75W140 or 80w90 SF 14 Bolt

[Woody35]

i got a semi floating 9.5 inch 14 bolt with the G80 under my truck. doing the fluid and im wondering which one should i fill the diff with. on alldata theres two specs. just one for the rear axle which is 80w90 and one for a locking diff which is 75w140. can someone eleivate my confusion. thanks

 

[ak diesel driver]

IIRC 80/90 is regular gear oil 75/140 is synthetic or at least semi synthetic and probably has additives for locking diff

 

[Woody35]

so i should go with thw 75w140 synthetic?

 

[ak diesel driver]

I would. But I would also read the label on the jug for compatibility

 

[Woody35]

thank you for the info

 

[btfarm]

Woody if it's a G80 locker and similar to our HDs then 75W90 synthetic is the right stuff. PM Ashton (Wrecker). He'll know what you should be using.