Auto swap DMM690

[Mandrewoid]

Hi everyone, I have a DMM690EX with a em6275L and a maxitorque 8 speed.  It's a 6 wheel drive and the transfer case has a 2 speed air shift. I have another thread on here about the building of it. She's quite a beast and hauls 6000 USG of liquid dairy manure, on top of the weight of the truck of course. 

 

Unfortunately, as time goes on it is nearly impossible to find people who can drive. And even I am getting annoyed by the shifting at times. On some routes to the field we have a stop sign, 30 feet of level road and then Half a mile of 12% grade. It's impossible to get into 3rd gear before you start climbing the hill, so you gotta roar up the whole thing in 2nd. Annoying all the neighbors as you go. ( Rusted out exhaust system) 

 

I am wondering if people on here have any prior experience with these engines coupled to an auto transmission? I was thinking an automatic mack garbage truck likely would be a similar mechanical configuration.  

How much work would it take to switch? Do you put the transmission on underneath or do you have to pull the cab off?

[terry]

Probably be a lot cheaper to fix the exhaust.  Terry

[fullfuel01]

check for en ex fire truck. they all had Allison and they sell cheap.

[mechohaulic]

that's one project I never had involvement in ; and never gave thought to. possibly that's a good thing. the transmission or any transmission in a DMM sits above a set of axles! how does a jack cradle a transmission  or is it necessary to remove at least one axle for access ?? with that particular set up having a tank ,job has to be a nitemare. I would do some serious investigating (which is why your on here :I know) to get all technical specs terms of differences an automatic would make if any. defiantly favor the idea "repair the exhaust.  "  ; easy and most practical way out " doesn't solve the 2nd gear operation. 

[mechohaulic]

shape looking truck though. hood scoop :tip  turbine equipped ? 

[JoeH]

That's a monster of a truck!

Is the transfer case for AWD bolted to the transmission or is it a standalone unit further back? I know what you mean on finding people who can drive something other than an automatic.

If you do try to put an automatic on there then you need to do your research, and you'll need a donor truck year 2000 or older. 2000 has a cable shifted Allison HT740 mechanical (I think) transmission, with the only PTO port on the top of the transmission.  By 2003 they switched to an Allison HD4560 computerized automatic.  

I don't know how the automatic transmission's gear ratios will do going up those inclines, I don't think you'll be going any faster up that hill.  Looking at your bumper I'm guessing the top mount PTO won't be an issue because you're running it live on the engine.

[JoeH]

Those transmission models are from my minimal experience. I have a 2003 MR688 that has the HD4560, and just picked up a front cutoff of a 2000 MR688 with the HT740.

The computerized HD4560 has a top mount PTO port as well as a driver side PTO port.

[880joe]

You would probably have to use the 4560 Allison as the have a .60 overdrive where the 750's are direct drive your 2080 will be a .60 overdrive also

[Mandrewoid]

Thanks for the comments everyone. 

 

I do not require overdrive, technically I'm not supposed to exceed about 30Mph since this is technically a farm tractor. My farthest haul is 14 miles, but up and down several steep hills on the way there.  Still beats hauling a tanker behind an AG tractor. Much more efficient hauling.  Probably for most of the close hauls and especially on the steep hill, I could put the Tcase in low, which is about a 2:1 reduction. That would let the auto get out of low gear and do some real work. Or that's my thinking at least. 

To those who wondered, yes the transfer case is divorced. It sits about 2 feet behind the cab. I could slide the tanker off the back to do a big job like this, it's only held on by 8 big bolts. But what I'd never want to do is put a cab back on after taking it off 😂. 

Also, the retarder that autos often have would be really nice. This engine unfortunately is not equipped with Jakes. 

 

Or should I just get the engine+transmission combo out of a fire truck and swap them both in?

 

 

[JoeH]

I think if you had a strictly mechanical auto trans to put in there you'd be ok to swap transmissions, but you'd likely need to come up with a flywheel and possibly flywheel housing specifically for an automatic. You'll have gear control over the auto, so you can cap it at 1st, 2nd, 3rd for speed control to keep your engine speed up to keep your air compressor pumping for your brakes.

Finding a donor engine/trans from a firetruck that matches your current engine is a great idea, though you don't have to swap engines. Just flywheels etc.  Never hurts to have an engine for spare parts!

[JoeH]

Obviously you'll have to have a new driveshaft made up as the trans will likely be a different length than your current one.

[Mandrewoid]

4 hours ago, JoeH said:

Obviously you'll have to have a new driveshaft made up as the trans will likely be a different length than your current one.

Do you think the mounts will be in different spots too? Drilling new holes in the frame normally wouldn't be a big deal, but my fenders etc are in the way.  Perhaps this is why people don't do it. 

I already have an E6-350 spare engine for parts from a truck I dismantled 😅 but it has a 9 speed unfortunately. 

 

I have wondered about stealing the injectors and fuel pump to give me more power. I have already ground my fuel plate in the e6-275 that this truck has. The problem is that it's a 275L so with the low speed governor springs I'm still losing all my power about 1600 rpm on the top side. I'm sure if I had full fuel all the way up to 2100rpm it would be a different beast. 

[JoeH]

I think the frame side of the trans mount is the same, but the trans bell housing side is different. Uses the same rubber donut isolators I believe.

I'll still hold that a donor parts engine/trans combo is a good idea. Even if you don't need the spare parts engine, it'll have the flywheel and housing to match the transmission.