soft brakes - why?

Kegracing · 05-08-2010, 07:58 AM

I have replaced entire brake system on my 67 Firebird. Wilwood disc on all 4 corners, new Wilwood 1" bore mastercylinder that they recommended, Wilwood prop valve. Most of the hard lines are new, and replaced the soft line in rear, and put new braided lines to front wheels. I have checked all fittings, and no leaks.

The brakes are soft. I can pump them up, and get some pressure, and it will stop car. I have the new prop valve with the pressure switch built in, and it is getting pressure with only one pump, but I am not sure how much pressure it takes to make switch. I do not have a gauge on the system. I have only driven it slowly up and down street in neighborhood (open headers, etc. gets lots of attention) to check brakes, bed new pads, etc. I have bleed the lines, and got good clear fluid out - no bubbles (with the new system, there was not any old fluid left anywhere).

Feels like I need to bleed them again. I just wanted to run it out her, and see if I am missing anything.

Thanks in advance.

Ken

chris ok · 05-08-2010, 09:37 AM

did you bench bleed the master. did you bleed at the line lock and all connections?
did you gravity bleed before pressure bleeding?
push rod adjusted as they recommend?
brake pedal rod in top hole of pedal assembly?
all pistons coming out evenly and calipers spaced over rotor on center?
are they floating calipers? or fixed to caliper bracket?
You might need a few more trips to get all pads and pistons on center w rotors.
just some things to double check for you.

Bobby Zlatkin · 05-08-2010, 10:12 AM

Make sure you've installed all the calipars with
the bleeder valve up. At the top. Or you'll never get all the air bubles out.

rayfin · 05-09-2010, 12:20 AM

Try bleeding the master cyl at the fittings. If that don't work you could have a bad master cyl. Air will always go the the highest point in the system.

gmonde · 05-09-2010, 08:33 AM

all points mentioned are things to look at ,, normaly what i do is install the master on the car and bleed it before any lines are hooke up(have a helper in the car)hook up the rest of the system and gravity bleed from each wheel untill no air bubbles are present ,,close bleeders and start bleeding from the right rear,left rear,right front,left front,if the pedal still is spongie there could be several things,,brake pedal ratio to master,,brake pad not seated correctly in the caliper,,you might have to isolate the area by capping the lines going to the front or the rear and then check the pedal for firmnees,,,you should get a presure gauge to see if you getting the proper presure at the wheels

gmonde

Kegracing · 05-09-2010, 08:39 AM

Thanks all for suggestions and help. I put it in right, and have checked most all the things mentioned. Think I am going to just start at the master cyl and start over with it, and see what we get. All "looks" right.

Wonder if getting wife to help bleed brakes on a racecar is a good mothers day gift???

Not sure if this will get worked on today or not!

thanks again, and keep the ideas coming

Ken

Jim B · 05-09-2010, 12:21 PM

Quote:

Originally Posted by Bobby Zlatkin

Make sure you've installed all the calipars with
the bleeder valve up. At the top. Or you'll never get all the air bubles out.

I assume the pedal is rising after pumping. The posts cover 99% of what I've seen may cause your problem but if you are pressure bleeding the system correctly (closest to farthest point without an "X" system) I would take a real good look at Mr. Zlatkin's post. Also, make sure the master is what you think it is. (1" bore)

Mark Yacavone · 05-09-2010, 02:05 PM

Ken , As mentioned..Where is the push rod mounted to the brake pedal?
If it's in the PB position , it needs to come down at least an inch.
The leverage ratio and clamping force is actually better with it up high, but the pedal will never feel right to you.
First thing to check.

Kegracing · 05-09-2010, 03:48 PM

Thanks Mark.
Car was original 4 wheel drum, manaual brake car. Have it in the same hole. Push rod length is good.
Brakes are actually soft. At low speeds, have not had it going over about 30, have to pump brakes to get any pressure. Will stop the car, but have to pump the brakes to get pressure.

Just feels like I have air in it to me. I pressure bleed them, starting at back pass, back driver, front pass, front driver, and got all the bubbles out, then several shots of good clear fluid at each wheel, before moving on. The Wilwood wheel cylinders have 4 bleeders. I use the top, outside for each wheel...

Think I am going to just start at the MC and start over, unless I find something that I am missing.

Ken

Jim B · 05-09-2010, 04:51 PM

You Said "Just feels like I have air in it to me. I pressure bleed them, starting at back pass, back driver, front pass, front driver, and got all the bubbles out, then several shots of good clear fluid at each wheel, before moving on. The Wilwood wheel cylinders have 4 bleeders. I use the top, outside for each wheel..."

OK I believe that could be your problem.... in a fixed/opposing piston caliper configuration with 4 bleeders you usually need to bleed BOTH uppers in each caliper half. (Not just one)

05-08-2010, 07:58 AM	#1
Kegracing Member Join Date: Jun 2002 Location: Red Oak, TX Posts: 441 Likes: 0 Liked 0 Times in 0 Posts	soft brakes - why? I have replaced entire brake system on my 67 Firebird. Wilwood disc on all 4 corners, new Wilwood 1" bore mastercylinder that they recommended, Wilwood prop valve. Most of the hard lines are new, and replaced the soft line in rear, and put new braided lines to front wheels. I have checked all fittings, and no leaks. The brakes are soft. I can pump them up, and get some pressure, and it will stop car. I have the new prop valve with the pressure switch built in, and it is getting pressure with only one pump, but I am not sure how much pressure it takes to make switch. I do not have a gauge on the system. I have only driven it slowly up and down street in neighborhood (open headers, etc. gets lots of attention) to check brakes, bed new pads, etc. I have bleed the lines, and got good clear fluid out - no bubbles (with the new system, there was not any old fluid left anywhere). Feels like I need to bleed them again. I just wanted to run it out her, and see if I am missing anything. Thanks in advance. Ken

05-08-2010, 09:37 AM	#2
chris ok Senior Member Join Date: Jul 2002 Location: Long Island, New york Posts: 592 Likes: 131 Liked 46 Times in 29 Posts	Re: soft brakes - why? did you bench bleed the master. did you bleed at the line lock and all connections? did you gravity bleed before pressure bleeding? push rod adjusted as they recommend? brake pedal rod in top hole of pedal assembly? all pistons coming out evenly and calipers spaced over rotor on center? are they floating calipers? or fixed to caliper bracket? You might need a few more trips to get all pads and pistons on center w rotors. just some things to double check for you.

05-08-2010, 10:12 AM	#3
Bobby Zlatkin Member Join Date: Mar 2003 Location: Mills River, NC Posts: 417 Likes: 0 Liked 0 Times in 0 Posts	Re: soft brakes - why? Make sure you've installed all the calipars with the bleeder valve up. At the top. Or you'll never get all the air bubles out. __________________ Bobby & Norene Zlatkin L/SA

05-09-2010, 12:20 AM	#4
rayfin Member Join Date: Mar 2009 Location: sioux city Posts: 134 Likes: 1 Liked 0 Times in 0 Posts	Re: soft brakes - why? Try bleeding the master cyl at the fittings. If that don't work you could have a bad master cyl. Air will always go the the highest point in the system.

05-09-2010, 08:33 AM	#5
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 165 Times in 59 Posts	Re: soft brakes - why? all points mentioned are things to look at ,, normaly what i do is install the master on the car and bleed it before any lines are hooke up(have a helper in the car)hook up the rest of the system and gravity bleed from each wheel untill no air bubbles are present ,,close bleeders and start bleeding from the right rear,left rear,right front,left front,if the pedal still is spongie there could be several things,,brake pedal ratio to master,,brake pad not seated correctly in the caliper,,you might have to isolate the area by capping the lines going to the front or the rear and then check the pedal for firmnees,,,you should get a presure gauge to see if you getting the proper presure at the wheels gmonde

05-09-2010, 08:39 AM	#6
Kegracing Member Join Date: Jun 2002 Location: Red Oak, TX Posts: 441 Likes: 0 Liked 0 Times in 0 Posts	Re: soft brakes - why? Thanks all for suggestions and help. I put it in right, and have checked most all the things mentioned. Think I am going to just start at the master cyl and start over with it, and see what we get. All "looks" right. Wonder if getting wife to help bleed brakes on a racecar is a good mothers day gift??? Not sure if this will get worked on today or not! thanks again, and keep the ideas coming Ken

05-09-2010, 02:05 PM	#8
Mark Yacavone Veteran Member Join Date: Mar 2002 Location: Miles From Nowhere Posts: 7,815 Likes: 2,903 Liked 5,120 Times in 1,951 Posts	Re: soft brakes - why? Ken , As mentioned..Where is the push rod mounted to the brake pedal? If it's in the PB position , it needs to come down at least an inch. The leverage ratio and clamping force is actually better with it up high, but the pedal will never feel right to you. First thing to check. __________________ "We are lucky we don't get as much Government as we pay for." Will Rogers

05-09-2010, 03:48 PM	#9
Kegracing Member Join Date: Jun 2002 Location: Red Oak, TX Posts: 441 Likes: 0 Liked 0 Times in 0 Posts	Re: soft brakes - why? Thanks Mark. Car was original 4 wheel drum, manaual brake car. Have it in the same hole. Push rod length is good. Brakes are actually soft. At low speeds, have not had it going over about 30, have to pump brakes to get any pressure. Will stop the car, but have to pump the brakes to get pressure. Just feels like I have air in it to me. I pressure bleed them, starting at back pass, back driver, front pass, front driver, and got all the bubbles out, then several shots of good clear fluid at each wheel, before moving on. The Wilwood wheel cylinders have 4 bleeders. I use the top, outside for each wheel... Think I am going to just start at the MC and start over, unless I find something that I am missing. Ken

05-09-2010, 04:51 PM	#10
Jim B Member Join Date: Dec 2008 Posts: 100 Likes: 0 Liked 1 Time in 1 Post	Re: soft brakes - why? You Said "Just feels like I have air in it to me. I pressure bleed them, starting at back pass, back driver, front pass, front driver, and got all the bubbles out, then several shots of good clear fluid at each wheel, before moving on. The Wilwood wheel cylinders have 4 bleeders. I use the top, outside for each wheel..." OK I believe that could be your problem.... in a fixed/opposing piston caliper configuration with 4 bleeders you usually need to bleed BOTH uppers in each caliper half. (Not just one)