Need advice ford trans

[NortheastPest]

Hi all. My father in law has a 99 ford f150 and calls for mercon v.
The truck has 120000miles and of course the trans was never serviced.
He is hesitant to do it because he thinks the trans will go if we flush it.
Fluid is not burnt but is discolored. I guess it would be brownish in color. Truck shifts fine. Should I flush or just drop pan, replace screen and refill? Should I just leave it alone all together? I believe it's a 4r70w. (not sure if I got the model right) if I change fluid what brand? Thanks in advance!!!

 

[bepperb]

No question I would buy a new gasket and drop the pan. What you do from there will probably depend on what you see, but you can't go wrong with a couple drain and fills.

 

[brian12]

Do a couple of quarts at a time. Change two quarts, drive 500 to 1000 miles and then do another couple. Just keep doing it till youve gone through however many quarts it holds.

 

[Cutehumor]

a couple of pan drops every few months is what I would do especically since the trans shifts fine.

 

[NortheastPest]

I agree so far. I'm going to do a few drop and fills. Any additive that could be a benefit? I never had a trans that had mercon v so I'm not familiar with this oil

 

[Donald]

The only additive I would consider would be Auto-Rx. But you should run it for the mileage listed in the directions which is 1000 or 1500 miles (I forget) then get it out along with whatever has been loosened.

A Magnefine filter will catch most of the crud yoru new ATF and/or AutoRx is loosening. Good investment of $20.00.

 

[c3po]

I ran auto-rx in a 4R75W trans with great results.