My brakes-your thoughts, please....

[slocrow]

I've got way to much pedal travel and not enough left to really apply enough pressure to lock them up. They can't be pumped up so I'm assuming (maybe incorrectly) there isn't a air in lines problem. I'd like to get a higher pedal that isn't so soft.
Here's what I've got; Disc's at all four corners, Willwood two piston calipers with 11" rotors all around. Up front it's a Heidts Mustang ll super ride and hats in the rear. The lines are 3/16's with braided hoses. I don't know what the master is or it's size but it's not a power unit and it's under floor.
I did check and found a blue residual valve for the fronts and a red one for the rears. I don't know their manufacture but they do have a rivet (7/32 dia) looking button towards one end of the part. Both have this button towards the master and are no more then a foot to 18" from the master.
I believe the red is incorrect as I think it's for drum brakes but maybe there is a reason I'm unaware of, for it's use.
Once when I checked the master level by removing the top. The rubber gasket sprung out and because of it's distortion couldn't be reused. Kind of like soaking a rubber piece in brake fluid and having it grow.
Thanks for any thoughts or direction....Frank

[purplepickup]

Are you using DOT 3 fluid or silicone?  I ask that because I run silicone and have a somewhat soft pedal.  I'm going to change it back to DOT 3 when I get time.

[Bruce Dorsi]

I've got way to much pedal travel and not enough left to really apply enough pressure to lock them up. They can't be pumped up so I'm assuming (maybe incorrectly) there isn't a air in lines problem. I'd like to get a higher pedal that isn't so soft.,

You are correct that ONE of the rpv's is the wrong one, Frank.  .....Since you have discs all the way around, they should both be the same.  ...Disc circuits should have 2psi valves.

From your description, it sounds like your rpv's were made by Wilwood.

The wrong rpv on disc brakes, should not create the problem you are experiencing.  .....If a 10psi rpv is used on a disc circuit, usually the brakes will drag.  The 10 psi is usually enough pressure to move the pistons /pads against the rotor.

The symptoms you describe are indicative of a FAULTY valve, however usually a "double-pump" will make them feel normal and the brakes will function adequately.   .....When the valve fails, the pistons actually retract too far.  When the brakes are applied, much of  the pedal travel is used to  move the pistons/pads out against the rotors.   .....Wilwood 2psi rpv's are not very reliable!

You can visually inspect how far the pads/pistons retract from the rotors.  You should only have a few thousandths gap.  ....If you see a much larger gap, try inserting some non-compressible material temporarily  to close the gap.  Depress the brake pedal, and your pedal should be high & hard. ....If it isn't, your problem is probably elsewhere!

Were your brakes better before, or have they always been this way?
.....If they were OK before, then I would suspect a faulty rpv or air.  
.....If they were never good, then it could be a bad rpv,  the wrong size master cylinder,  poor pedal ratio (insufficient m/c stroke),  or air in the system.   ....Excessive lengths of braided hose can "balloon," creating the need for more pedal travel.

[Bruce Dorsi]

Here's some more info, Frank:


http://www.mpbrakes.com/trouble18.htm

:b-d:

[slocrow]

Here's some more info, Frank:


http://www.mpbrakes.com/trouble18.htm

:b-d:

Thanks for the insight guys. I'm not using silicone George though I had given it some thought. Bruce, the brakes have been like this all along. maybe they've gotten a little sponger and lower in the last couple of years. I just noticed how close the pedal was to the floor when talking brake lights and giving them a push last weekend. I had also heard that Wilwood rpv's were questionable, any suggestions? I'll have to try that shim idea shortly.
I was looking for ideas and thoughts at this point. I'll check out the mpbrake site too......Frank

[Dave]

Here's some more info, Frank:


http://www.mpbrakes.com/trouble18.htm

:b-d:

Thanks for the insight guys. I'm not using silicone George though I had given it some thought. Bruce, the brakes have been like this all along. maybe they've gotten a little sponger and lower in the last couple of years. I just noticed how close the pedal was to the floor when talking brake lights and giving them a push last weekend. I had also heard that Wilwood rpv's were questionable, any suggestions? I'll have to try that shim idea shortly.
I was looking for ideas and thoughts at this point. I'll check out the mpbrake site too......Frank

Dam frank id sell it and buy a new SUV to go with the vette. I hate to see you spend any more money on the 32. Tell ya what ill give ya 12k for it sight unseen and with bad brakes. Id have offered less but you did get the carb fixed and thats got to be worth sumpin...
Dave

[1FATGMC]

I've got way to much pedal travel and not enough left to really apply enough pressure to lock them up. They can't be pumped up so I'm assuming (maybe incorrectly) there isn't a air in lines problem. I'd like to get a higher pedal that isn't so soft.

Sounds like mine when the master cylinder quit a couple months ago.  I went from normal pedal to no pedal over about a 50 mile period though, so if this has been getting worse over a lot longer period than that it is probably one of the other items that have been suggested.

c ya, Sum

[Pope Downunder]

Here's some more info, Frank:


http://www.mpbrakes.com/trouble18.htm

:b-d:

Thanks for the insight guys. I'm not using silicone George though I had given it some thought. Bruce, the brakes have been like this all along. maybe they've gotten a little sponger and lower in the last couple of years. I just noticed how close the pedal was to the floor when talking brake lights and giving them a push last weekend. I had also heard that Wilwood rpv's were questionable, any suggestions? I'll have to try that shim idea shortly.
I was looking for ideas and thoughts at this point. I'll check out the mpbrake site too......Frank

Check to see if your pedal and linkage can actually make full travel in the master cylinder.  A lot of rods without boosters have pedal ratios, up in the 6:1 to 7:1 range.   That is fine for leverage, however obviously this also affects travel; so unless your pedal is a long way out of the floor at rest, and has sufficient travel, you will run out of physical travel, long before the stroke capacity of the cylinder is reached.  Not may rods interiors can accomodate that amount of pedal travel.

Also check the bore and stroke, to get volume, and compare that to that required at the discs.

[phat rat]

Here's some more info, Frank:


http://www.mpbrakes.com/trouble18.htm

:b-d:

Thanks for the insight guys. I'm not using silicone George though I had given it some thought. Bruce, the brakes have been like this all along. maybe they've gotten a little sponger and lower in the last couple of years. I just noticed how close the pedal was to the floor when talking brake lights and giving them a push last weekend. I had also heard that Wilwood rpv's were questionable, any suggestions? I'll have to try that shim idea shortly.
I was looking for ideas and thoughts at this point. I'll check out the mpbrake site too......Frank

Dam frank id sell it and buy a new SUV to go with the vette. I hate to see you spend any more money on the 32. Tell ya what ill give ya 12k for it sight unseen and with bad brakes. Id have offered less but you did get the carb fixed and thats got to be worth sumpin...
Dave

$12,001, do I hear $12,002

[Dirk35]

http://www.hotrodheaven.com/tech/brakes/brakes2_index.htm
(WilWoods Brake Tech)
 

You might find some real useful insight in this site. Its very indepth.

[Fat Cat]

$12,001, do I hear $12,002

No but I will go 12,001.35  

[Rochie]

Here's some more info, Frank:


http://www.mpbrakes.com/trouble18.htm

:b-d:

Thanks for the insight guys. I'm not using silicone George though I had given it some thought. Bruce, the brakes have been like this all along. maybe they've gotten a little sponger and lower in the last couple of years. I just noticed how close the pedal was to the floor when talking brake lights and giving them a push last weekend. I had also heard that Wilwood rpv's were questionable, any suggestions? I'll have to try that shim idea shortly.
I was looking for ideas and thoughts at this point. I'll check out the mpbrake site too......Frank

One idea to check Frank...check the actuator rod from the pedal to the booster or master cylinder.  If the rod is NOT touching the back of the booster or the piston in the master, adjust it so that it DOES just touch (NO PRESSURE on the booster or piston)  I had a problem just like yours when I first built my car.  The adjustment brought the pedal up and provided a good high/hard pedal.  Just something to look for OK
Rochie

[2buck]

I have experienced this problem & seen it on quite a few street rods. I believe the problem is that the brake pedal's ratio is incorrect.

I reworked the brakes on my F100 with a power booster and a fruit jar master cylinder. I had to use the fruit jar master cylinder because the dual type would not clear an intermediate crossmember. I bleed the brakes conventionally and with a vaccuum gismo several times. I could hear the brake return springs squeek and when the pedal was at the floorboard the brake drums would not turn by hand. All this & no firm pedal!
My pickup had an additional hole in the brake pedal. It was further away from the pivot by 9/16" over the hole that was normally utilized. I had to drill out my clevis rod and get a new pin because the other hole required a 7/16" clevis pin.
Once all this was done I had a firm pedal at 3-1/2" off of the floorboard!

In conclusion,- I believe the pedal arrangement does not provide enough stroke at the master cylinder to displace enough fluid to move the calipers' and wheel cylinders pistons.
The original master cylinder had to displace fluid for wheel cylinders with a diameter of 3/4" to 7/8". Now we are substituting GM disc brake calipers with a bore of 2-3/4" & larger. I realize the disc brakes are running with less clearance than the brake shoe arrangement.

The solution would be to increase the length of the clevis mount by 9/16" or so and lower the position of the master cylinder to keep the actuator rod's alignment. This would require a welding operation to the pedal. I do not think this would increase the pedal effort enough to matter since we are decreasing the pedal ratio.

This is something that has been bugging me for a year! I would appreciate others thoughts.

Lance Bucky

[slocrow]

Thanks for all the good suggestions guys. It will take me some time to sort through the info and check things over, though I'll let you know what I find and fix.....Frank

[purplepickup]

Frank if you're going to be at the BBQ trailer build tomorrow we can fix it there.  Frank has a few BFH's and a huge tapered reamer.   There should be enough of us to flip it over on it's roof so we can see things better.  We can fix you right up in no time at all.

You are bringing the tequila and lemons...right?