A fact not known to most but once it is explained it is very understandable. “The rubber products that were produced prior to World War II (and during the war there were rubber shortages) did not combine well with petroleum based lubricants.
One of the best examples in the automotive field was leaf spring shackles. These connect leaf springs, usually with the frame rails of trucks and cars. Because the friction point of a shackle is a steel pin moving inside a brass bushing, there “must” be a lubricant separating the two materials. Otherwise, at least the softer brass will be short lived and much rubbing noise will be heard.
As most know, shackles have grease fittings so this lubricant can occasionally be forced between the two materials. With this proper maintenance the shackles can be used for many years.
When lubricating the shackle through the grease fitting a seal at each end of the pin has a seal that prevents the lubricant from leaking out of the shackle. Then the seals cannot overcome high pressure and they leak!
NOW FOR THE POINT OF THIS ARTICLE:
To eliminate the pre-World War II rubber seals from contacting the lubricant and deteriorating, GM used rubber cork seals. This solved the problem! Oil based material did not affect cork.
The photo is an excellent example of early round shackle seals of cork in an often driven 1938 Chevrolet ½ ton belonging to Glen Andrews in North Carolina. He “ground up” restored this show winning pickup that is about as it came off the assembly line 85 years ago. There was no question. The shackle had to have cork seals.
THIS IS THE BEST PROOF THE ABOVE IS TRUE:
This photo is from the Master Parts Catalog, effective March 2nd, 1942. It shows Group # 7.440 (Front) and 7.443 (Rear) use the same part # 593705 for front or rear in cork.
Front
Rear
