Okay, going to be doing the rear differential fluid changeout it is a 2004 fx4 6spd manual and has the 3.73 limited slip.

whats a good oil to use?
whats a good friction modifier to use?

 

Many of the Pros on this site use Mobil 1 Synthetic (75-140). So I did too. From what I read you don't need a friction modifier as its already has some in it. MoyockPowerstroke
showed me a site (www.partsguyed.com) that sells an Ford aluminum axle cover for $50.00. I ordered that too as I do a lot of towing and I found the axle fluid gets very hot. The seller is on this site somewhere.

 

Thanks! Randy777

 

I really enjoy the amsoil that I put in. Its in both diffs and transfercase. One thing is that the 4X4 is not as loud now.

 

Rule of thumb:

The cheapest name brand (not off brand, not store brand) like Chevron, etc. synthetic of the right grade beats the most expensive / best dino.

 

I used Motorcraft SAE 75W-140 Synthetic Axle Lubricant along with 8 oz's of Motorcraft Friction Modifier (by the book).

Ford can't holler if you use their stuff.

 

Does anybody have a link to a DIY writeup on changing fluids in the rear/front diffs?

I should get this done.

 

Here's a good one for ya!
Welcome to guzzle's Rear Differential Maintenance Web Page

 

Awesome! Thank you!

Now how about something similar for the front diff and the transfer case?

EDIT: I better see if there's something in Mark's spreadsheets about this.

 

Welcome to guzzle's Rear Differential Maintenance Web Page

Welcome to guzzle's Front Differential Maintenance Web Page


Front and rear. I know this is a 4 year old post, but may help someone.

 

I have tried front diffs at 100k, 200k, and 300k intervals. Of course it all depends on the 4wd usage,, but when I dropped my fluid at 100 n 200k,, it was still clean. So I have been running a 300k mi interval on front diff fluid. But time and cost are factors for the front diff change (the front diff gear oil is much cheaper). But 100k is enough to burn the best fluid in the rear diff. I've tried Amsoil, ford, and Mobil 1. I only put full synthetic Mobil 1 75w140 LS now. No friction modifier needed(the LS stands for "limited slip", which means the modifier is already added), the 140 is almost $20 a bottle. Mobil 1 full synthetic 75w90 in the front diff. No need for any friction modifier in the front also. This is what I have been doing in my personal truck. It's got a couple miles on it and all is well. Just my input on it.

 

The red is the understatement of the year.
You have just a few miles on it. I used the same in mine and right after
I was getting the sound like I was short on the LS additive. I put in 1/3
more of the Ford stuff a little at a time and got to a point where is quieted
down and stopped. The rear end seems to be very happy and does a good
job at locking up when needed. The stuff I drained out was not in bad looking
shape. I think it may of been done in the past. The truck had 140K when I
got it and I changed it at about 150K. That also gave me the chance to check
both covers and make sure that I did not have any rust problems. Everything
was nice and solid. Cleaned then up, primed and painted.

On other things. Anthony what the status on the new shop?


Sean

 

I changed my rear dif just after I bought it (around 145,000), and it was pretty nasty. I doubt it had ever been done before and I replaced my cover with a Mag-Hytec cover and the Mobil-1 oil with just a little modifier and it is noticibly smoother. People take their differentials for granted untill it's too late..

 

In my life time as a licensed driver I have chewed 2.
The first was my 67 VW Beetle and the second was my
79 Bronco.


Sean

 

Good stuff, I believe I'll be going by the book on this one