i have just installed 4.56 gears in my 8.8 rear end on my 97 f150. i have done gears before with no problems. But have never noticed any heat. i had put on about 100 miles of city driving with them before i had to go back to work which is a 5 hour drive. after 2 hours i stopped for lunch and didnt notice anything. But about an hour later into my ride i pulled over for a break, and could smell diff fluid. it wasnt a burning smell, just could smell it. I dont have a temp guage(on order now) and didnt have a laser thermometer to check the temp, but i could only put my hand on the diff for a second or 2 before i had to pull it off cause of heat. I talked to a guy from a gear shop in the city, and he said that this is normal for a new set of gears. I just wanted more peoples oppinions as i need to drive 200plus km where there is nothing around, and dont want to be stranded on the highway late at night with a blown diff. the guy i talked to said if i had made a mistake i would here noise coming from the differential, just want to see if anyone else that has done there diff noticed anything.

 

Some heat is normal when new, and even after breakin the rear will still get hot enough to make it uncomfortable to touch with an open hand for long.

Plus, with 4.56 gears that pinion is turning faster, each tooth on the pinion slides against a ring gear tooth 4.56 times for each revolution of the axles where as with stock gear maybe only 3.55 times.

If you have a 275/55-20 tire that's about 32 inches diameter and that spins 652 times per mile, that's 2,973 times per mile with a 4.56 versus 2,314 times per mile with that 3.55s. Watch closely as the gears mesh and you'll see they rub or slide along each other's teeth.

If you are concerned, maybe slow down a bit and take a few stops to let things cool off while new.

 

Check it with an actual temp gun, I seen 160°F with my 10.5 and stock gears.

 

I would drain all the fluid again and replace it with new....and take the diff cover off and get all the shavings off the magnet

 

i have the same setup and now i havent measured the temp i havent had any problems at all even on long highway trips (3hrs)

 

i have now put about 500 miles on them, on the way home i stopped after the first 150km, and the temp was way down, so i am assuming it was just cause they were new, it is running good and quiet, and there is a diff temp guage on the way just to be safe.

 

I've done 4.10 and 4.56 in the 8.8 on my old 95 F150 and it was amazing how hot they got during the break in period and even a while after a 1000 miles or so. You could not hold your hand on them for more than a couple of seconds. I originally thought I had done something wrong. I didn't have any problems with them after they broke in. It is still a good idea to change the fluid and clean everything up after are good and broke in.

Tim

 

Be sure to change the oil.