Gunny65

Yep, I think that is accurate. My color order is the opposite (in actual order) but that sounds correct. I am not towing anything though. The Red is always off/out. If I hit red it sets the other two to off/out. The yellow is on/in for normal operation and the blue doesn't do anything if I push it. While it has the Knob, I think they replaced the trailer lines when they put in the hydraulics and mechanisms for the rail road wheels/axle/etc. I need to look closer but I don't see any glad hands anywhere. There are old stowing spots for the hands but no actual plumbed lines.

I imagine the PO used the rope going through the engine cover as a way to set the basic start up idle where he wanted it. I don't see any other on demand use for it as you can't let loose of the rope and hope it goes back to the starting point since it is pinched as it comes into the cab. I ordered a replacement idle/throttle cable. All the other linkage is there I just may need to clean it up and lube it.

The hand throttle is missing. I found the cable sheath under the dash and followed it to the linkage under the cab. The throttle handle, dash mount and cable are all missing. At least I know what it is now. Thank you.

I have ordered replacement switches. They will be in next week.

Here is what i think is the buzzer box. One of the spades is busted off and there are no wires close to it that have spade connectors. Another shrug.

This on the passenger side of the engine down on the lower end and back of the engine. The rope goes into the cab. I assume to pull on. Anyone know what this is and why anyone would put a rope on it?

I haven't decided what I am going to do with the railroad wheel axles and associated parts. It is a lot of weight but it isn't in my way either. I would like to take it all off at some point. Maybe repurpose the hydraulic cylinders and valves. I also will more than likely never use the turn table for dumping as it would be way off balance and I have no track to hook the stabilizers onto. It would be a bit dangerous I would think. It is cool and all but I really bought the truck simply because it was $1,600 bucks, it ran and it dumped. I put a clutch in it and some work on the electrical and I have an inexpensive dump truck.

Yep, I have three knobs. Emergency, tractor parking, and system parking. I think the system parking is if a trailer is attached. It also has a jake brake (trolly brake, Johnson bar) on the steering wheel post.

I unplugged that switch you saw on the left of my pic. When I did, the low pressure light turned off. I plugged it back in it came back on. I then unplugged the white square looking switch on the right of my picture and the low pressure light came on. I did notice the square switch on the right has 70psi written on it. The switch on the left has no markings at all and looks to be original. Rusty and beat up really. Now that I know where the buzzer is, I am going to see if that has something to do with the buzzer. I am getting closer. Thanks everyone.

THAT!! I have a black box right where you are talking about. It is not connected to anything and I didn't know what it was. Excellent. Thank you. I will take a pic tomorrow. There are not any unconnected wires hanging near the box that I remember seeing but then again, I wasn't fixated on that part. I switched the wires on the new valve I posted a picture of and now the brake lights are not on constantly...however...they do not come on when the brake pedal is pushed, nor at any other time (IE: air pressure at zero, or at full, with parking on or off). The bulbs come on when the running light switch is flipped. At normal brightness now but I just couldn't get the brake lights working, yet. Yep, I expect it to take me a while to figure out the wiring. Lots of wires not connected to anything and lots of wires that are newer that run to headlights, spliced to old wiring, etc. The marker lights do not work. The turn signals do not work (I put in a new flasher unit, no luck there). Right now I just need brake lights and turn signals. I can work the other stuff over time.

Wow, I don't have any of that in the glove box. Mine is totally empty. There is a fuse block under the box but there are no blue boxes anywhere over there. I looked under the drivers side dash for boxes as well but found nothing obvious. I am replacing both of the switches behind the brake pedal. The one you are pointing at and the one to the left of it. The one on the left is the one that shuts off my low air light. The one on the right, you are pointing at, is a 70psi switch. It did not do anything when I disconnected it. I looked inside the dash by all three air knobs (emergency, park, and trailer/system). I do not see a button type switch anywhere in there except on the emergency knob. Thank you for the pics. I am done for today but I will pick it back up tomorrow. I noticed my blinkers are not working. Joy.....

I don't know where the buzzer is. I can't see anything that looks like one. It is a mess in there (in the dash). Lots of disconnected wires, cut wires. Where, in general, might it be mounted?

There are no switches, that I can see, that are directly connected to the main parking system push knob. I took the dash apart and can see in there. There is a threaded opening on the back of the knob assembly with nothing in it. No leaking though. There does looks to be a pressure type switch on the emergency brake knob. For now, these pics show what is connected to the low pressure switch. I can not find the low pressure buzzer. The manual I got is not very helpful. It shows a low pressure switch but I see nothing that resembles that switch. The book pic has an electrical connector on each end. Everything I see has connections on one side. I just don't know what I am looking at. Anyway, pics. The first pic is of the switch I replaced. It is directly under the brake pedal and connected to the brake valve assembly. That assembly is on the outside of the firewall. The second pic shows a switch on the left that has a wire that connects to the switch on the right and that switch wire goes to the low pressure lamp. The other wire connected to the right switch it goes into the wiring loom. Both of those assemblies are directly behind the brake pedal and mounted on the inside of the firewall.

The low air buzzer has been disconnected or does not work, which is totally fine with me. Yes, I have had the truck running with no air in tanks and brake lights stay on with no buzzer. I also plan on pulling the low air indicator light and trace the lines. I am going to assume they should attach to the faulty low-air sender?

I am going to take the dash apart and check the parking brake sensor. Does the parking brake sensor have anything to do with the constant low pressure light staying on even though air pressure shows 120 psi?

D-Day, Are you talking about a mechanical switch that is manually activated by the brake pedal? I did replace what I believe is called the air pressure sensor switch. That switch is activated by air pressure off of the valve assembly that connects to the brake pedal. This valve is located on the outside of the firewall right under the brake pedal. The switch is round and has two wires connected to it via two small nuts and the switch itself is connected via threads to the valve assembly. I will look around for another switch near where you indicated Joey.

1979 Mach Dump Truck, DM685SX. Air brake system. The brake lights are staying on all the time. Even when the truck is not running and the key is off. I can only shut it off by turning the battery power disconnect switch off. I replaced the air pressure sensor switch as the old one was rusty and one wire was disconnected. That didn't help. I have ordered a manual but it won't be in for a few more days. Suggestions on what to do next? The low pressure air light never goes off even when the system is fully charged. The low air alarm does not go off either, which I don't mind. I am not sure if these problems have anything to do with the brake lights staying on at all times.

I went out to warm the truck up (1979 DM685sx T/A Dump Truck) and noticed the tach and speedometer are not working...again. They started working for a few days and now they are not working again. No movement on either one. Suggestions on where to start my testing? I have two manuals but neither one covers gauges. If anyone can also point out where I could get a manual for the electronics end of it I would appreciate it. Thanks.

It took me a while but I got the new clutch in. I put in the Eaton 9 spring ''Easy Pedal'' clutch. Yes, I went ahead and paid a local guy to put it in. He was backed up so it took a while but I now have a new clutch. Thanks for all the suggestions. Now I need to get some other things working. It is fully usable at this point but there a lot of little things that need attention. I will make new posts for those questions. Again, thanks everyone.

Yep, it is the swivle, Ex-railroad dump truck. I thought T/A meant Tandem Axel? Is that correct? At one time I was thinking triple axle but later reading led me to believe it is tandem. Correct me if I am wrong. Thanks. The transmission is connected via linkage rather than cables. External linkage anyway. Not sure inside but it looks like the triple shaft "V" shape that JoeH described. I did have a helper but he had to move for job purposes. Now I do things alone but with a lot of safety/self-preservation planning. I will buy a trans jack and modify as noted above. Make a cradle on the jack so to speak. I MAY have a diesel engine mechanic that could help but he is pretty busy. We will see. I didn't see to much oil leakage around the rear main but thanks for the heads up. Good ideas on what to accomplish while I have the engine more accessible. The good thing is this truck model does not have a passenger seat so I don't need to remove that. I need to clean the cab out any way to access the panel you are referring to. That would not have crossed my mind, I doubt. Thanks. I planned on removing the prop shaft, lowering the trans, securing it, and then doing the clutch work in between the open space if possible. I think it is possible based on looks under the truck. I believe I found the proper E7 flywheel. Not as expensive as I had expected. That was nice. Still have not found a clutch plate, springs, etc. I need to do more reading. Thanks everyone for the input/help. All of it helps. BTW, this operation isn't going to happen till spring but I need to research and buy in preparation for the job.

I did find the switch and it is bad. It is right under the floor board, outside of the cab, where the brake pedal air hoses connect. When I hooked the wiring back up, it just made the brake lights come on at all times. Thanks all.

Joey, I like the idea of changing to more readily available parts that fit. I need to take it apart anyway so why not? I will look around the posts here and see if I can find more info on what you are describing. Thanks. JoeH, I am pretty sure I can do the repairs. I did rebuild a 700R4 once. The weight of this trans is the biggest issue. I can do the work, it is the crashing down weight thing that worries me. LOL. I will need to invest in some tools specific to this operation though. I have no clutch tools at all. I have Lots of tools, just never worked on clutches before. It has always been: how much does the repair cost, can I buy the tools needed and so it myself cheaper than it would cost to pay someone? Then I do it myself and end up with more tools. Win, win for me.

I have a 1979 DM685sx T/A Dump Truck. The clutch is worn to the point it can no longer be adjusted and it is slipping. I believe I have the MaxiTorque Transmission (TRL107) with MACK clutch. The ID plate says: (REGU.S. MACK Maxitorque Transmission PAT.OFF) There are no other numbers or markings on the plate (top left side rear of trans housing). Where should I go to buy clutch parts for this year and model? I found a service manual that will help me remove and install the clutch. Any pointers would help as well. Thanks!

I came here to learn so no big deal to me if it goes further than my intended questions. This is all helpful. I read up on how to adjust the clutch engagement and clutch brake. Hopefully I can get to it in the next few weeks. You know, before the snow falls. I have to work on it outside so weather is a factor. Hopefully the clutch isn’t to far gone to adjust it properly.