Auto trans fluid, flush or change?
 

Like the title says, I've got about 130k miles on my 91 4runner and I'd like to change the tranny fluid. There's quite a bit slip when it changes from 3 to 4 until full throttle. I pulled the dipstick and the fluid looks OK, no specks or metallic flakes. I called some transmission shops and they said if it's over 50k miles don't flush, just change gaskets/filter and top it up. What should I do? This truck is my highway commuter so it has to be reliable, I can't afford to drop the transmisison in a few hundred miles if the flush brings out some problems.

Shop is right.

:wabbit2:

Flushing can lead to serious problems when that much new fluid and detergents are introduced to a trans that has been neglected. You think it's slipping now, well........

Dropping the pan, changing filter and adding whatever you need to top it off is what I would do. Even then your taking your chances.

Do not flush it, some of the manufactures out there say to never flush, I dont know if Toyota is one of them, but yes it will cause more problems on a neglected transmission. If anything just drop the pan and change the filter like the shop says, but start saving for a new or new to you transmission.

Hasn't been changed in 130k miles, and slips quite a bit between 3 and 4.

Fluid looks OK? To the untrained eye maybe. But you're not looking for specs or flakes. You're looking for discoloration/darkening of the fluid, which I'm fairly sure is a dark brown to nearly black color at this point. And another distinguishing feature of over-worked ATF is a burnt smell, which if it's slipping that bad is going to be quite distinct.

The advice on not flushing is no good IMO. Dropping the pan and replacing the filter, then refilling it with the old fluid is a waste of time. And will solve nothing. ATF does NOT last forever, and it's most likely why the transmission is slipping in the first place. The friction modifiers break down, and shift quality suffers. If you planned on using new fluid to refill it, that's called flushing anyways. So you may as well flush it thoroughly. The risk involved with flushing the transmission, as in replacing the worn out fluid with fresh, doesn't necessarily involve the lubricity of the new fluid causing additional clutch slippage. New fluid will help shift quality, GREATLY in some instances. The concern is that any redissolved gunk will potentially clog hydraulic lines/valves and cause the transmission to have troubles shifting at all. In my experience this is a myth. Though it may happen occassionally, it's never happened to me. And I've flushed many automatic transmissions with up to or over 100k miles that have never previously been flushed. Successfully flushing your transmission can vastly lengthen it's operational lifetime as well as restoring it's performance qualities. On the other hand, if the damage is already done, flushing can't help that and will be of little use.

You can do what I would, and have done, in similar situations. Which is to go buy the filter and a case of ATF. Drop the pan, drain the fluid, and clean out the pan thoroughly. Re-install the pan, and refill the transmission with fresh fluid. Run it for 50-100 miles or so. Repeat the process except this time installing the new filter too. You'll notice that the first run of fresh fluid will also be pretty fouled from what's been left in the torque convertor, and all the residuals it's cleaned out of the transmission. You'll also notice the second fill will be relatively nice and clean, and will remain that way untill it needs changed again at the recommended interval. I've done this many times in my life, it's never caused any issues, and I highly recommend it. If you're especially concerned that the old filter won't have the ability to handle any more contamination before being clogged, then buy 2 and replace it twice. I've never done that, again it's never caused a problem and is a waste of money IMO.

BUT, if you have the money it can be handled by specialists who have the required equipment to flush even heavily neglected transmissions in a much safer manner. You apparently didn't go to one of them.

These are my personal opinions based on my actual experiences. I can by no means guarantee you that ANY flushing, meaning adding ANY new fluid other than what will be lost when you replace the filter or otherwise, is going to be a safe procedure. It's a risk you have to be willing to take. You're welcome to take my advice, or leave it. That's up to you.

Good luck!

whoa hold on there MudHippy, nowhere did anyone say to put the old fluid back in.

I spent several years in Lube centers as well as a transmission shop. I have seen at least 4 transmission damaged further because they were flushed and were acting up before the flush, since customer insisted we flush it, well....

Draining and refilling is probably only gonna change about 1/2 the actual fluid in there. I don't know off hand what the capacities are though so I might be a little off.

The problem is the detergents in the new fluid not the lack of friction modifiers in the old fluid. If any gunk is actually "holding" the transmission together actually helping the clutch packs from slipping or filling the voids in the gears themselves because they have been worn out more than they should be from not changing the fluid in a timely manner. The new fluid tends to wash this gunk out. Guess what happens then? The clutches slip more than when they did before the flush, or the gears make one heck of a racket now that you basically created a void in the gear sets.

One of the guys who helps me at my shop on a regular basis is a Toyota tech and he did not recommend I do anything to my 99 Taco auto tranny with 140k miles on it. He said flushing after 50k just causes more problems.

If it's already slipping, probably just postoning the inevitable regardless.

:wabbit2:

I'm not calling you a liar. And I do believe that CAN happen. I just believe, based on what's worked for me, that it can also be helpful. I happen to think that falls into another category altogether though. Which is why I included the words "On the other hand, if the damage is already done, flushing can't help that and will be of little use" in my statement.

Oh, BTW, I think that customer learned a valuable lesson. Which, as harsh as it sounds, he rightfully deserved. That being, respect your vehicle and it's needs. Or you will pay the ultimate price in the end. People that think that they don't need to keep up on the required maintenance of their vehicle should pay a higher cost for neglecting to do so in a timely manner. It was totally his fault, and not yours. He was on borrowed time anyway. But, to give the guy some credit he may or may not deserve, manufacturers can be very vague in stating what that maintenance interval is/should be in regards to automatic transmission servicing. The owners manual in my 98 Monte Carlo says that unless it's been used for severe-duty(extended idling, taxi service, steep hills, towing, etc.) that the ATF should be inspected every 50k miles and there's no need for it to be changed if you judge it to be in fair condition. Which is ridiculous, and undoubtedly leads many to believe that they shouldn't change the ATF when they should. Shame on the manufacturer.

Quite a good discussion here. :D Lots of good advice, let me just add my 2 cents. To me flushing or changing ATF would be a preventative maintenance thing just like changing motor oil. I wouldn't expect it to fix an existing problem.

Let's clear one thing up, this is going to a toyota dealer or a tranny shop for the flush, I am NOT going to do it myself. actually the fluid is still red and does not smell burnt at all.

trans pan drop and filter changes are easy. What I don't know on the auto truck is how easy it is to get that pan outta there. If it's anything like some chevy/fords that have either a crossmember in the way or an exhaust crossover in the way then it's a PITA.

Can someone tell me or direct me to the proper fill procedure for a third gen auto trans. I'm just doing a drain and fill and was wondering if I just fill through the dipstick hole. My truck is a 98' runner with a 5VZ. thanks guys

Yup, fill via dipstick hole, a long funnel with the right size end is essential. Make note of how much you took out, so you know how much to put back in. Then check the level and top up if required.

Should I stick with Toyota ATF or will any brand do?

You can use any brand of Dexron III fluid, should be around 4 quarts to drain and fill, most likely a tad bit more. Put in your fluid, start and go through all the gears pausing at each one for a few seconds, then check your dipstick with the engine running and trans in park, there is a cold mark and hot mark, you will want the cold mark.

Very good thread you guys have going here. But I must say that i tend to lean in the MudHippy direction as stated. Although I believe that I read that the fluid still had good color and no cooked aroma. Therefore its my belief that a flush will serve no purpose. Would be nice if it was actually the convertor lock up slippen? Buy the way what is the shift pattern? 1-2, 2-3, Convert Lock, 4? Interesting!