Changing front and rear diff oils with truck up on lift

[bergxu]

Hi all,

Wondering if anyone can shed some light on whether these trucks need to be sitting on their wheels or if the differential fluids can be drained and accurately refilled with the truck up in the air on a two post lift. I have the truck up in the air as we speak and I noticed that the differentials are at somewhat of a different angle since the suspension is fully extended and I’m concerned that I won’t get an accurate refill, which sucks because I have a drum of gear oil on a roll cart which would make refilling quite easy. Thanks and I appreciate the help!

 

[Jgrauman]

I did mine on a 2 post. I checked the levels after when on the ground a few weeks later, seemed fine to me.

 

[1911garand]

Up on the lift is fine. Auto technicians do not roll around on the ground filling diffs.

 

[Zjohnsonua]

The only watch-out with full floating diffs (which your 80 may or may not have, depending on its year) is that you don't overfill it. There should be a gap between the pool and the bottom of the fill hole. I forget the spec, but when you check it, you'll want oil on just the tip of your finger. If you fill to the bottom of the hole then you'll be setting yourself up for messes and seal leaks in the future as there isn't meant to be a pool of oil running from axle flange to axle flange.

 

[bergxu]

Thanks guys. It’s a locked ‘95.

 

[Qball]

The only watch-out with full floating diffs (which your 80 may or may not have, depending on its year) is that you don't overfill it. There should be a gap between the pool and the bottom of the fill hole. I forget the spec, but when you check it, you'll want oil on just the tip of your finger. If you fill to the bottom of the hole then you'll be setting yourself up for messes and seal leaks in the future as there isn't meant to be a pool of oil running from axle flange to axle flange.

Interesting, why is that? There is no pressure inside of the housing so I don’t see the harm overfilling it a little. Per your instruction I overfilled my diffs for many years and no issues.

 

[Zjohnsonua]

It's definitely not a 100% fail. That's why I said, "setting yourself up for". I've been through my fair share of weeping seals in leaking rear axles that had been overfilled. Removing some oil removed the symptom to the owner's satisfaction, but most had other issues like weak seals / grooved spindles, improperly functioning housing vents, or even just a lot of time sitting still. These other items also needed attention, but cost money the owners weren't willing to spend.

He probably won't have issue, just as you and many others haven't.

 

[Manuelsv]

Interesting, why is that? There is no pressure inside of the housing so I don’t see the harm overfilling it a little. Per your instruction I overfilled my diffs for many years and no issues.

Yeah... Me too!!!

 

[ZackR]

If the breathers are clear fill up until it drains out the fill hole and call it good.

 

[Tools R Us]

If you don't want it to leak, leave it empty, otherwise, if there is a bad seal, it's likely to leak.

 

[inkpot]

When the vehicle moves the diffs are SPLASH LUBE, so gear oil goes EVERYWHERE! it's a bloody sh1tstorm in there when you are cruising down the road. If yur seals and gaskets are good, it won't leak, regardless of how full it is. I have worked on industrial scaled splash lube gear boxes for nearly 40 years and I am pretty good at keeping them dry.

 

[ZackR]

 

[sunrk]

When I change diff, gearbox or transfer case oil, I fill them until oil runs out the filler port.

I don't remember off-hand the gear oil quantity for front and rear diff's, but for my 80 with h150f and factory part-time transfer the box takes 2.7 L and the transfer takes 1.3 L. Diffs, gearbox and transfer are all 'splash lubed' (ie. there's no internal 'oil pump' moving the stuff to specific locations like you get with a very big diesel motor) and as someone else mentioned if the breathers are not blocked it's better to fill until oil runs out, then you know for sure. Otherwise there is no 'accurate' way to determine the fill level.

NB. I don't have a garage/workshop or access to a hoist, so my gear oil changes are oldskool on the ground with a big oil drain pan to collect the stuff when the old oil comes out.

PS. Remember the most important rule - do *not* take the drain plug out until you have got the fill plug out. And when they're done up again, they don't get tightened massively.

 

[Tools R Us]

...
PS. Remember the most important rule - do *not* take the drain plug out until you have got the fill plug out. And when they're done up again, they don't get tightened massively.

From above... Torque: 49 N·m (500 kgf·cm, 39 ft·lbf)

 

[BILT4ME]

The only watch-out with full floating diffs (which your 80 may or may not have, depending on its year) is that you don't overfill it. There should be a gap between the pool and the bottom of the fill hole. I forget the spec, but when you check it, you'll want oil on just the tip of your finger. If you fill to the bottom of the hole then you'll be setting yourself up for messes and seal leaks in the future as there isn't meant to be a pool of oil running from axle flange to axle flange.

This is shown as a MAXIMUM gap. In other words, fill it to WITHIN 5mm of the open hole or above. But do not set it at 6mm, or it will be considered "low".

Fill it until it runs out. With the diff's hanging, you will be on the very bottom of the fill amount because the diff's are leaning toward the fill hole and you won't get as much in.

Contrary to that, I have checked my levels with my truck facing uphill for the front, and filled until it ran out. Unfortunately, it was a lot overfull and it puked oil out my breather tube when I got out on the highway and got it good and warm.