Change trans fluid or no?

[Echomirage]

96 K2500, 454 and 4L80e. 150K miles, brand new/rebuilt motor, original trans, and from the amount of neglect its had, im sure original trans fluid. the shadetree mechanic who swapped my motor said NOT to change the trans fluid....which ive heard before, as new fluid in an old trans will cause it to slip and die in months.

what does the forum think? it shifts fine as of now, and the only good thing i can think of is it rarely towed, if at all, in its previous life. it never had the trailer wiring done, and the receiver wasn't even rusty from a hitch being inserted and removed. i dont know why someone would buy a big block burb and never tow, but 2 people did before me.

im going to use it sparingly, but will be used for towing/hauling -thats why i bought it, and made sure it was a big block, in the first place. but it may only tow 5-8 times a year, and maybe around 5K lbs at that.

should i change the trans fluid, or just keep the original? are there any trans fluid additives that DO work and are worthwhile?

 

[Colonel Sanders]

How does the fluid in there now look? If it's still clear and red/pink a drain and fill probably wouldn't hurt anything but if it is brown/black and hazy then there is clutch material in the fluid itself which is why they start slipping if changed. The material in the fluid provides extra friction to the likely worn clutches and removing it with fresh fluid reduces friction and can cause slipping.

 

[jkeaton]

I changed the fluid and filter on mine at approximately 200k. About a month after I lost second and OD. $2000 later I had a rebuilt transmission.

 

[Justin S]

If it "shifts fine as of now" .... leave it.

 

[Goose 3406]

Well this answers all my questions I had. I too have a 4l80e, and I also believe mine to be original. But if mine is original, it has just shy of 300000 miles on it

 

[df2x4]

Personally I'd change (not flush) the fluid and filter regardless of what it looks like. If it's going to go, it's going to go. No point in running nasty fluid.

 

[Echomirage]

How does the fluid in there now look? If it's still clear and red/pink a drain and fill probably wouldn't hurt anything but if it is brown/black and hazy then there is clutch material in the fluid itself which is why they start slipping if changed. The material in the fluid provides extra friction to the likely worn clutches and removing it with fresh fluid reduces friction and can cause slipping.

fluid looks good, doesnt smell burned. so youd drain and fill, but not change the filter?

 

[Echomirage]

I changed the fluid and filter on mine at approximately 200k. About a month after I lost second and OD. $2000 later I had a rebuilt transmission.

yeah thats what ive heard, so i figured ask here before doing anything.

 

[Colonel Sanders]

Doing a drain and fill would still involve changing the filter (or not), it's opposed to a flush. Because of the fluid in the cooler and torque converter a drain and fill only replaces 1/3 to 1/2 of the fluid. A flush would introduce 100% new fluid and the pressure from the machines could also cause damage. As long as the existing fluid is in good shape and you're not flushing it the risk of damage from the fluid change is low, under/over filling would be a bigger concern. Like df2x4 said if a fluid change causes it to go bad it was going to go out anyway, but leaving old fluid in a good transmission can reduce the lifespan. It's a risk you take either way, but that's how it goes with old cars.

 

[Jorge6.5]

God I love my manuals! Lol