Lucas 75W140 Synthetic Gear Oil

[tinkering]

Can I use Lucus Synthetic V Twin Gear Oil 75W140 in my 1997 Ford Expedition rear end differential? Ford calls for synthetic 75W140 gear oil. It doesn't say anywhere in the Lucas data that it can be used in a differential. I was going to use it no problem but thought I would see what others say first.
Thanks

 

[MISTERgadget]

I have used Motorcraft, Amsoil and Mobil 1 for gear oil in 9.75" rearends in the past, all worked well. I would be a little skeptical of using a motorcycle oil as the additive pack may be different, but I don't have particular experience with it.

 

[tinkering]

I have used Motorcraft, Amsoil and Mobil 1 for gear oil in 9.75" rearends in the past, all worked well. I would be a little skeptical of using a motorcycle oil as the additive pack may be different, but I don't have particular experience with it.

I wound up using a 2:1 mix of Pennsoil Platinum 75W140 Axle Lube, and The Lucas V Twin Gear Oil. Simply because I didn't want to go to the APS and get more Pennsoil I don't have any problem with that.

If the V Twin was all I had, I personally would use it. The stuff is designed for applications in higher temp (and RPM?) situations. Maybe in a Limited Slip Differential application though, the V Twin Tranny Oil might not contain the required additives.

By the way, how do you tell if you have a LSD or standard diff?

I sent Lucas an email asking if the V Twin would work in the Expy. I did not hear back. I will post their reply if one eventually comes.

 

[MISTERgadget]

If you have a limited slip diff, you do need to add the motorcraft friction modifier - otherwise it will fry the clutches. Easiest way to tell is jack up the rearend and turn one tire - if it turns easily and the other rotates in the opposite direction, you don't have an LS.

 

[tinkering]

If you have a limited slip diff, you do need to add the motorcraft friction modifier - otherwise it will fry the clutches. Easiest way to tell is jack up the rearend and turn one tire - if it turns easily and the other rotates in the opposite direction, you don't have an LS.

Thanks.
It's still in my garage so I will jack it up and turn the wheel.

 

[tinkering]

I think this info would like to live here too

There are a few ways to ID an LSD:

1. On the door jam, find the data sticker, get the axle code, and look it up.

2. On the differential housing, there should be a metal tag. It will have two rows of characters on it. At the beginning of the bottom row, it will start with something like 3L55 or 3 55 for example. 3L55 means it is a 3.55 limited slip rear, while 3 55 means it is a 3.55 open rear (the L stands for limited slip).

3. With both front wheels carefully chocked on level ground, trans in neutral, emergency brake off, jack up one rear wheel. If the wheel will spin freely with the other rear wheel on the ground, it is an open rear. If it will not spin freely, it is limited slip.

4. Don't worry about whether it is limited slip or not, just drive it and enjoy. (but make sure the juice has the required additive package if it's an LSD

 

[tinkering]

Apparently the 9.75" differential needs very close examination to tell if it is an LSD or not; the clutch packs are hidden beside both the left and the right bevel axle gears; some diffs are more obvious when viewing with the cover off.

This is a neat 4 part youtube video that shows among many other things, how the clutch packs are 'hidden' in the differential carrier.

https://www.youtube.com/watch?v=6tOvM9fl3xc

 

[tinkering]

It is in fact an LSD. The second line on the tag starts with an 'L'. When I lifted both wheels off the ground, and turned one wheel, the other side turns in the same direction. When I lift just one wheel it is very hard to turn it... limited slip. I tried these things on both wheels in both directions, so it couldn't be confused with brake drag and stuff

There you go, I had added the 2 liters of Pennsoil Platinum (which contains a "moderate" amount of friction additive "3%"), and I added the 1 liter+ of the Lucas VTwin Gear Oil to fill it up to the plug hole. The VTwin Gear Oil for transmissions would not have the LSD additive so I thought I should add a small bottle (4oz) of LSD friction additive (ACDelco of all things to bring it all up to *****.

My personal conclusion would be that the VTwin Gear Oil 75W140 could be used in a non LSD... but in an LSD only if the friction additive is used in conjunction.

I'm done! Any comments?