05 Tahoe only shifts when it leaks fluid

[Tboyle778]

I bought a used 2005 Tahoe about 15 days ago. All was good until about 6 days ago It suddenly stop shifting in mid drive. So I let it cool off and then again started to drive and stop shifting again. Now I grew up in an auto shop as my dads helper he was a BMW and foreign car mechanic as well as domestic car mechanic his whole life so I picked up a thing or two or more just from working with him and learning from him but the first thing I thought was oh boy the transmission has gone out. So then I looked around on the internet and YouTube and I found a video of someone saying that the specific transmission 4L60E stops shifting when a new filter is needed. I thought okay I could do this so I bought a filter and I replaced it . Fired it up went for a drive no problem continue driving for another 3-4 days not a problem except I was leaking transmission fluid because I forgot to tighten up some of the nuts so I go back underneath the Tahoe and I tighten them up all the sudden it stops shifting again. My question is that could there be a vacuum issue causing the transmission not to shift because it works fine when the transmission pan is loosened but it leads transmission fluid obviously which is not a good thing but I wonder if anybody else's experienced anything like this before or if anybody has any answers as far as the vacuum lines go?. Thank you for your time and responding .

 

[justirv]

I bought a used 2005 Tahoe about 15 days ago. All was good until about 6 days ago It suddenly stop shifting in mid drive. So I let it cool off and then again started to drive and stop shifting again. Now I grew up in an auto shop as my dads helper he was a BMW and foreign car mechanic as well as domestic car mechanic his whole life so I picked up a thing or two or more just from working with him and learning from him but the first thing I thought was oh boy the transmission has gone out. So then I looked around on the internet and YouTube and I found a video of someone saying that the specific transmission 4L60E stops shifting when a new filter is needed. I thought okay I could do this so I bought a filter and I replaced it . Fired it up went for a drive no problem continue driving for another 3-4 days not a problem except I was leaking transmission fluid because I forgot to tighten up some of the nuts so I go back underneath the Tahoe and I tighten them up all the sudden it stops shifting again. My question is that could there be a vacuum issue causing the transmission not to shift because it works fine when the transmission pan is loosened but it leads transmission fluid obviously which is not a good thing but I wonder if anybody else's experienced anything like this before or if anybody has any answers as far as the vacuum lines go?. Thank you for your time and responding .

1st off I'd look for any codes. When you say it "shifts fine", do you mean you can drive around and have normal upshift progression (1-2-3-4) and downshift (4-3-2-1)? When it stops "shifting", can you drive at all, and the trans stays in 1st gear, or you haveno forward (or reverse) movement? Or is it possibly in limp mode (3rd gear only)? The shifting in an '05 4L65e is electronic, and not controlled by vacuum. If you disconnect the trans connector you should be able to drive around in 3rd, if there are no internal problems. You had mentioned changing the trans filter; there is a small seal hiding up in the valve body where the filter slides into. If this is not removed, it can cause seating problems with the filter, as one would double-up the seal with the new seal installation. That may explain why the pan pressure/tension affects the operation when fully secured.

 

[Tboyle778]

1st off I'd look for any codes. When you say it "shifts fine", do you mean you can drive around and have normal upshift progression (1-2-3-4) and downshift (4-3-2-1)? When it stops "shifting", can you drive at all, and the trans stays in 1st gear, or you haveno forward (or reverse) movement? Or is it possibly in limp mode (3rd gear only)? The shifting in an '05 4L65e is electronic, and not controlled by vacuum. If you disconnect the trans connector you should be able to drive around in 3rd, if there are no internal problems. You had mentioned changing the trans filter; there is a small seal hiding up in the valve body where the filter slides into. If this is not removed, it can cause seating problems with the filter, as one would double-up the seal with the new seal installation. That may explain why the pan pressure/tension affects the operation when fully secured.

It is not throwing any codes. You may be right about the filter seating and the seal I'm going to go remove the filter again and double check thank you

 

[Joseph Garcia]

@NickTransmissions is our resident transmission expert, and he will chime in with his thoughts and perspectives.

 

[NickTransmissions]

My question is that could there be a vacuum issue causing the transmission not to shift because it works fine when the transmission pan is loosened but it leads transmission fluid obviously which is not a good thing but I wonder if anybody else's experienced anything like this before or if anybody has any answers as far as the vacuum lines go?. Thank you for your time and responding .

I have never heard of a trans working only when the pan bolts are loose but stranger things have happened.

Please explain what you mean when you say it "stops shifting".

Does that mean it doesnt move in any range position (Reverse, Drive, D3, Manual 2 or Manual low)? Or does it move but wont shift out of first gear? Or something else entirely?

 

[Tboyle778]

I have never heard of a trans working only when the pan bolts are loose but stranger things have happened.

Please explain what you mean when you say it "stops shifting".

Does that mean it doesnt move in any range position (Reverse, Drive, D3, Manual 2 or Manual low)? Or does it move but wont shift out of first gear? Or something else entirely?

I'll be driving along and it will just go into neutral. Then I will shut it off for a little while and start it up and it'll go in reverse and go and drive but it will slowly stop going forward or reverse it'll just go into neutral again. The shift selector moves perfectly but nothing engages in the transmission until it cools off but then as it heats up within a minute it's not driving again.

 

[NickTransmissions]

I'll be driving along and it will just go into neutral. Then I will shut it off for a little while and start it up and it'll go in reverse and go and drive but it will slowly stop going forward or reverse it'll just go into neutral again. The shift selector moves perfectly but nothing engages in the transmission until it cools off but then as it heats up within a minute it's not driving again.

Do a line pressure test when cold and again when warm. The best way to do this is to thread a transmission pressure gauge into the transmission's pressure port (dr side, just behind the bell housing). Then drive around with it, observing the readings. At idle, in drive - you should have 54-70ish psi, moving will be 1.5 to 2x that. If you see it dropping to zero, drop the pan and check the filter - it may be like 90-95% clogged...Cut it open to confirm or deny...Next, continuity test the electronic pressure control solenoid - you should see between 4-6 ohms.

Note - if you see a bunch black, charred clutch material and/or metal in the pan, yank the trans out and rebuild it).

ETA: re-read your first post and looks like you already changed the filter...

So check line pressure and also consider the VSS may be failing intermittently. Malfunctioning VSS will result in false neutrals...your VSS is either in the ext housing if you have a 2WD or transfer case if it's a 4x4.