I agree fully with Disco Mike, Drain, refill, no filter. The added boost in flow and pressure that you will recieve with a flushed system will likely start blowing seals and affecting the shift servos. With Trannys, you service them at the prescribed intervals, and thats it. If you, or past owners did not follow the intervals, especially after 100,000 miles, then its best to not start now. just drain, refill, and thats it. Hell, If my fluid was clean and not all brown and smelled good, I wouldnt even do that. Chances are your disco will make it much longer with the fluid thats in it, than if you flushed it, or drained it.

 

ok guys, the reason you should be carefull flushing a tranny after 60-70k miles is that the friction material on the clutches is deteriorated and floating around in the oil. When you drain the fluid and put new "thin" oil in the transmission you loose all of the lost friction material. This could cause your tranny to not work at all, or not well. However on the flip side some trannys hold up and can be changed no problems. I would say that it is a risk you have to weigh out.

 

I would think the tranny filter would remove these particles from the oil. Especially clutch band material. If it didnt, then the small passages and ports would clog very quickly, and cause shifting problems, or the lack thereof. Either way, its pretty much the same conclusion, dont change the tranny oil.

 

All of these reasons not to change the trans fluid and filter are all wives tales.
Change the fluid every 50k and the filter every 100k.
If you dont know when the filter was last changed, then change it and start from there.

 

Go ahead and go for it man, take it to the local service shop and get a full system flush and a new filter. Then tell us how it goes. You can be our guinea pig. And whoever was wrong can foot the bill for the repair.

 

After 60,000 to 80,000 miles, I would suggest you change the fluid every 20,000 miles simply cause the original factory recommendations are based on a new tranny, the older they get the more the need for fresh fluid.

 

1) I'll just pass along FWIW that the GM rebuild manual for their TH350 touches on this subject and their research shows it's always better to change all the fluid rather than leave it in ...which many old-timers would recommend. You get rid of suspended particles which lead to increase wear and they say failure unless it is near failure anyway, isn't increased.I always replace all the fluid on my tranny's, even on usedvehicles and I've never had problems.

2) You can get all the fluid out on your own. Drain and replace the fluid like normal, but don't start the vehicle. Adda couple extraquarts, then remove the cooling line at theradiator (or tranny cooler, whichever is easier). Hook a 2-3ft clear plastic hose ontothe line (and/or radiator)and put it into a 5gal bucket. Have a helper start the vehicle and the fluid will flow into the bucket. It comes out quickly and doesn't take much more than 15 seconds. Watch closely. Oncethe fluid color turns to clear red, and it's obvious when it happens, have the helper shut the vehicle off.Reattach the lines and fill the tranny to the right level. What's happening is the pump pumps through the radiator and back to the tranny. This way you intercept the fluid that was in the torque converter before it makes it's way back to the tranny. The torque converter doesn't run dry because new oil is pumped from the pan through the tranny. I do it all the time. I've got a bunch of vehicles too and several over 200k mi. Just a tip