So I’m working on a 46 Chevy pick up with power brakes and Four wheel disks. I’ve had one car with a disk drum setup and the rest are old forties drum brakes. so I have the system bled with a mushy pedal so I’m thinking once the motor creates vacuum I will get pedal. I start the motor, pushed the pedal and it goes to the floor and stays there. The motor is a blueprint 383 that came ready to run. I know I put the vacuum line to the correct port because it had a tag that said brake booster. So what do you figure is going on?
Is it a new system? or did you replace some parts? or modify it? Could be lots of things, giving us a few more clues will speed up troubleshooting.
Sounds like air still in system , Also many off brand fitting & hard lines The concave inverted shapes are not correctly shaped , engine off should have a hard paddle. Loose bleeder's threads can **** air @ bleeding if using Vac pump to bleed , If doing byself use a Clear quart / 2 liter Bottle , Fill few inches of brake fluid ,hose Keep eye on reservoir, bleed each wheel Slow & steady on pedal to floor then slow back up. If helper , you can bleed @ hose fitting @ each caliper or bleeder , Pump up a few time slow , Then have helper Push peddle slow steady to , then close bleeder ..
What size pistons and how many per caliper on the front and rear? And what size master cylinder? It's possible you don't have the volume in the MC to push the pistons out enough to clamp the discs. What pedal ratio do you have? What size hard line? Also, check your brake lines for swell under pedal pressure. Is it a complete kit? Or a setup you pieced together.. These questions answered will help everyone guide you in a better direction
Everything is brand new. Sort of off topic for the motor as it has a sniper F.I. Installed from Blueprint. Motor dyno’d at 458hp so is there a chance of low vacuum?
there are a lot of things that could be wrong with a new system...you might want to list what parts it has, ie what calipers, what master cylinder, pedal ratio, etc. We can't see it all, you can.
It’s a ccp master/booster for a 48-first gen 55 Chevy pickup bought through TCI. Was told this would work for a 46. It worked with a bit of mount modifications which is irrelevant. Front brakes are also supplied through TCI for a not to be named front suspension. Rear brakes are speedway disks that fit there fabricated 9”. An adjustable proportioning and front and rear residual valves were used bought thru speedway
A properly bled and set up power ***isted brake system (ball park master cylinder bore size, 3-4:1 pedal ratio, correct booster output pin-to-master cylinder primary piston distance) should result in a high and hard pedal without any power ***ist, so your engine's vacuum level is irrelevant at this point. All bleeding should be done without any power ***ist to minimize fluid air formation.
Get one of the cheap bleeder kits. EXAMPLE https://tomsoffroad.com/products/brake-master-cylinder-bleeder-kit You can do it on the car, but you might want to do it on the bench (vise) just to have visibility. You aren't a newbie so you know brake fluid is nasty to everything else, take precautions to keep the mess to a minimum. A pack of disposable diapers is cheaper than a repaint!
That should get you the high, hard pedal with engine off. The start and pedal to the floor may require more work, but get the hyd part fixed before moving on. If you do take the M/C off, when reinstalling, make sure that with the pedal up, there is a little bit of free play (not preload) between the pedal and booster, and the booster and M/C.
....also, likely not a problem with no pedal, but the residual valves on the rear may present a problem... used with drum brakes but not disc... good luck
If you didn't bench bleed the master you'll need to either remove it and do it or you might get away with raising the front or rear to get the master input pointing upwards slightly and re-bleed. If the master is in the correct orientation it might just require a little more elevation. I've found myself setting the rear on the ground with the wheels removed and jacking the front also! It's a trade off of what's easiest to do. My master is very awkward to remove. Chris
Thanks for all your guys help. The master has ports on both sides I’m going to try and remove the ports that are not used and bleed it while it’s in the car.
A "bench bleed" can be accomplished on the car with both primary/secondary ports opened, as long as the master cylinder pistons can be bottomed out before the pedal runs out of travel. This should be the first item to check when working with a custom built brake system.
@rusty rocket, NO. To properly bench bleed, you do not open another port. The piston must force the fluid (and air) out thru one port. Having one port with air and fluid and another pushing the fluid out and back into the reservoir is not going to get the air out. Think of it like this; if you have a straw with a crack in the side (second hole) it will not only pull the soda, but also air. The line out has air and fluid.
The Jalopy Journal
