Thread: Brake problems

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Hey Guys,

I have a problem with my brakes on my street rod and can't figure it out
This is an all new set up that came with the car with all wheel disc and with a booster, now here's the deal, very low pressure. I did bench bleed the master cyclinder 3 times, and it does shoot the fluid out like 8 feet across the garage I then put it back on and bleed all the lines untill there was no more air but there is minimal pressure at the pedal , but when I start the car the small amount of pressure that is there is gone like right now.
I have checked for leaks but found none and there is vaccum to the booster. I've never had a problem like this before with any other brakes and I'm out of ideas as what to do to fix the problem.
Maybe one of you guys can help me.

Rocky

its a dual master don't know what it is off of. its mounted under the car there is no excessive clearance and I am running a porpotioning valve. trying to get some pictures. believe the calipers are off of a ford explorer. can get more photos of brakes if it will help.

Hey Denny,

Thank's for getting back to me
I do have 2lb residual valves front and rear, and I did adjust the rod between the master and the booster. I also realized that the guy that was helping me put the rear calipers on upside down so I made it right and then bled the lines again and still no pressure. I took both lines off the master and put bolts in the holes to see if there is any pressure and now you can't even move the pedal there's so much pressure.
I'm truely lost on this one. I've been building and messing around with cars for close to 30 years and this is the first time that I have no idea what the hell is going on.

Rocky, when you say that there is "no pressure at the pedal" do you mean that the pedal goes to the floor? If so, and it doesnt go to the floor when the output ports on the M/C are blocked (as you said), you should check the calipers vs. the rotor thickness. Could you have put thin rotors on so that the caliper has to move the pad too far and thus making you run out of fluid volume?

mike in tucson

Yeah Mike, the pedal goes straight to the floor. I checked the calipers and it seems that the rotors and pads are like they should be, but the calipers don't push the pad at all. I know that when I was bleeding the system I checked to see if the fluid would shoot out of the bleeders but instead it was more like a trickel.

OK, if the calipers were mounted upside down when you bled them originally, you probably still have a pile of air in them. The caliper should be mounted with the bleed hole at the highest point. Open the bleed fitting and wait for a minute or so and then have someone push the pedal slowly while you watch the bleed port....there should be fluid coming out. If there is air, it will rise to the highest location in the caliper (which should be the bleed port) so you will expel some air. Of course, close the port before the pedal is released. You might have to get a MityVac power bleeder....we had to run 2 quarts of fluid thru the rear master cylinder to get one bled.

Also, check your rotor thickness vs the pad opening. You shouldnt have more than 2 RCH clearance with the brakes released. One other thought, watch each caliper as someone depresses the brakes to see if the bracket is deflecting....this shouldnt be the problem in your case, the deflecting bracket usually shows up as a spongy pedal.

mike in tucson

Thank's Mike

I'll try what you said , I have to wait till my help gets home from work. I sure hope this works cause my patients is wearing thin on this one.

Rocky

Hey Mike,

Tried everything that you said and still no brakes I tried something I saw on a webpage that said to take the caliper off and hold it up to try and get the air out of the lines, and it seems to me that there is no air for when the pedal was pumped it has just enough pressure left that if you crack open the bleeder that the fluid comes out, but when its closed the caliper will barely move. One more thing , I took the brake line off the caliper and pushed the brake pedal and the fluid shot out. It seems that when its hooked back to the caliper there's not enough pressure.

Should the brake lines be hooked up on the master so that the back runs to the front and the front to the back, cause thats how this was set up

What if????? What if you have a master cylinder that is
for a disc front and a drum rear combo? You would be
severely lacking in pressure on the back wheels and,
since the calipers take more fluid than do drums, you
would over tax the master cylinder's ability to deliver
fluid.

Do you know that you have a disc/disc master cylinder?

Also, the power brake push rod is adjusted so there is
just a smidgen (a technical term) of play when the brakes
are released. If there is no play, the master cylinder may not
fully return to the released position.

mike in tucson

You know I thought of that , but I don't know what the master cylinder is , because that's what came with it (the rolling chassis) . But I think that I have the push rod adjusted right , because it was worse before. Could be that I should get a dics/disc master cylinder and try it , hell at this point what do I have to lose.
Do you think that the way the master cylinder is plumbed is right???

A couple of thinks come to mind. The brake pipes should be 3/16". If 1/4" pipe is used you will get a pressure drop in the system. Make sure the brake pipe flares are a double flair. Single flares will crack and leak or suck air into the system. You don't mention what type of hose your running to the wheels. If it's an automotive hose from a production vehicle, check that theres nothing inside the hose blocking the fluid flow. If it's -AN hose, it should be -03 w/ teflon liner, and the proper fittings. Also check your banjo bolt/ hose/ sealing washer/calipier for fluid flow thru the fitting. Sometimes there isn't enough clearence between the bolt and hose, or between the end of the bolt and the inside of the calipier [the bolt bottoms out]. Hope this helps.

When I've had a problem like this in the past, I start with the basics and work rearward. First, plug off both outlets on the master and REMOVE ALL VALVES from the entire system. Pump the brake and hold it for 30 seconds. Do you have a hard pedal? If no, then the master is bad. If yes, then the master is good and you can move on to the next test. Hook up the front calipers, leaving the plug in the master where the backs hook in. Pump the brake and hold it for 30 seconds. Do you have a hard pedal. If no, then the front calipers are at fault. If yes, reconnect the rear brakes and pump and hold the brake for 30 seconds. Do you have a hard pedal? If no, then the rear calipers are at fault. If yes, then one of the valves are at fault.

YOU ROCK

Thanks for that break down. dam it makes things simple

Dwayne, I'm using 3/16 lines and AN 3 hose (braided lines) to the wheels , but I'm going to check the banjo bolts to make sure that there is flow to the calipers.

Tech, I blocked the ports and had a rock hard pedal , but when the lines are hooked back up there's no pressure at the calipers. I'm going to try blocking one at a time like you said and see if its a valve. I have been suspecting the master cylinder almost the whole time, I'll be on it here in just awhile and let you guys know what happens.

Thanks Rocky

Well Guys tried everything said on this thread and some other things and still NO BRAKES I had a buddy of mine up today and he is as confused as me as to why there is no pressure . We came to the conclusion that its time to get a new master cylinder , at this point I have nothing to lose and everything to gain . I'll definately keep you up to date.

Thanks for the help Rocky