Any tips for chaning rear differential oil?

[Drew Bru]

Alright, so I've changed engine oil and the many, many filters on the bus but I have have no idea what's in the differential. I don't recall seeing anything in the service records, but the bus was pretty well maintained so I assume this was part of the regular maintenance. I'd kinda like to know that what's in there is fresh and clean, so I'm looking to change it regardless of what condition it's in. Anywho...is there anything special about changing the differential oil in a school bus? I've done it on other vehicles and it's always been drain out the bottom, then pump oil into the fill hole until is starts weeping out. The differential on the bus looks like it's the same setup.
How many quarts am I looking at, and should I splurge for synthetic or nah?


Maybe I should just send a sample to Blackstone Labs, huh?


Any tips/tricks/advice?

[banman]

What diff? Look it up and see how many qts (more likely 1 to 2 gallons)
And what oil's recommended -- remember you now drive the bus different than how the school did, so maybe go by how the same axle's use in an otr truck is.

I would remove the diff cover and inspect. Wipe out any crud/debris.
I would expect a metallic sheen to the used oil but any solid bits is cause for concern/exploration...

Are any of the hub bearings lubed from the diff or are they isolated, greased bearings?

If you can jack up the rear end you can easily rotate all the parts to inspect all the teeth surfaces.

A synthetic multi-weight oil will give you a bit better mpg. Cold gear oil has a high rolling resistance and doesn't warm up as quickly as engine oil...

[Brad_SwiftFur]

On medium-duty axles, there's no cover to remove. Most axles will want something in the 75-90 wt. gear oil, or 80-120 (for warmer driving), something close to that. And plan on closer to 5 gallons of it - 34-36 pints I seem to recall for my N175 axle.


Don't mix synthetic and mineral oil, so unless you plan to drain and thoroughly clean out *ALL* the remaining oil residue, I'd stick with mineral oil (unless it previously had synthetic).


The wheel bearings are lubricated from the axle differential, so unless you plan to drain those too .... service manual says to fill, raise each side (to let gravity fill each 'lower' bearing), then top off on a level surface.

[Drew Bru]

Originally Posted by banman

What diff? Look it up and see how many qts (more likely 1 to 2 gallons)
And what oil's recommended -- remember you now drive the bus different than how the school did, so maybe go by how the same axle's use in an otr truck is.

I would remove the diff cover and inspect. Wipe out any crud/debris.
I would expect a metallic sheen to the used oil but any solid bits is cause for concern/exploration...

Are any of the hub bearings lubed from the diff or are they isolated, greased bearings?

If you can jack up the rear end you can easily rotate all the parts to inspect all the teeth surfaces.

A synthetic multi-weight oil will give you a bit better mpg. Cold gear oil has a high rolling resistance and doesn't warm up as quickly as engine oil...

If we weren't living in the desert on public land I might be brave enough to take off the cover and give it a look, but if I break a bolt or something I'm kinda screwed. I had assumed the bearings are lubricated by the diff, but I really don't know TBH. The Operator's Manual I got from the school district says it's a Rockwell differential (is there a way to verify this?) and to change the oil every 100k for class A, more frequently for lower class/off-road. A bit better MPG would be awesome and probably worth the price difference.

[Drew Bru]

Originally Posted by Brad_SwiftFur

On medium-duty axles, there's no cover to remove. Most axles will want something in the 75-90 wt. gear oil, or 80-120 (for warmer driving), something close to that. And plan on closer to 5 gallons of it - 34-36 pints I seem to recall for my N175 axle.


Don't mix synthetic and mineral oil, so unless you plan to drain and thoroughly clean out *ALL* the remaining oil residue, I'd stick with mineral oil (unless it previously had synthetic).


The wheel bearings are lubricated from the axle differential, so unless you plan to drain those too .... service manual says to fill, raise each side (to let gravity fill each 'lower' bearing), then top off on a level surface.

Ah...many thanks. Maybe I'll rethink this project for now. The district used synthetic motor oil, but I have no idea what they used in the differential. I'll probably send a sample off to Blackstone and let them tell me what to do.

[EastCoastCB]

Originally Posted by Drew Bru

Alright, so I've changed engine oil and the many, many filters on the bus but I have have no idea what's in the differential. I don't recall seeing anything in the service records, but the bus was pretty well maintained so I assume this was part of the regular maintenance. I'd kinda like to know that what's in there is fresh and clean, so I'm looking to change it regardless of what condition it's in. Anywho...is there anything special about changing the differential oil in a school bus? I've done it on other vehicles and it's always been drain out the bottom, then pump oil into the fill hole until is starts weeping out. The differential on the bus looks like it's the same setup.
How many quarts am I looking at, and should I splurge for synthetic or nah?


Maybe I should just send a sample to Blackstone Labs, huh?


Any tips/tricks/advice?

I've never heard of skoolies being prone to any rear end problems.
Sending it to Blackstone wouldn't be something I'd at all worry with.

I'm considering changing mine soon. Since I won't be paying any labor I'm going to splurge and run synthetic.

[EastCoastCB]

Originally Posted by Brad_SwiftFur

On medium-duty axles, there's no cover to remove. Most axles will want something in the 75-90 wt. gear oil, or 80-120 (for warmer driving), something close to that. And plan on closer to 5 gallons of it - 34-36 pints I seem to recall for my N175 axle.


Don't mix synthetic and mineral oil, so unless you plan to drain and thoroughly clean out *ALL* the remaining oil residue, I'd stick with mineral oil (unless it previously had synthetic).


The wheel bearings are lubricated from the axle differential, so unless you plan to drain those too .... service manual says to fill, raise each side (to let gravity fill each 'lower' bearing), then top off on a level surface.

Synthetic and conventional will mix just fine and nothing scary will happen.

[Brad_SwiftFur]

Originally Posted by EastCoastCB

Synthetic and conventional will mix just fine and nothing scary will happen.

Just what I read on the Dana website. Of course, they also want you to buy their proprietary brand of oils too, so ....

[Drew Bru]

Originally Posted by EastCoastCB

I've never heard of skoolies being prone to any rear end problems.
Sending it to Blackstone wouldn't be something I'd at all worry with.

I'm considering changing mine soon. Since I won't be paying any labor I'm going to splurge and run synthetic.

Yeah, seems like a straightforward job, it's just the unknowns of it...that and I'm sending a motor oil sample off anyway...is why I was thinking of getting it analyzed. It might be new oil in there for all I know. It's not a pressing issue AFAIK, no problems with the rear end.

[Jolly Roger bus 223]

yours isnt that old so it might be ok.
but i have messed a few times on older vehicles transmissions and a few older rear ends by removing all of the small metal particles in the pan during tranny filter change and the inside of the rear housings.
always thought i was doing right by cleaning everything out while i had it open but 2-3 years ago i bought an older 77 truck and for christmas my son bought it a transmission filter and in the effort to teach them basic mechanics we went and changed the filter
clean the pan and all the stuff out of it,cleaned and painted the outside, put it all back together.
new filter,new fluid ready to roll.
wasnt even a daily driver but within a month the transmission went out.
decided to take the transmission in for rebuild to a shop that has doing nothing but that since before i was around here (50 year old family business) but told him what had happened and he said come here. walked into his shop and showed me tranny fluid with a zinc addittive and said everytime he has to replace a pan with a new one that that is what he uses for fluid because those particles came from the transmission and they circulate in the fluid and cushion and or fill the gears or bands that they came from.
so filter change leave them there.
i would say the same for a rear end unless its beefier pieces which would indicate real problems.
not trying to scare anyone.

[Jolly Roger bus 223]

and for this transmission i couldnt ever find a definite fluid spec for that transmission it jumped around.
for this older ford transmission i heard you have to use type f another said dex/merc which didnt sound right and another said can only use dex/merc 3 and the type f is double the price of the other to so i had to ask what type fluid i needed to run when i picked it after rebuild and he said it doesnt matter. run whichever you want cause they are all the same and i was like uh ok you just re-built my old transmission i dont need any of the zinc addittive stuff and he said nah man i re-built if you ever have any problems give me a call.
so i think for fluids whether oil,tranny fluid,rear end is more of a sales gimmick except i do believe in selecting the correct thickness of engine oil or gear oil for the climate you are going to be running in colder temp areas need a thinner oil warmer temps can use a thicker oil what brand type is up to you.
all of my companies diesel equipment and all of the mobile equipment mechanics in my area use DELO and the weight varies for each piece of equipment.
only had one problem in over 20 years and the mechanic when he came back to fix it admitted that he didnt know what kind of problems it would cause and didnt start the machine before he left.
straight 90 weight in a 3 cylinder perkins welding machine even at 40 degrees dont quite work.

[TheHubbardBus]

Originally Posted by EastCoastCB

Synthetic and conventional will mix just fine and nothing scary will happen.

https://www.machinerylubrication.com...s-mineral-oils

Personally speaking, if a manufacturer states their product is incompatible with another, I take them at their word. They know a lot more about the chemistry involved than I do.

If I'm switching from mineral to synthetic, I heat the fluid up to operating temp & then drain overnight. May be overkill, but it doesn't cost even time when the work's being done while I sleep.

[EastCoastCB]

https://www.lubricants.total.com/can...mixed-together

There are four main families of gearbox oils:

Mineral oils
Poly-alpha-olefins (PAOs)
Esters
Polyglycols, also referred to as Poly Alkylene Glycols (PG or PAG)
Mineral oils, PAOs and esters may all be mixed together.
Only polyglycol type synthetic oils (PG or PAG) may not be mixed with the other lubricant types. They can react together and form gum gels in the casings. Furthermore, they can sometimes be incompatible and immiscible with other polyglycols.

[Booyah45828]

Originally Posted by Brad_SwiftFur

On medium-duty axles, there's no cover to remove. Most axles will want something in the 75-90 wt. gear oil, or 80-120 (for warmer driving), something close to that. And plan on closer to 5 gallons of it - 34-36 pints I seem to recall for my N175 axle.


Don't mix synthetic and mineral oil, so unless you plan to drain and thoroughly clean out *ALL* the remaining oil residue, I'd stick with mineral oil (unless it previously had synthetic).


The wheel bearings are lubricated from the axle differential, so unless you plan to drain those too .... service manual says to fill, raise each side (to let gravity fill each 'lower' bearing), then top off on a level surface.

All of this.

Get a 5 gallon pail. You'll be money and frustration ahead.

Everything medium/heavy duty will be a full floating axle. So the wheel bearings will be lubed by the axle fluid. However, if you don't drain the oil from the hubs, there's no need to raise each side to refill.

I looked up and read the manual from dana. I had to laugh when they said the fluid service interval is 3 years 180k miles for synthetic. I don't think I've ever replaced that fluid based off of an interval. Typically it's only replaced because of component failure or water submersion.

[Booyah45828]

Oh, and as far as mixing synthetic vs conventionals go, I wouldn't fret too much. Most are mixable without issue to a degree. The big issue is the differences in additive packs between the two.

I doubt you'll see problems mixing gear oils in a rear axle during a fluid change. The little bit of residual fluid left inside won't amount to much when you're changing out 5 gallons of it.

[Drew Bru]

Originally Posted by Booyah45828

I looked up and read the manual from dana. I had to laugh when they said the fluid service interval is 3 years 180k miles for synthetic. I don't think I've ever replaced that fluid based off of an interval. Typically it's only replaced because of component failure or water submersion.

So...that begs the question..."is it even worth bothering to do this?" AFAIK there's no component failure or water submersion. The bus has around 230K miles, but the diff oil age/condition is unknown. It may or may not have been changed at the school. It doesn't sound like too big of a hassle to do. My reason for the question was mostly because it seems simple enough to do, and if I change the oil then I can be sure of its condition. If, however, it's not something I should be worried about then I'll hold off on it.

[EastCoastCB]

Always make sure you loosen the fill bolt before you drain it. Just in case.

[Drew Bru]

Originally Posted by EastCoastCB

Always make sure you loosen the fill bolt before you drain it. Just in case.

Smart tip, what a clusterfuck that would be!

[Booyah45828]

Originally Posted by Drew Bru

So...that begs the question..."is it even worth bothering to do this?" AFAIK there's no component failure or water submersion. The bus has around 230K miles, but the diff oil age/condition is unknown. It may or may not have been changed at the school. It doesn't sound like too big of a hassle to do. My reason for the question was mostly because it seems simple enough to do, and if I change the oil then I can be sure of its condition. If, however, it's not something I should be worried about then I'll hold off on it.

If you're concerned about it, pulling the fill bolt and inspecting the fluid is simple and costs nothing. Top it up to the bottom of the hole if it's below the level.

After the inspection, I'd then decide on a course of action. If you plan on putting serious mileage on it, then sure, replace it for peace of mind. However, it would be cheaper to send a sample to a lab and see the condition that way. That test should be around 30 bucks, where a bucket of gear oil is around 200, so 30 bucks might be worth it for your peace of mind.

It's hard to tell people what it should look/smell like, because the sulfur in the gear oil smells so bad anyways.

[brokedown]

Yeah the trick with gear oil is it turns dark immediately and already smells bad so it's hard to say if it's bad or not. I always say if you don't know the last time a fluid was changed, it's time to change it. GL5 is cheap, it'll tak eyou half an hour mostly waiting for slow moving fluid to drip.