So i was out doing a little snow wheeling this weekend and i noticed my rear diff was making a whining sound before it locked in. Its kind of a light grinding sound but more of a whining. nothing nasty sounding. it was doing it a couple months ago when i was going through a twist ditch but i ignored it because i thought it was my other tire spinning on some grass or something soft (thats the kind of sound it makes) but then it did it in the snow. sometimes it will do it and sometimes it wont. then it locks in and stops

the way the G80 is designed i dont really know what could be grinding or whining before it locks, or maybe thats just the sound of one side of the diff spinning faster than the other before it locks?

i always make sure i baby the gas to get the tire spinning fast enough to get the diff to lock, i dont stomp on it or anything lol i like being able to drive my truck home in 2WD after im done.

So maybe someone with a G80 could tell me if they hear this too? i never listened to it on previous offroading trips to hear if it was doing it (mainly because i didnt know i had a G80) I also really need to replace the diff fluid in the rear differential because i dont know when it was done last.

 

if I were you I would change your differential fluid. Make sure you get the fluid that is made for limited slip differentials and not just the regular stuff.

 

The G80 isn't a "limited slip" diff and does not call for friction modifier. It doesn't hurt anything, but it does not help. When one tire turns faster than the other (25rpm or 100 rpm depending on who you listen to, either way, it's not much) a centrifugal weight swings out and catches on another centrifugal weight (if vehicular speed is 25mph or less*). This then locks a swash plate to the carrier against which is another swash plate on the end of the axle gear. The next 1/8th revolution of the axles causes these plates to ride up, one on the other and compress the clutch pack until the diff is completely locked. Each action (time you get stuck in a ditch) causes no more than 1/8th turn of the clutches so no friction modifier is needed.

Indeed, there is no need to hammer the gas pedal to engage the G80, just get the one wheel to spin a little and you should feel the diff lock up. During that time, the spider and axle gears will run against each other and you may hear that action. I guess I've heard it but never noticed it over the sound of my snow tires spinning.

Good 80-90 weight grease comparable with modern Hyperboloid gears is all that's needed back there.

* above 25mph, the G-80 will not lock up. So, if your are rolling down the highway, hit a ice, only one wheel may spin leaving the other in-traction so you don't drift sideways. I love the G80! check out http://www.youtube.com/watch?v=tTGZOJQQBeE

 

^^ yeah lol studied that video a lot already thats why i was saying i really dont know what could be causing the whining noise. I just got oil today i picked up 75W-90 and i got a 7.625 diff seal, im not sure if that is the right one. im trying to figure that out right now.

Edit: so i dont know how to find out what size seal i need. i know 7.625 is common but i know the ZR2 with the 3.73 and G80 has the 8+ seal (dont know exact size) and thats the same as my diff. so i just need to know how to check it.

 

No the zr2 g80 is not the same as yours. The zr2's have a full size 8.5" axle. Im sure if you go to advance or napa you can tell them u need a seal for a non zr2 blazer

 

My G80 doesn't make any sound before or after it locks.

Edit: Now that I think about it, I do hear some grinding/humming sounds sometimes.

 

i was talking about gearing wise its the same, and i tried that lol they gave me two options, the 7.625 and the 8+. i dont think my other option was 8.5 tho, it was 8 something.

And Thog, it sounds like it could be normal then. i dont hear it all the time just sometimes and its never very loud. but ill still change the fluid because i dont know then it was changed last. Wouldnt surprise me if it wasnt ever changed before i owned it.

 

ah yes. lol I have a 7.625 g80 with 3.73 ring sitting in my garage...

 

oh well i suppose i got the right one then :P i guess ill find out later this week when i get a break from life to change the fluid lol