C30 Chassis

[Charlie Down]

I have found drawings of both types of chassis from Maple Leaf up Forum and from the GM Heritage Centre website. I have grouped them together for comparison. The CMP chassis is a generic view and needs to be 33"s longer I think, between frames 3 and 4 to become a 134" chassis, but its the clearest view for comparisons sake. The most obvious difference is the angles at the front of the chassis with the MCP chassis having a more downward pointing end to the frame. This, I presume, is to accommodate the I beam axle for 2 wheel drive as opposed to the driven front axle on the C30 CMP chassis. There are other differences such as strengthening gussets on various cross members of the CMP chassis, as well as the lack of strengthening plates on the mid section of the CMP chassis. Despite my research I haven't found the width of the CMP chassis (more likely didn't notice it when looking for other details). I know the MCP chassis was 25-7/16" at the front and 36 at the rear and had a wheel base of 134-1/2". The MCP chassis diagram isn't great but ok for comparison. Ideally a better diagram would be helpful. I have attached another drawing to show the MCP strengthening plates on the mid section of the chassis. Hope that helps.

[Grant Bowker]

By coincidence we were walking around the CMPs in the field today and the width of the frame (outside of rails) is 34".

[Charlie Down]

I got some measurements for a chevy Blitz chassis courtesy of Allan Mazlin, from MCP Vehicles Australia. I've added the measurements to my comparison slide of the MCP chassis for clarity. The MCP Chassis is wider at the back and narrower at the front compared to the CMP chassis. I would have thought the CMP would be wider for military use to make it stronger and more stable. Surprising result. Also the spring hangers seem to be arranged differently. According to the GM Heritage site the MCP rear springs with auxiliary leaves were 46" or 1168mm long and 2-1/2" 63mm wide. It would be interesting to compare blitz rear springs to see if they have been modified (lengthened or shortened) with the rest of the CMP Chassis. I believe the MCP chassis had extensions to fit the Military front bumpers on, which made the chassis even longer.

[Hanno Spoelstra]

Good work Charlie.

See http://www.mapleleafup.net/vehicles/.../chevspec.html for spring specs

[Grant Bowker]

I'm not sure when it started (one source gives 1938) but I'm fairly certain that the 34" outside width of frame rails is a SAE standard, established to permit interchange of bodies between chassis of different manufacturers (to save body makers from having to make different bodies for Ford, Chevrolet, Dodge, etc.). In the same vein, the distances from back of cab to rear axle are also very close to standardized - for the same reason.
One reason that the lighter modern pickup trucks still have wider frames is that they are pretty much designed to have proprietary bodywork and single rear wheels rather than specialist manufacturer bodies and dual rear wheels.