I've got 2 2001 Expys, 4x4, big engine, and both are right around 65,000 miles.

One of them has been pulling a 4000 pound trailer from one side of the country to the other and I'm guessing it has 30,000 towing miles on it.

Was doing oil changes to both last night [M1 5W-20 and M1 filter] and decided to check the front axle fluid. The fluid in the Expy that has been doing a lot of towing was slightly orange and had slightly more 'odor' of the Expy that doesn't tow much.

I'm wondering what the best fluid would be to replace the front axle fluid in the Expy that tows a lot. My SO picked up some 75W-90 from AutoZone or one of the chain stores but I'm wondering if I should buy the Fort dealer product, or find some sort of synthetic?

Also, both fluid levels were about 1/2 inch from the edge of the fill hole. IIRC according to the manual there is a specification for the fill level. What do the rest of you do?

 

I would try the LUCAS brand differential oil.
I think is has synthetic in it.

 

I have used M1. Just drained the front and it looked good, did not need to be changed after 30,000 mi. I am sold on M1 synth. I am changing my transfer case to M1 Mercon. I drained it at 30,000mi and the fluid was burnt, so I put some dino Mercon in it to clean it up some, then add the M1. I would plan on at least changing the transfer case also. What does the rear axle look like? If the front is a little burnt the rear is most likly do for a change also as it is turning with power applied to it all the time.

 

I would replace all your fluids with synthetic (both diffs, t-case, trans and motor). I havent done it yet but people are reporting milage gains after doing it, usually with royal purple. I'm picking my new (98) exp next week and thats the first thing Im doing to it, then shocks and tires.

 

double check your owners manual, my 98 takes75w90 in the front diff and 75w140 in the rear diff.

 

I changed the rear differential oil a couple years ago on the Expy that pulls the trailer.

The rear end was making a low pitched noise for a while and when I got to the easy coast one time it was leaking on the floor. So I checked the preload on the input shaft and it had never been set properly, it was loose.
A few days later, new crush washer, seal and fluid with modifier and I was good to go. There are a couple of tools you can make to do the job a lot easier.

I forgot about looking at the transfer case fluid, I'll check that now.

What's the best brand and source of fluid for it and the front axle?

When you say M1 could you be more specific?

 

I believe they mean Mobil 1. It has a synthetic blend to it. I got mine at Advance Auto and it was around $15 for the 75w140 and $9 for the 75w90.

 

With regard to the best fluid for the transfer case of a 2001 Expy w/ 4x4 and large engine, I called AutoZone and the have Mobil1 transmission fluid spec'ed as Mercon 5.

Since I use plain mercon in by transmission, would the Mobil Mercon 5 be OK to use in the xfer case?

There is just a seal between the xfer case and the transmission so there is a possibility of mixing?

 

I used the Mercon Mobil 1 in my transfer case. I think the automatic 4x4 is hard on the transfer case so the fluid gets a work out. I used castrol MerconV in my transmition, and I used Mobil 1 in both axles.

 

Omahastro1, what year is your Expy?

 

Front and rear axles, transfer case, engine, and transmission; I use only the Motorcraft brand of fluid (& Motorcraft additive for the rear axle). The tcase needs to be changed with the newer approved Mercon 5, so I use the Motorcraft synth version of this, and I change it every 30k minimum, the tcase takes a lot of beating and load, so don't wait and use Ford's longer interval, besides it's only two quarts of fluid. All fluids are available at Walmart now, cheaper than the dealer.

 

At WalMart, I found the Mobil 1 brand of synthetic Mercon that on the bottle says it's OK to use in place of Mercon or Mercon 5.

I use Mercon in the transmission, my Expy is a 2001 and since there is just a seal between the transmission and the transfer case to keep the two fluids from mixing, I'd like to be sure the 2 fluids I use in each place are fully compatible.

I'm getting ready to change the transfer case fluid to the Mobil 1 Mercon replacement and the front axle to the mercon 75w-90 synthetic in the next few minutes.

Then we're going to pull the trailer down to SC for a couple days at the beach and then out to CO on the southern route, maybe, if there is bad wx in the forecast. Any neat places we should see on the way?

 

Just pulled the 'fill' plug from the transfer case and a lot of very dark fluid came out indicating that fluid from the transmission is migrating into the transfer case.

Next I pulled the 'drain' plug and drained the rest of the fluid.

After draining, there doesn't seem to be any further flow indicating that the leakage between the xmission and the Tcase is slow.

I think it is a good idea to pull the transfer case 'fill' plug every couple oil changes to check on the seal and to establish/maintain a proper level.

 

Be sure you have right stuff to transfer the fluids.

Also the union guys at the factory tightened the ft axle drain plug so tight I was afraid I'd break it getting it out. Had to use a 2 foot cheater to loosen it.

 

Should be using anti-seize on both of those plugs. You won't have a problem removing them next time.