Today I had a differential pinion seal replaced due to a small leak. When I put the truck in reverse and cut the steering wheel hard I'm hearing a faint grinding sound. Anyone have any ideas? 2002 Ford 7.3 L dually with Dana 80 rear end.

 

Welcome to FTE.

Who changed the seal?
Do you know for sure they put 470 ft/lbs of torque on the pinion nut?
Did you check the fluid level?
Might need friction modifier.

 

I had a certified mechanic whom I trust do it. I'm starting to suspect a warped rotor.

 

Sounds to me like maybe they didn't put enough friction modifier into the diff fluid. A warped rotor will cause your brake pedal to pulsate while braking. If you are not experiencing this pulsating, your rotors are true.

 

My understanding is that friction modifyer is in synthetic 75w-90 severe gear oil. Do you add more and would this do any harm?

 

Are you talking about Amsoil Severe Gear? It says on the bottle that it's compatible with most limited slip diffs, but if you experience chatter to add friction modifier.

I take this to mean that there is friction modifier in it, but some LS diffs may need more.

 

Yes.... Amsoil 75-90W severe gear is correct. Would it hurt to add a bottle of friction modifer to this? I'm going to purchase a bottle and see if this is the fix. The noise is only at a slow speed, no grinding. Just enough to be concerned when backing up.[/LIST]

 

I used mobil 1 with the modifier in it already. But I seem to recall having to use a heavier 75w 140 or the like, I could be wrong though.

When the modifier is needed the rear end will jerk (chatter) a bit going around corners especially under load.

 

My "Precious " isn't jumping or anything. I just hear the noise when turning to back out of the drive way. By the way I had to annoy the parts guy at Ford to verify which rear end I had. First they told me a DANA 60 but I insisted they pull it up by the VIN. DANA 60 uses 75-140W, DANA 80 uses 75-90W. My mechanic questioned this also but verified I was correct in my persistence. Ford apologized and just assumed they all use synthetic 75-140W. (That was also initially giving him the numbers stamped on the differential).

 

It takes the torque needed to crush the sleeve and give the proper pinion drag.

 

LS rear end? I wouldn't worry about it.

 

Never heard of putting in a new crush sleeve when just changing a pinion seal. One should always install a new flange nut though.

Rotational torque should be checked before removal of flange nut and then after new seal is installed new flange nut should be torqued to remove play and slowly increased until a specified torque is reached above the initial recorded rotational measurement. Probably around 3-5 in. lbs more than the original recorded measurement.

That's the general procedure, one should always check manufacturer's procedure and to verify spec numbers.

 

I totally disagree. If you go by torque you can't attain the slight drag it needs. Besides, those specs are for a dry rebuild on a bench. 470 pounds on a sleeve that is already crushed? YIKES!., you wouldn't be able to turn the yoke by hand.

 

Thats what I am thinking as well. It is the preload on the bearings as well and I don't think I have ever seen any torque numbers over 100ft lbs for any sort of taper bearing. In fact almost all taper bearings require just a snug nut or even allow for a positive tolerance. Over torquing them will burn them up no matter how much oil they are in.

 

The nut torque can't even be used on a seal job. They just need 2 things; a little drag on the pinion and a nut that will stay tight. The old crush sleeve can be used if it applies enough pressure on the nut which is possible due to it's springiness and the wear on the 2 bearings.