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Old 08-17-2012, 09:07 PM
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Help Bleeding new Brake System

Hey All,

Here's my situation...

I haven't got the motor running yet. Keep that in mind for the end of this message.

New brakes, discs, on all four corners
Frame mounted master cylinder w/booster, remote reservoirs
All new lines, proportioning valve on the rear circuit
Residual valves on front and rear circuits

I've tested all valves to be sure they are installed correctly. I bench bled the master cylinder and tested it for good pressure and no bypass leaks

I've been trying to bleed the system to get a good high pedal but no luck. I'm using DOT 3 synthetic fluid. I know that synthetic usually gives a soft pedal but this soft????

I start bleeding and the farthest point both front and rear.

After bleeding the system over and over again I get a good shot of fluid, no air, from each caliper but I can never get the pedal higher than an inch or two off the floor. After bleeding, the first pedal pump usually hits the floor then I can pump it up to the inch or two height.

Once I get the motor running, will the vacuum booster help raise the pedal higher?

Any suggestions will help in my frustration. Thanx in advance.

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Old 08-18-2012, 08:06 AM
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Where does your pedal sit as it is installed without any fluid in the system? The return spring pressures in the MC and booster are going to be at their furthest extension even without any fluid.

My first thought is that the physical location of your pedal or the push rod needs to be adjusted (This assumes you have the system properly bled and residual valves place for the low mounted MC, which it sound like you have) So, that static position needs to be physically positioned even before hydraulics come into play.

You may also consider the bore of the master cylinder. A small bore will allow easy pressure but will need a longer stroke to push enough fluid to engage the pads on the rotors. A larger bore pushes more fluid with shorter stroke but very difficult to press. Since you are running a booster, you can go with a larger bore MC.

Balance the physical position of the pedal with the MC stroke needed to engage the brakes and you should get dialed in.
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Old 08-18-2012, 10:00 AM
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Here is the master cylinder I have Master Power Brakes - REMOTE FILL POWER MASTER CYLINDER WITH PLASTIC RESERVOIR

Based on your response I went out and measured the pedal heights
from the floor...

6 inches high before pumping it.

first pump, it hits the floor

after a couple of pumps it builds resistance and stops about 2 inches from the floor

when released it goes back to 6 inches from the floor...
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Old 08-18-2012, 01:59 PM
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First of all, thanks for sharing that link. It gave me some ideas for a problem I am working with...

Anyway, a 1" bore should be big enough. But, each application is different. You may need to go bigger. When I did mine, I tried a few before I got it right. But, I was working with cheaper parts.

The fact that you have to pump it up makes me think somethings up with the residual valves. Or still a possibility there may be some air still in the lines. That lower MC doesn't make it easy

Was this a kit or are you putting it together yourself? If it is a kit, is there a tech phone number you can call?

Sorry I'm not being very helpful here.
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Old 08-18-2012, 04:36 PM
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You are being helpful!!!
I also think it is air in the line(s) but I've never had to deal with this for as long as it has taken. I just wanted to have a sanity check.

The MC and booster came together. The calipers are GM with 11" rotors.

I'll try bleeding some more to see if there is a stubborn bubble stuck in there somewhere. Then go to spend more bucks on a bigger bore.

Again, thanx for the help.
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Old 08-18-2012, 05:36 PM
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tc33,

You may need to use a pressure bleeder. If you can not find one then make one using a hudson type sprayer. Instead of weed killer use brake fluid. The hardest part is a plate for the reservoir that will not leak. Pump the sprayer a few times and wire the trigger down. Then open the bleeder valves one at a time until you have good pedal. BTW are all four corners disc?
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Old 08-18-2012, 05:45 PM
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While mine is a disk/drum system, it's pretty much the same as yours. I used a vacuum bleeder, took quite a while to get all the air out but it sure did the job far better [IMO] than pumping & releasing !!
dave
p.s. Did you mean DOT 5 ??..... no problem , that's what's been in mine for 12 years.
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Old 08-18-2012, 08:54 PM
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Does anyone know if the proportioning valve can cause problems with the bleeding? I did a search for low mounted master cylinder bleeding and one of the posts mentioned this issue. I don't run a prop valve in mine so I didn't run into this problem.
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Old 08-18-2012, 09:06 PM
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One of the techniques I use is open the bleed valve on the caliper and let the system gravity bleed before I start the normal "press and release" bleeding. But, I have a high mounted MC.

So, I was doing some more reading on low mounted MC's and I read some posts where guys were doing one of two things to replicate the gravity bleed: 1) jack up one end of the car to make the MC higher than the calipers you're bleeding; or, 2) Unbolt the calipers and let them hang lower than the MC.

Two more questions...Are there any places in the line where an air bubble might get caught and not get pushed through? Also, are your calipers mounted with the bleed valve at the top?
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Old 08-18-2012, 10:10 PM
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OK Guys, I'll comment on all your comments...

Discs are at all four corners
Prop valve is open all the way to prevent any restrictions. I read that post too...
All bleeder valves are at the top of all calipers.

I'm pretty sure the rear circuit is air free. Good flow out of both sides.
I think the air bubble is in the front circuit since I had to replace a line and got lots of air from the passenger side caliper before fluid. Did the driver side and got some air before fluid. Can't be 100% sure but I'll do all corners until I stop the pedal from hitting the floor.

I love trial and error and error and error. Oh well I don't have anything better to do tomorrow.

Gravity bleed: unmounting the calipers or using the jack are options to consider but alot of work. I'll keep those as a last resort. The car is up on a drive on lift.

I like the vacuum bleed suggestion. Found one at Harbor Freight for $23. I don't have a hudson sprayer but thanx for that suggestion.

Will keep you advised.
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Old 09-11-2012, 05:29 AM
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Help bleeding new brake system

With a new brake system you need a vacuum pump or brake pressure bleeder more than ever. I replaced the master cylinder and brake lines on my Camaro. I followed the instructions on making this power bleeder and it works great. I went to Advance Auto Parts and bought a new master cylinder cap. You could get one cheaper off a wrecked car. Here are the instructions. The DIY $20 brake bleeder
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