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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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If you didn't have the hills id say it's be a waste on the maxidynes powerband, they make 90% torque from 1200rpms up. Extra gears are kind of a waste, you're pretty much always in your powerband. And the maxitorque trans has 3 countershafts to handle the torque, the Eaton only has 2. Do you have an engine brake on there? It'll make a huge difference on your stock setup, makes the tall gearing a breeze when you use the engine brake for shifting. I'd start by putting a Jake brake on before swapping transmissions.

Not sure what the top gear ratio comparison is between the two transmissions, that'll tell you if you'll gain or lose top speed.

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1 hour ago, JoeH said:

If you didn't have the hills id say it's be a waste on the maxidynes powerband, they make 90% torque from 1200rpms up. Extra gears are kind of a waste, you're pretty much always in your powerband. And the maxitorque trans has 3 countershafts to handle the torque, the Eaton only has 2. Do you have an engine brake on there? It'll make a huge difference on your stock setup, makes the tall gearing a breeze when you use the engine brake for shifting. I'd start by putting a Jake brake on before swapping transmissions.

Not sure what the top gear ratio comparison is between the two transmissions, that'll tell you if you'll gain or lose top speed.

The top gear in the six spd is direct, no overdrive, and a 4.17 rear with a direct trans means about 60 to 65 at top RPM.    terry:MackLogo:

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Posted (edited)

In this diagram the first ratios shown are reverse:

image.thumb.png.0d821a71c61ad646df6d07f56044eedc.png

I've swapped several Fullers behind "Maxidyne" engines in years gone by. Mostly nine, and 13 speeds. Some drivers liked it, some didn't. Nearly all had to have the governors recalibrated. I would suggest you recalibrate the fuel pump to an ETAZ673A specification, boost fuel delivery by 15%, and if not there already, install a working pyrometer and use it because into a hard pull she'll smoke and get hot if not watched. You'd be pleased with the power output of that "little" engine however. 

Edited by Rob

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Thank you guys for the suggestions. I’m having difficulty trying to post now for some reason 

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Ok I do know the maxitorque has triple countershafts and I like the transmission. We’ve had very good luck with them. But the others are in dumps and mixers. Short haul trucks. This is a tractor. It does not have dynatard or jakes. Never had that on any. So I don’t have a jake available to me. The 9LL is laying here so it would be a very cheap swap. It has a.73 od vs the direct in the Mack. Should bring highway rpms down a bit. The 9LL also has low gears, at least one even lower than the 107 in the truck now, and 3 reverses. By comparing ratio charts side by side the Eaton also has a gear or two between what is 4 and direct in the 107. Rob, I’m a little ignorant about the different engine codes. What is the ETAZ673A and is it still a maxidyne? I haven’t messed with this pump. It doesn’t smoke excessively.  I believe that the puff limiter is disabled. I love the low end grunt these have for crawling around off-road and for the many gravel backroads. But for highway use it could use another gear before direct and after the current 4th gear for hills and then an overdrive for tooling down the long stretches. Thank you guys again 

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If I didn’t live in the hills and if the speed limit on the highways were still 55mph, I wouldn’t touch it. It would work great. The mechanic that’s helping me now is good. He’s great on Cummins and pt pumps. We just haven’t ever tinkered with the Mack pumps. I’m not opposed to that and I’m the only driver of this truck. But I also need it to be reliable and live.  So I’m not interested in tinkering with the pump if it will cause problems down the road 

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The ETAZ-673A engine is commonly referred to as a 300+ engine. It is factory rated at 315hp and a conventional torque rise engine. Very responsive and a 285 "Maxidyne" is easily modified to run very close to an original 300+ by a competent fuel shop. Both engines look identical on the outside. That 9LL will work well and is a very good transmission for low speed work. As you mentioned I think it would work well if your "Maxidyne" engine is converted to a conventional torque rise engine. Nothing wrong with that engine mounted charge air cooler system but do ensure that core is clean on the backside where the air can readily flow through it. Seen a bunch of them plugged over the years as not given a thought during air cleaner service. \

If'n you have any left over parts from your original cab once done with it I may be interested in the balance. I don't throw anything away Mack and have room to store what other's call "Junk".

What part of OK are you in?

Thanks,

Rob

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2 minutes ago, Macktruckman said:

 I’m the only driver of this truck. But I also need it to be reliable and live.  So I’m not interested in tinkering with the pump if it will cause problems down the road 

You got the right attitude out of the gate. Don't go any more than 15% additional fuel over the 300+ setting an you won't have any problems driven sensibly. The ENDT, and E6 series engines are very capable of destroying themselves if maxed out in allowable settings. No need for that at all.

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I’m 50 miles east of Tulsa and a little ways west of Siloam springs Arkansas off 412. Rose Oklahoma near a little town called locust grove. 

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Rob I don’t wanna lose the maxidyne grunt. It crawls out of the gravel pit loaded heavy with authority. Lol if calibration would cause me to lose the 1,000-1200 rpm power, then that might not be for me. 1st through 4th I’m happy with. It’s long between 4 and 5 and an overdrive would be nice. So I would have to recalibrate the pump to use this 9LL? Couldn’t leave it a maxidyne?

thank you

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As for the cooler, I had it apart about a year ago to replace the gaskets. It was losing boost. So it got a good cleaning last year. 

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Won't hurt that at all. The "Maxidyne" calibration was a lot more flat and constant pulling because of the gear spacing in the transmissions used. With a Fuller and it's closer spaced gearing, the conventional torque rise is more favorable. However instead of running in first you will shift more often much the same as you will with a Cummins engine and Fuller transmission.

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1 minute ago, Macktruckman said:

As for the cooler, I had it apart about a year ago to replace the gaskets. It was losing boost. So it got a good cleaning last year. 

Clean it with every other air filter change. That cooler really drops the intake charge air temperature when clean.

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I know a few people that swapped in a Over drive Eaton be hind a maxidyne to get down the road faster and at a slower RPM. It worked for them but if does change the driving style of the truck.  the low end grunt was there but the gears were shorter. most skiped gears when empty. when on the highway as long as the engine cruised around 1600 and above EGT temps stayed cool and was happy. the engine was built for low RPM grunt but it liked upper rpms to stay cool.

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13 minutes ago, Macktruckman said:

I’m 50 miles east of Tulsa and a little ways west of Siloam springs Arkansas off 412. Rose Oklahoma near a little town called locust grove. 

Spent a lot of time in OKC so know where you are pretty close.

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I have a sister in Norman. They don’t have hills. I’m about 30 minutes from the Arkansas line so we’re in the foothills of the ozarks here. This is the only truck I’ve had with the tip turbine and the water/air charge cooler. So I need to pull that aluminum top off and clean the back side of the cooler fins?

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17 minutes ago, Macktruckman said:

I’m 50 miles east of Tulsa and a little ways west of Siloam springs Arkansas off 412. Rose Oklahoma near a little town called locust grove. 

loaded turkeys outside Siloam Springs one time,interesting trip down, was following another truck that thought he knew a short cut,I don't remember the highway # we got on south of Joplin,but we spent alot of time in the wrong lane to keep from knocking top row of crates off the trailer.

 

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Lol. There ya go superdog 

you know the kind of the roads I have to travel then. Kinda sounds like highway 10 out of tahlequah 

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Posted (edited)
7 minutes ago, Macktruckman said:

I have a sister in Norman. They don’t have hills. I’m about 30 minutes from the Arkansas line so we’re in the foothills of the ozarks here. This is the only truck I’ve had with the tip turbine and the water/air charge cooler. So I need to pull that aluminum top off and clean the back side of the cooler fins?

Pretty flat down there for sure with a lot of red dirt.....

There is a radar site in your area I worked on upgrading some equipment at a few years ago. Last five years working I was engineering projects and replacements for that type of navigation equipment. Been to Norman a lot over the years but don't really know anybody there.

Some of those tip turbine engines we had were slightly modified and had a static pressure gauge added right after the cooling fan but before the core to ascertain when it needed cleaned. I never did those installs but seen several and think they were modifications from owners. Not perfectly certain but thought it a very good idea.

Edited by Rob

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2 minutes ago, Macktruckman said:

Lol. There ya go superdog 

you know the kind of the roads I have to travel then. Kinda sounds like highway 10 out of tahlequah 

we loaded west of Siloam Springs,turned of the highway a little ways and then turned onto basically a solid rock trail up to the turkey farm ,right beside a cannery of somekind.

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51 highway. That cannery is not far from westville. Mine and my wife’s family farmed long before I was born and they both took produce to that cannery

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Rob, where do I find the specs and directions for pump adjustments?

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Or anyone who can direct me for that matter and thank all of you guys again 

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Let us know how it turns out once you have it running.

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