Diff fluid / friction modifier

[usapadyra]

Have been reading around some threads from the past regarding adding / not adding friction modifier to diff fluid in the case of having a limited slip. Seems kind of inconclusive.

My axle code is D4 and the metal tag on the axle says '75W140 synthetic oil only' so I figure it must be limited slip.

Honestly, I've never noticed any 'limited slip' behaviour, having got stuck a couple of times with one wheel on dry ground and one spinning on something slippery.

I like the look of Valvoline's offering, since it has the easy fill squeeze bag. It says it comes with limited slip additive...

Do I need to add the friction modifier or will the included stuff suffice?

 

[EB4X]

I would guess the Valvoline with LS additive would suffice, on other inquiry, my guess is your L.S. clutches are used up / worn down being you don't notice anything happening back there so an overhaul would be in order.

 

[usapadyra]

I would guess the Valvoline with LS additive would suffice, on other inquiry, my guess is your L.S. clutches are used up / worn down being you don't notice anything happening back there so an overhaul would be in order.

Almost certainly, but at this point it wouldn't be worth it.

I used to drive a little off road but not anymore. Just asphalt.

Assuming there's no issue driving with the LS parts worn out? It just behaves as an open once that happens right?

 

[EB4X]

Almost certainly, but at this point it wouldn't be worth it.

I used to drive a little off road but not anymore. Just asphalt.

Assuming there's no issue driving with the LS parts worn out? It just behaves as an open once that happens right?

"Assuming there's no issue driving with the LS parts worn out? It just behaves as an open once that happens right?"
NO issue leaving it .... and yes, you're now open diff

 

[410Fortune]

The factory limited
Slip uses a series of Clutches to provide the grip… yes the clutches wear out.

The limited slip additive is useful even without a working Limited slip, it helps with the friction that happens between the clutches but it also keeps the gear Lube from Foaming up
I would add it

It’s not Going to Explode without it in there, but you can run the additive even if you don’t have a traction device

 

[usapadyra]

The factory limited
Slip uses a series of Clutches to provide the grip… yes the clutches wear out.

The limited slip additive is useful even without a working Limited slip, it helps with the friction that happens between the clutches but it also keeps the gear Lube from Foaming up
I would add it

It’s not Going to Explode without it in there, but you can run the additive even if you don’t have a traction device

Is there any particular friction modifier you would recommend? Doesn't have to be the Motorcraft one, right?

I'll be filling with Valvoline 75W-140, on sale at NAPA atm for $14 a quart which is a pretty good deal.

 

[410Fortune]

$15 a quart! Crazy days we live in
At least it now comes in a bag
I usually get ford additive or Lucas is what they carry in town

I got tired of paying $14 a quart for 75 140
So I broke down and bought a whole 5 gallon bucket at the farm store with one of those pump lids… made my life so much easier. I think the 5 gallons was $150

 

[usapadyra]

$20 typically!

I thought of re-using the bag with a cheaper variety (you can unscrew and refill), but at $13.99 sale price it's actually cheaper than any of the in-house offerings from Autozone / O reileys etc.

 

[410Fortune]

That’s how they make their money!
Gear lube and exotic transmission fluids are up there with Starbucks coffee and printer ink! $15 a quart! Oh brother

 

[C420sailor]

The bags are definitely nice. Although getting the last bit out of the bag is a pain.