I'm having a tough time with some brakes one of the Gurus on here might know about. I have a roadster with four wheel discs, power booster and the proper residual valves in place. The MC is under the floor. There are no leaks we can find anywhere. The MC is the correct one for the install and there are no obvious screw ups anywhere in the lines etc. My problem is you need to pump the brakes once, maybe twice to get pedal. We have bled the system several times and can't get any more air from the system. I have pulled the calipers and held them up, tapped with a hammer on the case to loosen any bubbles etc. No luck. Would the adjustment of the booster rod have anything to do with this? What else? This is driving me nuts!!!! There isn't a lot that stumps me but this is a tough one. Suggestions gentlemen......
on my '31 my M/C is under the floor and it took me about 20 times to get most of the air out. I still have to pump one time to get a top pedal. I don't like it either. it drove me crazy bleeding after bleeding. try going to the to the furtherest wheel and just crack open the bleeder valve don't touch the pedal, and just let the air naturally rise to the highest point in the line for about an hour or two. then go to that highest point and tap on the highest point with a screwdriver handle to move the air out. then close the valve then go to the next. ect. ect. GOOD LUCK. JAN.
Try a pressure bleeder first. Was the master bench bled ? Can trap air that takes forever to get out.Check to see that the pads arent retracting. Good luck.
I agree with bench bleeding of the master. You can mark the pushrod throw when it is on the bench too to make sure the pedal has the proper throw. Maybe there is an easier way but I have done that in the past.
The master was bench bled and has zero air in it. The brakes have been bled with both a vacuum bleeder and a pressure bleeder to no avail. We changed the MC to the largest cylinder I can find, (power, mid 80's Trans Am, ), and I was thinking the volume may not be adequate for volume of the rear brakes, no luck! The rear calipers are from a Cad Seville and the front brakes are the usual GM caliper kits that everybody uses. Even if the rear brakes need a pump or two the ftonts should lock up and they don't. I wondering if the booster might need more stroke or adjustment? The pedal assembly is TCI, and of great quality. I'm also concerned about the routing of the lines although it shouldn't matter.
To answer your original question yes the rod from the brake booster to the master cylinder can cause this if it does not allow the piston in the master Cylinder to return all of the way back to its rest/normal position. I believe that causes air to be trapped in the system
IOC your rear. Alipers are the ones with a parking brake you may need to adjust the pistons try applying a little parking brake and see if the pedal is any better.
Excessive wobble in the rotors will also cause low pedal, as the runout kicks the pads back in the cylinders and causes the master cylinder to have to push them past design limits for 1 stroke. Wobble without rotor thickness variation cause little or no pulsation in the pedal when compared to worn rotors. Check with a dial indicatorr.
I would plug off the back at the master cylinder - see if the brake pedal is better . Isolate the system and find if it is frt or rear brakes causing the problem.
I am using 2 lb. valves, front and rear. I'm going to get it up and reset the booster push rod next. I did go through hell getting the parking brakes to come up. We've been through two sets of calipers, both acted the same. Rear discs are always a bitch to get working right but these are especially a PITA! I trued the axles to within about .001 before I installed the Wilwood rotor hats. I'll check runout but Wilwood stuff is usually pretty good. I've come upon that problem before. The car will do the same thing when it hasn't been moved so I don't think it's runout. It may be the pads retracting too far, that's hard to determine. I can't get either of the sets of rear calipers to "ratchet" like they usually do. No idea if that's a problem. I set the E brake manually. Speedway supplied all the components and their Tech is pretty clueless but he can read the same instructions they sent with the kit off his computer. Whatever the problem is it probably relates to both front and rear as neither "locks up" like they should. If it was just the rear I would just replace the rear set with drums and eat the cost. I have more time in this now than the brakes cost but that doesn't account for the lack of front brakes until they pump up. To be honest, they aren't what I would expect from 4 wheel power discs anyway. They should put you through the windshield with light pedal pressure. The other part is my ego just won't let these suckers beat me.
That's a sure sign you still have air in the system. Try some speed bleeders or at least a bleeder bottle with the end of the bleed hose submerged under brake fluid. Make sure you are not cracking the bleed screw too far open and sucking air back in. That's why I like speed bleeders, you don't have to worry about sucking air and one person can bleed the brakes. You can also plug the distribution block to see if it's the fronts or rears that has the air.
What is the MC bore size? 1-1/8" bore corvette with booster should be able to loc wheels at will...Through frame fittings sometimes trap air..
Dane, been through the bleeding routine at least five or six times with three different people doing it and I still think there is air in there somewhere. There are no through the frame fittings.
if you are thinking air still trapped ///jack car up at different extreme angles to release trapped air......
We tried that on Friday with the back on the lift. I'm thinking that if I can't get the booster rod to solve the problem I may reroute the brake lines to provide for nothing higher than the calipers, (air always goes to the top), and take the calipers off again and bleed them with wood blocks in the pads to hold them apart. If that doesn't work, I'm just going to start at the MC and work through everything again. I've never used speed bleeders but I'm going to get some and give it a whirl.
So if you stiff think there is air in it .... If you pressure bleed it you should be ok.... Do you use a small hose and catch bottle? I know this might be a dumb question but do you have abs? And what wheel order do you do?
Are the front calipers G.M.? Are they the low drag type that take the quick take up master to operate properly? Very common problem. The front low drag calipers have a square cut o ring that allows them to back away from the rotor, making you pump the pedal twice to get them out far enough.
Oktoma>>> I would plug off the back at the master cylinder - see if the brake pedal is better . Isolate the system and find if it is frt or rear brakes causing the problem.>>> Best suggestion yet, IMHO. Do it! Might even be the M/C. Jack E/NJ
up until this post I did not see where you mentioned Wilwood just four wheel disk brakes, if the pushrod does not do it most of the Wilwoods have 2 bleeders top and bottom and you have to rotate the caliper.
The rear brakes are caddy Seville calipers and Wilwood hats and rotors. the front calipers are typical GM metric, nothing fancy. I'm considering drilling the calipers for a second set of bleeders. Could be a solution as the bleeders now face down on the rear calipers so I always have to take them off to bleed including undoing the E cables.
All of this stuff is Speedway kit stuff including the rear brake kit. the owner supplied everything and I've been working on it since! Calipers can be in any position as long as they are bled in the proper position. The kit is installed as per Speedways instructions.
You can prove it to yourself by disconnecting the brake lines at the master cylinder and installing plugs in the master cylinder outlets. If you then get a hard pedal you know it's air somewhere. Reconnect the lines and move to the distribution block where the front and rear lines are connected. Plug the front or rear outlet at the distribution block itself and see if the pedal is still hard. Did you bench bleed the MC? If not or if you still have a soft pedal after blocking off the MC outlets you can bleed the MC on the car like this -
The calipers don't know what position they are in after they are bled. SoCal front brakes, the ones that look like Buick drums, are always flipped and they work perfect but you always pull the calipers to bleed them. If I flip the calipers the other way it is impossible to use the E brakes because the cables go directly into the cross spring. It does the same ting if we have the calipers the other way around as we tried that early on. I haven't had a chance to work on it but I'm pretty sure it has to do with the booster rod.
You are correct about the calipers do not know or care how they are mounted, and like you mentioned you are rotating the bleeder to the top to bleed which should work, if those front brakes look like the Buick style(functional fakes) - don't those use the Wilwood caliper ? If so they have 2 bleeders per caliper, one on the top and one on the bottom and they also have to be rotated to get all of the air out. I just remembered you saying that they were GM metric calipers if so forget what I mentioned previously. But I would like to see the front brake setup
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