Popular Post South of Heaven Posted September 3 Popular Post Share Posted September 3 (edited) Good morning gentlemen. I'm Jason , I own a small trucking company and just bought a 1991 Mack MH 600 cabover to add to my fleet. It's got the 350 Cummins small cam with an 8 speed manual tranny. I'm really excited! My mechanic is going through everything now. He just did the PM , all fresh oil in the differentials and new wheel seals , bearings and shoes on the drives. Next hes gonna tackle an exhaust leak. He also fixed all the lights and fixed the wiper fluid pump that wasn't working. The AC is not working but we don't have time to dig into that right now. Ok, now the fun stuff.... The cab lifter isn't working. He removed all the hydraulic lines and had the drivers side Piston rebuilt because it was leaking badly. That was a hassle... But after that the cab still won't lift. Hes removing the pump now and is taking it the same hydraulic guy. He thinks that needs a rebuild too and and maybe the check valve inside is bad. Anyone have any experience with this??? I really wanna get this cab up because he doesn't wanna put the new fuel filters and then not be able to prime it. TY Jason Edited September 3 by South of Heaven 11 Quote Link to comment Share on other sites More sharing options...
cruiseliner64 Posted September 3 Share Posted September 3 Cool truck Jason,we bought a Cruiseliner a few weeks ago and couldnt get the cab to jack up.it turned out to be the hydraulic cab lock seals at the back of the cab.the seals were gone and the system would not build enough pressure to release the locks and let the cab raise.dont know if the MH has the same set up but that was our experence.the truck looks really great. Paul 1 Quote Link to comment Share on other sites More sharing options...
BottleHauler84 Posted September 6 Share Posted September 6 (edited) On 9/3/2024 at 1:29 AM, South of Heaven said: Good morning gentlemen. I'm Jason , I own a small trucking company and just bought a 1991 Mack MH 600 cabover to add to my fleet. It's got the 350 Cummins small cam with an 8 speed manual tranny. I'm really excited! My mechanic is going through everything now. He just did the PM , all fresh oil in the differentials and new wheel seals , bearings and shoes on the drives. Next hes gonna tackle an exhaust leak. He also fixed all the lights and fixed the wiper fluid pump that wasn't working. The AC is not working but we don't have time to dig into that right now. Ok, now the fun stuff.... The cab lifter isn't working. He removed all the hydraulic lines and had the drivers side Piston rebuilt because it was leaking badly. That was a hassle... But after that the cab still won't lift. Hes removing the pump now and is taking it the same hydraulic guy. He thinks that needs a rebuild too and and maybe the check valve inside is bad. Anyone have any experience with this??? I really wanna get this cab up because he doesn't wanna put the new fuel filters and then not be able to prime it. TY Good to see a fellow MH guy. Jason, I just recently replaced my cab jack pump on my 93 MH. PowerPacker makes them and it was around $400 brand new. https://ohiohydraulic.com/power-packer-hp50034204-hand-pump-4000psi-35ci-69-spindle/ Also, beware when putting new fluid in that system. Don't mix hydraulic oils or use transmission fluid. It's recommended to use the military aerospace grade hydrulic oil MIL-H-5606A in that hydraulic system for the cab, especially if you are in cold winter area. This (or an equivalent)is technically the correct oil for that system. It's kinda pricy, but it's the recommended oil. I bought a gallons worth and they were super fast on shipping. https://www.aircraftspruce.com/catalog/lgpages/hydfluid5606qt_09-27000.php Edited September 6 by BottleHauler84 Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted September 6 Share Posted September 6 Being a '91 it should have a Big Cam NT88 so if it has a small cam the engine has been changed. By 1992 I think the N-14 was out. If a NT88 350 it will be a CPL 840, good engine, I had many miles on one. When you get the cab up, post the CPL number off the engine tag, that will ID it. If he pre filled the filter, it will start and clear itself. May run rough until the air is out, but I have changed a few from underneath. Quote Link to comment Share on other sites More sharing options...
mowerman Posted September 7 Share Posted September 7 Looks great good luck. I was also thinking the same thing. Small cam doesn’t sound right….. bob Quote Link to comment Share on other sites More sharing options...
Popular Post South of Heaven Posted September 9 Author Popular Post Share Posted September 9 Hi guys, sorry for the late replies. We got a new cab lift pump and that did the trick. Unfortunately we did use ATF fluid.... ughhh. Yes, I was definitely mistaken. It's not a Cummins. Definitely a mack engine. I'll post the serial numbers this week . My first impression is that's it's lacking power. I was around 17-1800 roms and at 66-67mph. How high can I rev this motor? I'm used to running way less rpms in my other trucks (newer Volvo and Freightliner). Lots of fun though! Head turner! 5 Quote Link to comment Share on other sites More sharing options...
70mackMB Posted September 9 Share Posted September 9 Make sure the safety latch drops in place with the cab up. Or get something to brace up the rear of the cab while you are under it. Don't trust just the lifting pump to hold it up. Just mentioning this for a friend............ .....Hippy 1 1 Quote Link to comment Share on other sites More sharing options...
BOBWhite Posted September 9 Share Posted September 9 Yes definitely make sure it's latched before you crawl under there! Check the cab hinges too and make sure they are in good shape and greased. Its a 30+ year mechanical motor so it takes some getting used to when your only around electronically controlled stuff. Check your boost pressure, it should be in the 20-30s depending on load. Macks don't let the fuel rack move much until there is boost so if there is a boost leak it could be your issue. Being a 1991 it should have the E7. Very nice truck! 2 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted September 9 Share Posted September 9 Its likely governed at 2100 rpm's. E-7 will pull, just need to be patient.. much slower than many other trucks, especially the new trucks. 1 Quote Link to comment Share on other sites More sharing options...
mowerman Posted September 9 Share Posted September 9 Looks great have a ball with it bob Quote Link to comment Share on other sites More sharing options...
cruiseliner64 Posted September 9 Share Posted September 9 Looks fantastic.you just cant beat a cabover Mack......well thats my thoughts anyway.good luck with it. Paul Quote Link to comment Share on other sites More sharing options...
Freightrain Posted September 10 Share Posted September 10 Macks are small cubic inch compared to cat/Cummins. They don't drive the same, but will do the same job. Is the 8spd OD? Likely has 4.17 gears and puts you about where you're at speed/rpm wise. 2 Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
Joey Mack Posted September 10 Share Posted September 10 728 C.I.D. in the E-7. 1 Quote Link to comment Share on other sites More sharing options...
Freightrain Posted September 10 Share Posted September 10 Ohh, big block.... 😆 1 Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment Share on other sites More sharing options...
South of Heaven Posted Wednesday at 07:29 PM Author Share Posted Wednesday at 07:29 PM Gentlemen, What are these 2 air actuated switches? And the one/off switch? There are no labels. Is one the 5th wheel slide?? Quote Link to comment Share on other sites More sharing options...
South of Heaven Posted Wednesday at 07:30 PM Author Share Posted Wednesday at 07:30 PM Quote Link to comment Share on other sites More sharing options...
BOBWhite Posted Saturday at 03:00 AM Share Posted Saturday at 03:00 AM Is this truck air ride? It might be to dump the bags. Our truck had the bag dump and diff lock switches in the middle and top of the dash. I know the cartoons warn you about red buttons but I'd say flip it and find out! Quote Link to comment Share on other sites More sharing options...
mowerman Posted Saturday at 01:43 PM Share Posted Saturday at 01:43 PM one looks like fifth wheel slide or jaw release. I don’t think they had those yet. It’s probably fifth wheel slide or like Bob says airbag dump possible I’m thinking it’s too old for that too. I see you got all kinds of good old steel toggle switches. I drive a brand new Peterbilt pretty much everything on the dashboard is plastic….. bob Quote Link to comment Share on other sites More sharing options...
mowerman Posted Saturday at 01:51 PM Share Posted Saturday at 01:51 PM My God dashboard calendar you are old-school. I didn’t even think they made those anymore…. Bob 1 Quote Link to comment Share on other sites More sharing options...
BOBWhite Posted yesterday at 12:22 AM Share Posted yesterday at 12:22 AM I get a new one of those calendars from my bank every year but the newer trucks don't have as many places to put em. Once they get wet they are not much of a use either. 1 Quote Link to comment Share on other sites More sharing options...
South of Heaven Posted 21 hours ago Author Share Posted 21 hours ago Thanks guys. Funny about the calendar! But it works! Yes, it does have an air bag dump and sliding fifth wheel. But I don't get why it's not labeled. Lol 1 Quote Link to comment Share on other sites More sharing options...
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