Do I need friction modifier?

[Se77vN]

Hello, I am going to be changing my front and rear diff fluids this weekend. Not sure if I have a limited slip diff or not. I asked the dude at autozone whether I needed this, and he said I don't. It's just a 'treatment" that I can add. Is this true?? Or should I go back and get some?? Thanks, John

[jim henderson]

Don't know your model year, but the mid 90s F250s had different fluid front versus back.

The rear if it is limited slip will have a tag on it that I believe says blah blah L or LS somewhere in there.

Even if you don't put in the additive you can check easily. Just do some tight slow speed turns. I seem to get most obvious results while backing out and turning tight.

If the truck chatters then you need additive. Usually 1 toothpaste tube will do.

Chattering feels like the tires are grabbing or rubbing against the wheel well.

I forget what fluid is in the front diff. I think it is ATF but I forget.

Jim Henderson

[Se77vN]

Originally Posted by jim henderson

Don't know your model year, but the mid 90s F250s had different fluid front versus back.

The rear if it is limited slip will have a tag on it that I believe says blah blah L or LS somewhere in there.

Even if you don't put in the additive you can check easily. Just do some tight slow speed turns. I seem to get most obvious results while backing out and turning tight.

If the truck chatters then you need additive. Usually 1 toothpaste tube will do.

Chattering feels like the tires are grabbing or rubbing against the wheel well.

I forget what fluid is in the front diff. I think it is ATF but I forget.

Jim Henderson

Thanks for the advice. I have a 1999 F250 SD, lariat, 4X4.

I believe the front is a dana50, and will require 70W-90 gear oil. The rear requiring 75w-140.

Here's my VIN: 1FTNW21L0XEEJ6930 can anyone out there answer this one way or another??

Thanks,
John

[Se77vN]

I check on the rear diff, and one tag says: 75w-140 synthetic oil only, the other one has some numbers and letters but nothing about L or LS

[Se77vN]

Sorry if this has been asked/answered a million times already. I just want to make sure I do things right. I am still very much a shade tree mechanic, so I learn as I go.

Your help is greatly appreciated.

[ken kenmnedy]

need to look at the cert,label in the door will be a 2 place axel code then check the sticky on top of this fourm

[Se77vN]

Originally Posted by ken kenmnedy

need to look at the cert,label in the door will be a 2 place axel code then check the sticky on top of this fourm

Roger that, will do. thank you.