I'm sure the title alone is going to get me some interesting replies....

Sorry to those of you on the Bronco forum who already saw this....I am posting here too, in hopes of getting a little more feedback....Thanks!

78 Bronco with a 9" rearend, 400 with an automatic.

I just got this rig back on the road after being parked for 6+ years with engine problems. I have been working my way through all the bugs of brakes, exhaust, etc. I am wondering how warm does the rearend get with normal use? Just slightly warm (you can tell it warmer than the outside air)? Very warm (it is quite a bit warmer than outside air, but can hold hand to it)? or Hot (holding hand to it is uncomfortable)?

How much will this change when towing a 6'X12' enclosed trailer with a snowmobile in it (not much of a load in my mind)? The reason I ask is mine got very warm to hot when doing this type of towing.

Thanks in advance for all you help.

David

BTW...I have changed the rear diff fluid as I had to replace an axle shaft...what weight/type of gear lub should have I used...I think I used 90W140W.

 

Hey, in my opinion I can't see it getting insanely hot.. like now i haven't but would think you should be able to put your hand on it... is it original to the truck? if not could be gears set too tight? The 6x12 trailer i would think would barely faze this setup. Maybe someone else would have some more info. oh an make sure your vent tube is clean an clear from obstruction. If its getting that hot she's bound to build some pressure, an rather it go threw the blow hole then pop a seal.

 

180-200F isn't unheard of during highway runs with a load. Much warmer than that, and there could be a problem.

 

It depends on what your doing with the truck. Long trips pulling heavy loads can easily get the differential oil temps over 200degF. If temps are that much of a concern install a temp gauge. I'd just keep good quality fresh oil in it and run it.

What does Ford recommend for the year of your truck? I'd bet not 90w140.

 

I have seen a few nice hot rearends. There was this gal in Dallas that I still don't know how her shorts didn't just burn off her backside she was so hot.

 

What does Ford recommend for the year of your truck? I'd bet not 90w140.[/QUOTE]

I'm not sure the manual I have just says hypoid gear lub but now weight specifications....it seemed when I was in the parts store their were many different weights of hypoid oil. Do you think the 85x140W will harm it?

Thanks for everyones help!!

 

Don't know if that weight would harm it or not. For that year I'm pretty sure 80w-90 or something in that viscocity range is recommended. My sterling 10.5 in my SD specs 75w-140 but its quite a bit larger than a 9". I always used 80w-90 in the 9" on 74'.

 

A rear end will get hot enough under certain conditions, like a race car, that they'll run an oil cooler. NASCAR. Others, and many of them are running the Ford 9 inch. But they have a few more horsepower unleashed, pulling against the rear end. The rear end in my last two motor homes was loaded with synthetic and recommended synthetic grease when the axle was loaded to near max. I know for a fact under normal use a differential will get hot enough that I don't want to hold a bare hand on it. My SWAG would be you could see a couple hundred degrees, F pretty easy when towing.