Dark Brown Burnt Tans Fluid

First, thanks for the prior advice given about changing the transmission fluid. The van I just purchased has 75000 miles on it and I think has never had the trans fluid changed.

I have changed the fluid in the pan (5 qrts) with new fluid by sucking it out the fill tube. The fluid that came out was a very dark brown color and smelled burnt which I was not happy to see. The main question I have now is, how long should I wait before changing the pan fluid again?


I know that I have only changed less that half of the total trans fluid. Should I redo the pan fluid again right away or wait a few weeks to allow the new and old fluid to completely mix?


Also should I change the pan fluid more that twice to get a better mixture of new fluid in the trans?

One last question, based on how burnt the fluid is, should I drop the pan and clean it out or even have a complete fluid change done?

At this point I am concerened about the condition of the trans so any advice is greatly appreciated.

Thanks

Mark

Um, it is NOT suggested that you change ATF if ANY of the following apply:

1) It is over 75,000 miles old
2) It looks/smells burned (mildly or worse, very slightly is OK)
3) It has never been changed, and the transmission is acting "wierd" (shifting poorly, erratically).

The reason for this is that ATF contains calsium, and as the ATF ages, the addatives break down that "hold" the calsium in the fluid. It then migrates (deposits) onto the clutch material. This is made MUCH worse with excessive heat (towing, heavy loads, high ambient conditions, poor cooling). When you change ATF, the new has MUCH more calsium than the old. Old ATF is "aggressive", it grips well. New ATF is not aggressive. Two things happen, 1) the EEC knows how long a shift *should* take, with aggressive (old) ATF it has slowed things down hydraulically because the fluid is so grippy, with new fluid, shifts are much slower because it takes time for the EEC to adjust (very often too long) and you get excessive slippage on the upshifts and in converter "lock-up"; 2) Since there is now an overabundance of calsium (imbedded IN the clutches AND in the fluid) you have an even worse time with slippage. The calsium molecules act like tiny ball bearings, and the clutches just cannot grip as well as they could before. Once you have imbedded too much calsium into the friction elements, it's only a matter of time before they cannot generate enough friction to drive the vehicle.

I'm sorry to say, but your BEST bet is to disconnect the battery for 15 minutes to clear the adaptive strategies, and leave the ATF ALONE from here out.

Hopefully, you will get another 25,000+ miles of service, but I've seen an AT die in under 500 miles when the fluid was badly "burned" then changed.

Mark- the ATF in my 2001 LX was starting to darken & smelled pretty bad at 36K miles (right when I bought it). I did what you did. Pumped out 5-6qts thru the dipstick tube & added new merc 5 ATF. 2 weeks later I had the ford dealer I bought it from do a pan drop & filter change ($80). I agree with modmech, that a high milage, under maintained unit will often fail after a an ATF changeout, but this is not always the case. Some do, some dont. If your tranny performed fine prior to your 5qt changeout, you should be ok. Drive it for a few thousand miles & then do pan drop & filter change. If your AX4N is still holding it's own at that point, keep up on regular mercon V pump out & re-fills. The more often the better!
G/luck
Joel