i have a 1998 E-250 van with a limited slip differential. i need to add differential fluid to the rear axle till i have time to deal with a leaking seal on the axle.my manual states that model 60 ,70 axles require 80-90 gear lubricant while the 8.8 and 9.75 axles require synthetic. what do these dimensions refer to and how do i identify the type of axle i have. i know the obvious answer but there is not much left to the identification tag on the housing. thank you

 

The sticker on the drivers door will state what differential you have.

The numbers 8.8 and 9.75 reference to the diameter of the ring gear.
Thus call the 8.8 rear end.

Models 60 and 70 are reference to Dana manufactures model numbers.

If you have the 'limited slip differential', you need to add Posi-trac additive to 80-90 weight gear oil. With Synthetic's, you don't need to add the Posi-trac.

You have a '98 E250, there is a good chance you have the Dana 60 back there, if you have the heavy duty weight package.
70's were used on E350 one tons and Dulles.

 

i checked the sticker on the drivers side door and under axle it listed B4 does that translate to one of these differentials?

 

Here is a link to the diff codes. You have a 3.73 limited slip, but no info as to which axle.

However, at the bottom of the chart are some pictures of the shapes of the different rear ends. The 10.25 Ford has 12 bolts and the Danas have 10. If you have a Dana, my guess is that it'll be a 60. (I had Dana 60's on 2 Mopar Street Hemi cars a few years ago.)

What rear end ratio is in my Ford , do I have positraction? - Drivetrain

You will likely need the additive, but a lot of axle lubes (like Mobil 1) already contain limited slip additive so they can be used whether or not you have a limited slip unit.

Good luck,
George

 

B4 — 3.73 ratio, limited slip (Dana)

 

thank you for all the help. it is amazing the depth of information available thru this site.it is a 10 bolt cover with a D shape gasket so it appears to be a dana 60 rear end.now my next question when i change out the fluid if it was 80/90 gear lube can i switch to a synthetic lube.

 

Should be no problem, and like I said, Mobil 1 and very likely most other syn fluids will have the LS additive. Use the proper weight (and something like a 75/90 would be fine in place of an 80/90). Only app I know that does not want a syn lube is an Eaton Posi, which I had installed in my van in the first month I owned it. (Out of dealer stock for a great price with an open rear axle.) For some reason Eaton specifies non-syn fluid--it is the same posi I had in my 60's and 70's GM musclecars and a couple Vettes.

Lot of great guys on this forum with a really wide range of deep knowledge.

Take care, and drive safe,
George