The Stovebolt Site Forums The Parking Lot Tons 'o Fun Master Cylinders-Residual pressure valves

I have alot of questions I Have been reading threads from the past. I have a old 1.25 TON. It has the old hydrovac on the ecan't afford a new one but this one is JUNK . The truck in cut down to a 7' wheel base a bug NOW. I took a power brake system off a old school bus it runs to the power stearng pump and runs off a vacumn. I do not have power stearing on the truck so I disassembled it. I disassbled the power stuff off the master cylinder now all I have is the master cylinder which has a 2" bore I am going to try to mount it down on the frame were the old one was.It will have no booster on it though with a 2" inch bore I should be able able to stop it right? What I don't understand a residue a pressure valve what does it do ?? and what does it look like ? combination valve ?? what does it do what does it look like ??. The Master cylinder had a big line and a small line coming off of it the big line to back and small to the front the back has Dual wheels on it .8.25 X 20 . If anyone can shine a light on the subject would be nice ! Thanks t MIX !

Sounds pretty confusing, and not so great with a 2" bore and no power assist....

IIRC residual check valves are used to hold a little pressure like 10 pounds in your brake lines and cylinders so your braking ability is quicker and Also so the fluid won't drain back to your master cylinder. The valves are usually just inside the outlet ports on your master.
With a 2" bore you'll have fun stopping without assist.
If you put a master on that has no valves in it you can plumb some inline residual valves into your lines. Napa or Summit have them.

Hy tmix, on drum brake master cylinders the resisdual pressure valve[s] are built in, disc brake master cylinders do not have resisdual pressure valves. Resisdual pressure valves keep a pressure in the lines, approx. 10 p.s.i., this keeps the wheel cylinder cups against their bores, and hopefully stops air and moisture from being drawn in past them when you release the brake pedal. As has been said, separate residual pressure valves can be purchased and installed into the system when a disc brake master cylinder is used. If you mount a master cylinder so that it is below the level of your brake calipers [disc brakes], then you must install 2 p.s.i. resisdual pressure valves to keep the brake fluid from draining back towards the master cylinder. The combination valve is used when you use a mixed system of brakes the most common setup is disc brakes on the front axle and drum brakes on the rear axle. The combination valve performs a variety of functions, it meters pressure to the rear brakes to prevent lockup, should a leak in either system occur a valve shuttles over to seal off the leaking system and provide a visual warning on the dashboard that a braking system malfunction has occured I hope this helps explain the different braking systems somewhat, it is a technical subject, and in my opinion the most important system on any vehicle. The safety of yourself and everyone around you on the road is dependant on your braking system being adequate to the job, properly installed, and properly maintained, hope this helps.