Brake problems

Hey Guys,

I have a problem with my brakes on my street rod and can't figure it out:confused:
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:rolleyes: 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.:confused: 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.:mad:

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:CRY: 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 :confused:

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:mad: 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

I may be wrong but I don't think you can't block one port and use the other for a test unless the blocked port can bleed off how will the pedal move??:confused:

Quote:

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Originally Posted by cffisher

I may be wrong but I don't think you can't block one port and use the other for a test unless the blocked port can bleed off how will the pedal move??:confused:

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The pedal isn't supposed to move if the master is good. That's the whole idea, to find out if the master is leaking back internally and not providing pressure to the calipers.

Well Guys I'm almost positive its the master cylinder now, last evening I pushed on the pedal and it seemed that there was a small amout of pressure and then the pedal hit the floor. When this happened I heard the fluid in the master cylinder as if it is just passing through the master and going nowhere else.
Only when I take one of the lines off at the wheels does the fluid move, other than that once the line is put back on and the system is closed then the fluid seems to only move in the master cylinder.

Thanks, Rocky

master cylinder is bypassing

Thats what I thought

Rocky72...You ask if the lines should be hooked up back-to-front and front-to-back,this is right when you have disc/drum, front/rear, but shouldn't matter with discs all around. By the way, your master is facing the "wrong" way, so it should be front-to-front in this application.
I agree that your master is either faulty, or not the right one for your setup, but it could still be a bleeding glitch. Have you checked that the master piston is actually returning when pedal pressure is released? Sometimes the system locks and holds the piston down.

Well , I put the new master cylinder on today and bled the hell out of it and still no brakes:mad: I am completely out of ideas. Had another guy up and he can't figure it out either.
Shouldn't there be some sort of pressure at the pedal even if there is some air in the lines ??? Everything that I've read says that if there is air in the lines that the pedal would still have some pressure, even a soft pedal.
Checked the master and the piston is returning so what could it be ???
and I adjusted the booster rod.
Is it illegal to shoot your own car, cause thats next on the list.

Rocky

Yep, thats what we did, and made sure that the master had fluid.

Yeah, we just went through and bled the brakes again and still nothing. It seems as if there is a very small amount of pressure and then its gone.

It seems to build minimal pumping it fast but does not hold at all.

Something we havent ask:
What calipers are on the front?
What calipers are on the rear?
What did the new master cylinder fit?

Do the pads have the correct clearance? Some pads have
automatic adjusters that need to be set.

When you bench bled the brakes, did you wait for 20 seconds
or so between strokes to allow the air to bubble up to the
top?

We will think some more on this....

mike in tucson

This is an interesting article but it doesnt have a picture of your
car in it.... http://www.babcox.com/editorial/bf/bf60133.htm

thay are talking about low drag calipers with the wrong master
cylinder..... just an idea

mike in tucson

I don't know what calipers are on this car, when I got the car it came with the brake setup on it . I did bleed the master as you said. The pads are against the rotors and it seems that they have some pressure but not enough to do anything.

I'm going to get in touch with the guy I bought the roller from and see if they had any other problems like this, maybe this isn't the first time. And then if that doesn't work then I'm going to shoot the car:LOL: For now I think it's time for a cold one and to chill out a bit.

Thank's Rocky

Hey Guys , guess what ??? I went out and tried a small adjustment on the end that hooks to the pedal from the booster. I took it out as far as I could and now I'm building pressure, the only problem is that the end is just about to come off the booster rod. I guess I'll have to find a rod end thats longer so it will be on by more than a few threads.

Ahhhhhh...the old "wishing for a longer rod" problem......

Funny how such an insignificant part can cause so much
beer consumption.

mike in tucson

Yeah I know, but I did adjust it and wanted to make sure there was enough threads to hold the end on. I just figured that the end was adjusted right but I guess not. Its a good thing that your here to keep me in line :LOL: But I will have to get another rod end , I don't want it to fall off now that I :LOL: figured it out.

Thanks Rocky
I think its to nice to shoot:rolleyes:

Yeah Mike and then there's that problem that I have with the car :LOL: :LOL: :LOL:

This has been an interesting thread, and it's full of wild guesses and faulty information!
1. Your m/c is a "Corvette" style, and is plumbed correctly. If you remove the cover, you'll be able to see that the rear reservoir will hold more fluid than the front reservoir. Notice the bulge in the side of the casting. The large (rear) reservoir goes to the front brakes. You can't tell by looking at the cap, as the cap is symmetrical. It DOES make a difference how it's plumbed!
2. The adjustment of the push rod between the booster and the m/c is VERY critical. There is a small fluid port in the bottom of the reservoir that MUST be uncovered by the pistons when the brake pedal is released. This can be checked by watching for a little spirt of fluid when the pedal just starts to move. If you don't get a spirt, remove the m/c from the booster and shorten the push rod in the booster until you get the spirt. If you get a spirt only after moving the pedal 1/4 inch or more, lengthen the push rod. Having too much movement before the spirt will cause the brake pedal to travel too far before the brakes work (maybe to the floor). You don't need to have vacuum on the booster for this test.
3. You can't plug one brake line, and then try to test the other line. The pressure will immediately build up in the blocked section of the m/c, and will not allow the other section to push any fluid.
4. Call SAC Hot Rod (714-997-3433). They have built lots of cars with this type of brake system.

Hot Rod Roy,


For one , this is not a vette style master. I did however find out that the pic of the master cylinder that you saw is from a GM all drum brake setup (far as we can figure) so there's part of the problem.
As for the problem at hand , as I said the end on the booster rod does not have enough threads on it and I can't adjust it out to where it pushes the rod
and piston far enough to create any pressure .
Denny had it right on the 4th post :) I should have checked it a 2 nd time.
But one thing I can say is I'm glad that these guys at least offered the help weather it be right or wrong.:)

Not a problem , I give credit where credit is due.:) As I said I think that it's great that you guys take time to try and help , this isn't the first time that CHR came to the rescue. :3dSMILE:

Thanks, Rocky

When you do get rod of the proper length as Hot Rod Roy pointed out the adjustment is critical. Adjusting it too far will cause the brakes to bind.

Are you telling me that rod length is not critical?

I guess it's just too early in the morning and I haven't had enough coffee yet. :( I didn't read the whole thread and that's my mistake and yes the weather here sucks too. :(

Rocky, if your master is from a four wheel drum brake car, there might be internal residual check valves in it. This would cause your disc brakes to drag all the time, since these residual check valves would hold about 10 psi on the calipers. You can check for these valves by carefull inserting a straightened paper clip into each outlet port. If the paper clip only goes in about 1/4 inch, you've got internal check valves. If the paper clip goes in to the centerline of the master cylinder, there are no valves.

True, this master is used on several GM vehicles, including vans. Take a look at an '82 or earlier (back to '68) Corvette . . . same m/c (but no internal residual check valves).

Have you checked the diameter of the bore in your m/c?