Pedal to FLOOR, New Brake System on 58.

[dyno]

Moved this over from my "Remote Brake Master Cylinder" thread.

Need some help here...brake pedal goes to floor, brakes just start to engage at floor level. I did cut 2" off the brake pedal to shorten it, but there is still way too much travel.

I clamped all the brake hoses with vise grips and have a rock hard pedal that has 1" of travel. So apparently the master cylinder is not the problem.

Once again, completely new brake system under my 58 4x4: 1980 chevy 3/4 ton axles, disc front, drum rear. Performance Online booster/double MC/prop valve down on the frame. All new brake lines, wheel cylinders, calipers, rotors, drums ect. Back brakes adjusted close to drums. Vacuum bled all lines several times, no air bubbles.

Thinking about trying residual valves.

[tmoble]

10lb in the back, 2lb in the front. Make sure the self adjusters in the back work or keep adjusted up.

Do you have a double flare tool?

tried pinching off just the back or just the fronts to isolate down on it?

[dyno]

Originally Posted by tmoble

10lb in the back, 2lb in the front. Make sure the self adjusters in the back work or keep adjusted up.

Do you have a double flare tool?

tried pinching off just the back or just the fronts to isolate down on it?

I don't have double flare tool.

Pinched off all lines, 1.5" travel and hard pedal.

Remove rear clamp, goes about halfway to floor.

Pinch rear line, remove fronts, goes about halfway to floor.

Remove all, pedal all the way to the floor.

[_Ogre]

with all brake hoses clamped you should have minimal pedal travel, dang near zero since your not moving any fluid
first, i suspect you have excess play in your pedal linkage

check to make sure all your bleed screws are on top of the caliper, impossible to bleed that way
calipers can be swapped side to side, they are usually mirror duplicates (unless you have a 3rd gen camaro)

for the pedal to travel that far you have: excess freeplay, air in system, too much gap between pad and rotor or
another possibility is your 3/4 ton axles have too much volume for the mc
i cut off 3.5'' of pedal off my 58 after i had all my brakes setup and bled
i found it impossible to get all the air out with the cut off pedal when i had a caliper go bad

[OrrieG]

Can you build pressure and pedal by pumping the brake pedal, or do you run out of fluid in the MC? Are you using the truck type MC? My 4x4 used 74 MC proportioning valve and wheel cylinders/calipers. Usually on 4x4 you do not need residual valves the MC is much higher than the calipers and wheel cylinders. I had three issues bleeding mine to hard pedal.

1. Calipers swapped side to side, like Ogre says, if the bleeder is down you get an air pocket at the top. They will bleed clear (no bubbles) but you will not get pedal.
2. I had the looped lines out of the MC vertical not horizontal, this caused air pockets in the bottom of the loops.
3. Took about 6 hours in three tries to get all of the air out. Ended up buying speed bleeders with check valves to get the last little bit of air out. I remember in 1985 when I first changed to 4wd the brakes were a pain to bleed too.

If the pedal is traveling to the floor and there are no leaks you either have air in the system or bad mc or wheel cylinder seals. Your clamping seems to disprove the latter so try manually bleeding instead of the vacuum to see if it makes a difference. I still remember as a kid being the designated seat man and Grandpa Orrie hollering to "pump it a hundred times making sure you take you foot off every time" to work the air to the end of the lines. If you are not using the truck MC like Ogre said there may not be enough volume for the system. I know my truck ones look a lot larger than the ones that come in the aftermarket kits, but I have never seen the two next to each other.

Good luck....

[Apachemike]

I thought residual valves were required when running a frame mounted mc with power brakes. A prop valve is not a residual valve

[dyno]

Thanks for trying to help guys... No the pedal does not pump up. Calipers correct, bleeder is up. Rear wheel cylinders are new. Pads and discs touching drums and rotors.

This is the booster/MC set up I have. Ordered for disc/drum. Is that a residual valve on the back of the prop valve going to the rear brakes?

[Wheelie]

If your not getting air after numerous bleeds and pedal still goes to floor assuming all pedal geometry is correct, you most likely need a larger bore master cylinder and or your running too large a brake line with that master. Your not moving enough fluid. I use 3/16 line. Also If your master cylinder is below the calipers you will need a 2Lb residual valve in the front brakes due to bleed back from the calipers. This usually gives you the feeling of air in the system and having to pump the brakes once or twice then the pedal gets hard. If the master sits higher than the calipers then you don't need it. The 10psi residual valve appears to be installed on your prop valve in the pic so your good there unless someone removed the internals of the valve which is possible if its aftermarket.

[OrrieG]

Here is a photo of mine, stock 74 4wd MC and prop valve with an aftermarket 8" booster for scale. Ignore the coil direction, it was wrong and got turned 90 degrees, but notice how much larger the rear MC reservoir for the front discs is compated to the front one for the drums. Also notice that the drum line is larger to match the larger line that goes to the back, I included a photo of my back line too. The photo in yours shows equal sized reservoirs and equal size lines.

Someone can chime in but I think that means you are running out of pedal before the back brakes engage??? I think the truck caliper and wheel cylinders are larger and need more fluid so you MC might be undersized? Maybe the system you got was designed around smaller auto calipers and wheel cylinders?

Something else that may or may not be a factor, I am on MC number three because the truck has set so long and I forget to exercise the MC that on the first two the seals hardened up.

[dyno]

You may be onto something Orrie...but I hope not! Changing the MC to a larger unit would require another custom cap to tap into the remote reservoir.

I think I will pull the MC and adjust the pushrod as Ogre says. 1.5 inch travel with all the lines clamped off seems like quite a bit. Supposedly, the rod is "set at the factory".

I also changed the front calipers last night. 2 different bore sizes were offered and I had the large ones on it at first. I seem to have more pedal with the smaller bore calipers.

Also, putting 2 lb residual valves on the front lines may help. Hopefully making all these changes will add up and get that pedal up to a safe position.

[dwcsr]

Originally Posted by Apachemike

I thought residual valves were required when running a frame mounted mc with power brakes. A prop valve is not a residual valve

Residual valve are needed only if the master is below the wheel cylinders or caliper usually a lowered truck. The original master was below the floor and never had a residual valve. Residual valve should have no effect on bleeding a system out or getting a pedal. If it does then something is wrong in the system

[dwcsr]

Originally Posted by dyno

You may be onto something Orrie...but I hope not! Changing the MC to a larger unit would require another custom cap to tap into the remote reservoir.


I also changed the front calipers last night. 2 different bore sizes were offered and I had the large ones on it at first. I seem to have more pedal with the smaller bore calipers.

The change of the smaller bore caliper and getting some what of a pedal mean you have a way to small master. What size it the master?

[dyno]

Originally Posted by dwcsr

The change of the smaller bore caliper and getting some what of a pedal mean you have a way to small master. What size it the master?

You may be right. I think I read somewhere that the master in this kit is used on Corvettes. I don't know what size bore the master is without pulling it. Tech info did not say. I'm going to get a pump up tank style pressure bleeder and give that a try before I take a dive into putting in a bigger MC.

[dwcsr]

Did it say corvette or corvette style master. I had a similar issue and had to go to a 1.125 master. Make sure you use the prop valve tool when you bleed it, if you don't lock the valve in the center its a nightmare to get the air out

[dyno]

The descriptions say "Corvette style". I'll bet it's a 1" cylinder. I will give POL a call Monday and quiz them again. Going to take a break from the brakes and work on assembling my bed today.

[_Ogre]

try to find a stock length brake pedal too
it's possible your not getting all the air out of the mc with a partial stroke

[dwcsr]

Originally Posted by dyno

The descriptions say "Corvette style". I'll bet it's a 1" cylinder. I will give POL a call Monday and quiz them again. Going to take a break from the brakes and work on assembling my bed today.

Corvette style comes in 7/8" to 1.25", most commonly these companies use a 1" to "get line pressure up" that thinking baffles me but that's what POL told me. I think you have the same kit I used and had to change to a larger master to get volume to the wheels. It still felt soft but stopped very well.

[OrrieG]

Stock diameter for 73+ K10/20 trucks is 1.125" Does not sound like much but doing the math it is 1.27X more volume than 1", 1.76x more than 7/8" bore. That means per unit of travel it will push more fluid thru the system. You might also still need to upgrade the back line size. Once you have FULL pedal without bottoming out (I get mine about 1/3 - 1/2 way to the floor with stock pedal geometry) pressure will be a little less in larger bore, but with modern systems should still lock up the tires. Oh and at Oriellys the stock mc is about $35 compared to $85 for the Corvette "upgrade"...

[dyno]

Originally Posted by OrrieG

Stock diameter for 73+ K10/20 trucks is 1.125" Does not sound like much but doing the math it is 1.27X more volume than 1", 1.76x more than 7/8" bore. That means per unit of travel it will push more fluid thru the system. You might also still need to upgrade the back line size. Once you have FULL pedal without bottoming out (I get mine about 1/3 - 1/2 way to the floor with stock pedal geometry) pressure will be a little less in larger bore, but with modern systems should still lock up the tires. Oh and at Oriellys the stock mc is about $35 compared to $85 for the Corvette "upgrade"...

Orrie, you are on it man! I dinked around with the brakes again today, bleeding and making all the adjustments I could. Got a bit more pedal but not enough. I agree, it's got to be an undersized MC for the K20 brake components I am using.

I looked at the MC on my 1980 K20 and the bolt centers are the same as what's on the 58's booster. Also, the billet cap clips right on the k20 MC that I am using with the remote cylinder on the firewall, so that's good news.

Autozone has 2 K20 MC's in stock, one has a 1.125 bore, the other has a 1.250 bore. do you thing I should jump up to the 1.250? It may give me a nice, high pedal.

[dyno]

And BTW, the rear brake line is larger than the fronts. Just can't tell from my pic.

[dyno]

Originally Posted by dwcsr

Corvette style comes in 7/8" to 1.25", most commonly these companies use a 1" to "get line pressure up" that thinking baffles me but that's what POL told me. I think you have the same kit I used and had to change to a larger master to get volume to the wheels. It still felt soft but stopped very well.

So Dave, did you end up using a 1 1/8 MC? I'm trying to decide if I want to try a 1 1/8 or 1 1/4 MC

[dwcsr]

I used 1.125 on 2500HD calipers that were dual piston so I think you should be ok with 1.125 if that's what the original calipers used. Match the master to the calipers your using.
If the calipers were K20 the get the k20 master.

My system ended up being 1.125 master 7" dual booster, 3/16 Lines in a 47 1 ton that had a 14" lever . The pedal still felt soft but it started stopping at 2" down and could lock up at 3" leaving about 4" to the floor although you could push it to a little over half way when standing still.

You need 800-1200 PSI to stop with disc brakes depending on who you ask.
This chart tells you the psi with a booster or non booster with a 7:1 lever
http://www.classicperform.com/PDFs/B...ssureChart.pdf
This will tell you the ratio calculation which on ours ends up between 8 and 9.5 to 1.
Much higher than the 7:1 in the classic chart.

So with the 9:1 pedal and a 1.125" master you should get about 1400 psi without a booster, you maintain minimum line pressure and you also get the volume to push the dual piston calipers the distance they need to clamp the disc. 1" in would give about 1800 psi but you don't move as much fluid making the throw of the pedal longer and closer to the floor to get the same clamping effect.

Adding the booster gives you about 495 more psi so you end up with 1400+ 495=1895 psi with a 1.125" master 9:1 lever, and a 7" dual booster. I measured 1800 PSI at he calipers on my system with that setup and it stops this 1 ton like its a Corvette. We went overboard because he wanted to carry two granite slabs in it to home shows and it needed to stop with that weight. As long as your in the 1200 1400 range your good. This is the point that the prop valve does its work by limiting the volume to the back brakes, you still want the pressure but not the volume that the front needs.

if you went to 1.25" it would drop the pressure and increase the volume but you'll still be in the acceptable pressure range and a firmer pedal

[1project2many]

I'd tend toward the larger piston front calipers and larger bore master cyl to start. These trucks are heavily weight biased toward the front. Putting more stopping power on the rear tends to lock wheels up sooner which can cause the back of the truck to spin around unexpectedly in a panic stop. The larger piston calipers apply more force to the pads at a given fluid pressure, the larger m/cyl delivers less pressure to rear wheel cyls for a given pedal pressure.


Nice to see folks calculating pressure differences, lever ratios, etc. I cringe at the guessing games people play when it comes to brakes.

[dyno]

Originally Posted by dwcsr

I used 1.125 on 2500HD calipers that were dual piston so I think you should be ok with 1.125 if that's what the original calipers used. Match the master to the calipers your using.
If the calipers were K20 the get the k20 master.

My system ended up being 1.125 master 7" dual booster, 3/16 Lines in a 47 1 ton that had a 14" lever . The pedal still felt soft but it started stopping at 2" down and could lock up at 3" leaving about 4" to the floor although you could push it to a little over half way when standing still.

You need 800-1200 PSI to stop with disc brakes depending on who you ask.
This chart tells you the psi with a booster or non booster with a 7:1 lever
http://www.classicperform.com/PDFs/B...ssureChart.pdf
This will tell you the ratio calculation which on ours ends up between 8 and 9.5 to 1.
Much higher than the 7:1 in the classic chart.

So with the 9:1 pedal and a 1.125" master you should get about 1400 psi without a booster, you maintain minimum line pressure and you also get the volume to push the dual piston calipers the distance they need to clamp the disc. 1" in would give about 1800 psi but you don't move as much fluid making the throw of the pedal longer and closer to the floor to get the same clamping effect.

Adding the booster gives you about 495 more psi so you end up with 1400+ 495=1895 psi with a 1.125" master 9:1 lever, and a 7" dual booster. I measured 1800 PSI at he calipers on my system with that setup and it stops this 1 ton like its a Corvette. We went overboard because he wanted to carry two granite slabs in it to home shows and it needed to stop with that weight. As long as your in the 1200 1400 range your good. This is the point that the prop valve does its work by limiting the volume to the back brakes, you still want the pressure but not the volume that the front needs.

if you went to 1.25" it would drop the pressure and increase the volume but you'll still be in the acceptable pressure range and a firmer pedal

Thanks for your input. I decided to try the 1.25 bore MC first and picked one up yesterday for 19 bucks at Autozone. I still have the large calipers that I pulled off the other day and will probably put them back on after I install the new master. Hopefully it fits into the booster. Will get back with the results.

[_Ogre]

at least it didn't break the bank on that one