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Macktruckman

Eaton behind maxidyne

Question

I have a 1978 R685ST with a 285 maxidyne and the 2 stick 6 speed with 4.17 rears and tall 24.5’s. Truck is getting a new cab this week and paint job. Old cab is rusted out badly. I have an Eaton RTO14909MLL from a wrecked mixer truck with E7, I think has mounts that will work. Now would be the time to swap transmissions if I want. I was thinking it would help lower my rpm at highway speed and give me a little more top end and maybe help me out on hills. I live in an area with lots of hills. Pull a lowboy to move my equipment and pull an end dump. I like the 2 stick but the gap from 4 to 5 is pretty big with all the hills and I can only get about 60 mph or so on flat ground to the floor tached out. Transmissions look to be within 1”-2” of each other in length. U joints different. Would it be worthwhile to swap? Since the cab is off anyway 

thank you 

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You can always ask around here and see if someone has a Jake brake on a spare engine they'd part with. You need all the under valve cover parts including the risers, plus an offset tip turbine adapter/plus offset hose going from intercooler to tip turbine, plus clutch/throttle/dash switches.

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We have a couple old mixers with the 4 valve engine. Mid eighties models they were 250’s with the 2080 transmissions that the dealer upped to 300 and restamped the id plates. Pump and injectors out of one of those work to recalibrate the 285?

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Thank you.  I like the idea of the jakes. But I’m really after that taller top gear. Reduced engine speed in high gear is a big reason for the consideration 

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With my handle of course I'm gonna argue for the Maxidyne. That said, there's applications where a conventional torque rise engine and more gears works better. But first you might want to make sure your engine is putting out the power it should- with the gearing you've got a 285 HP Maxidyne should be good for about 63 MPH on the flat at which point the 2100 RPM governor starts to shut off the fuel flow. If you're running over OK's 85,500# weight limit you might need more power to run 63 MPH, and going up to the 315 HP rating might not be enough.

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Well I’ve used it like this for a few years. I just remembered the Eaton out there and my imagination started churning since it’s in the shop and all apart. Lol. Thought it would be nicer and could pick up a few more hay haul jobs that would be a little further mileage. Would make it a little more comfortable for the longer days

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I really like the maxidyne too. It will pull a full load down the flat road no problem. It’s very sting in the pits and on sites. And it probably runs really close to that 63 at 2100. Running 65 at 1750-1800 would make me happier and Like I said before, in the hills a gear between the last two would help. 

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I’ve heard that the jakes or dynatard is hard on cams...

is that not so?

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By the way this truck doesn’t work solely on its own. It works together with my dozer a backhoe and a 15 ton excavator. 

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The equipment doesn’t tax it. 

That end dump loaded heavy is a little different. 

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Whatever I decide to do, I have a whole lot more information to work with than what I knew and I am very thankful to each of you guys again for your helping me out. I appreciate it more than I can tell ya

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Rob,

The old cab and doors are rusted out severely. It was an oil field tractor that pulled salt water tanks. The engine has about 300,000 miles and does not leak or use oil. It’s rough and it’s loud. But it’s been very trustworthy. Refurbished cab and interior with new dynamat and sound insulation and some interior panels from a wreck. I’m actually going to install a stereo if it works out. Lol.  I’m fabbing up a cab air ride (to help counter those camelbacks, lol) and it’s getting a pair of new used 6” stacks and new rubber. A Lund sunviser off another wreck and new paint. I like the truck. Very simple. It is awful to service... has 3 big oil filters and holds 14.6 gallons of oil. Lol. That hurts. Lol

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I’ve rode many rough miles in r models. Riding along with my dad. The old mixers didn’t have a passenger seat so I sat on a rotella box. 

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You'll love the air ride cab. Nice thing about the big oil pan and 3 filters is 25,000 mile oil change interval. What's hard on the cams is when a tappet lifter face breaks. Wipes the lobe off the cam pretty fast. We just had to replace one for that last year. Good thing we had a spare motor here, Mack can't get the cam anymore. Maybe PAI has them? I've only heard of PAI from guys here, never dealt with them.

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Thank you for the info Joe. We have an 81 model that is spec’d about identical to this one. Difference is it has the charge cooler in front of the radiator and it has air ride on the cab. It’s where I got the idea for that. It is quite a bit better riding. So I agree. I think I’ll love that. 

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If I can figure out how to put up pictures I’ll do that and some before and after pictures when I’m finished. Be a week or two more. I won’t haul anything off so it’ll be here if us Mack guys need something. Lol. Where do you hail from? We got a little snow here today too

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Found the PAI with a little google help. Didn’t know about that place 

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Bout the same here. Supposed to be 3 or 4 in the morning. Hey I bought the vinyl covered cab rear wall liner and door panels out of a mid 80’s cab. But I need a headliner. Both my old cab and new are the old plastic looking one and both are cracked up pretty bad. You have any suggestions on where to look?

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You ask for Mack at a salvage around here and they act like you’re asking for spaceship parts 

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I tried putting up a couple pictures but it says upload failed 

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1 hour ago, Macktruckman said:

I’ll try again another time 

I haven't figured it out yet either, but I think you have to downsize the picture file size.

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Well men, I’m making some headway. I still haven’t figured out how to resize and put up pictures. When I do, I will. I have the cab and hood off and the transmission out. I’m in town today getting a new clutch and some pto parts. Little by little it seems. Lol

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