Dear Fellow Roadster-ites,
Last Sunday, Bill Wessel posted an interesting note about rear brakes (see
below) that includes what, for me at least, was a new and subtle detail
about the orientation of the fore-shoe on the rear brakes. As Bill writes,
the point is not covered by the manuals.
The delicate point is that the front brake shoe is not symmetric -- one
tail of the metal frame is longer than the other -- yet the shoe fits into
the rear brake equally well in either orientation, either with the long
tail up (against the brake adjuster) or with the long tail down (against
the wheel cylinder).
Aside: The aft-shoe also is asymmetric, with one tail longer. But the
issue doesn't arise for that part since it fits in only one way, tail down
against the cylinder, in order to accommodate the emergency brake lever.
Bill's short note also covers this point!
So, the question is how to position the fore-shoe. Bill advises putting
the longer tail of the fore-shoe up, against the brake adjuster. As he
puts it simply, "alternate the gaps." That set-up distributes the brake
material more evenly around the circumference than what results under the
alternative set-up, with the long tail down against the cylinder.
After Bill's post, I examined my rear brakes for just this detail. To my
surprise, I found that both rear brakes had the opposite arrangement: The
longer tail of the fore-shoe was down, against the wheel cylinder, not up
against the brake adjuster. (This was how I received my 69 2000, one year
ago.)
Recall, the brake shoes "attach" at their endpoints. (And, of course, they
are held together by upper and lower springs.) The lower endpoint of the
brake shoe floats on the wheel cylinder, where the hydraulic force is
transferred to the shoe, and the upper endpoint sits on the brake adjuster,
which serves as the fulcrum around which the shoe pivots.
With that in mind, it seemed plausible to me that the shoes were arranged
with a left-right symmetry across a vertical line connecting the adjuster
with the cylinder -- all in accord with how my brakes were set-up, and
contrary to Bill's note. This amateur "theory" calls for the same
distribution of torque (along the brake lining) in the fore and the aft shoes.
So, I performed a pseudo-experiment. I reversed the fore-shoe on the right
side only (setting it as Bill advises) for one day's daily driving, about
35 miles' worth. Then I changed the fore-shoes on both sides and ran the
car with the recommended set up on the left side only, also for the same
daily drive. (By the way, both sets of shoes were about equally, evenly
worn to approx. 5/32" - worn to the top of the printing, 'AK B40 FE', that
you find on the edge of the brake material. Of course, I did the best I
could to set the adjusters similarly on each side, each time.)
The outcome was surprising to me. Both days, the brake that was set up as
Bill advises ran noticeably warmer than the other one. I interpret that to
mean that it was working better!
So, I've reset both sides to agree with the configuration Bill recommends:
"alternate the gaps"!
At least on my shoes, I can double-check that arrangement easily, as
follows. On one side of the aft-shoe metal frame is stamped the number
'3909' and on the reverse side is stamped 'XG' On the the fore-shoe are
stamped '3925' and 'XF'.
When you examine your rear brake shoes on a given side of the car, make
sure that either both shoes have numbers showing out, or both have letters
showing out. Numbers out on the right side. Letters out on the left.
OK. Now, can someone explain (in fewer words than I've wasted here) what's
wrong with the "theory" about left-right symmetry across a vertical axis
connecting the adjuster (i.e., the fulcrum) and the cylinder (i.e. the
point of force)?
Thanks,
Teddy
Pgh PA
SRL311 08018
OROC
>Date: Sun, 1 Aug 1999 22:43:33 -0500
>To: datsun-roadsters@autox.team.net
>From: bill/liz wessel <bwessel@itis.com>
>Subject: Re: Adjusting Brakes
>Sender: owner-datsun-roadsters@autox.team.net
>Reply-To: bill/liz wessel <bwessel@itis.com>
>
>One more thing on brakes...
>
>
>True roadster rear cores are very rare these days. Most rear shoes are 510
>style with the holes for locating pins and a emergency brake lever cutout
>in each shoe.
>
>
>This makes it difficult to set the shoes properly on the backing plate.
>
>
>So if you're staring at your shoes wondering just how it all went back on,
>here goes:
>
>
>Find a shoe with the gap in the material on the same end as the emergency
>lever slot and place it on the lever and the piston side of the rear
>cylinder. Then, find a shoe with the gap at the top (adjuster end) and
>place it on the opposing side (keeping the emergency brake lever slots at
>the bottom on either side of the rear cylinder).
>
>
>You want to alternate the gaps in the two shoes, but the piston side (and
>emergency brake lever side) is the one that gets "the gap".
>
>
>Because most shoes these days look identical it can be confusing, but the
>above is how it was originally set up (and the pictures in the manuals
>don't help 'cause they show gaps at each end).
>
>
>Hope that helps.....
>
>
>Bill Wessel
>Madison, WI
>'68 1600, '69 2000,
>and GP race roadstersAt 11:49 PM 8/3/99 -0700, Toby B wrote:
>Hmmm,
> Bill, when my brakes are adjusted just about right, the pedal STILL
>firms up a bit when the parking brake's on. Doesn't there need to be a
>bit of travel in the rear shoes to keep them from grabbing and binding
>as they heat? I've always adjusted 'em down until the shoes scuff the
>drums, them backed off half a turn...
> I LIKE your adjuster trick- beats the open-ended wrench!
>Toby
>
>Do this simple check. Pull your emergency brake on (if it works) then
>hit
>the brakes. Pedal feel firmer? Then you need to adjust 'em.
>Bill Wessel
>
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