

Edited by Michael Litzner
Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted (edited)

#1 is most likely the neutral safety / gear indicator sensor on the tranny - these have to be set a certain way upon install. The procedure has long since been forgotten by me, but I'm sure you can dig that info up on the net.

 

As far as #2 goes, it's behaving like something was plugged in backwards. It should behave oppositely of what it's doing, so it only makes sense that something is reversed. Transmissions aren't my area of expertise, so there could be another issue there that I'm not aware of. 

 

I do know there is a small seal on the input shaft of the tranny that if nicked or damaged will cause erratic, or no lockup whatsoever. Something to check as a last resort, if it's indeed a lockup issue.

Edited by Jsdirt
Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

My 2000 Pontiac GTP had the electronic transmission and would unlock the convertor if you took your foot off the gas, or touched the brake pedal.  It would then take a second or two to lock back up again after you put your foot on the gas.  Perhaps you old transmission was not doing this and that is what you got used to.  When I got my first GTP in 97(98 model) I took it back the day I picked it up because I thought there was something wrong with the high gear clutch pack.  My only experience with lockup convertors prior to that car was the Chryslers back when they introduced it back in 77/78.  It was a complete hydraulic lockup, and behaved completely different to GMs version 20 years later.  In my 2010 truck it behaves different to my 98 and 00 GTP.  They have tightened up the engagement and disengagement points to do a good job at hiding the locking and releasing of the lockup.  I used to tap the brake pedal in my GTPs when going up a steep hill on the highway with cruise control on to unlock the convertor.  If I didn't, the transmission would delay the unlocking until it figured it also needed to downshift.  Tapping the brakes would unlock the convertor and it would stay unlocked until it could hold the speed.  Tapping the brakes also cancelled the cruise, so I had to also step on the gas at the same time.

Michael Litzner New Member

Michael Litzner

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9 hours ago, Doug_Scott said:

My 2000 Pontiac GTP had the electronic transmission and would unlock the convertor if you took your foot off the gas, or touched the brake pedal.

Its not unlocking the torque convertor when you take your foot off the gas, its when you just lift a little to stay at 55-60, instead of continuing to accelerate.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Easiest way to see if it is unlocking is to downshift manually into 3 and see if the RPMs increase.  This may just be the transmission relearning the shifting based on your how you drive.  Does RockAuto also include the TCM with the transmission?

  • 2 weeks later...
Michael Litzner New Member

Michael Litzner

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On 8/23/2020 at 10:44 AM, Doug_Scott said:

Easiest way to see if it is unlocking is to downshift manually into 3 and see if the RPMs increase.  This may just be the transmission relearning the shifting based on your how you drive.  Does RockAuto also include the TCM with the transmission?

I believe the TCM was replaced in the rebuilt unit, but it sounds like the solenoids were not. The computer is now throwing a solenoid error code after some miles. I have new solenoids in hand, just have to get around to replacing them to see if that solves the issue.

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