To Change Atf Or Not To Change Atf

[mhorgan]

My 02 Z71 has now gone north of 200k miles with the original transmission. I bought the truck with 165k miles and I really had no idea how long it would go, but its what I could afford. Needless to say, it's not too bad. The tranny has never given me any trouble- no missing shifts, not even a rough shift. I know that usually the 3-4 solenoids or the sun gear housings go bad in these trucks, and I drive up to 250 miles a day but it still runs great. Im debating whether I should tempt fate and change out the tranny fluid.

 

I wrote service for a few years at a Cadillac dealer and I remember there always being the debate on fluid changes in high mileage vehicles. My dealership had a waiver to work on cars with over 100k or more than 10 years old, and it was a general practice not to flush a transmission with over 90k. I actually got into it with a customer over flushing fluid in an Escalade ESV with 120k. I tried to warn him that it might be a good idea to skip the flush and he wouldnt listen. We did the flush, and no more 3rd gear. He had been a good customer too, did all of his 30k services.

 

Im the 3rd owner of this truck and it was my understanding that the trans fluid got changed at 100k. The guy I bought it from casually mentioned it when I asked so I imagine that it was a drain and fill only becuase people usually remember spending nearly 200 bucks on a full flush and they make sure they tell you when they sell it. Im wondering if another drian and fill is worth it. The fluid is worn and can use a change for sure but Im not sure if Id be losing too much of the clutch particles suspended in the fluid that may be helping those shifts. Anyone have experience with miled up trucks like this? My gut is saying no but Id like a few more miles out of this tranny before I have to scrape the money to rebuild it. Like I said, Ive never changed trans fluid in anything with more than 120k.

 

If it makes a difference, the truck is stock height with 285 tires on stock rims, nothing fancy.

[Zembonez]

I'm like you... I'd be a little scared to change the fluid at 200K if the trans is working fine. You have to wonder if you'd be extending its life or causing it to start having issues...

 

I'd probably leave it alone and hope for another 50K unless the fluid looks like crap or smells really burnt.

[Black02Silverado]

Yes, this is one that might serve well to just leave it. I've changed out two vehicles with high mileage on the transmissions and they both went out shortly there after.

 

On a side note, I did my neighbor's grandsons 2000 GMC with 159k on the clock. Changed the filter and exchanged all the fluid. That was three weeks ago and it is running fine. This is on a truck that is getting abused because it is a 16 yr old that is driving daily. Even taking it on three hour trips the past couple of days.

[jro909]

i think a filter change would atleast benefit it, forget any flushing though

[mhorgan]

Hmm, not the answer I was hoping for, but it was the one I expected. The most I'd do is drop the pan and change the filter, definitely not a flush. I havent checked the fluid in a month or two, but I believe it is still somewhat red. Ive always driven it like an old lady and never hooked up a trailer. I figure its fine for now and I might change it later provided Ive got the cash on hand to rebuild it. I tried changing the rear end fluid a few months back and the clutch particles left over in the diff bound together and ate up the pinion bearing, so Im a little hesitant to mess with it.

 

Ive heard stories about 4L60E's going past 300k- I know a few people who passed 300k and Im starting to think that if I havent had to overhaul the trans yet, maybe Ive got myself a unicorn here. Seems like most GMT400's and 800's need rebuilds somewhere north of 100k. Guess we'll see.

[txab]

If I did anything, it would be a pan drop and filter only. No flushing.

[Zembonez]

My comment is solely based on older vehicles I have seen that had service done and then had issues. I have nothing more scientific than that... so take my suggestion for what it;s worth!

[jro909]

Hmm, not the answer I was hoping for, but it was the one I expected. The most I'd do is drop the pan and change the filter, definitely not a flush. I havent checked the fluid in a month or two, but I believe it is still somewhat red. Ive always driven it like an old lady and never hooked up a trailer. I figure its fine for now and I might change it later provided Ive got the cash on hand to rebuild it. I tried changing the rear end fluid a few months back and the clutch particles left over in the diff bound together and ate up the pinion bearing, so Im a little hesitant to mess with it.

 

Ive heard stories about 4L60E's going past 300k- I know a few people who passed 300k and Im starting to think that if I havent had to overhaul the trans yet, maybe Ive got myself a unicorn here. Seems like most GMT400's and 800's need rebuilds somewhere north of 100k. Guess we'll see.

 

 

yeah the 4L60 is kind of like that pet zombie in the basement, it will either eat you alive or hang in there for the long haul and eventually just decay...i know atleast 3 4L60s passing the 150k mark with heavy abuse and towing

[txab]

My comment is solely based on older vehicles I have seen that had service done and then had issues. I have nothing more scientific than that... so take my suggestion for what it;s worth!

I agree with earlier post, unless the fluid was extremely bad or burnt, I probably wouldn't mess with it at this point. I've changed fluid on high mileage TH350 and TH400 without any problems, but only doing a pan drop and filter change. I figure 4 qts or so won't throw a wrench into the mix. Also I find actual Dex III, not the DEX VI stuff to mix with the old. I'd never do a flush on anything as old as OP's.

[yukon25008.1]

i have an 01 chevy express 2500 van,i got it used cheap with 187.... not sure of any service record, so i took the chance and changed it, did the filter but no flush, and used dex-6 synthetic..no problems yet and its been 6-8 months 6-8000 miles.

good luck

[Sly]

If the fluid is not burnt I would drop the pan and do a filter change and refill with DEX VI. If the fluid is burnt then drive it until grenades.

[oldscsc]

As far as I know I'm on my original transmission with over 300,000 miles. Not sure of any service records, but I sure don't have the guts to risk changing the fluid.

[kmborland]

hey guys, i have a question that is kinda to this. i just got my truck yesterday with 144k and the fluid doesnt look so good. i was thinking of dropping the pan and changing the fluid and filter. but from what i have read here, the trans might go if i replace the fluid. would i be ok if i drained some of the old fluid and put new fluid in? i remember on my 98 jimmy with 126k when i bought it, the first week i changed all the fluids and did a tune up. 1.5years later, the trans blows at 150k was changing the fluid the cause of that? if it was, i dont want to relive that again.

[Doug_Scott]

I used to overhaul transmissions at a dodge dealer back before the back gave out. If the fluid has not been changed on a scheduled basis, leave it alone completely. Trans fluid is a great varnish and gum remover. Even changing out half the fluid will put some nice new varnish remover in there. Varnish has a way of helping seals, well, seal and changing the fluid may disolve some of that and create issues. Would not touch it if it were mine and would do my damndest to disuade a customer of doing it as well. If the fluid is already burnt, changing it will not do it any favours now.

[dlstewart01]

Transmission shops don't want to change fluid on a tranny that wasn't maintained because they might be blamed for future failure. In addition people that change their fluid at high mileage sometimes do it because they are already having problems.

 

In my humble opinion what may cause high mileage problems is when certain pressure flush machines are used to get the fluid out of the trans may push some of the ware material into valves or small orifices and cause the trans to fail.

 

A simple pan drop or a fluid change using the transmission pump to transfer the fluid will never hurt a transmission that is in good operation condition to begin with. Most people change the fluid when they began experience problems and guess what they blame the trans failure on shortly there after.

 

I had much rather have nice clean fluid with fresh additives than to continue to use the worn out contaminated fluid that will only get worse as time goes on.