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

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.

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.

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.

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

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

Re: soft brakes - why?
 

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)

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.

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

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)

Re: soft brakes - why?
 

I will try that before pulling everything apart. I called Wilwood, and they said outside should do it... but she really did not sound real positive.

Easier to start there than to start at the MC!

Thanks again everyone!

Re: soft brakes - why?
 

Put a couple of Viagra in the master cylinder. That should stiffen it up some. HA HA HA HA HA HA HA HA .
Chip

Re: soft brakes - why?
 

I had a similar problem and bled all bleeder screws on the calipers and that solved the problem.

Re: soft brakes - why?
 

Thanks Jim and Mark. Will do this as soon as I get a chance. Wife was not much help today...

Mark, hope you are doing well. See if you can keep Chip in line.

Chip, do you have a lot of experience with Viagra? Is that what the "Legend" is all about???

Re: soft brakes - why?
 

Ken,
Don't use it. At my age I value my sleep too much. LOL
Chip

Re: soft brakes - why?
 

Yeah kinda like that cialis everyday commercial......and they really expect me to get anywork done like that ? I mean seriously.......

Sleep is a good thing......sometimes very underrated.

Re: soft brakes - why?
 

I have to agree. Amazing how much quicker I can get caught up on something that 10 years ago I never thought I would get enough of!

Maybe that is why she would not help me with the brakes today?

Re: soft brakes - why?
 

x2.

Re: soft brakes - why?
 

Re: soft brakes - why?
 

A way I heard of but never tried... You can do it by yourself. It may take a lot of fluid. 4 hoses to fit over the bleeders (or 8 reading the previous post), open all bleeders, drop the hoses in jars or containers at each wheel. Put about a couple of inches fluid in each container. Make sure the hose ends are submerged. Start pumping the pedal, keep filling the MC and pump the pedal until the air goes out and fluid gets sucked in. Keep pumping and filling the MC. If there was a lot of air you will see bubbles but I think almost all of it is out now with a little trapped somewhere. So when you think you have pushed the air out or flushed the fluid well, tighten the bleeders and remove the hoses. Top off the MC and see what you have. A defective MC comes to mind too.

Re: soft brakes - why?
 

I recently converted my 68 camaro from drum to disc. I used the Aerospace brakes. The pedal seems a little softer with the disc brakes than with the drums but the stopping power is amazing. All I have to do is rest my toe on the pedal and it stops great. On the first run i hit the pedal like I did when I had the drums on it. I had to put the car back in gear to drive to the end of the track. I used a similar master cylinder but did not use a porportioning valve. Follow the instructions on seating the pads. I took a couple of runs before the line lock held real good.

Re: soft brakes - why?
 

Does the car still have rubber lines at the calipers? Maybe they are expanding when pumped the first time. Just throwing an idea out there. Never mind reread your first post

Re: soft brakes - why?
 

Thanks again all for the help and suggestions. Worked all weekend and long hours, still have not had a chance to work on car.

Will let you all know what I find.

Ken

Re: soft brakes - why?
 

I learned this from Pustelny and it works every time. Fill the master cylinder, open the bleeders at all four corners and just let the car sit for a few hours. Obviously, check the master cylinder regularly, to make sure it doesn't go dry. The system will gravity-bleed just fine. To make absolutely sure you're done (though it is not necessary), close all four bleeders and put one pump on the brake pedal at each corner. You should get solid fluid, with no sputtering.

One other thing. the basic rule of master cylinder bore size says that too large a bore will make the pedal go too deep and the brakes will tend to feel spongy and too small a bore will make the pedal too hard and require a ton of pedal pressure.

Re: soft brakes - why?
 

************************************************** ************************************************** ****
Good info except you got it backwards regarding the ratio of master cylinder size vs. wheel cylinder / caliper size.

The smaller the bore on the M/C the more PSI you generate within your brake system with all things equal. Now you with a small bore M/C you have HIGH PSI and LOW VOLUMN per pedal stroke.

With a large bore M/C, you have LOW PSI and HIGH VOLUMN.

Due to the large caliper bore size a small M/C might not apply the brakes fully with 1 (one) pump of the brake pedal.

A small bore M/C will feel softer than a large bore M/C due to the mechanical advantage of the small bore = higher line pressure.

A large bore M/C generates lower internal pressure and the pedal will feel harder because of the lower mechanical ratio.

Don't forget there is also a pedal ratio that can be used to your advantage but the same mechanical rules apply.......high multiplication = less M/C stroke...lower multiplication = more M/C stroke.

Just make sure that you have enough volumn to fill the calipers / wheel cylinders with 1 (one) pedal stroke.

With a high muliplication pedal ratio, a small bore M/C and large wheel cylinders we used to bend the backing plates in half prior to the use of trans brakes.......


Hope this helps,
Bob

Re: soft brakes - why?
 

Thanks for setting the record straight. When I wrote it, I spent 10 minutes re-reading it, thinking I might have gotten it backwards. Kinda like when you try to remember the old "set the intake lash when the exhaust is opening, set the exhaust lash when the intake is closing" thing.

Re: soft brakes - why?
 

First, thanks everyone! Jim and Mark, you were on the money. Amazing how much better it is after you get all the air out. I went back thru all the bleeders, and was just a little air at each bleeder screw.
Feels much better now. Have not had it out on the street(God bless my neighbors), its raining, but have a very good pedal now.

Ken

Re: soft brakes - why?
 

Glad to hear the mechanical problem is solved...I wonder if your wife will get over Mother's Day as quickly?

Re: soft brakes - why?
 

she is still a little grouchy, but she did climb in and push the brakes for me today... fussed some, but did it!
I got a pretty good one, but dont tell her I said so :)

Ken

Re: soft brakes - why?
 

Now get her to go to the track with you and do the fuel and tires and cooling ,while you ride around and socialize with fellow racers..lol

Re: soft brakes - why?
 

This won't affect the race car, but the tow vehicle. A guy at work replaced the front pads, turned the rotors, packed the bearings,and replaced the master cylinder on a 98 Suburban with around 50,000 miles on it, and had a problem getting a pedal.Before he was done, the yellow ABS light stayed on,as well as the red brake light on the dash. He had some pedal, but it was soft and low. Trying to bleed it with a SCAN tool didn't help much,even though he followed book proceedure verbatum. I got an idea. It had been rainy earlier, and the street a mile from the shop had some dirt washed out into it, so we took off on a road test.As soon as I got to the wet dirty spot in the street, I slammed on the brakes hard when we got into it. The ABS activated, the pedal vibrated like it was supposed to,the ABS controller made that funky noise it makes,and the light flickered. The pedal got noticibly firmer, and so we did it a couple more times. At the end of about three brake system ABS assisted stops, no lights, firm pedal, brake system normal. We came to the conclusion that the ABS solenoids in the controller must accumulate a rather large air bubble in one or more of the solenoids,giving a soft pedal.Activating the solenoid through a panic stop or two purges the bubble and restores the brake system performance. I also have noticed that vehicles without a noticible brake system issue get a firmer pedal after activating the ABS that way, too. It apparently needs to occasionally be activated.