Transmission Drain & Flush or No?

[hntndawg]

My philosophy is if it has had regular scheduled transmission maintenance, then I will keep it up. If is has gone well over the schedule, especially if it was worked during that time, I leave it be. I changed the fluid (not flushed) on my 1990 F350 knowing it was well overdue and shelled the transmission in a few days. I have also seen this happen on a couple others that friends or family have had. Was told by the transmission mechanic that it had something to do with fresh fluid leaking internally.

[Fightinaggies]

I’ve always done the drain, clean pan up with engine cleaner, change filter/gasket and refill job. Never has it been a waste of time. Hell its been recommended by my mechanic over the flush.

I’ve always heard bad things about a full flush on a higher mileage transmission that hasn’t had regular maintenance.

This is exactly right, drain and fill. NEVER full flush one that old that you haven't been meticulous on the maint.

[Scubasteveo]

Never flush a high mileage transmission. I know this sounds crazy, but all that dirt and grime in there is actually helping hold the clutches together. Once you try to flush it it removes it all, and your transmission will start slipping, and be burned up shortly after. I don't even trust flushes on new ones after talking to buddies who own transmission shops. Always drop the pan and refill.

[Mike D]

As already mentioned, drain, filter, refill.

You don’t want to be doing a flush with that many miles in it.


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[175gr7.62]

The reason a "flush" can cause problems on an high mileage un-serviced transmission is the instant addition of full strength detergents and the loss of friction material. As you clutches wear the friction material remains suspended in the fluid so they still tend to "work". The fresh detergent load will clean the gunk and glaze that has built up and then goes into suspension in the new fluid. You now effectively have "trash" floating around inside the transmission.

Even on a well maintained transmission I would never do a power flush. I service my F250 every 60,000 miles by disconnecting the line going from the tranny to the cooler and let the pump push out old fluid and top off. Repeating until the exiting fluid is clean an bright.

[Fordnandez]

I did the "flush" at home method. I found a video on youtube. If I recall correctly I disconnected one of the cooler lines that dumped into a 5 gallon bucked. I had a helper with me pouring in new ATF fluid in as I periodically shifted through the gears to try to get as much fluid out of the torque converter as possible. Now that I think about it I did drop the pan since my filter was inside the transmission. The only bad thing about doing it this way is that you go through a bunch of fluid to get the old fluid out because you are mixing the two.

You might want to start off with an oil analysis from a company like blackstone labs to see if you even need to replace it. The analysis is like $30 bucks so not super cheap but wont break the bank either.

Now that I am typing this all out I think I am about at the 100k mark on this fluid which is what Amsoil shows to be the life span of their fluid. Looks like I will be doing a flush in the near future.

[KX500]

Yeah transmissions are one of those things you might think - it can't hurt to have it serviced, right?

Last time I did that, I was replacing a transmission within a few weeks.

As our newest vehicle (2016 Nissan Rogue) was approaching 100k, I remembered it has a CV transmission, which Nissan has had some problems with. After realizing how much a dealer would charge to replace fluid (at $25+ per quart), I just did it myself - twice. Pretty sure trans holds about 8 qt, of which only 4 qts comes out when you pull the plug. So drained it once, put in 4 quarts, drove it maybe 1000 miles and then drained it again.

The fluid that came out the 1st time did look pretty grungy. The fluid that came out the second time, looked really good. Not entirely sure the 2nd drain was necessary.

And since I replaced fluid that looked really good, with new fluid, I felt pretty good about it after all said & done.

Easy to change.

[droebuck]

I’ve always done the drain, clean pan up with engine cleaner, change filter/gasket and refill job. Never has it been a waste of time. Hell its been recommended by my mechanic over the flush.

I’ve always heard bad things about a full flush on a higher mileage transmission that hasn’t had regular maintenance.

I have always done the same on all my trucks and never had any transmission problems. Dad and Grandpa are/were both mechanics so the flush was not an option when I was learning. I did have one issue on my wife's Tahoe where the factory torque spec on the pan was not tight enough and some of the ATF leaked out the week after I serviced it but I noticed and fixed it before any damage was done. It really irritates me that they don't put drain plugs in the pans anymore, it really made draining a cleaner job.

[muzzlebrake]

Never ever back flush an auto tranny else you will be buying a new one or having the old one rebuilt. The ONLY way to flush and clean an auto trans is to remove and clean out the pan, replace or clean the filter if present. Especially true for Allison transmissions. Trust me! I know all too well what they cost
There is a lot of clutch band particles that get deposited in the pan over time and back flushing from the radiator will stir this mess up and send it all up into the valve body and other parts of the transmission leading to a rapid failure.

[RebeccaCreekKid]

Thanks fellas

Will drain and fill and see how it goes/what the fluid looks like. No filter in Nissans, so holding off on dropping the pan for now. Thankfully it’s an old enough design to still have a drain plug.

[coker737]

Sure. Normal Service