when i was changing the rear diff fluid in my dana 80 last week-i noticed that there was discoloration on the diff housing(i guess thats what it is)--its where the pins that hold in the spider gears end -- flush with the housing. there seemed to be like a blueish ,circular discoloration around the ends of each pin. it looked like it may have been caused by high heat. i did just change the fluid for the second time this year beacause when i first changed it, i added a non-chrysler lim slip additive -- and, from that point on it didnt seem like my posi was working like it used to(started spinning only one wheel).the gear oil ive always used is valvoline 85/90. i dont really ever haul heavy loads(light trailers and firewood occasionally).my engine does have the TST 280/680 plate kit. just wondering if its a problem or normal.

 

I would imagine there's a strong possibility you're heating up the rear carrier with your setup and 3.55 gears. Unlimited slip in a limited slip diff will generate quite a bit of heat as well. I'm running non DC oil in my diff, and my LS is still pretty tight.

I run the same plate in my truck with 4.10's turning 37" tires, and mine looked pretty good the last time I opened the pumpkin. I run it pretty hard too.

 

When you change your fluid out, here is a good trick to use:

Add only about 2 oz of the friction modifier at a time to your fluids. After each 2oz dose, go to a parking lot and do figure eights and listen for chatter. Add an additional 2 oz til the chatter goes away.

Some fluids do not require any friction modifier. I use Amsoil 75w140 and did not need any.

Too much of the friction modifier can render your no-slip inactive.

 

thanks for your info and advice. im wondering if i still have a problem and would switching to a synthetic oil help the heating - up issue? should i watch for anything else? all else appears fine to me.

 

Could be the left over pattern from factory heat treating.
Were there any metal particles in the bottom of the housing?
What does the wear pattern on the gears look like?
Is there any slop in the gears?
Does is make any unusual noises on the highway?

 

well, i cannot answer all of those questions cause the cover is on. but, i can say that i just dont remember seeing those circular blu-ish marks before. there wasnt alot of metal in there at any of the last 4 changes i performed.i guess i was hopin 4 someone else to say that theirs has it too and its normal :- well, i can say that now that weve had all of this reoccurring snow in pgh, my limited slip seems to work a hell of alot better now than it did before the fluid change. i may change to the synthetic oil in the rear--and, i definately am going to use factory additive at every change(just in case).