Jizzo17

I found a 90 that I need but it came out of a 75 Mack with a 5 speed. And the owner says it’s more like a .85 to one ratio. Does this sound like it could work for my truck?

@mechohaulic the ratio is 1:1. Tag may be there somewhere but just scraping the dirt off with a pick I couldn’t find it. There also wasn’t a washer in there when I pulled it apart. The only thing that came out were the two broken pieces in the picture.

The ID is 13/16. I’m not sure what ratio it is

Here is a picture of my the instrument cluster. The mileage also doesn’t move which is probably because the broke pieces I found inside the 90.

So the 90 is the problem. Where the rod is supposed to seat inside of a collar that has broken into two pieces and fell out when I took it apart.

1985 Mack R600st(?) VIN is 1M1N179YXFA099577 The tach and speedo in this truck is the style with the big clock in it. I am having issues with my speedometer not working at all and the tach bouncing rpms until it catches when I am in the throttle sometimes. I think there is a piece broken inside of the tube that feeds the cable running to the dash because I can turn one end and it won’t move the other any. Is there any way to have that piece rebuilt or can it be replaced? (I will attach a picture of the piece). I am also going to replace the cable. I am replacing the yoke seal coming out of the transmission so I decided to resolve this issue as well

@Geoff Weeks I’ll attach a picture of the wiring. You can see the 4wire and the 7. The blue wire the previous owner had run to a trailer brake controller that was under the steering wheel but it’s no longer there. So I just ran attached it to the left turn signal for the time being.

@Geoff Weeks, that junction box is where both the tail lights and the 7 pin plug for a trailer both meet. The 4 wire is ran from the rear up to the cab on the driver side then along the under side of the cab to the passenger side where it pops up through what looks like a factory hole in the cab corner floor. The 7 is ran from that box inside the cab to a hole somewhat behind the drivers seat. Where it exits between the glad hands. @cruiseliner64, thanks. Me and my brother think so too. We are planning to put a rear axle out of a wrecked truck in it so we can convert it to 10 lug and so the same for the front. But that later on down the road.

Link to the pictures since I couldn’t get them to upload

Found the junction box behind the passenger seat. Tucked in behind a black plastic cover. Thanks again for the help and here are some pictures. It was originally orange as well and the odometer shows 250k which I would think is about right for how clean it is.

Hello everyone. I recently purchased a Brig to use as a farm truck and am trying to get the tail lights and a 7 pin plug for a gooseneck wired in. Unlike my 85 Mack, this truck does not have a 14 point junction for the wires on the engine side of the firewall. It is set up with a glad hands and the 7 pin connector for a trailer and I could just tie in to that but I was hoping to do it a little bit cleaner than that lol. This truck does have the Cummins and 7 speed with a low ratio single screw rear end. Any help or wiring diagrams would be appreciated.

On my truck it’s the right turn that is the stop light. But the issue I’m running into now is that when I wire the red wire from tractor up, which is also the brake light, it flashes both my rear tail lights as if my hazards are on.

Hello again everyone. I am back again requesting help on my 1985 Mack R600ST dump truck. VIN 1M1N179YXFA099577 This time I am in need of some assistance with wiring up some new LED tail lights. I have ran a new 7 wire bundle from the 14pin junction block on the driver side firewall. There is also a 4 wire bundle that is ran from the same block but from different pins and I suspect that it is original to the truck. The issue I’m running into is I couldn’t find any lights that didn’t use the Red wire as a stop/turn multifunction wire. So that’s what I had to use. I will attach some pictures of the wire ends coming from the 4wire original to the truck and to the new LED tail lights, along with the wire diagram for the LEDs. There is also what I have wrote down from testing with a test light. Green from the 4 wire may be reverse but I can’t get that feature to work at the moment. The diagram is correct except I have a blue wire in place of the yellow. Thanks in advance

Update on my issue: With the help of a friend who spent a few years working as a mechanic at freighter we narrowed down the problem to be the emergency dash valve. I ordered a new one and installed it today. Lo and behold I was able to release the parking brakes AND have my parking brake light turn off. I also learned that I need another new brake canister now that I’m getting air to it. Thanks everyone for all the input. Even the remarks on the questionable welds to the frame😂. If yall really wanna rag on my truck I can post some more pictures. next on my list is to get the wiring for the tail lights and trailer lights in working order.

Yellow circle is the double check. Blue line feeds back to the relay valve which is circled in red. Red arrow feeds all the way to the cab through the firewall into the trailer emergency valve in the dash. Which is the one that is leaking out of the side when I push in the parking brake valve. But does not leak when I push the tractor park brake valve in.