Jim,
I think a better question we might ask ourselves is why didn't those GM
engineers put larger cylinders on the mid axles ?
Pass along to Richard Anderson that my parts book says all GMCMH came with
identical wheel cylinders on all four back wheels.
If GM made this change, it seems it was after May, 1979 when my 78z GMCMH
parts book was published.
I think you and Richard will probably find some owners, rather than GM,
changed rear wheel cylinder size in an effort to improve the braking.
GM designed the system so all four rear wheels supply equal braking in
normal braking situations. My guess is their engineers probably felt this
was the best compromise.
After one makes this modification the mid axle brakes will run hotter than
the rear axle brakes because they do a greater share of the braking and
generate more heat.
This might be a step backward under some conditions, especially bad on long
mountain grades where brakes often get very hot.
So it seems the single benefit of a rear wheel brake cylinder size change
may be to shorten panic stop distances slightly.
I wonder if any proof exists that stopping distances actually improve after
this modification or do we have only opinions ? Does anyone know what the
actual reduction in the panic stop distance is ?
If not, some data on locked wheel tire friction versus the maximum
obtainable tire friction would provide some interesting insight and food for
further thought on this issue.
Don Miller
Shenandoah Valley of Virginia
> From: Jim Davis
> Troops.........Richard Anderson said to ask you why the GMC engineers put
> larger wheel cylinders on the front set of wheels in the rear. This should
> give you some sort of a clue as to which set of rear wheels do the
> stopping. Also, in over twenty years in the driveshaft business I have
> never seen a CV suffer catastrophic failure. They always start clicking
> before they go. If you're insecure, go find a large parking lot and start
> driving round and round in tighter and tighter circles. If your CV is
> starting to go, it'll tell you. This is also a good way to find out the
> condition of wheel bearings.......Jim Davis on the Oregon Coast where
we're
> having another 70 degree heat wave.
I think a better question we might ask ourselves is why didn't those GM
engineers put larger cylinders on the mid axles ?
Pass along to Richard Anderson that my parts book says all GMCMH came with
identical wheel cylinders on all four back wheels.
If GM made this change, it seems it was after May, 1979 when my 78z GMCMH
parts book was published.
I think you and Richard will probably find some owners, rather than GM,
changed rear wheel cylinder size in an effort to improve the braking.
GM designed the system so all four rear wheels supply equal braking in
normal braking situations. My guess is their engineers probably felt this
was the best compromise.
After one makes this modification the mid axle brakes will run hotter than
the rear axle brakes because they do a greater share of the braking and
generate more heat.
This might be a step backward under some conditions, especially bad on long
mountain grades where brakes often get very hot.
So it seems the single benefit of a rear wheel brake cylinder size change
may be to shorten panic stop distances slightly.
I wonder if any proof exists that stopping distances actually improve after
this modification or do we have only opinions ? Does anyone know what the
actual reduction in the panic stop distance is ?
If not, some data on locked wheel tire friction versus the maximum
obtainable tire friction would provide some interesting insight and food for
further thought on this issue.
Don Miller
Shenandoah Valley of Virginia
> From: Jim Davis
> Troops.........Richard Anderson said to ask you why the GMC engineers put
> larger wheel cylinders on the front set of wheels in the rear. This should
> give you some sort of a clue as to which set of rear wheels do the
> stopping. Also, in over twenty years in the driveshaft business I have
> never seen a CV suffer catastrophic failure. They always start clicking
> before they go. If you're insecure, go find a large parking lot and start
> driving round and round in tighter and tighter circles. If your CV is
> starting to go, it'll tell you. This is also a good way to find out the
> condition of wheel bearings.......Jim Davis on the Oregon Coast where
we're
> having another 70 degree heat wave.
