Okay guys, I picked up my '02 F350 about a month ago (I've put on 1,580 miles without noticeable fluid loss since then). I decided to start a baseline on fluids this weekend. Engine oil & filter (done-what drained out was quite nasty); Fuel filter (looked fine, but I had to buy a new 25mm socket to pull the Carquest fuel-filter off.); Front Diff fluid - that was some nasty gear oil that came out... it was also pretty low, it took about 2.75 qts to fill to the point of draining out the fill hole and I got less than 2 qts pumped out.

I searched, but didn't see any answers to these questions:

My first question.. I put in Valvoline 75W90 gear oil unto the front diff... was that a good choice?

Second: the Haynes manual gives me some choices on rear diff oil based on the shaft... I have no idea if I have a Ford 10.50 shaft, a Dana 80 axel, or a Dana 135 axel. The first (10.5 diff) takes a 75-W-140GL and the last two take 75W0-90QL and 80-90QL respectively.

How do I figure out what oil to squirt into the rear dff?

Next is the transfer case and auto tranny fluid and filter, so if a better choice than MERCON ATF let me know.

Thanks in advance, I'm new to the diesel world so forgive my n00b'ness.

 

The 75w90 for the front is correct. A while back, guys were saying the 75-140 synthetic could also be used in the front. Check out these links, and good luck.

https://www.ford-trucks.com/forums/9...d-changes.html

Welcome to guzzle's Rear Differential Maintenance Web Page

 

Thanks for the links. Do I assume I have the 10.50 shaft and LSD? I'm not sure how to tell.

 

Easiest way to tell what axle you have is look at the door sticker or crawl under the truck. The housing cover will most likely have a metal tag like the one pictured below.

My tag on the Door Jamb reads D1 as a reference


The L in the tag number indicates Limited Slip

 

I have 75w-140 in both of mine.
Check this out.Most use synthetic here.

Changing ATF: 7.3L PowerStroke Engine and 4R100 Automatic Transmission. - Diesel Forum - TheDieselStop.com

 

Thanks. I'll check tonight.

 

I just changed my front and rear diff's with Mobil 1 syn. gear oil. Do I need to put the friction modifier in them. I'm not sure how to tell if they are working right or not.

 

I think the Mob 1 already has the modifier in, when I changed mine I looked at the Mob 1, it should say on the bottle. Most of the ones that already have it added have too much & you end up with a one wheel wonder.

 

Thanks for the reply! I'll have to check the bottle out.

 

I'm doing all my fluids due to just getting my truck but darn, these F350's are so confussing I'm getting a headache with all the ifs and buts.

There was me thinking a commerical truck would be a piece of cake

Seriously I found it easier finding out what fluids to use when replacing on my Japanese Nissan Skyline GTR, I'm going to go with the Ford handbook lol! and get as close as I can in England

 

I checked the bottle out and it says that it is designed for superior protection in conventional and limited slip diff's. Does anyone know for sure that this is adequate for our applications and doesn't need a friction modifier? If it does need it, I hope I haven't done any damage to mine.

 

Mobil 1 shouldn't need any additional friction modifier. If it was necessary to add any, you'd know it by the shudder that you would feel coming from the rear of the truck with every TIGHT turn.

If you DID feel shuddering, you'd add a few ounces of the friction modifier and drive another few miles. If it still shuddered, you'd add a few more ounces and repeat. And repeat, etc. Once it didn't shudder, you'd have reached the optimum.

After using Mobil 1, mine shuddered for about a mile, then just stopped. I never added any modifier at all.

The front is never a limited-slip unit, and should not use any modifier at all.

Pop

 

Thanks a lot Marv! Sure appreciate your chiming in. Always appreciate your comments and wisdom on these issues!