What fluid have you been running in the rear when you changed it? Some of the fluids like valvoline and royal purple have the friction modifier aready mixed in it. I'm sure you will have the 3 pinion heavier duty carrier. The 2 pinion was used in the lighter applications like the 7700 f250 light duty ect. I believe the excursions got the 2 pinion as well. You won't mess up the clutches by not running the fluid you would just get a chatter feel from the rear end when you take off and are turning . Kinda like when you leave a stop sign and are turning and accelerating at the same time. Might feel like wheel hop. Thats what the friction modifier eliminates. The 9.75 rear end in the f150's is very tight. Even with the modifier they will do it sometimes. Fords actually changed the clutch material at least once to eliminate it instead of having to change the design. The 10.5 really doesn't need it that I have found. They are a loose limited slip and don't give you much of a problem usually besides not wanting to lock up .
I had not changed the fluid since they installed it... I know I know... It was on the to do list for ever...
The fluid I installed this time was Shaffers 90wt IIRC.
The whole reason I even started digging is on the job the other day I was driving on one of the outlots and came to an off camber hill. Just drove up thinking I had a gear LS that locked pretty tight. Did the one wheel peel thing for a second and then backed up and hit it straight... Maybe it would have locked up had I waited a bit longer but I was pissed.
I will also add that I have found it rare for a 10.5 gear to break a tooth from the factory. Hell my e99 had 290k on it and the fluid only changed once and with truck pulling and 36's not to mention offroading they only had a slight bit of wear. After reading the invoice, I would assume you went to an aftermarket ring pinion set and the after market only makes a 10.25 gear set and you just have to use the matching install kit vs the 10.5 kit. All it really is is slightly different pinion bearings. Dumb ass should have known that. the aftermarket never felt the need to redesign there gear sets when the superduty came out. Hell if you were close i'd help ya set the front end up with the 4.30's.
The rear end...
And yes, the gears I brought him were out of Bigr's truck. They were already instaled in a 10.5... It was also the same time that Mike and I got into it over the gears, I got one set of 4.56 and one 4.30... So I had a rear 4.56...
So I had to buy a set of gears anyway.
