Transmission flush

Thread starter #1

tcward

Senior Member
I’ve got an 03 F150 FX4 with automatic transmission and about 185,000 miles. No problems so far with the transmission but feel like I need to change the fluid along with filter and new gasket. I have been told a total flush is better. I have also been told that a complete flush in an older tranny could cause issues??? What do you think? I know this truck had to previous flushes at about 75,000 and again at around 125,000? Thoughts?
 

Lilly001

Senior Member
The problem with a full flush at high milage is if the transmision is near needing a rebuild the deposits on the clutches may come off with the flush. They recommend only a filter change and refi on those older transmissions.
I figure it's going to go soon if all that's keeping it going is the deposits so I would do the full flush with a filter change and see what happens.
 

NOYDB

Senior Member
If it is going to fail, a fluid and filter change will not cause it to fail faster.
 
I built transmissions for 15 years at a ford Dealer. A transmission is a sealed unit. If there is a need in replacing the filter you've already got problems. I do believe in flushing the fluid. Use only Motorcraft Trans fluid tho as it's design with the correct friction Modifiers added to it. If you just feel the desire to change the filter, do the flush first, let it run and circulate the fluid for a awhile then drop the pan and change the filter. And you'll need to add about 6 qts back to the unit again.
 
That particular truck has a 4R70w transmission, a very durable unit, but you are nearing the end of its expected life, normally around 200k, maybe a little longer, if the fluid still looks decent ( not burnt and dark looking, or smells terrible) then it won't hurt at all to change the fluid, I prefer to change fluid and filter as opposed to flushing, flushing can sometimes dislodge particles that are stuck in crooks and crannies inside the unit, causing them to circulate and cause problems, a lot depends on the type flusher used, some use the vehicles own pump to do the transferring, some have a pump built into the flushing machine.
It likely won't hurt to flush that particular transmission, they aren't known for valvebodies hanging up on them. I agree either use ford fluid, or a good quality brand name equivalent, most of the oil change places use bulk fluid, generic no name.
Some manufacturers don't recommend flushes, Honda/Acura is one in fact that advises against them, but their transmissions are quite complicated and sometimes finicky.

p.s. unless that gasket has been swapped out in the past, it should be a reusable gasket, rather thick rubber with a metal core, its much better than anything you get at the parts store.
 
You should have the 4R100 transmission, as long as the fluid looks decent and doesn't smell bad, it won't hurt to do a fluid and filter change, I personally wouldn't want to flush that one, it could stir up particles that can cause the valvebody to act up.
 
What everyone needs to keep in mind is that changing the fluid and filter is a preventive measure, if you are having problems its not going to solve anything, and could potentially make things worse, most transmission issues today are not the result of not changing the fluid, most happen because of part failures, which won't be prevented by changing fluid.
 
It absolutely will cause it to fail faster.... Been there (was warned by a mechanic) and bought the T shirt!
If it's done correctly it WILL not cause any new issues. Does changing the oil on your truck cause it to Blow up?

Transfixer, I used a none pressurized system. The vehicle had to be running and at operating temps. I never had any issues. I loved the 4r70w's as you stated they are a great transmission and are easy to build. If memory serves me correctly the year model of the OP's truck is along the years Ford removed the drain plug for the converter. which to me always meant half a service unless you flushed it. Because 6 quarts of the 12 required in the 4r70w are in the converter.

To the OP, It's highly unlikely changing fluid either method will cause you a problem. Good luck.
 
fluid and filter and you should be fine. i wouldnt flush it with that mileage.
I have a two mechanics I have a lot of faith in, one a truck specialist, and the both refuse to flush a transmission with over 100K if it hasn't been flushed before.

What is important, as far as I am concerned, it to get all the old fluid out when you change the filter. That's what the Quick Lube places don't do because it takes extra time.

Learn how much fluid your trans takes, and if you aren't paying for that much, you are still driving around with old fluid in the system.
 
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