Voyager - Differential Fluid

The differential is lubricated by the transmission fluid, which, yes, needs to be changed periodically. Use ATF+3, *NOT* Dexron or any other fluid.

You must drop the pan to change the fluid. Many transmission shops can WELD a plug to the transmission pan once you get it off, so that you can more easily drain it in the future. Do NOT use any other kind of plug, and make sure the one they weld in is the type that you use an Allen wrench to get out, and that does not project out past the bottom of the pan.

Also, you should check the transmission computer, and if it is the original, non-flashable computer, replace it. The replacement is part# 4796122 for a 1990-1991 minivan transmission on a

3.3L or 3.8L engine, and 4796121 for a 1989-1991 minivan with a 3.0L engine. You could probably find one easily in a wrecking yard.

Ted

But since most manufacturers recommend channging the filter along with the fluid, the drain plug offers precious little advantage and is just something to get knocked off and cause you to lose your oil and then shortly after your transmission. Just loosen the pan bolts and pull down the lowest corner of the pan. The oil will drain almost as neatly as if you had a drain plug.

Matt

I have just drained and refilled the transmission fluid 3 weeks ago. I replaced the filter as well. I used ATF+3 purchased from the dealer. I gather by the responses that the transmission fluid serves as differential fluid as well, so there is no separate differential fluid to replace. And it's indeed quite some work to drop the pan, clean up the pan and the magnet, re-seal, etc.. A drain plug would have been very handy (if you do not plan to replace the filter). Thanks for the tip.

Hmm... the tranny was a reman one put on in around September 2000. But the transmission controller module was not replaced. Should I replace the computer, or just has its software upgraded would suffice? Thanks for the info on part #'s. Where is the transmission computer located? can I easily check the part #, or I need toi take it to a shop to check?

Even if you do drop the pan and replace the filter, the drain plug would still have been handy since it would prevent much of the mess of dropping the (full) pan. This (cost?) decision seems to drive customers toward the "dealer power flush" approach thereby leaving all that debris in the bottom of the pan and the dirty filter to contaminate the new fluid. I personally don't know what they were thinking when they saved the dollar or two by not adding a drain hole/plug.

Bob

The decision was made for the 1964 model year, long before there was any such a thing as a "dealer power flush". I agree that a drain plug is nice to have, but adding one is so easy that I don't see it being worth griping about.

Bad bad bad!!! Unless, perhaps, at some time in it's past life it had the trans computer replaced? But if it's the original you got to get it replaced! The original one has bad programming that will make the transmission wear out faster.

If it is upgradable, then having the software upgrade done is equivalent to replacing it. But the original computers (ie: tcms) were NOT flashable.

It is real easy to find. Open the hood, look at the left top of the firewall. There's a box there with a big cable, lots of wires, bolted to it.

Here's some pics off Ebay:

Here's the original one:

It's kind of hard to see but notice how ALL sides of the box are SMOOTH. The connector in the center is where the wire bundle goes.

Here's the newer one:

Notice on the left that it is FINNED. See also among the fins the 4 metal tabs? Those are heatsink tabs. Flashable TCM's that are pre-1996 have FOUR of those heatsink tabs. TCM's that are POST 1995 have SEVEN tabs and WILL NOT WORK.

Basically, ANY flashable TCM that is pre-1996 will work in your van AFTER it has been flashed to the correct firmware for your model year and engine size. The TCM must have the "pinion factor" set for your vehicle, as well as be put into a "quick learn" procedure. You can get refurb TCM's from the aftermarket or the dealer, with the correct firmware, (but the pinion factor and quicklearn will not be set) or you can find a used one in a wrecking yard (they are not uncommon) and take it to the dealer to be checked for firmware load and pinion and quicklearn.

Also, you pretty much need to go to the dealer for the firmware load since the dealers are the only ones that have the equipment as well as the firmware. Around here they charge $80 for labor if you were to drive your van in with a wrecking yard TCM on the front seat, ready to update and install, and have them do it for you.

Tranny places that deal with these transmissions regularly usually get TCM's from refurb houses that are correctly firmware loaded for the vehicle, and simply use a professional scantool to set the pinion factor and quicklearn.

Also, wire in cavity 49 of the tcm connector must be CUT when installing the new TCM.

The part number is on a tag that is on the bottom of the unit, use a mirror and read upside down and backwards.

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Matt, please explain how you knock off a welded-in plug that does not project out past the bottom of the pan. That would be an interesting one.

Do you really enjoy shower baths of ATF? :-)

Ted

I've not seen a plug that didn't extend past the surface of the pan. Do yoy have a picture of one of these plugs that you can email to me?

I don't know as I've never taken one. I find it fairly easy to carefully pry loose one of the low corners of the pan and let the oil come out. Changing the oil filter on my K1500 is a lot messier than dropping the tranny pan.

Matt

I would have to crawl under my 68 Torino to take a picture. The last time I changed the fluid in it I took the pan to a transmission shop. I think they simply welded a nut and washer inside the pan, but it's been so long ago I can't remember exactly what they did. An allen screw threads into the nut.

There are fancier pans like here:

that have fins that project up past the head of the drain bolt.

If the pan is gasketed then your fine. But if it's RTV what happens is you pull at it and pry at it and all the sudden it lets loose and a bunch of fluid comes out. Sure you can avoid it if your expecting it (I was) but why not put a plug in there when you have the pan off?

Ted

That is why you don't remove all of the bolts before pulling the pan loose. I generally leave at least a couple in and don't back them out more than 1/4" or so. That way the pan can only move that far when it comes loose. I'm not against a drain plug, I just think it is a waste of money and unnecessary.

Matt