1990.k2500 4x4 8600 GVWR SCLB

[90 K2500]

Yes I used search function. Want to add all fresh Dex/Merc 3 , Dex3, or Dex6.
Any concerns with the Dex 6?

 

[90 K2500]

Mileage 164 000 TH400 tranny 3 sp.
Fluid looks nice and red.
History of transmission unknown
Also any reusable filter gasket kits you prefer?

 

[stutaeng]

Either is fine. There was a thread just recently about III vs VI. I think the VI will just get you longer fluid change...

I don't remember that the filter on that unit looks like. But I think most transmission guys will put a double o ring on the tube where the filter bolts on, if it doesn't already have a double ring there.

Do you have an auxiliary cooler?

 

[90 K2500]

Thanks Stutaeng for quick reply. No auxiliary cooler. Service manual lists 22 qts.
I drove it 75 miles and it shifted great.
Purpose for double o ring please.
Looks like 3 gallons will be needed.
Owners manual states change trans fluid and filter every 24K unless severe duty then 12 K. Did this mean just drop pan and filter or all 22 pints?

 

[stutaeng]

I followed the method @Schurkey described on this thread I created and it worked great. Post #9: https://www.gmt400.com/threads/4l80e-fluid-change.53996/

Does your oil pan have a drain plug? If not, it's pretty easy to add one if you like.

BTW, the manual states 22 pints, or 10 liters...you are correct though: 3 gallons should do the job and you will have some left over.

I think the double o ring is to ensure you have a better seal. If the o ring gets brittle and sucks air, you can lose lubrication. Another o ring is cheap insurance.

Lastly, I would recommend you add an auxiliary cooler once you get a change.

Looks like filters are pretty inexpensive (doesn't seem to include the o ring): https://shop.advanceautoparts.com/p...?searchTerm=Automatic+Transmission+Filter+Kit

 

[90 K2500]

Great hope others can benefit from the info.

 

[Schurkey]

The filter has a rubber grommet. The O-rings go onto the plastic tube that's shoved into the "case" (it's actually the pump.) B&M used to recommend double O-rings; and that's how I've always done 'em.

I put Dexron VI into transmissions that are spec'ed for Dex VI. Otherwise, I save my money and buy Dex/Merc "Dexron III equivalent" from whatever supplier has it on sale at the time. Seems I wind up with NAPA trans fluid most of the time although I'm not afraid to buy sealed bottles at rummage sales or store-closing blowouts. I just finished the last of my Sam's Club "Certified" trans fluid a year or so ago.

 

[90 K2500]

Schurkey,
That is the belief of others even though GM says backward compatible V1. Toss up at $14 a gallon for Dex Mer 3 vs Maxlife VI @ $18.
Just wondered if the VI would cause any harm to the TH400 that is over 30 years old.

 

[Schurkey]

I wouldn't expect any "harm" from Dex VI on any trans new enough to be spec'ed for Dexron; or new enought that later-versions of that trans were spec'ed for Dexron. Example: '66 Powerglide should run on Dexron VI, because the '67 'Glide got Dexron.

I could be wrong, and it's not like I have a '66 'Glide any more. I use Dex/Merc to save a few dollars, not to gain compatibility.

Go back far enough, into the motor-oil or Type A trans fluid days, and things might be different with Dexron VI; and GM acknowledges that.

 

[stutaeng]

The OP Owner's Manual says "Dexron II or equivalent" which I don't believe they even make anymore. Dexron III is a replacement. I believe the only vehicle that still uses the TH400 is the millitary-spec HMMWV. I don't know what they specify for that unit, probably Dex III?

This specification for the millitary use of the 4L80e (shares a lot of geartrain with TH400) specifies Dexron III (page 21.) https://gear-report.com/wp-content/...ment_7_4L80E-Transmission_Troubleshooting.pdf

I don't see any harm in using Dexron VI either.

Even my 06 SUV's Owner's Manual specifies Dexron III!