I have a 1994 12 valve auto. Truck has 320000 miles. I'm not sure which trans I have, but it's the original one as far as I know. Trans was beefed up/rebuilt about 25000 miles ago. My question is should I just change the fluid and filter myself, or should I have the trans flushed? I appreciate any and all replies.

Barry

 

If it is an automatic, it is a 47RH. 3 speed plus OD. Many shops have told me not to change and/or flush the fluid because it can cause transmission failure. I've never had that experience. Why would you want to change it at 25000 miles?

 

Changing filter and fluid in itself is not harmful, and is done to be beneficial...As a working mechanic I did so on many customers' vehicles with never a failure due to that procedure...In most cases there was almost always an accumulation of metallic particles in the bottom of the pan...Having said that, I bought my current ride in 2018 with 145000 miles on it...The Aisin commercial six-speed appears to be untouched, and the fluid smells and looks as new...After four years and an additional 31000 miles, I'll continue to drive it as is......Ben

 

Thanks for the replies. I thought the manufacturer recommended changing fluid about every 25000...........................This truck has been run pretty hard, and I thought it might be good to service the transmission, but I don't know a lot about automatics. My other trucks are 5 speeds......

Barry

 

There are two essentially risk-free ways to flush the transmission.

After the initial drain and refill (including filter replacement), you can run it a bit and drain/refill again. You'll need to do this two or three times, since new and old fluid will mix each time.

This other way is what I and many others do, which is to disconnect a cooler line at the front where it connects to the liquid/air heat exchanger ("cooler") at the front of the truck and do a "running flush" where you dump fluid down the dipstick tube while the old fluid drains out the open cooler line (run a hose from the open line down to a jug or drain pan to capture the drained fluid). The advantage of this is it's a "one and done" job, and the fluid follows the same pathway through the converter, liquid/liquid heat exchanger, etc, that it would in normal operation. It helps if you have someone to start and shut off the truck while you stand ready with opened containers of trans fluid so you don't have to move to the dipstick tube while fluid is already pumping out. Just remember to reconnect the cooler line at the end of the job and verify it is solidly connected.

 

This is only in situations where fluid is very old and never changed. The detergent in new oil will break lose all the scum built up in trans and some say it eats the glue on clutches. If it is in that bad of shape it is on its way out anyway. My suggestion is to goto Tractor Supply and get 5 gallons of "TDH" oil on the cheep and pick up a filter. TDH is Transmission Differential Hydraulic fluid. They do not usually label the buckets TDH but if you look on the side where it says compatibility it will say "John Deere HYGUARD". This is the best to use in 47RH because it has better lubricity and makes the clutches "Grippy" for more neck jerking fun. Reduces wear too. Detergent is lower than red fluid as well.

 

DO NOT FLUSH! Just change 5 Qts and filter. Adjust bands, that's it

 

I've got 470,xxx miles on my '95 with the 47RH trans. Trans was rebuilt at ATS, to an ATS Stage IV, in 2001, with 107,xxx on the Odo. I've changed my trans fluid religiously every 20-25,000 miles ever since then. But with this rebuild I can use Dexron, which is cheaper than the ATF +4 that I used to use before I had the trans rebuilt. Also, with the ATS torque converter, I can drain the T.C. It is amazin' how much fluid comes out of the TC. I always buy 4 gallons of fluid, and use 3-1/2 gallons in changing the fluid.

 

ATS -That's useful.
The transfusion procedure is the one to avoid