1991 Sierra K2500 automatic transmission fluid

[sr17]

I am going to drop the automatic transmission pan on my 1991 GMC K2500 to change fluid and filter.

I don't use the truck much, but when it is used it is usually towing up to 5,000 lbs in pretty steep terrain.

The pan was dropped last year by a shop. I don't know what type of fluid they put in, other than that is was conventional.

I would like the best possible protection for the transmission - should I put in synthetic? Will it make any positive difference considering that it will mix with the fluid that is still in there after dropping the pan?

Some say to put in a bottle of Lubeguard Red. Is this advisable?

 

[Ramblejam]

I run MaxLife in 4L80 - full synthetic, and available locally for under $18/gallon. Of course, being in B.C., your availability may be different.

Originally Posted By: sr17
I would like the best possible protection for the transmission


Do you have a good cooler and temperature gauge installed?

 

[901Memphis]

Maxlife is a top choice as well as any licensed DexronVI which is a synthetic blend.

 

[SteveSRT8]

We use Lubegard Red here, it can instantly reduce temps. Maxlife is excellent fluid in this app as well, we have run 4L80 units well over 300k miles with no parts, just fluids and filters...

 

[Bgallagher]

Originally Posted By: SteveSRT8
We use Lubegard Red here, it can instantly reduce temps. Maxlife is excellent fluid in this app as well, we have run 4L80 units well over 300k miles with no parts, just fluids and filters...


beat me to it. this is an excellent combo for most applications. If the current fluid still looks good you can consider dropping a bottle of lubeguard red in it and call it a day

 

[JMJNet]

Is there any reason why you want to replace it again after only 1 year? You said it was not driven that much.

 

[sr17]

Originally Posted By: JMJNet
Is there any reason why you want to replace it again after only 1 year? You said it was not driven that much.


Not, really, other than it was the first time I had it done after owning the truck. I know nothing about past service history, so just though it would be good to do it again to refresh the total content of fluid in the transmission more fully.

It shifts very smoothly and quickly. The only complaint I have is that there is some clunking when switching from "D" to "R" and back to "D". I don't know if this is related to the transmission, or maybe a u-joint of differential.

No cooler or temp gauge.

 

[Farmer]

Castrol Transmax Synthetic Multi Vehicle is available at Napa for 6.49 a quart. It's Dex 3 and 6 rated. With the license on the back of the bottle.

 

[userfriendly]

I'll go one step further in the right direction;
Without removing the torque convertor, turning it upside down for a day and purging the cooling lines, at least 6 liters of old fluid is left in the system.
I do that once, then replace the stock pan with one with a drain plug.
The one thing I love about the Allison transmission behind the Dmax, is the drain plug, 2nd is the external spin on filter.
Save the old transmission fluid for purging your power steering pump.
Add an external transmission oil cooler and don't mount your spare tire in front of the grill.
I went overboard and used TES 295 synthetic @ 80K km in my Allison. If I keep the truck another 10 years, I will change the fluid again.
Canuck Tire or any of the major non-synthetic Dexron III+ will do.
Monkeying with additives, synthetics or boutique oils is asking for trouble.
An acronym missing form the bitog list is KISS.

 

[demarpaint]

Originally Posted By: Bgallagher
Originally Posted By: SteveSRT8
We use Lubegard Red here, it can instantly reduce temps. Maxlife is excellent fluid in this app as well, we have run 4L80 units well over 300k miles with no parts, just fluids and filters...


beat me to it. this is an excellent combo for most applications. If the current fluid still looks good you can consider dropping a bottle of lubeguard red in it and call it a day


LG Red is a great product. I used it in several transmissions over the years. It is in my 00 Century with Maxlife, nice combo.

 

[messerchmidt]

amsoil signature series atf

 

[Ramblejam]

Originally Posted By: userfriendly
I'll go one step further in the right direction;
Without removing the torque convertor, turning it upside down for a day and purging the cooling lines, at least 6 liters of old fluid is left in the system.


Negative.

All it takes is this, which threads in place of the return line exiting the radiator:

From the fitting, run some cheap clear tubing into a clear/translucent graduated bucket (that way, you'll know exactly how much came out, and how much new fluid to pour in each time; they're available in the painting section of your local big box retailer for cheap). You'll pump out a couple/few quarts at a time; exchange the system capacity, and you have virtually 100% fluid replacement.

 

[userfriendly]

We're on the same page Ramblejam, nobody in their right mind is going to remove the torque convertor unless the engine or transmission is out anyway.

 

[sr17]

ok, based on this I have settle on MaxLife and a bottle of LG Red.

Is there a big difference in quality of filters for these transmissions? Can I get a good one from places like Autozone or O'reilly's?

 

[clinebarger]

Originally Posted By: sr17
ok, based on this I have settle on MaxLife and a bottle of LG Red.

Is there a big difference in quality of filters for these transmissions? Can I get a good one from places like Autozone or O'reilly's?


SPX Filtran Micro-Felt, Which was OEM on all 4L80E's. I have seen aftermarket junk filters wad up & leave people on the side of the road.

Problem is '91-'96 4L80E's take a different filter than '97 & up units & GM no longer sources the early filter from SPX, Though they do for the Late filter.

There are NOS SPX filters out there, Or you can take the chance with the aftermarket, Or you can run a '97 & up pan & buy a GM filter.

 

[sr17]

Originally Posted By: clinebarger
Originally Posted By: sr17
ok, based on this I have settle on MaxLife and a bottle of LG Red.

Is there a big difference in quality of filters for these transmissions? Can I get a good one from places like Autozone or O'reilly's?


SPX Filtran Micro-Felt, Which was OEM on all 4L80E's. I have seen aftermarket junk filters wad up & leave people on the side of the road.

Problem is '91-'96 4L80E's take a different filter than '97 & up units & GM no longer sources the early filter from SPX, Though they do for the Late filter.

There are NOS SPX filters out there, Or you can take the chance with the aftermarket, Or you can run a '97 & up pan & buy a GM filter.


The transmisiiona in my truck is the 7R400. I believe that is the non computerized predecessor of the 4L60E.

 

[sr17]

How many Qts. should I expect to get out by dropping the pan? Need to make sure I have enough on hand.

(7R400 transmission)

 

[Ramblejam]

It's actually the 700R4; had completely forgot about them making light duty/heavy duty 2500's back then.

~5 quarts on a pan drop.

 

[sr17]

Originally Posted By: Ramblejam
It's actually the 700R4; had completely forgot about them making light duty/heavy duty 2500's back then.

~5 quarts on a pan drop.



Thanks you for that info!
Yeah mine is a light duty 2500 with 6 lugs.

 

[Ramblejam]

You're most certainly welcome!

I'd encourage you however to do the full fluid exchange I mentioned in an earlier post.