I have seen several Hydraboost systems on the GMC. I just saw one at the
Ukiah rally.
http://www.california.com/~eagle/powermaster.html
There have not been many problems with the pressure or travel of the
booster, just the size of the master cyl.
The issue has mostly been that with the vacuum booster, you loose your
brakes when the engine stops running, like when you vapor lock, going up
hill, at high altitude, on a hot day, with crummy gas.
The same thing happens with a Hydraboost. (The GMC also becomes very hard
to steer, but possible.)
So many are installing an electric vacuum pump as a safety for the vacuum
booster system. It is hard to get a backup for the Hydroboost.
http://www.california.com/~eagle/figs/vacpump/vac.html
gene
>I have a few questions about brake modificatios.
>
> On going to 80mm front calipers.
>You will increase pad pressure to the rotor, at the expense of more pedal
>travel. When you go to a larger master cyl., the increase in pressure will
>dissappear. There is a straight mechanical relationship from the pedal
>movement to the caliper pressure. When you have vacuum assist, the int.
>manifold vacuum will help to minimize pedal travel. That's right, the vacuum
>assist isn't there to raise the fluid pressure, but to lessen pedal travel.
>Of course they are the same thing, but in reality there should be some
>trade-off here, the device that sets ultimate pad pressure is the size of
the
>brake booster's diaphram and you leg muscles. Does the 80mm calipers use
>bigger pads, that would help.
> What about going to a Hydrolic Brake Booster like what's in a '83 diesel
>suburban. I have 2 suburbans, one with hydrolic and one with a vacuum boost.
>The hydrolic booster can lock the wheels up at any speed. The vacuum boost
>can't. Has anyone tried this. I've thought about swapping boosters to see
>what happens. As far as rear rotors, it seams like a lot of trouble for
>little gain. How has this conversion worked out for you all? Did it really
>help?
> I'm a new GMC owner, but I have the ability to try anything. I've never
>learned to be afraid of mechanical stuff, in fact I live for it. My GMC is
>32k miles fresh and bare bones stock so there is no place to go but up.
>Yours in mods;
>Markus
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
Ukiah rally.
http://www.california.com/~eagle/powermaster.html
There have not been many problems with the pressure or travel of the
booster, just the size of the master cyl.
The issue has mostly been that with the vacuum booster, you loose your
brakes when the engine stops running, like when you vapor lock, going up
hill, at high altitude, on a hot day, with crummy gas.
The same thing happens with a Hydraboost. (The GMC also becomes very hard
to steer, but possible.)
So many are installing an electric vacuum pump as a safety for the vacuum
booster system. It is hard to get a backup for the Hydroboost.
http://www.california.com/~eagle/figs/vacpump/vac.html
gene
>I have a few questions about brake modificatios.
>
> On going to 80mm front calipers.
>You will increase pad pressure to the rotor, at the expense of more pedal
>travel. When you go to a larger master cyl., the increase in pressure will
>dissappear. There is a straight mechanical relationship from the pedal
>movement to the caliper pressure. When you have vacuum assist, the int.
>manifold vacuum will help to minimize pedal travel. That's right, the vacuum
>assist isn't there to raise the fluid pressure, but to lessen pedal travel.
>Of course they are the same thing, but in reality there should be some
>trade-off here, the device that sets ultimate pad pressure is the size of
the
>brake booster's diaphram and you leg muscles. Does the 80mm calipers use
>bigger pads, that would help.
> What about going to a Hydrolic Brake Booster like what's in a '83 diesel
>suburban. I have 2 suburbans, one with hydrolic and one with a vacuum boost.
>The hydrolic booster can lock the wheels up at any speed. The vacuum boost
>can't. Has anyone tried this. I've thought about swapping boosters to see
>what happens. As far as rear rotors, it seams like a lot of trouble for
>little gain. How has this conversion worked out for you all? Did it really
>help?
> I'm a new GMC owner, but I have the ability to try anything. I've never
>learned to be afraid of mechanical stuff, in fact I live for it. My GMC is
>32k miles fresh and bare bones stock so there is no place to go but up.
>Yours in mods;
>Markus
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
