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Trans fluid flush questions...

bradleyheathhays

NAXJA Forum User
Location
Lexington, KY
'96 XJ here and I've added a trans cooler up front but haven't tied the lines in yet. When I go to splice these into the return line of the trans I'd like to do something of a fluid flush at the same time. After I split the return line I believe the flushing process involves letting some fluid pump out then stopping everything, filling up with new fluid, then repeating the process until what's coming out is fresh red fluid. Couple questions...

1- How much fluid should I let pump out at a time before refilling? 2qts, 3qts?

and

2- What starts the trans fluid pump to pumping? Is it when the engine starts or when it's put in gear? I'm just wondering what I need to do to start and stop the trans fluid flow.
 
Usually a machine matches the in/out flow rates. The transmission pump is engine driven and can be damaged if you run it too low. I don't know of any real way to DIY flush your trans. I've seen people try it by draining (like you said) but filling through the dipstick tube at the same time. That's one of the very few things I'll actually take to a shop to have done.
 
I agree, the shops use a 2-compartment system that provides the same as what's being pumped out(under pressure).
 
In my humble opinion the best way not to kill your transmission is to drain and refill with regular old ATF that you can get at the farm store for $10-12 a gallon. Drain the pan, refill, drive it a few hundred miles/2 weeks, and do it again and again until its as red as you want. It will take a few times if your fluid is dark/bad. Normal drain and fill is 3.8 quarts. If your fluid is severely dark, burnt, or you have existing transmission shifting problems, don't expect miracle fixes.
 
Some argue that the best way to service your transmission is to flush it first, then drain and change the filter. Some say change the filter, then flush it. Some even say you should change the filter, flush it, then change the filter again! I'm not made of money, but I also don't want to replace a transmission. For the cost of a gallon of transmission fluid (dex 3, as the AW4 was designed to use) and a filter, I like to change it every 30k miles (as was recommended by the manufacturer). You won't experience transmission issues if you stick to that. 291k miles here on the same tranny, something has to be going in my favor.
 
The AW4 has a metal screen, not a paper filter. There isn't much reason to change it. I leave the screen alone and drain and refill the pan every 20,000 miles or so. It has 343,000 now.
 
As cheap as they are, I'll stick with replacing it. It may be just a screen, but it's a very fine screen and can still catch chunks and globs. For instance:

IMG_1595.jpg
 
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