A transmission flush on an older transmission may take too much of the "grit" out of the fluid in the transmission and if the friction materials in the transmission are just about wore out, they may slip because they dont have as much bite as they did with the old fluid. IMO if a trans flush causes a problem in your transmission, the trans probably was ready to be rebuilt anyway. Flushes arent needed tho. Take out your owners manual. Does it say anywhere to have your trans flushed at any point in time? No, so why would someone have it done? Just follow the recommended maintanence procedure for the transmission and change the fluid how and when GM recommends it and you shouldnt need a flush for any reason.

 

I would agree, if a flush causes the tranny to slip, and fail, then it was already on its way out. However, if the fluid has never been changed, and you decide to go all out and flush the tranny, you may just speed up the porcess of it failing.

Just drop the pan, and change the filter, and fluid that comes out. On the 4T65E you end up getting a new filter, and 60% of the old fluid replaced with new fluid.

I'd definitely use Dexron VI, and change the fluid (pan drop method) every 30,000-50,000 miles depending on how you drive. I don't care what GM, or my owners manual says, I think 100,000 miles on tranny fluid is way to long, even if its all "easy" miles.

 

i have done trans flushes on my truck but the reson why i did that to the truck is do to when i moved to florida. but doing a rutine pan drop every 30-50k miles is good unless if planning to tow some thing and want to see if there is more dirt in the trans get out but. i dont recoment the flush on a trans that feels like it is slipping. if the fluid in the trans never been flushed from the frist 30k to 130k dont change it. do to it may cause problems as in bands clutches will fail quick when you change the fluid after 130k. if you plan on changinge the fluid do it in intervals as in every 30 to 50k or when you have a first chance to do it do it.

 

GM really recommends changing transmission fluid at 100k? I never knew that. I thought they always recommended 50,000 miles. I havent done mine yet so I never looked at my owners manual. Im not even at 50k yet anyway, lol and since the rebuild I wont have to do mine until about 80,000.

 

Wow, you have low miles Matt!!! Thats sad i'm already at 97K and change.

GM actually recommends 50,000 miles for "Severe Service" and 100,000 for "Normal Driving"

And, I've looked in both my mom's owners manual (2000 Bonneville) and my manual to compair the Dexron III and Dexron VI change intervals. They are the SAME.

GM has been using the 50-100K interval since at least 2000 according to what I saw in my mom's manual.

 

my book says every 150k miles =p, i drove all day today, and drove normal and hard and a little bit all over the scale, and no slipping, maybe it was just a weather change or something?