SLAYER6708

Hello I have a 1997 f150 4x4 and I want to change the oil in the diffs, the book calls for 75w90 in the front diff and 80w90 in the rear diff. I'm going to advance auto and they have 75w90 in syn and 80w90 in regular, is it OK to put either or in both? I have searched and have not found an answer. Thanks for your help!

w0lvez

The Rear Differential recommended Viscosity is 75W140. When I tried to used 75W90 on my Rear Diff it's making some noise which you can hear inside the vehicle if the Stereo is off. If you used Regular oil it will damage the Rubber Seals on your Brake when they leak. The Tag on the cover says Use SYNTHETIC FLUID ONLY

Shake the bottle of the Synthetic to give you an idea. If your Differential was not submerge in deep water much better not to change until you find a 75W140.

SLAYER6708

So 75/140 in rear then? Did they change the spec or am I missing something?

SLAYER6708

I didn't get a chance to crawl under the truck yet to look at the tag.

w0lvez

1996 Limited Slip is using 80W90. If Synthetic is not Required 80W90 Regular. If you want to use synthetic it's preferred to be 75W140.

Do you have a manual included with the vehicle?
Consider Replacing the Wheel Bearing as well because you will need to drain it again to remove the axle lock.

Wheel Bearing Failure = Total wreck Diff

SLAYER6708

My rear axle is 3.08 open diff, and yes I do have a Manuel

w0lvez

Is the manual says 80W90 without the word Synthetic it means Regular. Just shake the bottle of 80W90 regular & 75W90 Synthetic.

w0lvez

For Axle Ratio 3.31, 3.55
TSB says to to replace the old fluid with 75W140 Synthetic. Try downloading a manual sometimes there are revising it due to some errors.

TSB 05-23-3 Rear Axle Noise Repair

Carcrazygts2

Open diff uses 80w90. 75w-90 will be fine.

SLAYER6708

Thanks for the help guys!