Ricky Beals Posted July 27, 2023 Share Posted July 27, 2023 (edited) I had a stranf thing happen today. We were hauling gravel to a very sand soil area. I had just dumped and found an old woods road to turn around. Once i backed up my tires started to spin. I decided I better look for a better spot and as i started forward my tandems started jumping. I raised my bed and noticed the very back tires on passenger side were not turning. The other three sets were. I tried backing up and then going forward but the soft sand and that back passenger set of tires wasnt moving. I finally got back on the road but that back passenger set never moved. Got out made sure nothing was broke, slack adjusters were good. Got back in released parking brake and all four tires started moving. Any idea what happened? next question is how do the rears work. Do i have a power divider? Are the front set positive track and the rear set limited slip? I dont have a button inside to lock the axles. Edited July 27, 2023 by Ricky Beals Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/ Share on other sites More sharing options...
mrsmackpaul Posted July 27, 2023 Share Posted July 27, 2023 So the back RHS didn't turn at all ?? As in dragged thru the dirt leaving a skid mark ? Paul 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535712 Share on other sites More sharing options...
Joey Mack Posted July 27, 2023 Share Posted July 27, 2023 Ricky. The front diff. Will have a longer power divider with an air line going to it. There is a shift fork housing there. The picture of the front diff. Doesn't show the whole thing, but looks like it does NOT have a locking power divider. The rear axle is the main drive axle, the front is supposed to come in when a rear wheel looses traction.. it doesn't work very well. Did you have a stick or a rock stuck in the right rear slak adjuster, that held the brake on. Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535713 Share on other sites More sharing options...
Ricky Beals Posted July 27, 2023 Author Share Posted July 27, 2023 I didnt see anything JoJo but it could have been and just shook out when i got back on road. Mrsmackpaul i didnt have a long skid mark. I could just see where the other three sets were digging down in the sand. Hopefully that never happens again. Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535714 Share on other sites More sharing options...
mrsmackpaul Posted July 27, 2023 Share Posted July 27, 2023 So the wheel must of been rolling then or there would be a mark in the dirt were the none turning wheel was dragged Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535715 Share on other sites More sharing options...
Ricky Beals Posted July 27, 2023 Author Share Posted July 27, 2023 Mrsmarkpaul i dont really know the answer to your question. That rearend was bouncing. When that back tire was off the ground it seemed i was making little hopps forward. When i got out on the road and could watch everything that tire was not turning, the other three were turning and that whole rearend section was bouncing. Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535721 Share on other sites More sharing options...
Ricky Beals Posted July 27, 2023 Author Share Posted July 27, 2023 I think i fgured out my bouncing problem. I was taking off in 1st in that loose sand was not getting traction. Dont know why the back passenger tire wasn’t turning. This happened again this morning and i immediately went to lo and problem solved. Hey Im a rookie. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535733 Share on other sites More sharing options...
Ricky Beals Posted July 28, 2023 Author Share Posted July 28, 2023 Im getting ready to change fluid in the rears. Thinking of going synthetic 75-90 and have a few questions. If i drain all the oil there still has to be some old oil in there. This is not synthetic so will that hurt. now i cant get traditional 80-90 mobile for free. Is going synthetic worth it? Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535774 Share on other sites More sharing options...
mrsmackpaul Posted July 28, 2023 Share Posted July 28, 2023 I'm just trying to understand what happened So if there's no skid mark and no wheel turning then the wheel must not of been touching the ground So for this to happen either something is getting caught on the lead axle stopping travelling back up or the trailing axle stopping it going back down There's not a huge amount of parts on a camel back that could make this happen So perhaps a good look over it all might be the go Looking for any fresh paint missing etc Paul Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535784 Share on other sites More sharing options...
Joey Mack Posted July 28, 2023 Share Posted July 28, 2023 Those rears were born with 75-90 syn. Also the rear has 2 places to drain oil, and the front has 3 places. I would pull the big side cover on each after you drain the top reduction and inspect the bevel gears... When you're fill them, you start at the power divider on the front, then the top reduction, then the bowl. Rear , start at top reduction, then the bowl. 5 gallons should do both. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535791 Share on other sites More sharing options...
terry Posted July 28, 2023 Share Posted July 28, 2023 22 hours ago, Ricky Beals said: I think i fgured out my bouncing problem. I was taking off in 1st in that loose sand was not getting traction. Dont know why the back passenger tire wasn’t turning. This happened again this morning and i immediately went to lo and problem solved. Hey Im a rookie. They will wheel hop in loose sand and do all kinds of things trying to get traction. terry 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535832 Share on other sites More sharing options...
JoeH Posted July 29, 2023 Share Posted July 29, 2023 If you don't have a dash switch up next to the ash tray then you have a peanut style automatic power divider. It requires at least one wheel to spin on each axle before you're "stuck". Not exactly sure how to interpret your particular situation you found yourself in, but I'm guessing your power divider was engaging and you had traction on your forward drive but not as much on the rear, so you had some weird tire actions. If you have the dash switch up by the ash tray then your power divider is manually turned on/off. To use this style you have to stop all wheels, flip switch on, then try going. One of my trucks has this style, I tend to reserve it to get myself unstuck rather than using it to get stuck. If that makes sense. 2 Quote Link to comment https://www.bigmacktrucks.com/topic/73100-question-on-2000-mack-rd-688-rears/#findComment-535873 Share on other sites More sharing options...
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