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Transmission issue

Mike s

Full Member
Joined
Nov 30, 2021
Messages
21
Hey guys I need some help. When my trans gets hot, it starts shifting very hard. Itll throw your head back when shifting 1-2 2-3 gear. Has anyone else had these issues? If so have you found a additive or replacing the filter an fluid to help? I'm going on vacation at the end of the month an I need this fixed. Long drive..I have a 04 avalanche 1500. Thank you
 
One thing comes to mind immediately.

If you already know for sure the transmission is getting "hot", then installing a Tru-Cool - Max LPD47391 47391 Low Pressure Drop Transmission Oil Cooler would be a good idea.

Installing this cooler would be a good idea, regardless.

However, if your transmission is getting hot under normal driving, something else may be wrong.

If the transmission has not had regular service during it's lifetime, the fluid is most likely worn out and the filter may be past useful.

At this point, I would suggest dropping the pan, changing the filter and topping off with fresh fluid.

Don't waste any money doing a transmission "flush".

It's way too late in the game for a flush and fill.

Odds are your transmission is getting close to needing a rebuild.

So, drop the pan, change the filter, top off the fluid with fresh and install the cooler mentioned above.

Then drive the truck until you are ready to take your trip.

If the transmission runs much cooler, then that is great.

Still, start preparing for a transmission rebuild at some point.

I'm really surprised that 2004 hasn't already been rebuilt by now.

I rebuilt my 2004 back in 2012.
 
One thing comes to mind immediately.

If you already know for sure the transmission is getting "hot", then installing a Tru-Cool - Max LPD47391 47391 Low Pressure Drop Transmission Oil Cooler would be a good idea.

Installing this cooler would be a good idea, regardless.

However, if your transmission is getting hot under normal driving, something else may be wrong.

If the transmission has not had regular service during it's lifetime, the fluid is most likely worn out and the filter may be past useful.

At this point, I would suggest dropping the pan, changing the filter and topping off with fresh fluid.

Don't waste any money doing a transmission "flush".

It's way too late in the game for a flush and fill.

Odds are your transmission is getting close to needing a rebuild.

So, drop the pan, change the filter, top off the fluid with fresh and install the cooler mentioned above.

Then drive the truck until you are ready to take your trip.

If the transmission runs much cooler, then that is great.

Still, start preparing for a transmission rebuild at some point.

I'm really surprised that 2004 hasn't already been rebuilt by now.

I rebuilt my 2004 back in 2012.
I bought it last year. The guy I got it from said he replaced it an it only had a few thousand miles on it. It gets hot after 45mins to a hour of highway driving mostly. 70mph tacking 23-2500rpm
I'll put a new filter an fresh fluid. I'd never do a flush lol at this age anyway. Have you ever used any additives to help the seals an other rubber parts. Or no.... I've herd it's bad to use them. I've herd to only use certain ones. Lol thank you for your help btw
 
I bought it last year. The guy I got it from said he replaced it an it only had a few thousand miles on it. It gets hot after 45mins to a hour of highway driving mostly. 70mph tacking 23-2500rpm
I'll put a new filter an fresh fluid. I'd never do a flush lol at this age anyway. Have you ever used any additives to help the seals an other rubber parts. Or no.... I've herd it's bad to use them. I've herd to only use certain ones. Lol thank you for your help btw
I do have a oil cooler already. It's about the same size as the radiator if that's the right one. I actually have 3 cooler up front
 
If yours is in stock form, you probably have the engine radiator (largest and closest to the engine), and then the air conditioning condenser (right in front of the radiator and nearly as large as the radiator) and the power steering fluid cooler (much smaller and located toward the left side of the truck in front of the a/c condenser).

If so equipped from the factory (not many Avalanches are, but all EXT's are) the optional auxiliary transmission cooler is fairly small, rectangular and located in the lower center of the truck in front of the a/c condenser.

Your truck could possibly have an aftermarket transmission cooler installed by a previous owner, like the cooler I linked in the above post.

The Tru-Cool cooler is much larger than the factory aux cooler and mine in my 2003 Avalanche is pictured below.

IMG_5915.JPG

A factory installed aux transmission cooler is painted black and is almost half the size of the one pictured above.

All of these trucks are configured to run the transmission fluid through a cooler built into the radiator.

On trucks with the aux cooler, the fluid is then routed forward into the aux cooler from the radiator and then routed back to the transmission.

Some owners have opted to skip the radiator cooler when installing an aftermarket cooler.

I prefer to run mine through the radiator first then through the aux cooler and then back to the transmission.

And by the way, how do you know your transmission is running hot?

Do you have a transmission temp gauge in your instrument cluster?
 
No I dont. I'm assuming that's what the issue is. Tho after talking to you I'm thinking filter or fluid. I checked the fluid back in oct Nov an it was red. But I guess that might not mean anything if it is cheap fluid
 
what is HOT? what temp?
 
When the transmission in my 2004 EXT (4L65E) went out back in 2012, it had 125K miles on it.

The fluid looked and smelled fine.

I had only owned the truck for about 9K miles and had not had any service performed on the transmission.

When it first acted up, my mechanic suggested dropping the pan and changing the filter and topping off the fluid with fresh.

The truck drove fine out of his shop.

A week later, I pulled out of a parking lot into normal traffic and when it came time to shift into third from second, there was no third.

Or fourth.

Only first, second and reverse.

I had it rebuilt at a local transmission shop and did not request any fancy parts to be installed.

Just what the shop normally used.

I also had the torque convertor changed.

Now the truck has 236K miles on it and the transmission runs normally.

I had the pan dropped and filter changed after 50K miles.

The EXT may have other problems, but so far, the transmission is not one of them.

On the other hand, my 2003 Avalanche (4L60E) is on it's original transmission build at 268K miles.

You can just never tell with these things.

I really installed the aux cooler on that truck in preparation for the upcoming transmission rebuild, whenever that may be.
 
I also have the 4l60E. I had herd the trans dont hold up on these trucks. But I hoping to get a few more years before anything needed to be done. I was told the factory trans cant handle the power an that's why there always having issues. Thank you for your help
Hopefully new filter an fluid will do the trick. For now at least lol
 
When my 4L85e started to get hot while towing our camper, it shifted very hard, both with and without the camper hooked up. I had no lights on the dash but a scanner revealed a slipping trans error code. A remanufactured transmission fixed it. I also have the Tru-Cool 40k cooler. The stock one is a joke.

Have someone pull the codes on the trans. I'm guessing it will be time for a transmission soon unfortunately if it's getting hot and shifting hard. Any noise when the torque converter locks/unlocks?
 
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I also have the 4l60E. I had herd the trans dont hold up on these trucks. But I hoping to get a few more years before anything needed to be done. I was told the factory trans cant handle the power an that's why there always having issues. Thank you for your help
Hopefully new filter an fluid will do the trick. For now at least lol

Try some Marvel's Mystery Oil (either before or when you do the filter/fluid change). I have used it in all my motors and transmissions (when needed) for over 40 years, it does some great things. Or, before changing fluid if it still smells and looks good, try some Lucas transmission fix, also good stuff that I have used.

BTW, some people love talking about how bad the 4l60E transmission is. When I got my 1994 K1500 with 57K miles at the time (in 1996) all I heard was how bad the transmissions are, how they need replacing at 35K, 50K etc. Well, that transmission never failed me, was never rebuilt or touched other than filter and fluid changes every 50K miles or so and was working fine when I sold the truck with 267K miles.
 
When my 4L85e started to get hot while towing our camper, it shifted very hard, both with and without the camper hooked up. I had no lights on the dash but a scanner revealed a slipping trans error code. A remanufactured transmission fixed it. I also have the Tru-Cool 40k cooler. The stock one is a joke.

Have someone pull the codes on the trans. I'm guessing it will be time for a transmission soon unfortunately if it's getting hot and shifting hard. Any noise when the torque converter locks/unlocks?
Not alot. My f150 made a lot of noise locking an unlocking. I have gotten a slip code for the trans 2x now. I was hoping a fluid an filter change an maybe a trans additive would clear it up for a few months. It never acted up pulling our camper. An it weighs 3000lbs, plus a bed full of firewood an filled coolers. But our camp site is only half hour away.
 
Try some Marvel's Mystery Oil (either before or when you do the filter/fluid change). I have used it in all my motors and transmissions (when needed) for over 40 years, it does some great things. Or, before changing fluid if it still smells and looks good, try some Lucas transmission fix, also good stuff that I have used.

BTW, some people love talking about how bad the 4l60E transmission is. When I got my 1994 K1500 with 57K miles at the time (in 1996) all I heard was how bad the transmissions are, how they need replacing at 35K, 50K etc. Well, that transmission never failed me, was never rebuilt or touched other than filter and fluid changes every 50K miles or so and was working fine when I sold the truck with 267K miles.
Wow you got lucky bud. My brother is a mechanic now turned HVAC mechanic. An he said the same, those transmissions are known to fail. Someone else recommended lucus to me as well.
 
Sounds like rebuild time. My 4l60e went 145k before losing 3rd gear and I towed and hauled way more than it was rated for. I put a full size spin on 10 micron filter in the cooler line, and an oil cooler and changed it every 30k. Back in 05 when i bought mine the research i did indicated the valve body wore out due to abrasive particles in the oil. I reasoned that if It was filtered it better it would remove those and it should last longer. I think the stock filter is only like 25 micron and the amount of material in the pan was substantial when i serviced it. After installing the 10 micron filter the pan was spotless the next time i removed it. I also upgraded my cluster to one with a temp gauge. The truck is already wired for it, plug and play. Never let it get over 230 degrees, id pull over and let it cool off if it did. I think GM did everyone a disservice by not using a better filter and a good oil cooler on it.
 
This was my transmission temp on a 95 degree day, 70 mile round trip at highway speeds and not towing.

Without the Tru-Cool, this same trip would have the transmission running closer to the 200 degree mark.


IMG_5918.JPG

The highest I have seen since installing the Tru-Cool has been at the 150 degree mark.

The Tru-Cool gets the job done.

A small price to pay for a whole lot of piece of mind.
 
Not alot. My f150 made a lot of noise locking an unlocking. I have gotten a slip code for the trans 2x now. I was hoping a fluid an filter change an maybe a trans additive would clear it up for a few months. It never acted up pulling our camper. An it weighs 3000lbs, plus a bed full of firewood an filled coolers. But our camp site is only half hour away.

If you're getting slip then go with the Lucas Transmission Fix, make sure it's the Fix not the Conditioner. If there's nothing actually broken, it'll work.
 
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