1986 Mack DM 685S Restoration HELP!

[Burmy]

A couple weeks ago I purchased a 1986 Mack DM 685S for 10K from Manders in Lakeville. The truck has a 13 speed tranny, and an ENDT 675 motor (235hp). I was told by Manders it had 285hp which would be the ENDT 676. After getting the truck home and power washing the motor block off I discovered it was the 235HP motor (not to happy about it) at the time I did not know to look for the aftercooler and twin pipes to the intake or that DM685 stood for the 235hp motor and DM686 stood for the 285HP motor, I DO NOW THOUGH! I was just going off what the salesman's was telling me! This DM will be replacing our current 1994 RD690s which has 300 HP. The original plan for the DM with "285hp" thought I was getting was to add a bigger fuel pump and make it have 350HP so more then the current RD and then restore the old DM. The DM at least needs 285HP as it will be pulling a 200 series hoe from jobsite to jobsite until we get a lowboy setup. So my questions are now...

1. Can the ENDT 675 handle 350Hp?

2. Where do I find a stock or aftermarket aftercooler?

3. Where do I find a twin tubed cold air intake?

4. Is this motor a 2 valve or 4 valve? which is considered better?

5. Should I sell this truck and try to find a DM686 with ENDT 676 motor?

6. is this the Ecodyne or Maxidyne motor? Which is considered better?

7. How would a ENDT 675 Pair with a 18 speed tranny? over kill is fine 😜

 

***Any other thoughts, ideas or concerns are welcomed and thank you for your time and knowledge!***

 

Other plans for the truck paint it black, covert the bud rims to Hub piloted with Alco or ATX 24" rims. put in 4.17 rears or maybe go 3.94 rears or whatever Mack excepts after 4.17. air to pintle hitch. Hush mats and a better AC system (Any ideas???) remove the pusher axle (better off-road capabilities). Remove all old lights and convert to all LED. get rid of the 20" steering wheel for 16" or 18". Someday a smooth sided box for bigger logo placement with multi functional gate. Also toying with the idea of putting an 18 speed tranny in. I want the low end for hauling equipment and offroad but at least a truck that can do 75mph/ 80mph and not be revved out the entire time.

 

Ultimately  this is just a project truck for me, something old and cool to fix up that will be fun to drive, and will be put to work here and there as needed. 

[Freightrain]

My .02.  Find another truck with the power you want.

Thats a 2 valve Maxidyne motor.  Good reliable motor.  Collecting all the parts to upgrade will be be more then just repowering it if you can find a good 315hp version.  Not sure how safely you can go up with HP on that 2 valve engine?  There are guys on here that can give you that info.

It should have a 5 spd.  I put a 237 in my B and run a 15 spd triplex.  I like being able to split gears even though you are not supposed to need to.

[67RModel]

My 0.02. Pretty much what Freightrain said. Not sure why you would need (or want) to have a Maxidyne make more than 300 horsepower. They just are not designed that way. The torque rise on these engines is incredible. Mack knew what they were doing when they made that engine and matched it to the extended range transmission and proper rears (which makes me think the 13 speed was added by someone later). Trucks with this power train and these specs just were not set up to run 300+ horsepower and an 18 speed transmission. Could it be done? Probably. But I think you would be further ahead to just find one already set up that way with an E6-350 4V or E7-350/400. If I was trying to achieve more than 350 horsepower I would definitely be looking for an E7.

[terry]

Have you contacted Manders to see what they can do for you? I would speak to the owners. I have bought from them before and had real good luck.  terry

[MACKS]

So is that a 237 maxidyne,if so those engines have some serious balls ..

[Burmy]

I could settle for 300 HP I think because that's what I currently have and it does the job the (94 RD690s, which has an E7 I believe, the black and red one in the pictures). I also like the model of DM I have which I think only runs up to 1988 maybe 89 then the body style changes a little bit (more sunk in headlights). So I would have to find a DM 686 or 688 under 1988. I am not sure if they even put 300hp in these older Dm's???... 

 

Yes the 13 speed was put in later, by Manders which is how they ended up with it, to repair it. Somewhere in that timeframe the original owner decided he didn't want to put anymore time/ money into it. I did bring this up to Joe Mander who was my salesmen, I have not heard back from him yet. They were asking $15,500 for it but it had some many little things wrong with it I offered 10K. Which they excepted, which in todays market seems like a pretty good deal, I was always told you'll never be able to buy a tandem dump truck for less then 15K so I feel like I purchased it at the right price to play with it. I also like to split gears, especially running highway loaded on hills. A lot of these older trucks have the twin stick tranny which I would change out immediately if I ended up with a different truck then this one.

 

From what I have read on other forums the ENDT 675 has the same motor block and stroke as the ENDT 676 and 673. I also read the only difference between the 675 and 676 is the aftercooler and then some fuel adjusting. I will try and round up some of the forums on this.

 

Is buying the aftercooler straight from Mack still an option?

 

I have also read a lot of ppl like the 2 valve compared to the 4 valve that it pulls harder, but that you need to keep an eye on the pyrometer on a 2 valve 🤷‍♂️ 

 

Is there any chassis difference between 685, 686, 688 and 690 trucks or is it just the motor & tranny they are built with? I know the S stands for steel frame and SX stands for extreme duty and pry has 55K rear 22K fronts and a walking beam suspension no leaf springs.

[mrsmackpaul]

No matter what the motor you need to keep a eye on the pyrometer when climbing a hill

237 has balls bigger than you can jump over

But honestly if it needs this much changing to suit you are probably better buying another truck

 

Paul 

[Burmy]

Here are some of the forums I have read up on, Only one talks about putting an aftercooler on the ENDT 675.

https://www.motortrend.com/news/0707dp-1973-maxidyne-300-series-mack-engine/

http://www.antiquetruckclub.org/forum/?p=post%2Fmack-e6-675-300-two-valve-8181794

^^^ This guy talks about adding the aftercooler^^^ cgallamore

https://www.thedieselgarage.com/threads/237hp-mack-endt673-info-wanted.87742/

 

https://www.thetruckersreport.com/truckingindustryforum/threads/can-of-worms.36985/

https://www.thedieselgarage.com/threads/350-mack-engine-info.71604/

 

There was a couple more, but am having a hard time finding them now!

[terry]

Maybe manders will give you a good deal on a 676 engine, they are 285 horse, have to have a different air filter and different intake and maybe exhaust piping.  Terry

[blackdog2]

That engine is a 1974 it is not recommend to increase HP if it was mid 80's then yes with push in freeze plug's not screwed in ... 

[Dirtymilkman]

Another "Manders Special"   Everything they sell is pieced together. Getting parts for a truck you buy from them is a nightmare. You usually use your Vin number for parts, on a Manders Special, everything is mismatched and the Vin is worthless in identifying anything. You want a twin stick 6 speed in that truck or a 5 speed. 

[blackdog2]

Check trans to see if it is 12513 or 14513 if 12 the little Mack will tear it up ?

 

[Freightrain]

Agree, for $10k you got a decent buy.  Not sure what all is wrong with it but the combination of parts is likely worth it.

[67RModel]

Yea a good running triaxle for 10Gs it hard to complain about. However, I would verify the rear end ratio and install the proper TRXL107  6 speed transmission in it and go to work. Building that truck into what you are describing is honestly an exercise in futility. You would be so much further ahead to find one already set up that way and tweak it from there. You never did say if the trans was an Eaton or Mack 13 speed. I'm assuming Eaton. Like blackdog2 said if its the 12513 or even a little 9513 that 675 Maxidyne will shred it in short order if you are really working it.

[mechohaulic]

6 hours ago, blackdog2 said:

That engine is a 1974 it is not recommend to increase HP if it was mid 80's then yes with push in freeze plug's not screwed in ... 

i sure had some foul words for those screwin freeze out plugs ; quite a few had to be drilled out . no doubt they worked  better then push ins. lot of block heaters were installed in the day . magnet close by and many holes drill in center slot  to split  plug.

[Freightrain]

I had to remove my block heater on my 673 to install screw on filter housing.  Ya, what a PITA that was to get that insert out after 60 yrs.  Luckily the screw in plug I replaced it with sealed okay.

[Burmy]

On 6/21/2022 at 6:12 PM, mrsmackpaul said:

No matter what the motor you need to keep a eye on the pyrometer when climbing a hill

237 has balls bigger than you can jump over

But honestly if it needs this much changing to suit you are probably better buying another truck

 

Paul 

Yes agree, it is weird a lot of the trucks i'v driven don't come with EGT gauge from factory. 

 by big balls do you mean torque? it seemed to get up to speed quick but going up a hill empty it seemed to want to lug down. So i'm just wondering how it will do loaded doing 55mph up a hill. I'm not worried about its capabilities off-road at the jobsite. 

[Burmy]

On 6/21/2022 at 7:27 PM, terry said:

Maybe manders will give you a good deal on a 676 engine, they are 285 horse, have to have a different air filter and different intake and maybe exhaust piping.  Terry

That would be nice however I am yet to get a response from them. Im thinking they are happy this truck is off there hands at this point!

[Burmy]

On 6/22/2022 at 3:32 AM, blackdog2 said:

Check trans to see if it is 12513 or 14513 if 12 the little Mack will tear it up ?

 

I tried to locate these numbers on the trans, it seems the info plate is missing or is there another place?? Im assuming by how everything else is going with this truck its probably the 12!!

[blackdog2]

Mack trans will take 1800 lbs torque ......12-14 is the torque of fuller ?......being in a dump truck it will be work hard ?

[Burmy]

On 6/22/2022 at 9:08 AM, Freightrain said:

Agree, for $10k you got a decent buy.  Not sure what all is wrong with it but the combination of parts is likely worth it.

That's what I was thinking when I offered $10K, that I would have some $$$ left over to fix and switch some of these things! and by no means do I plan on doing all these things to this truck over night, I would probably run the motor and trans until they need rebuilds then swap them to what I want instead of rebuilding. It does suck the motor is only 235hp and not 285hp I'm just not sure how it will handle pulling the 20 ton hoe from jobsite to jobsite.  First thing will be the rims converted to hub piloted with 24.5 tires if I decide to keep the truck. Then I will probably put 4.17 rears in (just for better highway speed). I am also trying to figure out if the rears in my 94 rd could be switched to the DM. The RD has 4.17's or 4.11 (which I know the 4.11 are not true Mack then, we switched out the rears in our RD 2 years ago and now it does 75mph wrapped out!. 

[mowerman]

Yes my opinion are used to run up 237 you are not going to be happy with her if you’re doing any kind of highway work i’m trying to figure out how an 86 still has a 237 it should be 02 85 or 300+ good luck take it back and tell him you want your money… Bob

[67RModel]

50 minutes ago, Burmy said:

by big balls do you mean torque? it seemed to get up to speed quick but going up a hill empty it seemed to want to lug down. So i'm just wondering how it will do loaded doing 55mph up a hill. I'm not worried about its capabilities off-road at the jobsite. 

Yes they are torque monsters given their displacement but as you know low on horsepower so you wont be breaking any speed records and hills at highway speeds will slow you down noticeably. That is just the physics of moving 70-80,000 pounds with 235 horsepower. However, you can lug this engine down to around 1100 - 1200 rpm and let it pull there without any adverse affects.

Edited June 23, 2022 by 67RModel

[67RModel]

4 minutes ago, mowerman said:

i’m trying to figure out how an 86 still has a 237

The engine is a 1974 model.....must have been swapped out somewhere along the line.

[Burmy]

On 6/22/2022 at 9:40 AM, 67RModel said:

Yea a good running triaxle for 10Gs it hard to complain about. However, I would verify the rear end ratio and install the proper TRXL107  6 speed transmission in it and go to work. Building that truck into what you are describing is honestly an exercise in futility. You would be so much further ahead to find one already set up that way and tweak it from there. You never did say if the trans was an Eaton or Mack 13 speed. I'm assuming Eaton. Like blackdog2 said if its the 12513 or even a little 9513 that 675 Maxidyne will shred it in short order if you are really working it.

Trans is a fuller 13 (least what I was told) it looks like I could see eaton cast into the top of the trans. the info plate has been removed from the trans so not sure what type of 13 it is. Probably not the right one judging by all the other miss leading info I have been given on this truck.

If I did find a pre 1988 DM the way I wanted which I haven't been able to yet. It would be a $30K - $40K truck probably (350hp motor, 13 or 18 speed, converted hubs to hub piloted, 4.17 rears for better highway speed, pintle hitch with air ran to it, with demo box and multi function gate, and painted black ( we paint all our equipment black ). If I slowly build this one into what I want I will probably still have $20K- $30K into it, but the paint will be fresh the motor and trans will be new. I wouldn't be replacing a lot of this stuff until it goes bad either. But maybe you are right also, that's what I kinda trying to figure out I guess.

How quick will the motor shred the trans? 200K miles 50K miles? It will be worked. Overloaded with dirt spilling over the side off road (sometimes in soft soil) is 100% in its future that's why I got a Mack and that's why I wanted a DM. That is what our RD has been doing for years now.