How can I identify which transmission is in my 2WD, 08 GMC 1/2T Sierra with a 5.3 Automatic (4sp)

08 GMC · May 26, 2023

I've had my truck since new and never had a single problem until now with 174K miles. While driving down the freeway it suddenly downshifted or the OD kicked out and the rpm went from 2200-2500 to 3,000 and it would not upshift even if I let off the throttle.

Pulled off the freeway, checked the transmission oil and it appears to be full and it appears to be clean

Got back on the freeway and for 35 or so miles it was fine and then it downshifted or went out of OD and I took the next exit and then it acted like it was in neutral.. Hmmm.

Coasted to a stopping place and shut it off. Fluid is still clean. Fired it up and it made it 1,000' or so into a gas station and I got gas.

Went to leave the gas station, pulled forward and stopped for traffic and it acted like it was in neutral. Noticed that the light under the PRND2L was not lit up.

Pushed the truck out of the way. Went through a reset, key on, throttle full, key off 3 minutes and wait. Drove it forward about 500' and parked correctly.

Disconnected battery, grounded battery terminals. Unhooked the TCM cord and left it unhooked for 30 minutes and then reconnected everything. Fired it up and it drove like there was no problem for 500' and stopped like it was in neutral.

Shut it off, luckily dead end street that I was on, waited a few minutes and parked it next to the sidewalk. hmmm

Got it towed.. Rolled off the truck and fired it up, drove it 100' and parked it. Sat for a few minutes while I was handling the tow truck and went to fire it up. Went into reverse and forward but I decided to just sit and idle and try to go.. No go. Acts like it's in neutral. Shut it off. Wait a few minutes and it will go forward but I decided to shut it off. Fired it up and let it idle. Seems about 10 seconds into idle the engine pulls down a little and then if I try to shift, there's nothing there. Fluid is not burned nor brown.

Have no idea as to what the problem is, torque converter, valve body, pump or TCM or just a transmission at the end of it's life?

So I need to source a 4LE60, 4LE70 or?

Thanks!

bubbanbrenda · May 26, 2023

My ‘08 Sierra 5.3 has a 4L60, for what it’s worth. Maybe the RPO list in the glove box will help.

08 GMC · May 26, 2023

Thanks

dna9656 · May 26, 2023

Have you ever had it serviced; the fluid and filter changed? Your owner's manual has a scheduled maintenance page in it. It'll tell you the intervals for changing the fluid and filter. 174k miles of flawless performance; i think you got your money outta that tranny. Is the fluid dark, smell burnt, get some between your fingers rub your fingers together, is it gritty? You prolly have a 4l60E and my guess is you need a new tranny.

Ask around,check the BBB web site for a transmission shop. Go to the best you can find and expect to pay them like they are the best. That's what I did. My guy told me you can't tell by looking at the case a 4L60 E from the other 4L family of transmissions, they use the same housing. I had my 4l60E upgraded to the 70 (used in the Caddy version of the Avalanche and the SS models) series for another $500.00. You get more clutches and better internal parts. I think a truck should come with a upgraded tranny, not a car tranny. Trucks just might tow something or haul weight, that's reason for a tougher tranny. My guy also said NEVER use anything but AC Delco tranny fluid in it. He didn't care what the law says (all supposed to be universal) or what the label says on any body else's tranny fluid, use only the Dextron 6 be AC Delco. That goes for your transfer case too.

Edited May 26, 2023 by dna9656
More info

CamGTP · May 27, 2023

Losing 3rd and 4th is a super common failure on the 4L60e. You will want to whole thing rebuilt with a new torque converter.

08 GMC · May 27, 2023

7 hours ago, dna9656 said:

Have you ever had it serviced; the fluid and filter changed? Your owner's manual has a scheduled maintenance page in it. It'll tell you the intervals for changing the fluid and filter. 174k miles of flawless performance; i think you got your money outta that tranny. Is the fluid dark, smell burnt, get some between your fingers rub your fingers together, is it gritty? You prolly have a 4l60E and my guess is you need a new tranny.

Ask around,check the BBB web site for a transmission shop. Go to the best you can find and expect to pay them like they are the best. That's what I did. My guy told me you can't tell by looking at the case a 4L60 E from the other 4L family of transmissions, they use the same housing. I had my 4l60E upgraded to the 70 (used in the Caddy version of the Avalanche and the SS models) series for another $500.00. You get more clutches and better internal parts. I think a truck should come with a upgraded tranny, not a car tranny. Trucks just might tow something or haul weight, that's reason for a tougher tranny. My guy also said NEVER use anything but AC Delco tranny fluid in it. He didn't care what the law says (all supposed to be universal) or what the label says on any body else's tranny fluid, use only the Dextron 6 be AC Delco. That goes for your transfer case too.

Never changed the fluid as I heard horror stories when people did.

Fluid is clean, does not smell and no grit... So it's confusing

dna9656 · May 27, 2023

Error on the side of caution.

KARNUT · May 27, 2023

5 hours ago, 08 GMC said:

Never changed the fluid as I heard horror stories when people did.

Fluid is clean, does not smell and no grit... So it's confusing

In all years of being around vehicles. Even spent time having an auto repair shop. I only experienced one transmission failure after a fluid and filter change. We were probably set up. Should have driven before doing the service. I have experienced a marked improvement by changing transmission fluid. I’m not a fan of the flush. But a drop and fill for longevity. My 2004 Z-71 first recommended transmission change was 150K. My avalanche had its first at 165K. At 180K it’s going strong. I did a drain and fill twice. In contrast my CRV got 2 drain and fills before 40K miles. I’m now in the oil is cheap in comparison category. My wife’s Genesis from new followed the extreme service schedule. My daughters odyssey from the light probably averaged 8K oil changes. In just a few thousand miles my Genesis oil still looks new. The odyssey looks black. My avalanche had 3K oil changes per its maintenance log. Oil looks clean up to its oil change. Funny they never changed the transmission fluid on that one. Think about it you never really get it all at once. So changing it often just makes sense.

dna9656 · May 27, 2023

Oil with a reasonable amount of dirt is a good sign the oil is doing a part of it's many jobs, it's keeping dirt in suspension (so it can be removed at change, that's why you change the oil HOT. "Detergents" in oil isn't like detergents in the laundry room. Detergents in laundry make water wetter and the water breaks up the dirt. Oil breaks down over time, with heat, that's why we change it. I have read the horror stories about some one changing the fluid in the tranny and the tranny burns up, I think some thing else was going on, like they didn't get the filter installed correctly or they left dirt in the pan. I have changed a lot of fluid and filters and had a problem one time and it was my fault. I didn't change the insert seal on a 700R 4 and the tranny cavitated until it burned up. That was a $2600.00 seal. I Couldn't get the seal out, now i know how. Oil cools, lubricates, transmits power, carrys away soot and other crap. the oils today are better than in previous years and they just get better.

swathdiver · May 28, 2023

Well, after you replace or overhaul the transmission, put the truck on the severe service schedule from now on. Look for M30 on your RPO sheet for the 4L60.

You can upgrade the transmission to the 4L65 (M32) standard. 4L70 is wired differently.

If sourcing used, stay with same generation, 2007-2009 trucks with that transmission.

Edited June 1, 2023 by swathdiver

08 GMC · May 31, 2023

Been on travel since last week but the consensus is that the filter is clogged and thus stopping the engine lets the debris fall and starting it up sucks up the debris.

Time to find out and search for some $ to pay for this

Thanks!

swathdiver · June 1, 2023

18 hours ago, 08 GMC said:

Been on travel since last week but the consensus is that the filter is clogged and thus stopping the engine lets the debris fall and starting it up sucks up the debris.

Time to find out and search for some $ to pay for this

Thanks!

That's a new one for me. Dropped my pan for the first time at 185K and learned that I shouldn't have bothered. Unless the converter clutch come apart or something is broken inside the filter ought not get clogged like that.

Well, dropping the pan doesn't cost as much as taking it in. You take in, it's as good as done for.

08 GMC · June 30, 2023

Well after much regret, I bit the bullet and purchased a rebuilt 4L70e transmission. Installed it and everything is fine.

Have no clue as to the problem with the original transmission as when one describes the problems, the first comment/question is "how many miles do you have" and when I answer 174K "well that's your problem, you are lucky you made it that far" with no solid answers as to what the problem actually is.

Right before I swapped them out, I could put the truck in gear, smoke the tires and then wait 20 seconds and it would not move in any direction. Torque converter, cracked pressure piston or?

swathdiver · July 1, 2023

They can run much longer than that. The shops rarely do, they use the most generic terms like, your trans is shot and need a new one, instead of giving specifics.

It could have been something as a faulty electrical connection, a sticky check ball or valve or worse like a busted sun shell.

If you are on the SilveradoSierra forum, look up Nick @nicktransmissions and ask him. He's our resident transmission guy and is very helpful. He has a shop in Nevada.

What all was needed to swap in the 4L70?