Right - I don't disagree that there are horror stories about people having their transmission fail after a flush. But, being that I am an automotive engineer, I have always wanted to know exactly why it had happened. The best thing I can come up with is that people take the car in when the transmission is already malfunctioning and then blame the flush when it does finally fail shortly thereafter. The fact that the new fluid is highly detergent and cleans the transmission deposits up, might speed up the process in a transmission that is already failing. But I don't think that the process of flushing the transmission itself does anything harmful - if done right. That is a big if, and there is always a risk when you let someone else touch your car - be it an oil change, a trans flush, or anything else. That, and $$ is why I have always done the work myself.

Piotr

 

As the transmission ages a varnish builds on the internally lubricated parts.

Then new fluid is put in - with all of it's fresh detergents (why do you think it's such a great engine flush?) and the varnish comes off and clogs things up.

 

It is true - ATF does have a lot of detergents added. It also has chemicals added that inhibit the formation of varnish. Truckers would sometimes add ATF to the fuel due to its cleaning abilities, but because ATF doesn't burn well, that practice actually causes a lot of problems. In any case, if you are changing the ATF yourself, and first put in 6 quarts and then another 6 quarts a short time later, you end upwith almost as much new ATF (and as much detergent)as if you had done a flush. So, shouldn't changing your own ATF 6 quarts at a timeremove the varnish and clog things up just the same?

Piotr

 

If you just change 6, you only get half new fluid. Do that again, you get half again, mathematically that would be 75% new at most. I plan on doing the fluid 4 times. This will give me 93.75% new fluid at best, and any more is too small for the time.This is a gradual change, not putting full detergent in all at once, slowly breaking up any deposits (dissolving them slowly). Not throwingn chunks.I use Royal Purplesynthetic that doesn't break down with heat or time. Iam a distributor, so I can afford to do it this way.I am not worried about the fluid wearing out, and it will stabilize any left in. It blends well with anything out there.

This is still used against the best possible flush method, using the tranny as the pump in a completely clean environment. If any other method is used, pressures will be different, increasing the chances for little bandits to dislodge and make their way to small parts and really mess them up. Even using new fluid with the tranny pumping could cause different pressures just from the new oil flowing better.

I just an electrical engineer that loves cars, so I may be wrong in my assumptions. This is just how I see it, and why I won't be doing or recommending anyone else to do a flush. A flush may be ok, as long as it is done regularly from new. Even then, I would still not recommend it.

That is all I have to say (and more). Hope this answered your question.

Jason

 

Well, it does answer the question. Just don't ask me if I think that this is necessarily the right answer. I know - I am being stubborn and not in the majority here at all.
I would have my trans flushed if it was being done properly on my 97k mile disco without worries, but as I mention earlier I don't like someone else fussing with my vehicles - especially if I have to pay them for it.

Piotr

 

Well, I thank everyone for all their info and feedback. I have one more question though. When changing out the fluid manually, do you just drop the pan, change the fliter, then fill it back up with the same amount of fluid you removed? I have been looking for the tranny dip stick to check fluid level and cannot seem to find it. Is it some place other than the usuall place under the hood?

Thanks,

Wm

 

No dip stick, but there is a "level plug" on the front of thetransmission pan and a drain plug at the bottom (no need to drop the pan unless you are changing the filter too). There is also a specific procedure to fill it to the required level which must be followed:

Make sure the transmission is completely cool - when you touch the pan it shouldn't feel warm at all. I believe that the spec is 20 - 40 deg C ATF temp. If you can't tap into the temp sensor, and don't have an infrared thermometer, then feeling the pan with your hand is all you can do - and good enough. With everything back together (drain plug back in) fill the pan through the level plug untilATF starts to run out of it (~3 qts). Start the truck, and go through all the gears and back into park - stay in gear long enough so it actually engages as you do this ~1 second. Keep the truck running. Now you want to quickly get back under the truck and continue to fill until the ATF runs out of the fill plug. Put the plug back in quickly. Now feel the pan again with your hand - if it is still cool than you did things quick enough and the level is correct. If it is already warmer than your hand, then you will have to check the level and possibly add more ATF after it cools down. To do this, start the truck again, cycle through gears, and with it running pull the level plug out, and start adding ATF. If the level was right, it should only take a little bit to have it start running out. Repeat after a couple thousand miles to get to about 75% new ATF as OkDisco mentions above, and you should be good. It helps to have a simple manual fluid transfer pump to pump the ATF into the tranny quickly. A local parts store likely has one and they are usually only $20.

Let us know if you have more questions. As you might have noticed this is not a simple thing to do and it does require you to get under the truck when it is running - chocks under the wheels highly recommended, and I usually wear ear plugs when I do this.
Piotr
PS: one thing to add: the level of ATF is much higher in the trans when the truck is off - if you try to fill it with the engine off you will not be able to put in as much as you have drained out.

 

Piot, you may already know that a full cast iron engine or trans will not contaminate the oil nearly as fast as it's aluminum counterpart
Have you ever worked with an older oxidized aluminum ladder and look at your hands?
As the contaminants/varnish start forming in the trans, they may slow the movement of the solenoids and or valving in the valvebody.
This in turn slows the hydraulic signal to the clutchpacks (ie sliding into next gear).
As the clutchpacks slip, they add more contaminants ,etc. etc.

I believe that if you change trans fluid every 30k since new, your fluid will never get the chance to varnish.
However, I'll bet most people don't.

You may remember when everything had large clearances,volume & lots of oil, if you changed @ 70-80k it was good for life.
(This is only my opinionand may or may not have any basis in fact)
lol all