I've been building a 27 roadster since july, and can not get any brake pressure. started with 79 vette m/c,7' booster, s10 rear shoes, and wheel cylinders, front calipers are mid 70s gm car. Adjustable por valve to front, 10lb residule valve to the rear. After more research, changed to a 79 c10 master cyl with a 1 1/8 bore and no change. I have well over 8 days chasing my tail on brakes. I've been working and on in and around cars for alot of years, but I am completly at a loss! The kit is a spirit kit with the booster and master cyl under the floor, I drilled a new hole on the pedal push rod to get the correct pedal ratio with a small gain in pressure. Blead 4qts of fluid total and good flow when bleeding. All new shoes, plain spring set up no self adjusters. AM I missing something some where?
Plug the output ports on the master cylinder and see if you then get a hard pedal. If not bleed the master cylinder. I use loop back tubes and pump the brake pedal till there are zero bubbles.
So you are measuring the pressure somewhere or do the brakes not operate? Sounds like the fluid is leaking internally somewhere or something?
Bench bleed the master! I'm the third one saying this. Sent from my DROID device using the TJJ mobile app
Just a thought., the 10lb residual valve isn't on backwards right? Jus wondering and thinking out loud...
In my opinion, what you should have is this: Master matched to FRONT brakes (ie: same car as donor calipers). Combo valve from a car, plumbed correctly. That's it, to start. You do NOT want to have a right jumble of components to juggle fluid through before you really need them. And the reason to match master to front calipers is because GM make so many different rear W/Cs that it is fair easy to match a system by juggling those, rather than add-on a crutch (adjustable proportioning valve). Which (adj. valve) should NEVER be put in the front line, ever. Also, make sure the piston gets full stroke, many do not. And 1/8" free play, to make sure it is fully released. Too, IMHO, the 7" power booster is a total waste of money. Cosmo
Unfortunately this is the way the spirit kit is designed. Both the calipers, and the wheel cylinders use the 1 1/8th bore master cylinder. For all intense and pourpose the master wheel cyliders and master cylinder match.
Sir, you have a LOT of the basics wrong here, I'll try and help. The set-up I will give you is correct, PROVIDED the M/C does NOT have a Proportiong valve now. First off the P/V goes AFTER the rear 10PSI residual valve and again the REAR brakes, not to the front OK. So we wil have M/C line to rear, 10 PSI R/V, and then the P/V, and then to the flex hose to T into the rear drums. Now you will also need a 2 PSI R/V for the front disc brakes somewhere between the M/C and the T or the split of the front brake lines. You will get some of the know it alls later telling you that you don't need a P/V if everything in the system is correctly matched, and yes to a degree they are correct. I am here to get you brakes and a safe car to drive, NOT to design your braking system from start to finish. Best of luck sir, follow the above advice and you be be OK, TR There are threads on here regarding Pedal Ratio as well. If you do a search feature for pedal ratio, you will see the chart that is VERY easy to understand and that should complete your set up for now.
if you look in the brake section of the speedway magazine there is a pretty cool diagram that shows a 2psi residual valve in the fron and a 10 in the back with the prop. valve, if master cyclinder is mounted under the floor.
The booster have a long pekker to go into the master cyl? Theres a possibility of a mismatch between the mc and booster where the mc has a deep hole for the pushrod and the booster has a short pekker. Look into the mc and if you can see way down deep then cut a bolt about an 1" long and slip it into the hole so that it makes contact with the pekker on the booster.
That's a head-scratcher for sure. One trick a guy taught me that might help and takes little time or effort is to take an old pump oiler, fill it with brake fluid and pump fluid in through the bleeders. A reverse of the usual process if you will. Pushes any air that may be trapped in the system out through the M/C. Good luck.
There is a 10 r/v to the rear with no p/valve. I have the adjustable p/v to the front per the spirit set up. Exactly what basics do I have wrong?
Check the calipers. Make sure you bleeders are facing up, and not down. If they are down you have them on the wrong side. Very common.
perhaps the pedal is being stopped before it can fully return. Like the brake light switch is holding just a smidgen off? I am just throwin out things I have seen that have caused people alot of pain. Gotta be air somewhere. The only thing you can really do is block off the back at the axle T, and see if you get pressure, if not leav it blcoked do the front, if all blocked then its somethin with the M/C. You chasin at this point. But thats what I would do.
I couldn't get a lot of peddle and found out I hadn't adjusted the brake shoes on the rear. Did it and solved the problem.
Check to make sure you don't have too much freeplay in the pedal before the pushrod in the booster contacts your m/c piston.
A lot of information here, make it simple, first ditch the power it is not at all necessary on a full sized car and on a light car it is way overkill. Get yourself a stadandard (non power) master from a '79 Mailibu. Loose the proportioning valve and the residual valve, residual pressure is built in and the malibu will most likely match the calipers as well as the rear brakes that you are using. I find it very unlikely that your car is using the expensive Corvette brakes. Now you have done away with 2/3 of your problem spots, simplified the brake system and you can get it to function. Now that you have done that you can start adjusting things, make sure that you are getting a full stroke on the piston on the master. you may want to incorporate am adjustable push rod to do this. The master bled start bleeding the brakes. One the brakes are bled you can drive it and then determin if you want to change the brake bias, if so plumb the proportioning valve to the rear brakes and start tweeking. Unless the car is lowered a lot the brake propertion usually does not need tweeking. On a lowered car you can add bias to the rear and on one that is lifted a ton to can remove bias from the rear. The rear brakes are how you adjust the brake bias not the front.
When you do get it worked out please post how you did it and what was the main issue. Terry aka dirt t
I like to take the lines off the master cylinder and connect pressure gauges directly to the ports in the master cylinder to make sure I'm getting pressure. I had a pickup truck that I had to put three master cylinders in before I got one that put out enough pressure on both ports. Once you make sure the master cylinder is providing the pressure on both ports, connect the lines on the master, disconnect at the wheels and put the gauges in the wheel lines. Most hydraulic stores have the 3000 psi gauges for around $10 and you can get fittings at auto parts stores or you can buy gauge sets for brakes for about $50 each gauge. If you can't get enough pressure at the master cylinder, it might be a pedal leverage problem or a booster problem.
Lots of good advice here. The thing that I see you have wrong is the proportioning valve on the front brakes. The P/V always goes on the rear.... ALWAYS. Your trying to decrease pressure to the rear rakes so the front brakes lock up first. If the rear brakes lock up first in a panic (or semi-panic) stop your car will be swapping ends so fast you won't believe it and you'll be looking at where you came from instead of where your going. Frank
according to spirit cars the adjustable p/ valve is to back down the fronts to prevent lock up due to light front end and smaller tires. the corvette m/cyl is about the 1"bore, changed over to the truck m/ cyl to get the 1 1/8 bore this should have increased by 20%.
I am not sure what a spirit car is, I doubt that he is building a sprint car though. A proportioning valve can be run to any wheel or combination of wheels that one chooses to adjust the bias in whatever fashion is necessary. I have seen them from one side to the other on dirt track cars to get them to set up a slide differently. On a street driven car it is front to rear bias that is important, and it is normally done by increasing or decreasing the bias to the rear wheels.
Well, for one everything I have ever read or seen in a diagram and that's a lot says that the proportioning valve goes in the line to the rear brakes. Google location of brake proportioning valve and you will find a hundred diagrams and sets of instructions that all say that the valve goes in the rear brake line. That looks like the first thing you have wrong. Go back and read TraditonalRacing's post a couple of times as while some of the guys throwing out things to sound like they know something he actually does know what the hell he is writing about.. Other things to consider. What master cylinder does the booster manufacture say has to be used with that booster? These things don't come universal fit, they are designed for a specific master cylinder and just because other bolt on doesn't mean that they will work. The two you have tried are pretty well the standard hot rod dual master cylinder units of choice for rods that DO NOT have power boosters but may not be the correct units for using with that booster a the pushrod out of the booster may be the wrong length to use with either master cylinder. No doubt the vendor designated a particular master cylinder to use with that booster. I've seen more half assed ways to bleed a brake system described on here than I ran into in the 45 years that I worked on cars prior to joining the HAMB. The guys are right on one thing, it is a hell of a good idea to bench bleed the master cylinder before installing it. If you don't have a pressure bleeder and have to pump the brakes the proper method is: Make sure that the master cylinder is full and all bleeders are tight. Have your helper pump and hold the pedal and start with the furthest cylinder line wise away from the master cylinder and bleed it. Have your helper pump SLOWLY and hold the pedal until you have tightened the bleeder and TELL them to pump it SLOWLY again. You may not get all the air out the first time around but it shouldn't take too many rounds. I've found that running a clear plastic hose from the bleeder lets you see the air bubbles and keeps the brake fluid off the shop floor. Drum brake shoes have to be adjusted properly or you will never get the right feel on the pedal. Also if the shoes don't fit the drum closely they may be flexing a bit until the lining gets worn to the drum. One thing, I did a search and cannot find these "Spirit" brakes except the setup for a T bucket that takes a one inch master cylinder. Can someone post a link to who makes/sells this brake system?
Changing from the 1" bore to 1 1/8" increases the volume but also increases the pedal pressure required to get the same pressure at the wheels. If everything is adjusted correctly you shouldn't need any more volume.
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