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95 GMC rebuilt tran won't go into overdrive


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Sandman
New User

Feb 23, 2013, 6:38 PM

Post #1 of 8 (5299 views)
95 GMC rebuilt tran won't go into overdrive Sign In

Hey folks, hoping someone can give me some advice here..and I really hope this isn't too confusing. I've researched high and low and checked everything I can think of and here's where I'm at on a 1995 GMC Sierra k1500 5.7 4x4 210k miles:
2 weeks ago I rebuilt the transfer case, dropped the pan to replace the tran filter and replaced the fluid lost from the drop. Everything worked fine after that except it was slipping bad in reverse, and a little in first. While I was waiting on parts for the transfer case rebuild, I replaced my exhaust manifolds, radiator hoses, thermostat, power steering hoses, idler/pitman arms, tie rods, and ball joints. (I've been busy). For the past year it would randomly give me one click when I tried to start the truck. If I kept trying it would eventually start. I replaced the starter a while back and new battery. It still does it sometimes and has been getting worse so I got a brand new starter (not rebuilt) and replaced the ignition switch, tumbler, and neutral safety switch. I also added a push button starter for emergency situations. I should add, my battery has been relocated to the bed of the truck so I also went through all grounds throughout the truck, polished the attach points and made sure they're all secure. The clicking instead of starting problem has gone away. Ok now that we've cleared up everything I did electrically.
So here I am today, tranny shop can't hit overdrive so they tell me something else is wrong with the truck. (Overdrive worked when I dropped it off at their shop). They did say the put a new neutral safety switch on, test drove again, got it to hit overdrive, but then they shifted to 3rd to check lockup and it wouldn't get overdrive again. so..
Here's what I've done today: I Rechecked all grounds on the truck. Polished every bit of contact. I pulled the column again and checked voltage at all wires on the ignition switch. Every wire has about the same voltage, around 12.6 when I turn the key on, and over 13.5 when it's running. I check the power to the transmission harness and it reads the same. One thing I noticed right when I got it back from them was the tran pan kept looking like it's dripping. When I check the voltage at the wiring harness on the transmission, it's all wet there. As I'm popping the harness back on the connector, it moves and fluid starts coming out. So I get that pulled up tight and it stops leaking, and I'll be showing the shop that on Monday.
What else should I check?? I've read the engine might not be at temp and might not allow overdrive to work. Could a faulty thermostat cause that? The whole time I keep test driving it, the engine is running at about 180 degrees. I wouldn't think I got a faulty ignition switch since the voltage is consistent across all appropriate wires. I have no fuses out. Checked voltage at both sides of each fuse and nothing is wrong there. Live scan wasn't showing them anything but there could still be the possibility a solenoid isn't working correctly from their rebuild, right? Any help is appreciated!


Sandman
New User

Feb 23, 2013, 6:53 PM

Post #2 of 8 (5279 views)
Re: 95 GMC rebuilt tran won't go into overdrive Sign In

Oh ya more info, There are no warnings on the instrument panel. The instrument panel is working and all lights do light up when starting. Vehicle speed is accurate and 1-2 2-3 shifts feel perfect. Brake switch is working correctly. Cruise control is working.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Feb 23, 2013, 7:18 PM

Post #3 of 8 (5257 views)
Re: 95 GMC rebuilt tran won't go into overdrive Sign In

Someone needs to connect up a high end scan tool that can access the manufacture side of the PCM. Then they need to monitor the TCC solenoid command. They will also need to verify that the TCC solenoid command is occurring by either monitoring voltage at the TCC solenoid circuit at the PCM connector using a volt meter or an oscilloscope to verify circuit integrity. If everything looks fine electrically, then you have a mechanical problem inside the transmission or torque converter.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Sandman
New User

Feb 23, 2013, 7:24 PM

Post #4 of 8 (5250 views)
Re: 95 GMC rebuilt tran won't go into overdrive Sign In

Thanks for that info. I'm assuming that's what the transmission shop was doing when he said he did a live scan, got no error codes and all his work is correct. I think he was also getting annoyed he already put an extra day into troubleshooting it. I'm going to call him Monday morning and have him check all that I guess. Everything else I've checked electronically seems perfect.


Sandman
New User

Feb 26, 2013, 7:18 PM

Post #5 of 8 (5207 views)
Re: 95 GMC rebuilt tran won't go into overdrive Sign In

I took the truck back to the trans shop yesterday morning after I had exhausted all checks that I could on my own. Just got the truck back, fixed and running perfectly (I hope it's not a coincidence haha). He went over everything they did, replaced the wiring harness, and through his search ended up finding the manifold pressure switch was bad. He through a new one in and it has worked perfectly over multiple test drives. On the drive home the truck was shifting perfectly through all gears. Hope that was the problem! Thanks for the help


nickwarner
Veteran / Moderator
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Feb 26, 2013, 7:53 PM

Post #6 of 8 (5202 views)
Re: 95 GMC rebuilt tran won't go into overdrive Sign In

A bad manifold pressure switch would cause that issue. Glad you got it resolved.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Feb 27, 2013, 6:04 AM

Post #7 of 8 (5192 views)
Re: 95 GMC rebuilt tran won't go into overdrive Sign In

manifold pressure switch? Is that on the exhaust manifold? Crazy





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


nickwarner
Veteran / Moderator
nickwarner profile image

Feb 27, 2013, 9:40 PM

Post #8 of 8 (5179 views)
Re: 95 GMC rebuilt tran won't go into overdrive Sign In

Its next to the muffler belt.






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