Larger master reservoir

JF9 master with a G10 reservoir installed reversed has a very small reserve capacity for brake wear. Made up a larger aluminum reservoir with a sight glass and Toyota cap.

Paper pattern and partially done

sight glass is a watch crystal and sealed with an o-ring

Hydroboost with 40MM master cylinder pressure checks

Did a brake pressure check. Bob Stone hydroboost kit with 40 MM master. This was after 2,500 miles. 1,350+ psi front and rear, Calipers are 80MM front 80MM mid, and 66MM Kelsey Hayes rear with park brake. This is with about 1,400 psi available from the steering pump. Mounts are Lambke style mid and Branscombe rear. Manny reaction arm system. Rear pressure improved after it got some miles on. Bob Stones hydroboost kit came from http://www.appliedgmc.com/

                                   

 

Graph shows what the pressure was with a P30 and modified 40MM JF9 master cylinder. 

 

          Master cylinder booster combinations and theoretical pressure

Force available from vacuum booster panic stop 1,473 lbs

Force available from hydroboost 1.56” piston diameter and 1,350 psi steering pressure 2,579 lbs

                                                                                     Bob Stone

                                          Vacuum  Booster              Hydroboost

                                                                                  

1.25” master cylinder          1,198 psi                          2,098 psi

34 mm master cylinder        1,048 psi                          1,835 psi

37 mm master cylinder           852 psi                          1,549 psi

40 mm master cylinder           761 psi                          1,332 psi

The hydroboost force does not include additional force that can be applied by the pedal

Vacuum boost force does include additional force that can be applied by the pedal

Later on we got a 1,650 psi steering pump and even more brake pressure

JF9 40 mm master install

Hydroboost with 40 mm master cylinder

       Counter bore hydroboost so 40mm master nose fits in.

Spacer plate is .312" and along with the counter bore in the hydroboost lets the nose fit in so the master's flange mates up.

40 mm master cylinder reservoir swap

Should clear the hatch just barely. If it fits it stops?

Reaction arm and new brakes

Hydroboost gets a bore job

Opening up a hydroboost output end to accept a 40MM master cylinder. Going to use this in combination with a spacer. Not bored full depth so the spider that holds the output rod will still be usable.

Studs are left hand thread where they go in the boss.

GMC brake booster output stroke measurements

 Original motorhome booster, a "metric" replacement and Hydroboost. These are output rod strokes.

I used these straps and a rod to hold the input rods all the way in.