Rear Ends Oil Change

[randyp]

Please correct me ifn im wrong, but gonna do a complete oil change on rear tandem on 86 R-688ST dump truck tommorrow. I will need to drain and refill power divider on front, then drain side carrier bearing and refill on front, then drain bottom pot and refill it from rear plug in center of axle housing? and on the rear tandem, just carrier housing and refill then bottom and refill? Does this all sound correct? And if I was to only drain bottom, then would only need to refill from center plug on axle housing? Hate to sound long winded, but trying to get a mental picture of how all that works. Does oil in power divider do a lil swapping around with oil in bottom when your running? I will drain all at one time, and then go to refilling each one. I have changed power divider oil before, so I know it doesnt take much for it, but it has to have that initial fill. Thanks fellow mackians,,,randy

[hatcity]

Y'all pulling the axles too?

It's recommended that you put truck at an angle to fill valleys in axle housing. Leave it bout an hour each side. Then recheck level.

[randyp]

Y'all pulling the axles too?

It's recommended that you put truck at an angle to fill valleys in axle housing. Leave it bout an hour each side. Then recheck level.

no, not pulling axles or anything, just oil change. just a drain and refill and clean magnet plugs,,,thanks,,randy

[rhasler]

Please correct me ifn im wrong, but gonna do a complete oil change on rear tandem on 86 R-688ST dump truck tommorrow. I will need to drain and refill power divider on front, then drain side carrier bearing and refill on front, then drain bottom pot and refill it from rear plug in center of axle housing? and on the rear tandem, just carrier housing and refill then bottom and refill? Does this all sound correct? And if I was to only drain bottom, then would only need to refill from center plug on axle housing? Hate to sound long winded, but trying to get a mental picture of how all that works. Does oil in power divider do a lil swapping around with oil in bottom when your running? I will drain all at one time, and then go to refilling each one. I have changed power divider oil before, so I know it doesnt take much for it, but it has to have that initial fill. Thanks fellow mackians,,,randy

Randy, you should have a plug on the differentials (on the back side, just above the mounting flange) so you can drain the pinion housing oil (aka top housing). You'll be draining the oil from both the top compartments and the axle housings as well as the power divider. I think Mack still has a recommended lube additive for the power divider that has some kind of high end EP rating and a bunch of friction modifiers.

[fifth wheel]

Mack top loading tandems have five oil level compartments to maintan, three on the front rear and two on the rear rear, they all have drain points. None of the oil is shared except the lower housing, it is shared with the hubs.

FW

[rhasler]

It took me a while to find it, but the additive is called Bulldog® Power Divider Top Treat, The Mack part number is 9853-PDT1. According to Mack this additive is designed to prevent power divider snapping or binding. If power divider snapping or binding is experienced, this additive should be added at each rear axle gear oil change. One container (20 fl.oz.) is required for each carrier. I can't speak to it effectiveness, as I have never had the opportunity to use it, wouldn't think it would hurt anything though.

[randyp]

It took me a while to find it, but the additive is called Bulldog® Power Divider Top Treat, The Mack part number is 9853-PDT1. According to Mack this additive is designed to prevent power divider snapping or binding. If power divider snapping or binding is experienced, this additive should be added at each rear axle gear oil change. One container (20 fl.oz.) is required for each carrier. I can't speak to it effectiveness, as I have never had the opportunity to use it, wouldn't think it would hurt anything though.

Okay thanks FW and rhasler. I saw the drain for the top housing, it looks like its gonna be kinda a booger to get to also. I have drained power divider before, have never drained the bottom though. I am going to wait and run by mack place tommorrow and check on that additive you mentioned. appreciate the help fellows,,,randy

[Flynpenguin]

Mack top loading tandems have five oil level compartments to maintan, three on the front rear and two on the rear rear, they all have drain points. None of the oil is shared except the lower housing, it is shared with the hubs.

FW

There is no seal to keep the oils apart. The oil level in the upper is maintained at the level of the cross shaft bearing, which is the same level as the fill plug. As counter intuitive as it seems, if you have a leaking pinion seal, the oil level in the lower compartment goes down since the oil in the upper is replaced by oil from the lower. The oil level in the power divider is also maintained at the level of the bearing. Many of the side covers for the front differential even have a sloping shelf that catches oil as it is flung around by the gears, and drains into the front bearing to provide some circulation.

[randyp]

There is no seal to keep the oils apart. The oil level in the upper is maintained at the level of the cross shaft bearing, which is the same level as the fill plug. As counter intuitive as it seems, if you have a leaking pinion seal, the oil level in the lower compartment goes down since the oil in the upper is replaced by oil from the lower. The oil level in the power divider is also maintained at the level of the bearing. Many of the side covers for the front differential even have a sloping shelf that catches oil as it is flung around by the gears, and drains into the front bearing to provide some circulation.

Thanks Kelly, sounds reasonable to me, appreciate info,,,randy

[HK Trucking]

Mack top loading tandems have five oil level compartments to maintan, three on the front rear and two on the rear rear, they all have drain points. None of the oil is shared except the lower housing, it is shared with the hubs.

FW

That's incorrect.

On initial fill, you fill the upper & lower compartments (and the power divider on the front diff), thereafter for routine maintenance you just check the bottom compartment and keep it full to the filler hole.

If you keep checking & adding oil to the upper compartment each time, it will result in the bottom compartment becoming overfull, and you'll be draining the excess out each time, which makes absolutely no sense, unless you like wasting gear lube.

[randyp]

That's incorrect.

On initial fill, you fill the upper & lower compartments (and the power divider on the front diff), thereafter for routine maintenance you just check the bottom compartment and keep it full to the filler hole.

If you keep checking & adding oil to the upper compartment each time, it will result in the bottom compartment becoming overfull, and you'll be draining the excess out each time, which makes absolutely no sense, unless you like wasting gear lube.

Thanks HK, I filled power divider on front diff, filled upper compartment, then lower compartment, so only one i keep full now is lower diff? The power divider didnt hold much, it has a drain and not much came out of it either. I think I got and idea on how it all works now,,,appreciate info,,have a good day,,randy

[Ricky Beals]

I know this is an old post but since I’m going to be doing this service wanted to ask a few questions. How much gear oil will it take to do the service. I have a 2000 rd 688 so should be same rearend. Also should I add the additive mentioned per carrier? Thanks.

[67RModel]

Don't know if the additive is necessary if you aren't having any trouble now. If you put in a premium quality, full synthetic 75W-90 gear oil that meets the GO-J specification you won't have any trouble. A full drain and fill on the power divider and both upper and lower gear cases should be 34-36 pints for each axle so 72 pints total or 9 gallons. 

[mechohaulic]

interesting old topic; I have to question some of the statements (just for conversation only). 1- the top and bottom oil is not separate. oil from lower banjo feeds top with the rotating bull ring gear.2- with the cost of gear oil; especially todays synthetic  to drain/change oil in rears WITHOUT pulling axles/caps to at least drain wheel hubs of old oil is like taking a second cup of coffee after dumping first that had coffee grounds in cup without rinsing cup out;;; the grounds will still be in cup. the oil in hubs will still be contaminating new oil. just sayin.

[fjh]

yup good  thoughts on that there! But some people think differently ! My honda is auto trans they recommend  only change the oil every 50000 k  All the oil oil is never removed there is no way to flush the trans and torque  From my experience with the product you need to follow this drain and fill rescheme or you end up with a trans with sluggish shifts ! So accentually you do a half change every fifty thou!