2" Hydromax master with reservoir removed. Built like a "P30" master
Booster poppet valves
Hydromax master at assembled length. Volume ratio between sections 1 to 1
Hydromax rod does come out and a few styles are available or make what you
want. New grommets are available.
Hydromax is different than Hydroboost in that the hydraulic flow path can have
no restriction on the outlet, not a power beyond deal. Need a separate engine
driven pump on the GMC or some kind of dual section pump. Relatively huge
volume from the large master should satisfy all disk brakes with big pressure.
Backup electric pump on primary flow failure.
With Hydroboost brakes more steering pressure equals more brake line pressure. PSC sells a new Saginaw P style pump made by Delphi which is supposed to be set for 1,650 psi. http://www.pscmotorsports.com
After installing it I found it didn't quite make the pressure spec. I'm shooting for 1,650 psi pump pressure by making a new flow valve plug with a 20% smaller area seat for the relief valve ball. The thread on the plug is 3/8-24 so I started with bolts of like thread and went from there.
Had six flow valves to fiddle with!
Springs and balls were the same on all. There were two different lengths of valves and corresponding plugs. The orifices and seats were the same on all. Had a few shims to work with too.
Had four bolts to use and they needed the hex changed to 7/16" from 9/16"
Made a fixture to hold plugs for machining. Here is a screen ready to go in.
New plug, original plug with screen removed and original plug unmolested.
Made orifice .052" closest I had to .050" original
New plug with 20% less seat area.
Rolling screen in.
Screen rolled in new plug and original plug
Valve ready to test
where screen goes
With no shim the spring is very close to coil bind so I didn't pursue shimming the spring. No shims on the valve is about 1,400 psi.
After some more fiddling we got 1,650 psi from the Saginaw pump. Ended up shortening the end of the flow valve where the plug screws in .015"
rear brake pressure 40mm master 80mm front and mid, 66 mm rear calipers
front brake pressure 40mm master 80mm front and mid, 66 mm rear calipers
There is some concern running the steering box at a higher pressure than It really needs. To lower the pressure just to the box I put in an additional relief valve before the box. Sun Hydraulics has all this stuff.
I selected a AEJ manifold in steel
The relief cartridge I selected was an RDBALAN
Ready to install with Oring boss adapter fittings
To install I got a 20 inch hydraulic hose to go from the hydroboost outlet to the manifold and used Bob Stones kit original hose from the manifold to the steering box. Bob's hose clocked OK to hook up this way. The return tees in before the cooler. I set the pressure to be just enough to turn the wheels while stopped.
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
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
