I bought the front disk brakes and master cylinder upgrade for my truck. I just started driving it and when the truck is running the brake pedal won’t come back up all the way. I checked the fluid and it’s good. When it’s off it works fine won’t stick. Sent from my iPhone using The H.A.M.B. mobile app
It’s a brand new brake booster and master cylinder I got it all with the disk brake kit. Sent from my iPhone using The H.A.M.B. mobile app
I had the booster and lines installed at a shop and I don’t know what fluid they used. Sent from my iPhone using The H.A.M.B. mobile app
Take it back to that shop and tell 'em to fix their work. -Dave edit: hope you didn't buy a super cheap never work kit. The fix could cost a lot.
I’m going to because they also mad it a one hour task to check the damn fluid. Sent from my iPhone using The H.A.M.B. mobile app
If it is a floor mounted pedal and I have to believe it is you do indeed need a return spring. One more thing though, check and make sure that the pedal arm isn't hanging up on the toe board due to not being centered in the hole right. I've had that happen with stock pedals on my 48 and had to work a bit to make sure that they didn't catch on the edge of the hole.
Probably doesn't have the correct pushrod clearance. Turn on the engine, there is just enough pressure on the poppet valve from the pushrods lack of clearance and the pedal drops a tad. Booster won't self actuate the brakes, it just ***ists.
Not sure what you’re saying sorry. I bought the disk brake set up with master cylinder and booster for my truck so “it should of been right” for the pedal length and everything. But it is centered in the hole so I know that’s not the issue. It’s just when it’s running it’s not coming up very much. Sent from my iPhone using The H.A.M.B. mobile app
Should be and what it is are usually not quite the same. Trust but verify. Brake boosters at rest are a complete vacuum chamber, front and rear of the diaphragm is in negative pressure. This keeps the diaphragm from being stressed and eliminates and possibility of the booster to actuate against the master cylinder. Once you begin to depress the pedal, inside the booster is a poppet/control valve... In the above diagram it is the green sideways 'H' shaped device. At rest the poppet valve keeps the rear chamber(orange) closed to atmospheric pressure and maintains a negative pressure throughout the whole booster chamber. When you begin to depress the pedal, the pushrod pushes against the poppet valve. This valve does two things, it seals off the forward chamber(blue) from the rear chamber(orange) and also opens the rear chamber(orange) to atmospheric pressure. With atmospheric pressure now in the rear section, that pressure wants to go to the lower pressure section. But it can't so it presses on the diaphragm, which itself is prevented from self actuating as there is a large spring(not shown in the above image) that keeps the diaphragm from moving forward. This difference of potential is where a brake booster gets its ***ist. If the push rod from the pedal to the booster doesn't have the correct clearance, too long, the poppet valve may be actuated when the engine is turned on. This will allow the pedal to travel forward the distance that the poppet valve travels, to open the rear chamber to atmosphere. With the engine on there may be a slight amount of movement inside the booster from the engine being turned on as the rear chamber is open to atmosphere which allows for the diaphragm to move a slight amount. Since the pedal is keeping the poppet valve open, the booster is doing work that it normally wouldn't do if the booster pushrod was setup correctly. Turn off the engine the spring in both the diaphragm may relax slightly and poppet valve try to move back to their normal at rest positions and the pedal returns to its at rest position. My theory; When the pedal to booster pushrod length was setup, whoever setup the pushrod length set it too long. This is just enough that all the clearances needed to properly operate the booster are gone and the rear chamber is open to atmosphere when the engine is on, instead of being under vacuum and the diaphragm at rest. Turn off the engine, vacuum drops, check valve in the booster(to the intake manifold) does not close instantaneously, slight bleed which allows the diaphragm to move back just enough(because of the spring) which then pushes back the poppet valve and the pedal returns to its at rest position. With a functional system with the proper clearances, due to the poppet valve, there will always be a slight amount of dead pedal throw before the master cylinder is actuated.
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