I have a 1999 F150 V8 with 251,000 miles on it that I bought from a friend. Idon't know when the tranny fluid was last changed but it is brown. It mostly runs fine but sometimes it shifts hard. When I called a "mechanic" about changing or flushing the fluid, he advised me NOT to change it even though it looks pretty old, as it could damage my truck. Is this true or do I need to find another mechanic? I do not have a working knowledge of cars.

 

Change it. The 99 model has a torque converter drain. So drop the pan, install a new filter, drain the TC, and refill with about 11 1/2 qts. Or that is what it took to refill my 2000 4R70W. The pan gasket is reusable. Don't replace it with a cheap cork gasket.

 

I would change the fluid.

 

Change it. If the transmission goes, it was going to go anyway.

 

The brown color is clutch disc and band material plus deteriorated fluid.
You can't replace the wear so change the fluid to at least get clean fluid back into the unit.
The gears and metal parts still need lubrication.
Good luck.

 

Thanks for the advice.
I got a second opinion from a different mechanic who told me that I need to change the fluid a few quarts at a time because new fluid might tear up the clutches in the transmission. Is this good advice or does it need to be drained and replaced all at once, with a new filter?

 

It's not a given that it will happen because you have no way of knowing.
The clutch discs and band have been worn down from slipping and burning, from that slipping. This is the muddy color you see.
The old fluid is contaminated and adds to the slipping every time the trans shifts up under power because lining is in fluid suspension plus the fluid is worn out..
The new fluid does indeed create more friction on those linings that are left..
This could tare lining off their metal backings just from being so thin.
It's a gamble you take either way.
Running a trans to this point leaves you with this situation.
You have to accept whatever happens.
Change is slowly might be of help to get a bit longer life.
Good luck.

 

I'd change it. Fact is if its me I go to walmart and buy the cheap walmart fluid. I buy enough to change it twice. Change it run it for a few thousand miles and change it again.

 

Thanks guys. You have been helpful!!

 

At one time I was told that the old fluid had solids in it that helped keep it from slipping. Some of the transmission shops refuse to change the fluid in a vehicle that has ove 70,000 miles on it without having been serviced previously. Is there any truth to that?

 

Review reply #7.
The shops that does not want to change the fluid, does not what to be blamed for trans failure when it is not their fault.
It's as simple as that.
Good luck.