Need some help with what seems to be a differential chatter. Feels like a slight vibration in the truck, only occurs when starting out while turning left or right. Doesn't occur in a straight line. U-joints are good all around (even the axle joints), doesn't appear to be wheel bearings, brakes good. It's a 99 2500 cummins with approx 87K. I changed the gear lube and went with synthetic 85-140 six months ago. Anyone run this in the rear (dana 70 trac-loc)? I did add the friction modifier. Book suggests 90 weight hypoid. It started rather suddenly during the recent cold weather. But it doesn't do it when it's cold, only after 10-15 miles when it warms up. Any thoughts?

 

I'm getting the same thing. Mine started when I changed to Amsoil. I added like 3 bottles of friction Modifier but no improvement. Last week I drained the rear, sprayed it down with brake clean and put Mobil LS75-145 but no improvement. Next I'll try adding FM.

 

Tspooner3, what trans do you have?

 

factory automatic. It's odd that it only does it under acceleration when I turn left. Regular turn left, no chatter. Turn right, no chatter. Front end is okay (brgs, etc)

 

sounds like either a sticking u-joint cap or play in the carrier bearings to me. Last bad u-joint I had no play and only 1 cap failed and started to seize, with the vibe and noise I was really worried it was the differential.

 

Its normal for the discs in the trac loc's to be pretty much worn out in these rigs by 50K. Friction modifier may bring back a little grab but over adding it is just wasting money. The sure fix is rebuilding the carrier. Mine still locks up once in a while but I don't rely on it.

Chatter from the front end is usually u-joint related, either in the front driveshaft or the bearing ends on the axle shafts. If its occurring while turning in one direction and you are turning the wheel to lock I'd guess u-joint on axle end.

Are you running over size tires?

 

Yeah I am running slightly oversized tires. I added the FM and haven't driven it much except to warm it up and do some figure 8s. The rear is still chatty after it warms up. How much do you think it should cost to have it repaired? I think I'll add the second bottle of FM and will just run it till it gets worst, blows up, or gets close to an other 15K miles on it. I just hope it don't blow during boating season!

 

I got an estimate from a local mechanic for $350 to pull the carrier and replace the clutchpaks for the LS. I thought this was reasonable, but that was in '05 IIRC.

I have never liked not having the option to go into low range w/o engaging the front axle on these rigs, especially when dropping the boat on pavement ramps and having to turn out.

 

That's reasonable, I'm going to make some calls and see what prices I'm quoted. Thanks

 

I thought limited slip additive allowed more slippage? Is the friction modifier you're talking about something different?

 

mine took 2 bottles to stop the grab/chatter

 

Nick I know you are an Amsoil user, was this with Amsoil?

 

No, friction modifier and limited slip additive are the same thing. They do indeed allow more slippage; they allow the clutches to slip smoothly without chattering. The downside is that the more you add, the less effective the clutches are. They will slip too easily without transferring much torque.

 

I guess I'll add one more bottle before I start making calls.

 

it was with amsoil 75W-110, I had replace the clutches, and if I recall the parts were around 100$ and about 1.5hrs work, really simple to do.

here is what mine looked like