OK, driving along sounded like the cab was pretty solid on the frame... similar feeling to my old 3800 because the floor was so rotten the cab was sitting on the frame. Except the GMC has a very sound floor.
I looked under the front cab mounts and not a scrap of rubber left.

Curious what thickness rubber should be there I looked at what the restoration parts vendors sell and didn't find the answer listed, and no clear answer in my forum searching. Then I thought what about the manual, what does it say?
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0103.htm
It does not say what thickness rubber, better yet explains how much clearance should be between cab and frame bracket. Measuring my truck this equaled about 5/16" rubber.

The hardware for my mounts are in great shape, and removed quite easily. Nice working on something that isn't all rusty.

The round rubber washers on the bottom side were still there but extremely hard.

Picking through my collection of various rubber stuff found some new hay baler belt at 1/4" thick, perfect for those round washers. Found a scrap of a large conveyor belt from a quarry, it probably started out thick but had worn thinner in places. This was quite convenient because I could measure and pick where to cut the 2 square pieces from so they were just the thickness I needed.

PICTURE

Above picture shows the pieces. Cut the squares with a utility knife. Cut the round ones with an Allpax gasket cutter . A new old tool I had been searching for for years (new ones are pretty expensive). Finally found this one and it's about the handiest thing ever for cutting nice circular gaskets and washers; handy enough I should have bought one long ago.
The holes I drilled with a 9/16" paddle bit for wood with some little spurs on it, I had it and it worked. The thinner rubber I could have used a hole punch, but the thicker stuff was easier to drill. A brad point twist drill bit for wood is usually a good choice for rubber if you have such a thing, I didn't.

Then to install them used a little bottle jack and a piece of 2x4 under the very front corners of the cab, one corner at a time. Jack it up just enough to slip the new rubbers in. Then let it down and tighten the bolts just snug, not overly tight.

Replacing these cab mounts also improved the fit and function of the hood and the latch.


Next post, heater motor replacement,

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-