>.... seen
>many posts about moving up in size. Do the larger sizes bolt in directly
>and sit properly to the shoes?
I just upgraded my four rears to 1-1/8" cylinders. They are bolt-in, no
modifications required. Here are the part numbers that I have for wheel
cylinders:
Wagner F79767 1-1/16" rear brake cylinders
Bendix 29634 1-1/8" rear brake cylinders
CarQuest EW86000 1-1/8" rear brake cylinders
Wagner FD108361 1-1/8" rear brake cylinders
? K27-747 1-1/8" rear brake cylinders
I used the CarQuest number but I don't know if CarQuest operates in Canada.
I don't know for sure if this upgrade improves stopping distance but it
does substantially reduce the peddle pressure required during stopping.
I don't know how long you have been on the list but recently there was a
lengthily discussion regarding rear braking. My understanding is that
during normal stopping, braking on the rears is equal (this is supported by
the fact that the measured wear on my rear shoes is roughly the same). But
the geometry of the rear suspension applies downward force to the mid
wheels and applies upward force to the rear wheels during braking. So,
during panic stops, if you apply the same braking force to the mids and the
rears, the rears will lock up sooner than the mids. Thus, some people have
chosen to use larger cylinders on the mid brakes than on the rear brakes.
I made the decision to keep all four brake cylinders the same size for a
number of reasons. The first being that it was the original GM design. The
second is that I want to spread the braking load (and thus the heat) evenly
between all four rear wheels. Third, I want to keep the wear on all the
rear brake shoes even. Lastly I am thinking that I would prefer having one
set of rear wheels lock up before the other. In my mind the worst case
situation would be to have all four lock up at once. With all four wheels
in the rear locked up you loose lateral stability (you fishtail).
Of course the downside to having mid cylinders and rear cylinders the same
size is longer stopping distance. With large cylinders in the mids and
smaller cylinders in the rears, in a panic stop, the unbalanced braking
force will more closely match the unbalanced downward force on the wheels.
Therefore all four wheels will be closer to skidding and you should get the
best stopping distance (if you don't allow them to skid).
So I guess the choice is between even wear/heat distribution during normal
braking (with all four cylinders larger) vs. shorter stopping distances
during panic stops (using larger cylinders in the mids).
In either case I suspect that using the larger cylinders will improve
overall stopping distance. I am guessing that the rear brakes where sized
such that an empty transmode would not be prone to having the rear brakes
lock up before the front brakes. This would dictate using smaller brakes in
the rear, much like most front wheel drive cars and vans today. But if you
fully load the interior, especially if the center of gravity is low and
towards the rear, then you should be able to increase the braking force in
the rear without increasing the risk of locking up the rear wheels first.
Of course this is just speculation on my part so take it for what its
worth. But anyone who has driven an old pickup truck, with no load and rear
brakes sized for a full load, can relate to the relationship between
loading and stability during braking.
Dave
73 Sequoia
