I need help, Im still getting the brake fade. Its as if the booster is not assisting the power although if I really step on them when the power dosent feel like its there they still feel like there fading. Just installed the porterfield pads got the new vacuum pump/8" mp booster in the master is stainless steel bore. Calipers and rotors are replacement stuff but look great. What do I look for next, I want to go drag racing on fathers day and this thing has to stop! :mad: :mad:

Thanks Rich

Is it "hard pedal" you are describing... or "soft pedal" with a compression maybe related to air... do you have the right piston size... lot of questions, but I would suggest you go to

www.mpbrakes.com (http://www.mpbrakes.com)

and really read the ENTIRE site on brakes... both the frequent questions, and their flow chart...

hard pedal, if my memory serves me right I think it was 1.125 bore size

if the pedal is hard - this may indicate a powerbooster prob - have you tried disconnecting it to seee if the idle changes or put a hand vaccum pump\gauge on it to see if it leaks down? If you have a larger duration camshhaft you may need to add a vac reservoir to maintain adequte vaccum....sorry if this has already been cove smile.gif red...

I have a vacuum pump on the system it does not leak down and maintains 21 hg. I put a guage on it last night it looks good.

You might want to look at the proportioning valve. I am assumeing you have 4/w disc. Try teeing in a gauge and see what the line pressure is with brakes applied. Should be at min 600psi. Some where between 800 to 1200 psi is really what you want.

standard front disk/back drums. In my mind I am questioning line pressure but I do not have a guage to check it. Since I switched to the porterfields last week it seems worse. I have the stock distribution block w/ brake light switch, and another valve off the front brake resiviour to control pressure to the front calipers, I think its called a proportioning valve, its kind of round and has a bracket tieing it to one of the ears of the master.

I am considering purchasing a combination valve from mpbrakes to eliminate the proportioning valve. Im just shot gunning the situtation because I really dont know why I have insufficient pressure. Perhaps I should 86 the porterfields and try some performance friction metalic brake pads. I was getting off the highway a couple hours ago and that thing was fading bad yet the pedal feels firm. The harder I lean into the pedal the more it fades.

Thanks Rich

1st problem: You changed too many parts at once and are now chasing something elusive.

Possibilities~

2nd problem: Did you bed the rotors first before you installed the Porterfield pads? What color are your rotors right now? Is there any hint of bluing or dark grey?

3rd problem: Did you bed the pads after the bedding the rotors?

4th problem: How much vaccume does you engine produce under static no load and during brake application? How much vaccume does your pump pull? How much of the is applied to the booster itself? Are you sure that you are not losing vaccume signal to the booster?

My questions~

1. What calipers are on the chassis?
2. What distribution block are you using? (stock)
3. What prop valve are you using?
4. Vaccume of the engine at idle and at load? (21 inches)
5. Vaccume of pump itself not connected to the engine?
6. Vaccume at the booster port itself?
7. What is the pressure at the front caliper? Rear caliper?
8. What master cylinder are you using?

My observations~

The rounds valve on your system connected to the ear of the master is the 'residual pressure' valve. The button on the valve needs to be depressed when bleeding the system.

DO NOT BLAME THE PADS. This is not your problem. One problem which is making this worse is that you did not properly bed the rotors and then the pads.... What I think the real problems here are lie somewhere in between improper bedding and the metering and vaccume applied to the booster itself.

Simple things to do first~

1. Gravity bleed the system.
2. Ensure that you have the vaccume you think you do at the questioned points.
3. Get or borrow a brake pressure guage.....these are invaluable when doing brake work.

Let us know what you find out from the above questions.

Chicane,

1- single piston stock replacement calipers
2-stock distribution block original equipment when car was original 4 wheel drum brake
3-There is no proportion valve in the system, nothing connected to the rear brake line(even under the drivers door along the frame rail). Only the risidual pressure valve plumbed off the front reservoir.
4-Engine Vacuum is 9 to 10 inches, but is no longer in the circuit. The 8" dual diaphram booster is exclusively pumped by the MP-brakes vacuum pump. The pump maintains 20 to 21 inches. After letting the car sit for 5 hours it still had 20 inches, so I know its not leaking down. I performed the test on the booster that mp recommends. With the car off I pumped the brake pedal several times and then held the pedal down and turned the ignition on. The pump turned on and I could feel the pedal slowely drop slightly. With the vacuum guage on the booster it pumps up to 21 inches very quickly.
5- The vacuum pump is not connected to the engine.
6 - 21" hg
7- dont know
8- delco with a stainless steel bore/ 1.125"

I am aware of the button behind the valve and pulled it in with large tie wraps when I originally bled the brakes.

Allow me to clarify, the rotors were bed in from the previous pads, and I phoned porterfields and said they would prefer good used rotors. The rotors are not burnt. And I followed there pad bedding procedure immediatly after installation. Please dont get me wrong, Im not blaming my problems on porterfield, just trying to diagnose the problem with limited tools(brains & hardware).

Rich

67 go back to one troubleshooting trick for me... go out to the car, pump the brakes about 4-5 times, then with your foot STILL on the brake pedal after the last pump, start your car. If you do not hear the vacuum booster and FEEL your pedal fall slightly, replace your power booster first before you get into any more expensive and EXTENSIVE mods...

The distibution block has to do with the metering of the pressure/delay of the independant front and rear systems.

Using a four by drum metering block may be a bigger part of the problem. That was the other think I presumed to be the initial problem. I didnt want to, so far as going by my statement of improper bedding....but it is the most common mishap when switching to a pad as aggressive as this without prior use or knowledge. My apologies on my assumption.

The metering block also holds slight pressure in the individual system and this could be dragging the front brakes slightly.....you might just want to try a disk/drum metering valve.

I used the stock metering valve, residual pressure valve, stock calipers with rear drum brakes and the same master cylinder that you current use and had the best results with the exact pad compound during it's R&D. I didnt however, use the single piston calipers as my 67 had the four piston D3 units.

I'd be really interested on the brake pressure of the front calipers and to also note if there is any delay in the pressure application due to the four wheel drum metering block.