Why Is The Frame This Way

[tomcat44056]

Im not super familiar with mack but I have driven them and admire them. I saw an old r model frame in the weeds(old front hubs, no factory front brakes) and was wondering why the frame is wider at the front than the rear. I dont recall seeing another make that does this. Is mack the same width in the rear as other makes and just wider in the front?

[fjh]

Im not super familiar with mack but I have driven them and admire them. I saw an old r model frame in the weeds(old front hubs, no factory front brakes) and was wondering why the frame is wider at the front than the rear. I dont recall seeing another make that does this. Is mack the same width in the rear as other makes and just wider in the front?

Sounds like your looking at an RD frame!

I can't tell ya why but

i can tell ya the RD is one tough model , and that give or take a 1/2 inch the frame at the rear was made the same aprox width as most other trucks depending on wether it was a single double or triple frame rail.

[v8superdog]

the r model and a number of other models do that too, its to provide more room for working on the motor, says mack, kinda makes the truck unique. and your right fjh, the RD is one TOUGH model.

[Freightrain]

Unlike most other brands, Mack usually flairs their frames in the front to get the motor lower, giving a lower hood height.

[theakerstwo]

It makes it a lot more fun working on the engine mounts. The old whites and weatern star the GMC and volvos had the rear mounts bolted to the trans. Some dont like them and i dont when putting in a clutch but i think that was a stonger mount system than when the mounts were bolted to the rear of the engine.

[David]

The R frame is wide enough at the front for the steering box and the exhaust to be run inside the frame rails. The rear is only 33" wide (one inch less than most all other trucks) and the trunion is also 1" narrower than the MH, CH, and RW models. This may also explain a different bolt pattern. The exhaust run inside the frame allowed the cab to sit lower and keeps the heat away from the floor.

[mackdaddy]

The R frame is wide enough at the front for the steering box and the exhaust to be run inside the frame rails. The rear is only 33" wide (one inch less than most all other trucks) and the trunion is also 1" narrower than the MH, CH, and RW models. This may also explain a different bolt pattern. The exhaust run inside the frame allowed the cab to sit lower and keeps the heat away from the floor.

Even in the 50's Mack was flaring the front frames. On the LT Mack the supercharger cummins sits right down in the frame giving the LT the neat low profile long hood look. If you look at other makes in that era the superchargers either had to sit above the frame or they notched the frame and riveted a side support on. I saw a G-77 that was straight rails with a charger and Mack did the same technique by riveting the support. Even the CL and RW had a wider frame in the front??didnt they? Seems they also had the large front flare on both rails.

The RL or western R models came with straight rails and they were aluminum I believe. The grill and the height of the hood is a give away that it is an RL.

[David]

The CL, RW II, and MH all had the same frame. This frame had some flair, but also a drop. That was to allow the E9 to fit. The RW I and the Cruiseliner had the same frame. Each rail is in 2 pieces and overlaps and is bolted together under the cab. The front piece also has a drop. The westerns have some flair but mount the steering box different and the exhaust runs between the top of the frame and the bottom of the cab.

[Lmackattack]

My RS has straight rails nose to tail. they taper the top flange of the rails at the front to give more room around the engine compartment. The Steering box is mounted on the outside of the rails. exhaust is routed above the RH rail and runs under the cab. The eastern R models IMO have a better design with the spread rails. this allows better fitment and access to the engine and its componets.

Not shure if the trunions differ in width between east and west R models. My RS has "spacer" blocks placed where the trunion and crossmembers bolt to the frame. It looks as if the spacers are about 1/2. that would be about right if the narrow "eastern" rails were bolted directly to the trunion/crossmembers?

Trent

[David]

The spacer plates are used when there is no inter rail (double frame).