4l80E Slips when warm

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JavaMan

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I bought a 1996 Suburban 2500 4x4, with the 454 and 4l80e about a year ago with 113k miles on it. It was priced at $5000, but when I went in to look at it, they said it needed fuel lines replaced which was to expensive for them to do, so they offered to sell it to me as-is for $4k. They gave me $2500 for my 99 Sierra 1500 4x4, which they claimed they input the miles as 17k rather than 173k, but they honored their original offer of $2500 anyway. So my out of pocket was only $2100 after everything at the dealership, plus $280 in parts to replace the fuel lines and pump. Not bad for getting extra room for the family, dual AC, and 3/4 ton.

First month I replaced the fuel lines and pump, changed the oil, changed the trans filter and drained and filled 8 qts ATF (used Valvoline MaxLife, full synthetic Dex3 and Dex6 compatible), changed the rear diff oil, cleaned the AC coils as best I could through where the blower mounts. It drove great.

Then the problems, sorry it gets long here.
By February, I was noticing that going up hills sometimes it would jump to rev limiter, I'd back off the throttle and it would grab again. I found if I just stay easy on the throttle it would be fine, or I could speed up before the hill and let it easy slower getting to the top, and I could prevent the slip.
Well, I thought I'd try a B&M Electronic shift improver, supposed to boost the trans fluid pressure to make firmer shifts. It was great firm shifts 1-2, and 2-3...then neutral. 4th gear felt like nothing was there, it would shift from third and feel like neutral, slows down a bit, then shifts into third again and speeds up. I turned the B&M to stock position, and 4th would kick in and drive like normal. I thought that was weird, and didn't want to break anything, so I removed the B&M.

We took it on a trip to California beginning of June. It was hot going across the California desert, 115-118. Engine was running hot, approx 240. Driving along at 75 on flat road, the RPM goes up, start slowing down so I give a bit more throttle and the RPM jumps like it's in neutral. I manually shift to third, it kicks in and we keep going. Shifting to third helped cool the engine some too, down to 215. We get into Palm Springs, I bought some Water Wetter, and added it in. (Hindsight thought, no pressure was released when I opened the radiator cap). We get out of the desert, still driving in third. That week in San Diego area temps in the 80s, 4th gear would work fine for the first 5-15 miles, then would start slipping in 4th, so I'd shift to 3rd and continue on. On the way home, it was trying to overheat in the desert. About 20 miles from home, going up the hill (climbing from 3000 feet to 7000 feet), it was approx 240 for a way. Then it rapidly went up to 260, and I pulled over and turned it off. We started adding water, then noticed it going all over the ground. One of the nylon splitters for the heater hoses had let go. Got towed into town, it was Saturday so no one at the shop, I went to parts store got the nylon connector and replaced it myself. Filled it up with coolant, put a new radiator cap on it, because I figured out it wasn't holding pressure. Overheat problems solved, even when we towed a 6k pound trailer to Phoenix, with several up and over mountains from Flagstaff. Pulled in third of course.

Now that the temperature is going down, when it's in the 60s, 4th gear works fine. Even after 40 miles and going over hills, 4th does not slip when the outside temps are in the 60s.

I've tried searching the internet, and can't find what causes 4th to slip when the ambient temps are warmer than 70, but not slip when it's colder. Repair shops are money hungry, all three of them heard "slip" and without even looking at it told me rebuild the trans, $3k to $4k. That's just the internals, they don't think I need any work on the valve body, cause that part doesn't really wear out till around 200k miles, and I'm only at 118k.

Any ideas before I have somebody rebuild it? Should I drive it down to Phoenix where there's some better shops and build it as a 4l85e? We do tow 4k to 6k trailers a few times per year.
 

JavaMan

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Just adding some other details
The trans cooler, which appears to be a plate and fin type, has the inlet and outlet facing down. Not sure, but I've heard this type needs to have the outlet upwards to stay filled fully. Can anyone confirm this? Also, I've never heard the cooling fan get loud, so I may need a new fan clutch.
 

jdla140

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Any codes present? it should be throwing codes if you're getting slip, especially in 4th with the TCC locked. Maybe you just have a solenoid issue, which should show up when reading codes. However whenever I've experienced a trans slipping only when hot, it was because of worn out clutches, it's probably time for a rebuild. The trans cooler connectors are both supposed to be facing downwards.

if you REALLY need more life out of the trans, and it's looking like clutches are the issue, drop the pan change the fluid and add 2 bottles of Lucas transmission stop leak, then top it off with fluid. it's thick as hell but I've had that stuff bring back lost gears before.
 

df2x4

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Any codes present? it should be throwing codes if you're getting slip, especially in 4th with the TCC locked.

Are you sure? I never got any codes in my red truck when I burned up either of the 4L60Es. Does the 80E tuning behave differently?

As stated, the cooler ports facing down is normal. That's how they came from the factory.

I agree, it sounds like it's time for a rebuild.
 

jdla140

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Are you sure? I never got any codes in my red truck when I burned up either of the 4L60Es. Does the 80E tuning behave differently?

As stated, the cooler ports facing down is normal. That's how they came from the factory.

I agree, it sounds like it's time for a rebuild.

Absolutely, all 4l80e's have an input speed sensor as well as the output speed sensor, so it knows when it's slipping. Typically you'll get codes for ratio errors. The PCM is also capable of comparing engine speed to input shaft speed, if the TCC is locked and it senses any slippage it will throw a code for that as well. If the PCM has noticed any slippage, you will get a code and line pressure will be set to max to help prevent any more damage.

I don't think a 60e can sense a slip unless the TCC is locked, because they didn't have an ISS (until like 2007?) I may be wrong though.
 

JavaMan

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No codes, no check engine light. I did notice on the trip to California that when we first got into Palm Springs, it was shifting hard. So it must have detected slip and upped the pressure at that time.
There are a number of things this 96 ECM doesn't make available to scanners, or maybe doesn't even read, that's part of the reason the 411 swap is so talked about.
 

jdla140

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No codes, no check engine light. I did notice on the trip to California that when we first got into Palm Springs, it was shifting hard. So it must have detected slip and upped the pressure at that time.
There are a number of things this 96 ECM doesn't make available to scanners, or maybe doesn't even read, that's part of the reason the 411 swap is so talked about.

The blackbox ECM sucks, but you should be able to read transmission codes no problem. I can even read transmission codes on my 93 and the engine is fully mechanical.
 

Christian Steffen

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I bought a 1996 Suburban 2500 4x4, with the 454 and 4l80e about a year ago with 113k miles on it. It was priced at $5000, but when I went in to look at it, they said it needed fuel lines replaced which was to expensive for them to do, so they offered to sell it to me as-is for $4k. They gave me $2500 for my 99 Sierra 1500 4x4, which they claimed they input the miles as 17k rather than 173k, but they honored their original offer of $2500 anyway. So my out of pocket was only $2100 after everything at the dealership, plus $280 in parts to replace the fuel lines and pump. Not bad for getting extra room for the family, dual AC, and 3/4 ton.

First month I replaced the fuel lines and pump, changed the oil, changed the trans filter and drained and filled 8 qts ATF (used Valvoline MaxLife, full synthetic Dex3 and Dex6 compatible), changed the rear diff oil, cleaned the AC coils as best I could through where the blower mounts. It drove great.

Then the problems, sorry it gets long here.
By February, I was noticing that going up hills sometimes it would jump to rev limiter, I'd back off the throttle and it would grab again. I found if I just stay easy on the throttle it would be fine, or I could speed up before the hill and let it easy slower getting to the top, and I could prevent the slip.
Well, I thought I'd try a B&M Electronic shift improver, supposed to boost the trans fluid pressure to make firmer shifts. It was great firm shifts 1-2, and 2-3...then neutral. 4th gear felt like nothing was there, it would shift from third and feel like neutral, slows down a bit, then shifts into third again and speeds up. I turned the B&M to stock position, and 4th would kick in and drive like normal. I thought that was weird, and didn't want to break anything, so I removed the B&M.

We took it on a trip to California beginning of June. It was hot going across the California desert, 115-118. Engine was running hot, approx 240. Driving along at 75 on flat road, the RPM goes up, start slowing down so I give a bit more throttle and the RPM jumps like it's in neutral. I manually shift to third, it kicks in and we keep going. Shifting to third helped cool the engine some too, down to 215. We get into Palm Springs, I bought some Water Wetter, and added it in. (Hindsight thought, no pressure was released when I opened the radiator cap). We get out of the desert, still driving in third. That week in San Diego area temps in the 80s, 4th gear would work fine for the first 5-15 miles, then would start slipping in 4th, so I'd shift to 3rd and continue on. On the way home, it was trying to overheat in the desert. About 20 miles from home, going up the hill (climbing from 3000 feet to 7000 feet), it was approx 240 for a way. Then it rapidly went up to 260, and I pulled over and turned it off. We started adding water, then noticed it going all over the ground. One of the nylon splitters for the heater hoses had let go. Got towed into town, it was Saturday so no one at the shop, I went to parts store got the nylon connector and replaced it myself. Filled it up with coolant, put a new radiator cap on it, because I figured out it wasn't holding pressure. Overheat problems solved, even when we towed a 6k pound trailer to Phoenix, with several up and over mountains from Flagstaff. Pulled in third of course.

Now that the temperature is going down, when it's in the 60s, 4th gear works fine. Even after 40 miles and going over hills, 4th does not slip when the outside temps are in the 60s.

I've tried searching the internet, and can't find what causes 4th to slip when the ambient temps are warmer than 70, but not slip when it's colder. Repair shops are money hungry, all three of them heard "slip" and without even looking at it told me rebuild the trans, $3k to $4k. That's just the internals, they don't think I need any work on the valve body, cause that part doesn't really wear out till around 200k miles, and I'm only at 118k.

Any ideas before I have somebody rebuild it? Should I drive it down to Phoenix where there's some better shops and build it as a 4l85e? We do tow 4k to 6k trailers a few times per year.

Sucks you're having issues. It won't be fun, but honestly I'd just swap for a different transmission or have this one rebuilt. Personally I'd trust a low mileage (less than 100k) takeout more than most rebuilds, unless they offer a good warranty or you really trust the shop. A take is going to be the cheaper option too.
 

df2x4

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Absolutely, all 4l80e's have an input speed sensor as well as the output speed sensor, so it knows when it's slipping. Typically you'll get codes for ratio errors. The PCM is also capable of comparing engine speed to input shaft speed, if the TCC is locked and it senses any slippage it will throw a code for that as well. If the PCM has noticed any slippage, you will get a code and line pressure will be set to max to help prevent any more damage.

I don't think a 60e can sense a slip unless the TCC is locked, because they didn't have an ISS (until like 2007?) I may be wrong though.

This makes total sense. I actually forgot about the addition of the ISS to the 4L80E. Not sure how, because I had to add it to my PCM C3 connector when I did the 60E to 80E swap in my red truck.
 
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