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vtfireman85

GM 4L80E hard shift development

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today after having been in 4 wheel drive at low speeds for a bit, when i got back out on the road it started slamming hard into 2nd, doesnt seem to hold the shift from1-2 an abnormally long time just slams hard when it does. it was in fact out of 4 wheel before i got back on the asphalt. oil looks clean, smells fine and is at the cold full mark when it is cold and running. as soon as i get the Jeep off the pit i plan to change the filter and fluid and inspect. any ideas on this? 

truck is a 95 3500 SRW 6.5 diesel, 79K miles. and has a GoodWrench rebuilt trans in it, i dont know how long it has had that, but i discovered the sticker on it when doing exhaust. 

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TPS maybe?

 

 

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3 minutes ago, New Englander said:

TPS maybe?

 

 

that is what i come up with mostly on the interweb, and some pretty good instructions on how to test it, which i will do once it is not dumping buckets of rain. for now i am hoping it stays glued in the truck till we get through this weather we are getting and going to get in the next 36 hrs. up to 4" according to the weather guessers, you may be getting it worse? 

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Just now, vtfireman85 said:

that is what i come up with mostly on the interweb, and some pretty good instructions on how to test it, which i will do once it is not dumping buckets of rain. for now i am hoping it stays glued in the truck till we get through this weather we are getting and going to get in the next 36 hrs. up to 4" according to the weather guessers, you may be getting it worse? 

We've got nothing but wind on the coast, it all went inland over you! We really could use some rain. My lawn and fields are brown and crisp.

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My 1992 3500 with a 6.5 would do that mostly when the transmission got hot. The trans shop told me that it's HD mode in the computer causing that. Most of the time after cooling off or just shutting down and restarting the engine would make it go away. My 98 K2500 has done it before too. 

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I think that’s the transmission I had issues with. Wouldn’t shift past 2nd. 
It was a speedometer drive/ sensor if I recall correctly (?) This was after being told it would need a rebuild, from a reputable transmission shop 😱

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There are many engine management controls that will make you think it's tranny. Good luck. Highly synced between motor and transmission. Those are otherwise solid transmissions.

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Hopefully it will sling a light on the dash or a code reader will pick it up. That's a good tranny and usually wont wreck itself. that's just my experience. 

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It will take the gm scan II or snappon equivalent. $100 fee generally. Worth it when not sure.

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Drove it to the firehouse and then home, 12-13 miles total, shifted smooth as silk. 🤬

I hate mystery problems 

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56 minutes ago, vtfireman85 said:

Drove it to the firehouse and then home, 12-13 miles total, shifted smooth as silk. 🤬

I hate mystery problems 

Ive seen mine do that after being in 4 low , higher rpm to low speed blow computers mind and it needs to reset . The 4le80 is a overdrive 400 the experts say 

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23 minutes ago, shot_gun_red said:

Ive seen mine do that after being in 4 low , higher rpm to low speed blow computers mind and it needs to reset . The 4le80 is a overdrive 400 the experts say 

Wasn’t in 4 low, but crawling.. could be

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The 4L80E transmission has some quirks and over the years has had several updates, the reason your 4L80E started shifting hard was because it was sensing slippage. If not a 4 wheel ABS truck, that transmission uses two speed sensors to determine how much slippage is occurring and changes line pressure with a force motor on the valve body. The input speed sensor is on the left side of the transmission about in the middle, the output speed sensor is on the tail of the transfer case. On the non 4 wheel ABS trucks, those two sensors give information to the speed sensor buffer behind the glove box which made your speedometer, cruise, rear ABS, and transmission shift correctly. If you have continuing problems, it might be time to change the sensors.

When we had a 1993 K2500 6.5TD 4x4 new, it worked great, until it had about 36K on it. From then on, the 4L80E transmission gave us nothing but trouble, shifting hard and losing OD, but simply turning the truck off, then back on would cure it for a while. The very first time it did it, Dad was deer hunting and noticed it shifted hard, but drove it about 20 miles anyway and it lost OD. He went to back up and reverse was gone too, so he brought it back to our shop and told me to check it out figuring it was something electronic. Being it was a "new" electronic transmission, I bought a factory service manual and started working on it, found the rear servo was shattered, so replaced it, but it still wouldn't work. Pulled the tranny and took it to a rebuild shop who found the aluminum forward apply piston was also destroyed, they replaced it with a heavier duty aluminum piston and it worked, for 11 months before it exploded again, shifting hard just before this happened. This time they put in an aftermarket steel forward apply piston and said they don't know why this is happening, but are researching it, remember, this transmission was only out for about three years at this time, so the shops were still trying to figure them out. 

Turns out the 4L80E has several flaws, which can be fixed, but most all suffer from the flaws. The good news is the aftermarket offers different kits to fix these flaws and they seem to work. They wear their internal center bushings, which not all transmission shops change in a normal rebuild,  causing internal leakage resulting in slippage issues and spiking the line pressure causing harsh shifts and sometimes broken parts, they also suffer from front pump pressure regulator problems. You don't notice it as much when in a gas truck because they do not have the low end torque a good running 6.5 turbo diesel does and the transmission seems to struggle with line pressure to handle the torque of the diesel.

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4 minutes ago, ThirdGenRed said:

The 4L80E transmission has some quirks and over the years has had several updates, the reason your 4L80E started shifting hard was because it was sensing slippage. If not a 4 wheel ABS truck, that transmission uses two speed sensors to determine how much slippage is occurring and changes line pressure with a force motor on the valve body. The input speed sensor is on the left side of the transmission about in the middle, the output speed sensor is on the tail of the transfer case. On the non 4 wheel ABS trucks, those two sensors give information to the speed sensor buffer behind the glove box which made your speedometer, cruise, rear ABS, and transmission shift correctly. If you have continuing problems, it might be time to change the sensors.

This makes sense... I guess. I assume on a non cruise truck, the same would apply? Does this apply to the heavy duty transfer case? I have lost track of which I which, but I remember searching a long while for the right on as it was less common. It sits at around 7500-8000 lbs on a normal day with tools, body and lift gate. Normally  I would grab low range for such a trip but I didn’t bother. 

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35 minutes ago, vtfireman85 said:

This makes sense... I guess. I assume on a non cruise truck, the same would apply? Does this apply to the heavy duty transfer case? I have lost track of which I which, but I remember searching a long while for the right on as it was less common. It sits at around 7500-8000 lbs on a normal day with tools, body and lift gate. Normally  I would grab low range for such a trip but I didn’t bother. 

It will still have the speed sensors whether it does or does not have cruise, and should still have an output speed sensor on the tail of the transfer case if it is a standard or a heavy duty transfer case.  If the transmission senses slippage, it will raise line pressure causing harsh shifts, it may have not liked what you were doing and temporarily boosted line pressure to reduce the slippage.

Here is a link to rockauto.com to see if these style speed sensors look like what you have if the transmission starts doing this more often and you decide to change them.

https://www.rockauto.com/en/catalog/chevrolet,1995,k3500+pickup,6.5l+v8+diesel+turbocharged,1053368,electrical,speed+sensor,10634

 

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LOL

They used  4L80E behind the Duramax in vans never had any problems with  mine  and just about every LS motor put out more torque than those 6.5 turds  

 

"You don't notice it as much when in a gas truck because they do not have the low end torque a good running 6.5 turbo diesel does and the transmission seems to struggle with line pressure to handle the torque of the diesel."

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14 hours ago, vtfireman85 said:

till we get through this weather we are getting and going to get in the next 36 hrs. up to 4" according to the weather guessers, you may be getting it worse? 

Very little rain, wind gusts to 65. We went on generator at 18:45 and mains just came back at 07:15. One tree partially snapped and lots of branches down in the yard. Gonna fire up the chipper today.

How much rain did you get?

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1 hour ago, New Englander said:

Very little rain, wind gusts to 65. We went on generator at 18:45 and mains just came back at 07:15. One tree partially snapped and lots of branches down in the yard. Gonna fire up the chipper today.

How much rain did you get?

Couple inches, had an elm in the yard that has been loosing a limb in each big storm for the last ya. Now it’s snapped off from the top. Was not a huge tree , maybe an 8” base. Otherwise just lots of sticks around 

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11 hours ago, vtfireman85 said:

Drove it to the firehouse and then home, 12-13 miles total, shifted smooth as silk. 🤬

I hate mystery problems 

Mine did this for awhile, then it got to where it wouldn’t shift out of 2nd. 
Speedometer drive was $75(?) 10 minutes later it worked as new. Cheap enough to try if you don’t get anything else figured out

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42 minutes ago, Ihfan4life said:

Mine did this for awhile, then it got to where it wouldn’t shift out of 2nd. 
Speedometer drive was $75(?) 10 minutes later it worked as new. Cheap enough to try if you don’t get anything else figured out

That’s interesting, our first Quigley conversion was an 01 5.7 4L80E in pow range the speedometer was WAY off as I’m 4th gear read 80 at about 15 Mph shifted fine up through, I wonder how that worked. 

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3 minutes ago, vtfireman85 said:

That’s interesting, our first Quigley conversion was an 01 5.7 4L80E in pow range the speedometer was WAY off as I’m 4th gear read 80 at about 15 Mph shifted fine up through, I wonder how that worked. 

Sounds like the speedometer was reading the output of the transmission and not the output of the transfer case.  Did you have a REALLY low-geared low range in that transfer case?

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1 hour ago, 1586 Jeff said:

Sounds like the speedometer was reading the output of the transmission and not the output of the transfer case.  Did you have a REALLY low-geared low range in that transfer case?

No idea what the ratio was but it was a t-case common to similarly powered GM pickups. 

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My 91 would go into what I'm calling limp mode and shift hard as well as lock itself out of overdrive. Usually when my pos TBI 350 would act up. It's a farm truck so lots of rough driving. It would finally sling a check engine light then whatever sensor in engine would cleanup and run smooth I'd have to shut it off and restart it, then tranny was fine. I did eventually grenade my 4l80e but it deserved to die. I was stuck with 2 bales on back, no reception, and a very very long walk in the dark. I did what I had to do to a tired tranny and a week later It was leaking oil out the flywheel housing faster than you can dump it in. $2k later from a guy that did it on the side I'm rolling again. He told me as much mud and cow $hit was under there it looked like all highway miles for sure 😎

Also my brake switch was out under the dash causing it to no lockup torque in OD. He said it looked like a size 14 boot blew it off 🧐   I stand by my statement. tough transmissions. 

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today its driving like it oughta, I used low range today, maybe that helped. 

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10 hours ago, vtfireman85 said:

today its driving like it oughta, I used low range today, maybe that helped. 

The little temper tantrum was a cry for more appreciation.

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