Re: What size Rear Wheel Cylinders?

Posted by BH On 2012/2/28 11:00:32

Thanks for providing that copy.

Interesting that the bulletin number is handwritten (same as the photocopy that I inspected) - likely due to the hectic times that followed the shutdown of Detroit operations. The paper trail is rather curious over the relative timeline; for example:

56T-22 is dated July 12, 1956, and is signed as usual
56T-23 is dated July 20, 1956, and signed as usual
56T-25 is undated and lacking signature
56T-26 is dated November 20, 1956, but lacking signature

So, this bulletin, dated October 19, 1956, is rightfully noted and should be considered as 56T-24.

Getting back to nuts-and-bolts, SSB No. 344, in addition to advising of an improved type of rear drum for this problem, reiterates the recommendation of smaller diameter rear wheel cylinders. Given the additional steps provided in that bulletin to address the complaint, it seems that the brake shoes were not fully seated against the anchor pin, following pedal release.

Of course, that condition could result in dragging, which in turn, leads to premature wear of the linings. Given the self-energizing design, I can see how that could also lead to grabbing.

The idea behind using a smaller diameter cylinder must have been to provide improved shoe release and seating (vis-a-vis nominal residual line pressure) by increasing the relative effect of the return spring. Apparently it was easier to fine tune cylinder size than mess around with springs.

While there's no need to follow those recommendations if the vehicle does not exhibit such problems, this is good info to have on file.