2nd Gen Non-Engine/Transmission rear diff hot

[rspinks]

My buddy was following me yesterday on the highway, he said steam was coming off the rear pumpkin when I hit wet patches on the road. I crawled under and couldn't hold my hand on the diff it was so hot. I threw some snow at it and it just steamed and evaporated away. His 1/2t for comparison was just warm.



I'll check and see if there's any fluid in there, truck has 31,000km so if it's dry I'm surprised it lasted this long. If the fluid is OK then what? Maybe the diff was set up wrong from the factory? This is a Dana 80 in an '01 ETH/DEE 4x4, 3. 54 LSD.

 

[TSRAM]

something fairly easy to do without going into the punkin' is to check the preload on the pinion gear nut. RE: I put gears into a rear in another truck about 6 yrs. ago and the rear was a little loud not excessive, but got really hot. To make a long story short I had not tightened the nut on the pinion quite enough. I realized only after taking the ring gear and axles out , went to remove the pinion and it wasn't really tight... ... ... ... noone around to blame either.

 

[EricBu12]

Some new trucks off the lot have been reported to have low fluid in the dif. But one thing you can do to reduce temp and to keep metal suspended is to get a mag-Hytec diff cover.



www.mag-hytec.com



They are $235 US but one thing is nice is the dipstick and drain plug which means no more taking the cover off to chance fluid. (don't know why nobody ever thought of this before?????)

Anyway, I also have the front Dana 60 cover as well.



<img src=https://www.turbodieselregister.com/user_gallery/sizeimage.php?&photoid=2111&width=2/src img>



The dana 60 cover



<img src=https://www.turbodieselregister.com/user_gallery/sizeimage.php?&photoid=4406&width=2/src img>

 

[rspinks]

If the pinion nut isn't tight enough how does this cause the diff to run hot? Is it an issue with preload on the pinion bearings or does the pinion shaft move, causing poor ring/pinion gear mesh and excessive heat?



The Mag-Hytec is a nice piece but I need to find out why my stock diff is running hot under unloaded conditions. Could be oil level like you said, will find out shortly.



Edit reworded a bit, checked level and it's OK at 1/2" below plug, reasonable buildup of sludge on magnet, oil is really dirty though.

 

[TSRAM]

If the pinion nut isn't at the right pre-load (as in tight enough), that would mean that the pinion wouldn't be pulled up towards the driveshaft side of the diff. housing. The pinion gear and the ring gear would be meshed together so tightly they are more or less wedged together too tightly.

Make any sense at all?

 

[rspinks]

Yup, makes sense and I can see that condition being fairly quiet as well and not obvious. Maybe that's why my mileage has been only mediocre since new. I think it will be going somewhere for a professional checkup.

 

[Behr]

Just something else to think about is if you have limited slip diff... could slip clutches be malfunctioning... ??



But I would check oil level in diff first... ...



Keep us posted on what you find out... .

 

[TSRAM]

I'll be interested to find out too. Hopefully it's not a major problem.

 

[Joseph Donnelly]

I like to set the backlash toward the loose end of spec, say around . 007-. 008". This is not as good for shock loads drag racing, but helps the gears run cooler in "normal" use or towing.

 

[rspinks]

Well it's going to a small DC dealership just out of town tomorrow, will let you know what happens.

 

[rspinks]

Well here's the service report: "Completed road test after road test diff was 119F is normal in hot weather 150-170F". They said the backlash was fine, fluid level OK but the flluid condition was poor and broken down. They put non-synthetic 80w-90 back in it and said not to worry about it.



When I got home (20mi drive) I felt the diff very carefully. The cover and bottom of the housing were fairly warm, however the front "snout" where the pinion bearings ride was bordering on hot. Maybe a pinion bearing is running hot and slowly heating up the whole thing?

 

[TSRAM]

It is possible that the pinion could be too tight couldn't it? Anyone else? I would find it hard to believe the bearing was bad already if this weren't the case.

 

[rspinks]

TSRAM, I think you are correct that the pinion bearing preload is set too tight. The front pinion shaft housing is consistently much hotter than the main part of the diff housing, even the external driveshaft yoke piece is heated up a bit.



The next step, as another helpful dealer suggested, is pulling the axleshafts and driveshaft to check the pinion rotating torque in-lbs, subtracting 10 in-lbs for the side bearing drag. He is also willing to lend me the shop IR temperature gun to check the temp on a long highway trip. I'll talk to the first dealer tomorrow and see if he' s willing to do the above.



Maybe it's nothing abnormal. It would help if somebody else would crawl under their truck and feel the temperature of the pinion bearing area versus the rest of the diff. Thanks in advance.

 

[TSRAM]

If I can remember, I'll crawl under tomorrow after the ride home from work and cop a feel. It's only about 14 miles though maybe not enough to build any real heat anyway... ... .

 

[rspinks]

TSRAM did you check it? I drove around town last night for an hour, the rear cover and main diff was warm, the pinion shaft area and front seal area was hot.

 

[rspinks]

Well I had a good conversation with the DC mechanic that did the previous oil change/inspection. He says the pinion is typically the hottest part of the diff due to the preload on the bearings. I believe he is sincere so maybe I am chasing something that is not an issue.



It would still be nice if somebody could confirm that the pinion area is the hottest part of their rear diff.