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Brake Problem??

#1
Looking for some advise. I have duel Wilwood master cylinders and Wilwood 6 piston calipers on my race truck.
The brake peddle is great in the shop and lite testing, after a few miles in the beginning of a race the peddle goes to the floor.
I could pump the brakes five or ten times and barely get a peddle. After the race the peddle came back like it never had a problem. I have bled the brakes several times using three people and bled the master cylinders. Brake line are not to close to the exhaust.
Has anybody ever experienced this before or have any suggestions?
 
#2
Master cylinders good, one new and one rebuilt. Rotors seem fine. Think I will start with check valves.
Thank you


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#3
I have a couple questions. First one. How are you bleeding the brakes? I have found that pumping the pedal before opening the bleeder will cause micro bubbles to get trapped in the lines and will give the impression of a good pedal until driven. Especially on floor mounted master cylinders where gravity isn't working in your favor. My preferred method of bleeding is to use a pressure bleeder or vacuum.
Second question. How much flex line do you have at each wheel. An excessive amount of flex will cause a soft pedal. Will feel ok at lower speeds but go away with greater braking forces. Lastly. My experience with Elwood has been hit and miss when it comes to quality control. I have had master cylinders come out of the box full of debris from manufacturing, out of round bores, and nicked seals. I have had more issues setting up wilwood brakes than other manufacturers. I prefer c.n.c or pro-am stuff. Have had less frustration with these brands. But based on what you are describing it sounds like you either have trapped air or a fitting that isn't sealing. I would try finding a pressure bleeder and bleeding that way after putting a wrench on all the fittings. Flares that are over tight can split and not seal. Also if they are over flared when the lines were built they won't seal. I've had flares that sucked air but no evidence of fluid leaks. I hope this helps. Wipe down all brake connections after bleeding and go stand all over those brakes. Maybe you will get some seepage. It doesn't take muck to kill a pedal. Good luck.
 
#6
I am bleeding the brakes by pumping them. I think its time to purchase a pressure bleeder. I will agree Wilwood seems to have more problems.
Thank you Bert for all the recommendations. I now have several things to consider.
 
#7
No problem. I use an old 22 ounce beer bottle with a piece of coat hanger wrapped around the neck to hang under the truck and a piece of clear hose going from the bleeder to the bottle. This will allow you to see the bubbles as they leave the brake lines. Pressure bleeding uses a lot of fluid. About a half to one gallon depending on the amount of trapped air. Take your time. Go around the vehicle twice. Starting at the point furthers from the m.c.
 

firedog

Well-Known Member
#8
Are you bleeding front and rear at the same time? We were told with a dual master to bleed front and back at the same time??? We did this and it seemed to help???

We use these at the race track for the Spec Toyota cars with success:
One-Man Brake Bleeder Bottle with Magnet | Pegasus Auto Racing Supplies

From Wildwood site:
"In-Line residual pressure valves retain a minimum brake line pressure to help eliminate excessive pedal travel in both disc and drum brake systems. The two-pound valve is used in disc brake applications where the master cylinder is mounted below the horizontal plane of the calipers and fluid drain back occurs from gravity and vibration, thereby causing excessive caliper piston retraction and longer brake pedal stroke. The minimal two pound residual pressure prevents fluid from flowing back without causing the brakes to drag. With drum brakes, a ten-pound RPV valve is sometimes used to compensate for return spring tension in the drums."
 
#9
Pressure bleeders are great. But you can still get the air out if bled correct. Open the bleed screw, have someone slowly press the pedal, close bleed screw, release the pedal and repeat. A warped rotor or sticking caliper will cause heat and also cause a soft pedal.
 
#10
We are bleeding them right using 3 people, front and back at the same time. One master cylinder works the front and one the back. I do like the beer bottle way, that sounds good! I will ask around and see if I know somebody that would have one.
I had a long talk with Wilwood today, they said the same thing as Bert, flexing axles, spindles and rotors are knocked the pistons in. They recommend adding their springs to the pistons to keep them out Wilwood Part No. 300-2434.
What do ya'll think of that?
 
#11
What type of brake fluid are you using?
Maybe you need to switch to one with a higher boiling point.
Try DOT 5 synthetic?
 
#13
Bent axle or warped rotor will move the cylinder out as soon as the car starts to roll causing a soft pedal. Get the wheels off the ground and check. Should be pretty easy to see.
 
#16
Check wheel bearings, and hubs. As you get into off road and loads transfer to the wheel, any amount of movement can like already stated cause the piston in the caliper to push back in. So no mater how much you bleed and bleed you think there is air in the system, but air is not the problem.
 
#17
Check wheel bearings, and hubs. As you get into off road and loads transfer to the wheel, any amount of movement can like already stated cause the piston in the caliper to push back in. So no mater how much you bleed and bleed you think there is air in the system, but air is not the problem.
All bearings and hubs are tight. It may not take a lot of movement when there are six pistons in the caliper. Decided to go with Wilwood advice and add springs to the pistons, I have them ordered. They are not very expensive and think they would help regardless. I will report back after install. Thanks for the help on this one.
 
#18
Dodge had a service bulletin in 2003 or 2004 with a procedure for checking run out of brake and hub components using a dial indicator. If I remember correctly the spec called for no more than about .003 run out of the wheel. Rotors or hub. This was to cure vibrations while braking. I think this is a good number for just about any vehicle. Obviously the closer to zero the better.
 
#19
If there was more run out than that the repair was to turn the rotors using an on the car brake lathe. Theses machines account for all run out in the hub and rotor. Effectively Matching the rotor to the hub and eliminating distortion caused by wheel stud torque/stretch. Makes for an extremely smooth and straight braking vehichle.
 

burninfuel

Well-Known Member
#20
did you bleed the master cylinders before installing them.
bend up a return line back into the reservoir and had pump and see the bubbles clear out , then hook up your system
 
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