Im working on puttin in Yukon 4.88s with all new timkin bearings in my 8.25 and d30 this weekend. After the initial test 8 mile test drive the 8.25 diff was very hot to the touch especially in the pinion area. The backlash and preload was in spec and the pattern looked great. It seemed too hot so we pulled it apart again and everything still looked good. The pinion preload was about 10 in pounds when we had it apart after pulling the carrier, which isn't too tight by any means. So we put it back together again.

After another 6 mile drive, I could hardly hold my hand on the pinion area for a second. I let it cool down then drive the same 6 miles, and afterward I could hold my hand on it much longer.

Is this at all normal during break in? Any ideas what could be wrong? Should I keep driving it and see what happens or tear it down again? I don't want to toast the new bearings and gears!

 

well did you put in gear oil? and i dont know if it gets hot since i havent done gears yet. from me just thinking i dont think that it should get hot

 

Mine got real hot!! I don't remember how long, but Yukon does recomend a drive a cool off period. I drove about 2 miles and let her cool down. Drove some more and let her cool down. My first tow I did the same thing, and she got real hot then. No heat anymore. Short drives and long cool downs.

 

for new gears (Yukon especially) you require at least a 30 mile (50 is ideal) heat cycle and cool down. when i built my rear with new 4.56 gears i just put the jeep up on jack stands, got the jeep to 40mph in 4th gear and let it sit for an hour like that. i did mine that way cause it puts no load on the new bearings or pinion support and allows proper break in. then i let it cool overnight and mine is only warm to the touch after driving or wheelin. a high capacity diff cover is usually recommended after stepping up in gear ratio. i did my front end this way as well and i have no noise wut so ever.

also you can try and back it off for a slightly looser fit on the backlash, if it is to tight then it will cause an enormous amount of heat and destroy the gears.

also did you check your pinion resistance after install? it should be between 20-25in lb for fresh gears and just around 18-20 after break in (this is with no wheels on the car and the brakes installed but not engaged.

 

The heat is normal with the initial break in , just let it cool back down.



in/lbs

 

thanks...fixed

 

Heat is expected, but do make sure your pinion angle is not to high during break in, if the pinion is to high it can starve the new bearings of lubrication. Also make sure the rear end was level during filling or it won't take the full 2.5qt of fluid. I personally drove the rear of my jeep onto alignment rack and raised it till it was level lol

 

Thanks for the replies and suggestions. I have 4* shims and 1.5" shackles so my pinion angle is pretty high. I only put in 2 quarts I'll park on an incline and put in another half quart and see if that makes a difference.

When we pulled out the carrier after the first drive we had about 10 inch pounds of preload on the pinion

I'll take it easy and do the warm up cool down thing and watch the temp closely and see what happens.

 

I topped off the diff, and after a good drive, the temp was about 150 degrees. Is this acceptable?

 

Yes it is.

 

sure is, no bad at all.

 

huh, good info for newbies like me

 

Remember if you tow anything, to go through the same drive, cool down motions with what you tow. It will get hot the first time you tow, just puts more pressure on the R&P and pinion bearings.