Mack Rears Upper Diff. Oil Level

[Warpman89]

heys guys, i got an 88 r688 with what i believe to be mack rear ends. from what it looks like, there is a separate gear box on top of both carrier/differential housings, separate from the carrier housing. on the passenger side of these gear boxes, there is a 3/4" plug on a side cover, and when i opened them, no oil came out. also, on the front diff. where the driveshaft comes in there is another "box" that requires oil, and once again upon opening the plug, no oil came out...is this all normal or do i clearly need to add more oil? if this still doesnt make sense i will get pics...any help is appreciated

[daveigou]

Hope this helps. The plugs at the power divider and top carries side cover are magnetic. They are only for initial fill and should be checked (for metal flakes) and cleaned at service. After that check oil level at the middle of the lower axle housing.

Dave

Mack axle lube.doc

[Warpman89]

so are the power divider, bevel gear compartment, and differential housing all separate? they all have their own fill and drain plugs. the oil level in the differential is at the right amount, so am i ok, or do the power divider and bevel gear compartment need oil up to the fill plug too?

[HK Trucking]

so are the power divider, bevel gear compartment, and differential housing all separate? they all have their own fill and drain plugs. the oil level in the differential is at the right amount, so am i ok, or do the power divider and bevel gear compartment need oil up to the fill plug too?

As Dave said, the first time you fill the rear end after a drain or repair, you fill all 3 compartments, after that when servicing you just maintain the oil level in the bottom compartment up to the bottom of the hole where the plug screws in.

On the back rear, just fill the upper & lower compartments initially, then maintain the level in the bottom compartment as described previously for the front .

.

[LenRok]

So are the air bags supposed to be up or down when checking the rear bottom plug. As it makes about a 3L difference

Edited December 9, 2022 by LenRok
Typo

[Joey Mack]

Mack rears?  Not much,  but it is a good practice.. and you only check the rear plug for the level..  5mm from bottom of the hole is the low level..  jojo

Edited December 9, 2022 by Joey Mack
more content needed

[MACKS]

2 hours ago, LenRok said:

So are the air bags supposed to be up or down when checking the rear bottom plug. As it makes about a 3L difference

The air bags have nothing to do with it,check the bottom plug hot,after a run..

[mrsmackpaul]

Because I don't and have never had a air ride back end in a truck I didn't think bags up or down would make a lot of difference 

I guess it might rotate the axle housing and this reads different 

However if I think about a normal spring suspension the oil is checked at ride height as thats all it ever is

So to me even if it was airbag, common sense would tell me to check it at ride height as tgats were the axles are as you drive along

But I dunno with this fangled air bag stuff 

Apparently they enhance ride or comfort or some such thing, but really, aren't we kust taking away the good things in this whole experience ?

 

Paul

 

[LenRok]

8 hours ago, MACKS said:

The air bags have nothing to do with it,check the bottom plug hot,after a run..

The air bags rotate the axle when filled. I had a guy do maintenance on the truck and he added oil while air bags were down.  I checked the oil 2 days later while it was still in the shop but I aired up the truck first. When i pulled the plug almost 3litres came out. So i left it there as that's where the axle will be while the truck will be operating. 

[LenRok]

8 hours ago, mrsmackpaul said:

Because I don't and have never had a air ride back end in a truck I didn't think bags up or down would make a lot of difference 

I guess it might rotate the axle housing and this reads different 

However if I think about a normal spring suspension the oil is checked at ride height as thats all it ever is

So to me even if it was airbag, common sense would tell me to check it at ride height as tgats were the axles are as you drive along

But I dunno with this fangled air bag stuff 

Apparently they enhance ride or comfort or some such thing, but really, aren't we kust taking away the good things in this whole experience ?

 

Paul

 

Ha ha thanks for the info. Love the pic

[MACKS]

2 hours ago, LenRok said:

The air bags rotate the axle when filled. I had a guy do maintenance on the truck and he added oil while air bags were down.  I checked the oil 2 days later while it was still in the shop but I aired up the truck first. When i pulled the plug almost 3litres came out. So i left it there as that's where the axle will be while the truck will be operating. 

Ok yeah definitely check them when there level,also I was told to check them hot otherwise the top will leak down and give u a false reading..

[Mark T]

13 hours ago, mrsmackpaul said:

Because I don't and have never had a air ride back end in a truck I didn't think bags up or down would make a lot of difference 

I guess it might rotate the axle housing and this reads different 

However if I think about a normal spring suspension the oil is checked at ride height as thats all it ever is

So to me even if it was airbag, common sense would tell me to check it at ride height as tgats were the axles are as you drive along

But I dunno with this fangled air bag stuff 

Apparently they enhance ride or comfort or some such thing, but really, aren't we kust taking away the good things in this whole experience ?

 

Paul

 

That  "suspension"  must need torque rods or a rebushing. Lot's of side to side sway there.

[mrsmackpaul]

I do believe that rebushing those style of bags is outside my scope of works, or at least the very "Minister For War and Finance" would have a serious frown upon her face 

But a few Bourbons and it probably wouldn't take a lot of effort for me expand into that field of works 

 

Paul 

[Joey Mack]

You have a HELL of a way with words,  Paul...    

[MACKS]

8 hours ago, Mark T said:

That  "suspension"  must need torque rods or a rebushing. Lot's of side to side sway there.

I would like to give them a through inspection before deciding to re bush them or not...😂