You mentioned dual bore sizes on your WC56 wheel cylinders. I'm not familiar with the WC56
brakes. I'm assuming that you're talking about a single wheel cylinder unit with two
pistons, each with a different diameter. Does the WC56 have adjustable brake shoe pivots
that are anchored to the backing plate, rather than a floating adjuster?
If this is the case, I just want to make sure I understand the logic behind the
dual-bore-size design. See if you agree with my analysis:
Again, I'm assuming a top-positioned, dual-piston single wheel cylinder and brake shoe
pivots that are bolted to the backing plate. With this setup, the forward rotational
motion of the drum tends to apply additional braking force on the front shoe that is being
pushed towards its anchor and away from the cylinder), but it doesn't have this effect on
the rear shoe that is being pulled away from its anchor and towards the cylinder. This
"self-energizing" effect would tend to put considerably more of the braking load on the
front shoe. By using a larger bore size for the piston for the rear shoe, the rear shoe
would get enough extra pressure to make up for the lack of the self-energizing effect and
roughly equalize the amount of work the two shoes would be doing when stopping the
vehicle. Of course, this means that in reverse you'd be putting a lot more braking load on
the rear shoe, but that wouldn't be a big deal, since you're typically not moving very
fast and overheating that shoe wouldn't be a factor.
If my understanding is correct (and if I understand you correctly about the dual bore
size), then there would be either have to be distinct left and right wheel cylinders, or
"reversible" cylinders that could be flipped 180 degrees so that the larger bore is always
facing the rear.
I've seen other schemes used to apply the self-energizing effect to both shoes. Typically,
these would include the use of two separate, equal-size cylinders (one for each shoe), or
a single, dual-piston unit used with shoes that have a floating adjuster rather than solid
anchors (to allow the self-energizing effect to be transferred into both shoes). There are
other schemes as well, but they appear to be less common.
Anyway, is this your understanding of the purpose of the dual bore size? If I made any
obvious errors in logic, or misinterpreted the WC56 brake setup, let me know.
Regards,
Alan
(Salt Lake City, Utah)
Gordon.W.I. McMillan wrote:
> Hi Alan, I've gone to NOS for all brake parts, even if it means using a
> modern equivalent. The only exchange parts I used were Stainless Steel
> Brake Co rebuilt units on the Shelby calipers, and even that was after
> finding out exactly how they processed them.
>
> Using stainless / CuNiFer lines and fittings on an older mil-veh can be
> a problem if you are trying to match modern ends and fittings with DUKW
> distribution 't's for example, as brass 't's tend to strip when used
> with modern (very hard) stainless tubes and fittings. Nothing else for
> it but to persevere and keep spares. I have to sort out unbalanced
> front brtakes on the WC56 now, and the only reason for it I could come
> up with is that one of the front cylinders may be the wrong way round
> (dual bore size on WCs so only should be fitted one way.) regards,
> Gordon 8-)
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