elm Posted February 8 Share Posted February 8 hello, new here. My 79 R600 recently developed an oil problem. a few weeks ago, it blew out a rear wheel seal. I pulled it into the shop and found the top gear case (the carrier housing) to be very low on oil. I filled it back up and continued hauling for a few more hours to finish up a project. the next day I checked the diff fluids again, as it leaked a lot out of the bad wheel seal and found the carrier housing was low on oil again (after only a few hours of driving and sitting overnight). the lower case, was over full by quite a bit. I was in the middle of an important job and needed the truck for a few more days, before I could tear it apart, so I ran it a few more days, and each day, the top case was low a quart or two, and the bottom was over filled. It has no other leaks besides the wheal seal. I assumed there was a bad seal in the carrier housing, so I removed it and can't find anything wrong. infect it appears that right about at the level of the fill plug, there's a hole that connects to the other side (passenger side of truck) that is open to the bottom housing. so, I'm not really sure how it wouldn't leak down. The only other thing I found, was that all the bolts that mount the top housing were nice and tight except for the 3 hard to get ones were snug, but not very tight at all. including one of the ones inside the cover. if that bolt were crazy loose, id assume that was my problem, but I just can't imagine losing a quart or 2 of 90w day through a snugged-up bolt. I don't see any obvious cracks, and the vent wasn't plugged. I'm kind of stumped. I hate to put it back together without fixing anything. Its leaking bad enough, I expected to find an obvious problem, but I didn't. Anyone have any ideas? is this common? I've been running Macks for almost 20 years, and this is my first time ever having to tear into a rear end. although I have noticed it does seem like they normally VERY SLOWLY loose oil from the top into the bottom. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted February 8 Share Posted February 8 mack rears are filled starting at the power divider, then the side plug then the rear plug in the housing, and is only checked at the rear plug in the housing. the rear rear, doesnt have a power divider so you fill the side plug first then the rear plug in the housing.. they are splash lubed and any extra oil in the top reduction goes to the bowl via the spur shaft housing.. fix the leak you see and you should be good to go. Quote Link to comment Share on other sites More sharing options...
elm Posted February 8 Author Share Posted February 8 Well, besides the wheel seal, I don't see an obvious leak. Before I pulled the top case off, I drained about 4 gallons out of the lower housing. (The pumpkin) about twice what it should hold. And the top rear housing (the one on the large aluminum access cover) was so low I could jiat barley touch the oil with the tip of my finger. This can't be right. I don't see how fixing the wheel seal will fix the main problem of oil leaking from top to bottom. I don't think it matters in this case, but I'm working on the rear rear so no lockout mechanism. Quote Link to comment Share on other sites More sharing options...
JoeH Posted February 8 Share Posted February 8 Oil is splashed up from below into the top housing... As Joey said, on initial fill you hit the top housing and then bottom, but after that you only check the plug on the back of the axle housing. Oil should be to the bottom of the hole. You keep putting oil into the top, and it keeps draining that oil to the bottom because its not low up top. Quote Link to comment Share on other sites More sharing options...
JoeH Posted February 8 Share Posted February 8 51 minutes ago, elm said: I don't see how fixing the wheel seal will fix the main problem of oil leaking from top to bottom. It's all connected. Oil is flung up top by the gears down below. So oil is "circulated". There is no problem on your axle other than a wheel seal. Fix the bad wheel seal, then find a way to tilt the axle housing towards the replaced seal so that oil from the pumpkin floods the wheel bearings. Top up the pumpkin and you're done, good to go. Quote Link to comment Share on other sites More sharing options...
elm Posted February 8 Author Share Posted February 8 Interesting..... so how does the oil get back up top after it splashes down? Cus my lower housing (the pumpkin) was Way way over full, and the top was way low. That's normal? Maybe I removed the dump box and pulled the whole thing apart for no reason. I live in a remote town and have literally no mechanics to ask localy so I just jumped in head first. Quote Link to comment Share on other sites More sharing options...
JoeH Posted February 8 Share Posted February 8 It splashes UP! Then excess drains down. Quote Link to comment Share on other sites More sharing options...
JoeH Posted February 8 Share Posted February 8 Top wasn't way low, top was fine. You only check the lower axle housing plug when checking oil level. 1 Quote Link to comment Share on other sites More sharing options...
Solution Joey Mack Posted February 8 Solution Share Posted February 8 the bull gear carries the oil to the top part of the housing. the trough shaft carries it to the power divider like a screw pump. then the excess pours back into the top housing through drain holes. ( front rear),, the rea rear is the same with the bull gear, but the top housing is only splash lubed. 1 Quote Link to comment Share on other sites More sharing options...
Popular Post elm Posted February 8 Author Popular Post Share Posted February 8 Wow. I'm surprised I've never known this after driving these trucks for almost 20 years. I should probably go check my other trucks. I bet they've all got to much oil in them because I've always checked and add if needed to both top and bottom housings. Lesson learned. At least it's an easy fix. I just found out the hard way. Thanks for all the help! 2 1 Quote Link to comment Share on other sites More sharing options...
JoeH Posted February 8 Share Posted February 8 I'm sorry you took the differential out of the truck unnecessarily, that's a chore and a half. Taking the body off too is a other chore and a half. Last one we did we jacked the front axle waaaay up, and pulled the whole axle housing out from underneath the truck. Then did same to the front. Our truck bodies aren't easy to remove, and the truck ate a bearing which busted teeth off some gears, so we decided to swap differentials to get a better top speed than 48mph... Quote Link to comment Share on other sites More sharing options...
elm Posted February 8 Author Share Posted February 8 I should have came here first. Would have saved me alot of time! No worries though. The dump bed comes off easy enough, and the rest.... well, it was a good learning experience. I'm finding not a whole lot of people know much about these old dogs any more. I love them though because I drive almost exclusively off road, and you just can't kill them. And no electronics. You can work on them. In fact, besides a book for the 672ci engine, I never even had a shop manual. And I've got 5 trucks. Never needed a book before. Well... at least I thought I didn't lol 2 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted February 8 Share Posted February 8 really glad you came on board.. there are a lot of smart guys here.. not just Macks or even trucks,, farm tractors and other things too.. and we all get along pretty good too.. jojo Quote Link to comment Share on other sites More sharing options...
JoeH Posted February 8 Share Posted February 8 I know what you mean, these old dogs are great. We have a 79 r686st that we've about worn out, and a 1980 or 81 dm686sx that's been relegated to yard duty. A little mechanical know how and these trucks will last a long time. Having several of the same trucks pays tremendously with spare parts and know how on repairs. 2 Quote Link to comment Share on other sites More sharing options...
Popular Post glenbjackson Posted February 9 Popular Post Share Posted February 9 8 hours ago, JoeH said: I know what you mean, these old dogs are great. We have a 79 r686st that we've about worn out, and a 1980 or 81 dm686sx that's been relegated to yard duty. A little mechanical know how and these trucks will last a long time. Having several of the same trucks pays tremendously with spare parts and know how on repairs. having another truck is pricless motivation wise. im waaaaaaayyyyyyyyy more confident on pulling apart a backup truck.🤪 2 1 Quote Link to comment Share on other sites More sharing options...
elm Posted February 10 Author Share Posted February 10 Yup, you gotta have spare parts. Specially if your remote like I am. I've got 3 runners and 3 for parts. Oldest is a 74 newest is an 89. Plus there's 1 in the local scrap yard. I find my self yanking something off a parts truck a few times per year. Just yesterday it was a bent air can mount. And almost a differential🥵anyone else out there got one with a Detroit engine in it? All mine are 672 mack engines except 1 has a 6v92 Jimmy. It's a total pain to work on it. It doesn't fit real well. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.