Bought new to me 1979 Mack Dump Truck

[Gunny65]

I just bought a 1979 Mack T/A rotating bed dump truck. I know nothing about it other than it was used on the railroad. The railroad track wheels have been removed but the rest of the hydraulic mechanism is still attached and working. The bed rotates easily to both sides and raises and lowers as it should. It is hard to start but when I do get it running, it runs fine. Really, I know nothing about Mack Trucks other than the name. I don't even know what engine it has, the transmission, how some of the controls work, etc. I just got a very good deal and I needed a dump truck for working around on my property. It is a well-used but still a good looking truck. I want to get it running better. Find out what I have, model #, engine, trans, etc. It has years of gunk built up on it (motor, drive train, you name it). I am joining this site in order to read and gather information on the truck and get it into a trustworthy addition to my property enhancement equipment. I previously bought a 1991 M934A2 6x6 military truck and got it running and fixed up using a similar forum for military iron. I then bought a "well-used" excavator and used a similar heavy equipment forum and got it running/fixed up. Now I am hoping to access the cumulative knowledge here and then give back what I can. Thanks.

Oh, and if anybody has an initial idea of what I have, other than a Mack dump truck, please feel free to let me know. I like to know what I have and how to keep them running.

Again, thanks.

[mechohaulic]

quick look at picture you have a DM600. tag on drivers door or right frame rail by steer tire will have model/serial number.

[mechohaulic]

is there still a shift pattern  on the dash .one stick or two?

[Joey Mack]

Awesome !!  Welcome to the Dog Pound...    You will find out quick, that all of us love pictures..... lot's and lot's of pictures...   Jojo

[mechohaulic]

difficult to see in picture - must be a brown /wrap dash and dry air cleaner. more pictures always help== interior/ open hood engine pictures 

[mechohaulic]

have seen side dumps ; can't say I've ever seen a rotating dump. looks same as excavator turn table under dump body. municipality's and government  contractors are always good at coming up with weird ideas.

[mrsmackpaul]

Welcome to the forum, apart from.a Flinstone Mack with a off set cab I can't you much

 

But yeah a DM 600 Im pretty sure is what it is 

Paul

[The Rubber Duck 006]

2 hours ago, mechohaulic said:

have seen side dumps ; can't say I've ever seen a rotating dump. looks same as excavator turn table under dump body. municipality's and government  contractors are always good at coming up with weird ideas.

That's pretty much what it is. Most of the Rail roads use these for re-stoning the rail beds after new ties have been installed. They are really neat in person to see. Some landscaping company's use a similar style for dumping in tight places etc.

[mowerman]

Wow great choice welcome aboard… bob

[tjc transport]

yup, as said already railroad trucks had the rotator body for replacing track side stone

[67RModel]

Like others have said its a 600 series DM of probably 70s or 80s vintage. Can't really tell too much from the single picture provided. You can look on the outside of the passenger side frame rail just behind the front steer tire. Take a wire brush to that area and you will find the model/serial number. Or if the drivers side door tag is still intact it will be there too. My guess is its a DM685S or DM685SX. ENDT675 237hp Maxidyne engine and a 6 speed lo hole transmission. It could also be an ENDT676 with the turbine charge air cooler too. A picture of the engine will easily tell. Tube type rubber. probably 11.00x22 or 12.00x24. Pretty much the best site truck dump truck you can lay your hands on for work around the property/farm. Its a street legal farm tractor. Slow and low on power by todays standards but very reliable. With basic maintenance and upkeep they are almost impossible to kill. It could probably survive a nuclear blast and keep running like nothing happened. 😂

[Gunny65]

Sorry, it took me longer to reply than intended. Work and life.

Thank you all for responding. I do not have the truck in hand yet. I paid for it but the front tires were in rough shape and no brake lights. I am having a guy I know deliver it. It's going to cost more but I do not have a CDL and it is in another state. So crossing state lines, no CDL, bad front tires and no brake lights...I decided to have it delivered.  Sometime next week. I will get more pictures when I get the truck here.

I am chomping at the bit. I want to get to working on it. Cleaning it up. You know, making it mine. Once it is on the property, I will tear into it to fix the brake lights and get two good front tires.  Surprisingly, the rears are all in okay to very good shape. Thank you again and more pictures to come.

OH, and the first two letters in the VIN are DM. So, DM600 something for the model?

Edited October 7, 2023 by Gunny65

[70mackMB]

Gunny65, Welcome to BMT!     Let us know when it lands at home. Then you can send the VIN number to the Mack museum (with a small contribution) and get all kinds of build information.     .....Hippy 

[terry]

Looks like the big air filter used on the 285hp. series of engines.    terry

[MACKS]

Looks like 24” tube type rubber,good thing the rear tires are in good shape $$$..

[mowerman]

Right?????lol Bob

[DavCut]

Welcome to BMT @Gunny65!

Looking forward to seeing more photos.
Might be worth a bit of research on the working limits of current rotating dumps. Pretty sure most on rail have some sort of system that anchors the truck to the rail when dumping, but I could be off base here. You may even find that the swivel/hoist/bed manufacturer is still around as a resource. 

[Gunny65]

I got the truck home today. Drove it 115 miles with no break downs. I couldn’t find anyone coming this way to deliver it so just took a chance and drove it.  I had to adjust the clutch pedal as the clutch was slipping.  I can’t down shift at all.  Trans won’t stop rotation when down shifting and just wants to grind. Clutch started slipping going uphill.  That is when I stopped and adjusted the clutch pedal return bolt just to make it home.  Lots of little things wrong.  Rpm, speed and fuel gauges do not work. Got the brake lights working.  Bad wiring and rusty bolts were the problem there.  Anyway, it is home.  More pics coming in a day or two.  Guess I should start a thread in the proper forum after posting pics.  Thanks everyone for the welcome and help. 

[JoeH]

Unsure how familiar you are with trucks but I'm gonna guess not.

You don't shift it like a car/pickup, this is a Constant Mesh transmission.  You "double clutch" or dont use the clutch at all for shifting.  There's no Synchronizers to match gears for you, you have to do that yourself with the accelerator pedal with foot off the clutch while coasting between gears.

 

Also there is a "clutch brake" that stops the trans from spinning when you push the clutch pedal ALL the way to the floor.  These break, get abused and worn out, and are easy to replace once you're familiar with them.  There's a step by step process to adjust the clutch and clutch brake, so while what you did got you home, it wasn't the right way to adjust the clutch.  The clutch itself gets adjusted by a bolt head on the clutch itself that's accessed through the window on the underside of the bell housing.  Clutch brake gets adjusted through clutch linkage. One has to be done before the other, I forget which.  Done properly your clutch pedal should have 2 inches of Freeplay before you feel the clutch springs start to resist pedal travel, and the clutch brake should engage on the last half inch of pedal travel before the it bottoms out to the floor.

Take note, the clutch pedal should only ever be pushed to engage the clutch brake when the truck is stopped and at an idle. When "double clutching " you are only punching the clutch to about an inch or two into the clutch spring resistance zone. You are not punching it all the way to the floor.

[Gunny65]

JoeH, You are correct. I am not very familiar with them. I used double clutch when I was a young man in the military but that was a long time ago and not often. This trans is a single stick, reverse, with 5 gears. I did try the double clutch method but either I didn't do it right or it just didn't work. I think I pushed the pedal to the floor when trying the double clutch. I also tried a quick push/release to disengage, and then another quick push/release to re-engage. I tried to keep the rpms up when double clutching but no luck for me. I never tried to change gears without using the clutch. I still have some learning to do. LOL. Oh, and you are correct the way I adjusted the clutch pedal was not correct but it was just enough to get me home. An emergency fix. My knee was up by the steering wheel after moving the bolt about a quarter inch. It wasn't comfortable.

From the beginning, the clutch pedal had no play.  It was under tension immediately and disengaged, in about that two inches, of the initial movement. I assumed that was why the clutch was slipping when I started up the first major hill we came to. Unfortunately, I didn't notice the slip until I saw some smoke and smelled it.  I thought the truck was just bogging down due to the hill. I will read up on how to adjust the clutch correctly as I had no idea. Thanks for the heads up.

I did not know the clutch brake is only used when stopped. I thought it stopped them while driving as well. You know, to synchronize when shifting. Is this only in older trucks? Big trucks? or all trucks that use a clutch? 

Thanks for the help. That is exactly why I come to these types of forums when I get a new to me piece of equipment.

[Geoff Weeks]

Linkage gets adjusted 1st and should not need re adjustment unless someone has monkeyed with it. Because the lever is on a shaft it runs in a arc, you want the center of the arc, where mechanical advantage is the greatest to be where the clutch is pulled/pushed. The internal clutch adjustment is for wear and moves the release bearing in or out.

 Clutch brake is just so you can get it in or out of 1st or reverse with the truck stationary. It is not used in normal driving.

[JoeH]

Rear Trans(S)Forward Trans(C)Engine

(S) is the shifter (C) is the clutch.

You have three different spinning sections going down the road, which can be separated from each other at by either S or C, or both.

Rear Trans is fixed to the driveshaft, and all gear sets are always spinning, hence "Constant Mesh".

Engine is always spinning at whatever speed the RPM gauge says.

In a synchronized transmission (not what you have) unused gear sets are not spinning until you try pushing it into a gear.  Synchronizers match the gear speeds together for you.

Looking at my above diagram: when you're going down the road and you go to shift you break the connection between the wheels("Rear Trans") and the engine by putting (S) in neutral.  Now you have to use "Engine" to spin "Forward Trans" at the right speed for the gear set you want to be in.

"Double clutching" you tap the clutch to facilitate getting into neutral, then you match engine speed to the gear you want, then you tap the clutch as you slide into the gear you want.  Basically all the "double clutch" action does is take the tension off the gear teeth so that the shifting mechanisms can function without being under load.

[JoeH]

Once you understand all that, then you have to learn to do it, lol!  There's lots of factors that play into making it harder. Rolling resistances working to change your vehicle speed, whether it's soggy ground or going up a hill, or going down a hill, all throw off your timing and you'll have to learn to adapt to the miriad of scenarios you may find yourself in.

 

Because you said your truck is a 5 speed single stick, I'm gonna guess the VIN starts DM685SX where the 5 indicates is an ENDT675 engine, which is a 237hp Maxidyne. It's an 11 liter 2valve per cylinder engine.  It's pretty much the same as a 2 valve E6 mack engine. I have one in a yard crane here, and a spare as well. I've also got 2 of the 283hp variant "ENDT676" in running trucks as well as a spare parts engine from my grandpa's truck.

The SX is an extreme duty suspension, the rear tandem would be rated for at least 55,000 lbs on an SX. Sometimes rates higher.  If it's just an S in the VIN then it's typically be a 44,000 lb rear tandem. ST is typically 38,000 lbs, though sometimes 34,000 lbs a T with no S would be a single rear axle truck.

Edited October 13, 2023 by JoeH

[JoeH]

This truck is from an era where the VIN actually told you something about the truck.

[tjc transport]

enlarging the picture shows it has the"big" rears with bolt on axle caps.
those old trucks were built for men, not todays steering wheel holders. 

a lot of them had armstrong steering. 

great air conditioning in the winter, and even better heat in summer. 

get in one at 210 pounds on a summer morning, and get out 12 hours later at 195 after sweating your asterisk off!!!