Trans Fluid Flush...

Why shouldn't you do a transmission flush after a certain mileage? Also, what mileage is that? I've seen this in other posts and I was just wondering for future knowledge.

Thanks,
Brick

If I am correct, a flush on high mileage transmissions can shock the system, accelerating the eventual doom of needing a rebuild.

The safest bet is to just do a pan drop and filter change, but that doesn't get all the fluid out. If I am right, that's why the flush was invented.

I would say that if your car is at or below 50k, then it shouldn't be an issue. Above that, you are taking greater risk on accelerating the need for a rebuild after a flush, so just do a drop and fluid change. There are people who have had it flushed without any problems, there are others who within a few weeks have had it in for a rebuild.

If you aren't confident to service it correctly yourself and take it to a 3rd party, don't take it to Jiffy Lube, have a reputable tranny shop to do the service. They can also do an inspection during the service to make sure everything on your car is working correctly. It will cost you more, but it will be done right. With rebuilds in the $2-3k range last time I checked, spending more now will reduce headache later.

My two cents. Maybe more experienced people can chime in.

Thanks man,
I had a flush on my 00 GP SE at 60k with no problems, thank god!

I have an 04 GTP Comp G that my dealer recommends a flush at 30k. I'm at about 28,500 now so it's not too far off.

Thanks again,
Brick

The filter service interval is 30k, not a flush interval. Tranny flushes are BAD NEWS. The reason service places suggest them is that they don't have to get messy and drop the pan. Flushes don't "back flush" the filter like they claim. The only trans service I recommend is a pan drop and filter change.

The filter service interval is 30k

Did GM change that with the '04 and up models Rich?

With the '97 - '03 models there has never been any recommended interval for the tranny whether ATF or screen filter at that mileage. It was 50K under severe operation (police & taxi), etc. and 100K for normal as specified in the owner's manual.

I did all of my first pan drops and screen filters around 40K - 50K miles. Never performed any flushes whether full power or fluid exchange.

Dealers recommend or do flushes to make money.

Is there a raw, proven number on the co-relation between flushes on low mileage transmissions and the need for major repair work?

I'm just saying that 50kish-80k is the yellow zone and 100+ is the don't ever exchange or flush. It's in that green zone I guess of up to/around 50k that I wonder about. Not that I'm doubting you, but I am just curious more or less.

Is there a raw, proven number on the co-relation between flushes on low mileage transmissions and the need for major repair work?

Other than a general concensus in this forum probably not. There have been a lot of horror stories. Some had success with flushes. But first the data should be split or differentiated between what type of flush are we referring to? Technically there are two types performed or even recommended by GM. There are different flush fixtures used by GM dealers, trans shops and the fast lube places. GM only recommends two specific types.

They recommend one brand of fluid exchanger (Wynn Transerve) and one brand of flusher (Kent-Moore). Then on the flushing it was recommended only if there was a transmission failure or problem, otherwise not for routine maintenance. Also, GM only recommends a certain approved flushing detergent to encapsulate fine particles which is used with the real flush machine. The fluid exchanger which is technically not a flusher will not remove particles because it is low pressure and uses the tranny's pump.

I believe the bottom line is this, GM only recommends flushing if there is a problem, otherwise they only recommend a fluid exchange using the Wynn Transerve or similar probably to get all ATF out to include in the torque convertor which is really only for convenience and ease of maintenance.

Most of the flushes ever mentioned are not real flushes but fluid exchange. The fluid exchange doesn't sound too kosher to me and IMO a pan drop consisting of replacing at least 7.5 quarts of the ATF and screen filter is better for obvious reasons.

Thank you all very much! That's a lot of great information for the future.

When I get closer to 30K, I'll talk to my dealer service center about a fluid exchange and screen replacement rather than a flush then.

Thanks again,
Brick

Yes, a clear distinction should be made between flushes and fluid exchanges. The flush is meant only for major transmission failures, and is actually intended for the cooler and cooler hoses/lines to remove debris from a transmission failure. The fluid exchange offered by Wynns, BG, etc. Is merely that, a changing of the fluid. While I am unfamiliar with the Wynns machine, I use a BG machine regularly and the beauty of that machine is that it connects via the transmission oil cooler pressure line, and uses transmission fluid pressure to accomplish the fluid exchange. No outside source of pressure or "back flush" is involved, it simply uses the "old fluid" to push on a diaphragm which in turn displaces an equal amount of clean new fluid into the transmission. Done correctly, one ends up with a 1:1 replacement of the fluid, and typically we use 10L of fresh fluid. BG recommends a "flush agent" to be run in the transmission for 15 minits prior to the exchange, and that is where I deviate....I use the machine simply to change the fluid without any flush agents. While the filter screen should be changed and the magnet (if equipped) checked for metal debris, the fluid exchanged during a filter change is often less than half of the transmission contents. Ideally one would alternate between fluid exchanges and filter changes on whatever maintenance schedule you feel comfortable with, or in a perfect world a filter change WITH a fluid exchange.