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Post by mongoose on Jun 25, 2011 18:03:21 GMT -5
Ok... need some suggestions on where to look for the issue.
Started with a new master cylinder, and 9" brake booster (more clearance to remove valve covers), new stainless brake lines and rubber hose on the rear end (had to use an adapter to connect the 12-bolt rear rubber brake hose to the 3/16 brake line that runs front to rear), new rear brake cylinders, and freshened up rear brakes.
I can't get the brake pedal to firm up, and I had trouble getting the air to clear the rear lines. Thought the issue was the master cylinder, so I got another one. Bench bled the new one, same issue. No leaks I can find in the system... no brake fluid drips.
When I put the car in gear with all 4 corners up on jack stands, I can't hold the rear axles from turning with the brake applied fully. The adjuster are all the way in... and the backing plates don't have a slot in it to adjust them. Could be I have to put it on the ground and back up and apply the brakes to get them to adjust out.
Seems like the new master cylinder was allowing me to get the air out of the lines (although not 100%), but the pedal is still soft, and I can't hold the rear when put into gear.
Kind of afraid to put the car on the ground and put it into gear, for fear of a run away car.
Thoughts? What should I go look for? What should I expect? These systems aren't complicated... frustrating not to know where to go look next.
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Post by bubbasz1 on Jun 25, 2011 20:17:46 GMT -5
Ok... need some suggestions on where to look for the issue. Started with a new master cylinder, and 9" brake booster (more clearance to remove valve covers), new stainless brake lines and rubber hose on the rear end (had to use an adapter to connect the 12-bolt rear rubber brake hose to the 3/16 brake line that runs front to rear), new rear brake cylinders, and freshened up rear brakes. I can't get the brake pedal to firm up, and I had trouble getting the air to clear the rear lines. Thought the issue was the master cylinder, so I got another one. Bench bled the new one, same issue. No leaks I can find in the system... no brake fluid drips. When I put the car in gear with all 4 corners up on jack stands, I can't hold the rear axles from turning with the brake applied fully. The adjuster are all the way in... and the backing plates don't have a slot in it to adjust them. Could be I have to put it on the ground and back up and apply the brakes to get them to adjust out. Seems like the new master cylinder was allowing me to get the air out of the lines (although not 100%), but the pedal is still soft, and I can't hold the rear when put into gear. Kind of afraid to put the car on the ground and put it into gear, for fear of a run away car. Thoughts? What should I go look for? What should I expect? These systems aren't complicated... frustrating not to know where to go look next. First why don't the backing plates have slots for adjusting them?? Are they aftermarket cause mine have slot. Anyways I have a few thoughts. 1. I would pop of the rear drums and adjust the adjusters until the drums picked up slight friction while turning by hand. Drums come on and off a few times but basically no big deal. 2. If I understand correctly you added or changed your power brake booster. I would check the travel on the rod from the power booster to the master cylinder. Sometimes a tricky adjustment especially with power brakes. You won't be able to feel when that rod hits the master cylinder like you can sometimes with non power brakes so you might just brake the master cylinder nuts loose and have someone push the brakes pedal down while you watch the master cylinder for movement. Seems kind of a backwards way to do it but at this moment we are looking to make sure your getting your full movement on your cylinder and if you have someone push the brakes and the master cylinder doesn't twitch until the pedal is on the floor the rod needs to get longer. Ok thing about doing it this way is if you get the rod too long you can tell because you will get a constant drag on the brakes, easily felt by turning the tires by hand. 3. Check to see if their is an adjustment rod from the brake pedal to the power booster, this could be way out of adjustment, I don't have power brakes on my running car(post) so I'm guessing a little on how it's set up. See what that does, I have a feeling your not getting your full movement on your master cylinder which is causing your problems. Ask again if I boggled you a little, it's just hard to get your thoughts across by typing it down as compared to talking about it. |
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Post by BR[] on Jun 25, 2011 21:15:10 GMT -5
ANOTHER Thing to check:
Do you have front disc brakes?
If not and you have drums all around..... check to see that the dumb asses didn't give you a disc/drum master cylinder (like they did me) it will cause that symptom
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Post by mongoose on Jun 26, 2011 7:18:21 GMT -5
BRO... I have front disc brakes from a '69 Cutlass. I think the master cylinder is of the right style, same as I had before with the factory-style booster from the '69. But you're right... never put it past someone to give you the wrong stuff.
Bubba... All good suggestions... and I will work my way through each. The rear end is a 12-bolt out of a '69 Chevelle. It does seem odd that there is no adjuster slot. I guess I could drill a hole in the backing plate to provide access, but your approach should work out just fine.
The booster travel could very well be the issue. This booster is somewhat "universal" in nature... the booster to brake pedal rod was just a threaded rod, and I had to put make an adapter using the pedal bracket, a piece of all-thread, and a threaded adapter to join it all together. Your method to test makes sense, or I guess since the car has all 4 tires off the ground, I could feel for when the front brakes start to apply by moving/spinning a front wheel.
When the brake pedal is pressed, you can't manually move the front wheel (of course that really doesn't require that much caliper pressure to do), but at least I know I'm getting some pressure to build.
When I bleed the brakes, I get fluid to flow in all 4 corners, although this problem make me question if I'm seeing the rear flow out too slowly/weakly. It's not a vigorous shot out of the tube into the catch bottle. And yesterday my wife said the pedal wasn't dropping to the floor when I opened the bleeder screw... very odd. That symptom takes us back to the question of brake pedal/brake rod/master cylinder travel.
I'll go do some more investigation this morning.
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Post by 442scotty on Jun 26, 2011 8:39:58 GMT -5
There are two different length rods available between the master cyl and the booster. Not sure why. Inline tube mentioned it to me when I ordered my Master cyl so I asked for both to be sent. Perhaps yours is too short ? Just throwing it out there..hope it helps...Proportioning valve issues? assuming you have one..
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Post by shane on Jun 26, 2011 9:28:30 GMT -5
I know this might sound stupid but is you master cylinder reservoir filled to the max. The reason i ask is on my 88 chevy if the brake fluid level drops about 1/8 inch below the full line the brakes start to get a little spongie when bleeding them and they wont firm up till i top the fluid off.
just a thought.
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Post by nickthefish on Jun 26, 2011 9:54:00 GMT -5
Personal lesson learned..
Check the threaded piece that connects to the rake pedal for the proper distance. If you Google manual to power brake conversion, you should be able to find a page that lists what the proper dimension should be. 2 1/2" if I remember correctly but it is sensitive and more or less will make a huge difference. Had the sam problem on my 2nd to last 442. Bled everything and the pedal was fine. Took it for a ride and it was crap. Manual bled, power bled, the whole nine yards. Adjusting that distance fixed it.
Nick
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Post by mongoose on Jun 26, 2011 10:22:53 GMT -5
All good suggestions... very appreciative when I'm scratching my head on where to look next.
Scotty may be on to something, combined with Bubba's earlier comments. It looks like I might have a travel issue, just not exactly sure how yet. The brake pedal won't depress clear to the floor. As my wife begins to press the pedal, I can feel the brake start to apply when I spin the front wheel. But she has to apply all her force to get the wheel to lock under my spinning it by hand... and you know that isn't much force.
I'm going to pull off the master cylinder and see how much booster rod travel I have. Anybody have a spec on how much travel you should measure?
With the master cylinder removed, if the pedal still won't go to the floor, then I know something is up with the booster travel. I checked the firewall clearance with the all-thread union, to make sure that it wasn't hitting something... the union doesn't even get close to the firewall right now... so that's not a limitation of travel.
Who knows... could be that this 9" brake booster isn't designed to work with this master cylinder, but something else that requires less travel. Wouldn't surprise me if that was YET ANOTHER thing that Lynn @ Mondello's failed to tell me when I bought something from him.
So the diagnosis goes on... Thanks for your input guys.... always helpful.
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Post by bubbasz1 on Jun 26, 2011 12:40:15 GMT -5
Couple of more thoughts, one is a power brake car won't bleed like a manual brake car unless the car is running, that will help if you haven't been doing that. Second I bet the ajuster slots are on the front face of the drums.
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Post by mongoose on Jun 26, 2011 12:41:54 GMT -5
Too many other projects going on today... so I have to squeeze in the diagnostics between stuff.
Pull the master cylinder off of the booster. When the brake is pressed it will travel clear to the floor. That eliminates mechanical obstruction at the pedal. Booster rod travel is 1 1/2"... does that sound like a good number? Anyone know the spec for that?
I put the master cylinder back on, and we back to the pedal going only half way to the floor... which would seem fine, except that to keep me from being able to turn the front wheel by hand, you have to use leg-shaking force at the bottom of pedal travel to get it to hold the wheel firm.
I pulled one of the rear drums... when the pedal is pressed to the bottom of travel, the rear cylinders/brake shoes barely move.
Something is preventing fluid travel. Next step I think is to pull the rear brake hose from the rear line, and see if I get a good flow of fluid. If not... and there is no apparent damage to the hard line, then maybe there is an issue with the proportioning valve? But how could that be... nothing can go wrong with a proportioning valve, right?
Gotta head to a ball game this afternoon... so I won't get back on it until later this evening... and that depends on how much beer I drink... I may just not care. ;D
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Post by Deleted on Jun 30, 2011 6:41:35 GMT -5
Goose, just another thing to check. Just make sure, for posterities sake, that the bleeder screws are on top of the calipers in front. They will bolt on backwards. Assuming you had them apart for fresh grease, seals, and pads.
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Post by bil on Jun 30, 2011 10:54:37 GMT -5
I don't know if it will apply here,but I once had the opposite problem-step on the brakes and they stayed on! After much head scratching (fleas) we figured out it was one of the rubber flex lines,the outside looked good,but inside was damaged,and a small flap was acting as a one-way valve,letting fluid in,but not out.No reason the opposite couldn't happen,might be worth checking. ---bil
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Post by mongoose on Aug 14, 2011 17:22:26 GMT -5
Its finally cooled off enough in the garage to make it inviting to get back to work on the car. I'm still trying to diagnose the problem I'm having with the brakes... we can bleed and bleed, them... and they still won't apply the brakes enough to stop the rear axle from turning if I put it in gear (obviously up on 4 jack stands). I can also spin the front wheels back hand, and they will just grab when the brake pedal is at full travel.
I pulled the rear hard brake line from the rear hose, and when the brake pedal is applied, I get only a dribble of fluid. The brake pedal travels maybe 2/3 the way to the floor, then stops. And not a firm pressure stop either... its more of like a hard stop.
I pulled the master cylinder off of the brake booster (a 9" aftermarket) thinking perhaps the booster was limiting travel, or that the pedal rod was hitting something to prevent travel to the floor. With the master cylinder removed, I get full travel... smooth as silk. Put the master cylinder back on... the pedal stops hard 2/3 of the way to the floor. With my hand on the master cylinder, it vaguely feels like it's bottoming out.
So I think "ah ha!" this is not the right master cylinder, and the range of travel of the master cylinder bore is bottoming out. I disconnect the two master cylinder lines at the proportioning valve, and the brake pedal will go all the way to the floor.
DAMN! So much for that theory.
Can a proportioning valve go bad?
As I'm looking over things, I notice that the front master cylinder line is a 3/16" line, while the rear line is 1/4". This seems backwards to me, as I would think the front line, which I presume feeds the front calipers would be a larger line. The brake line that runs from the front to the rear is 3/16", and it would only be logical that the line from the master cylinder to the proportioning valve supplying the rear brakes would be the same size.
So maybe that has something to do with it. But then again... I looked at the size of the orifice inside the two fitting "ports" in the proportioning valve, and the rear port has a larger hole inside the flare.
I can't come up with a reason for the limited travel... although I can't say I completely understand the safety features built into the proportioning valve and master cylinder in the event of a brake hose failure. I know the front and rear systems are two separate systems to provide some braking in the even of a front or rear failure. But I'm almost positive that when you bleed the brakes... one cylinder at a time, that when you open the bleeder screw, the brake pedal will go all the way to the floor.
Can anyone that has a power brake w/ front disk conversion check the diameter of their brake lines for me and let me know if the way mine is set up is right, or if they're reversed?
And anyone that can lend any insight or suggestion on the limited pedal I will appreciate hearing from you.
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Post by RAM Z on Aug 14, 2011 17:45:19 GMT -5
I would fill the master, and work the brake pedal with the lines to the prop valve disconnected. If the pedal works as it should and the lines spew fluid, the problem isnt in the master/plunger rod/brake pedal. Disconnect the line after the valve, blow air thru it and see if it comes out the other ends.
Sounds to me the prop valve is bad.
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Post by BR[] on Aug 14, 2011 18:18:48 GMT -5
what type of prop valve do you have, factory or The Right Stuff, etc?
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Post by mongoose on Aug 14, 2011 19:39:57 GMT -5
The factory proportioning valve I pulled off the same 69 Cutlass I got the other parts for the disk brake conversion (and installed on my '65 back in 1987).
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Post by BR[] on Aug 14, 2011 19:54:50 GMT -5
The valve could be stuck. Here's a generic pic. They can jam if activated.
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Post by mongoose on Aug 14, 2011 21:00:25 GMT -5
Very interesting... thanks for the diagram. Earlier this evening, I found the following post regarding proportioning valve issues... forums.aaca.org/f138/69-442-brake-problems-229301.htmlThe started to build my understanding of how a prop valve functions, and how you test it/fix it. Your diagram really helped fill in the blanks, and now has be believing that the prop valve is the issue. Here is my prop valve...  The button on the front end, didn't appear to be able to move. After reading the post, I tapped on it with a hammer, and now the button will move in and out somewhat less than a quarter of an inch. I don't know how much it should move, but now I know the cylinder in the valve was frozen. When I open a front caliper bleeder screw, the pedal will press clear to the floor, and fluid flows out. When I open a rear cylinder, the pedal still stops hard after about 2/3's travel, and no fluid flow. Even pumping the brakes with the bleeder screw open doesn't result with any fluid flowing out. I was hoping to get the prop valve at least working so that I KNEW that was the problem, then I could replace it. But it appears from all this testing and your comments that the prop valve has frozen up. |
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Post by Deleted on Aug 15, 2011 6:12:27 GMT -5
The next logical think to check is loosen the steel line at the rear rubber hose to see if you have flow there. It will if nothing else eliminate the rear rubber hose. I was doing an 87 Monte SS Dana 60 conversion two weeks ago and a brand new out the box Wagner line was plugged solid. But the sympton was a super high pedal with no rear brakes.
The fix was taking the line off and having a bud at the local hydraulic supply house build me one out of 6200 psi braided Russel line.
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Post by Deleted on Aug 15, 2011 6:14:22 GMT -5
Just another thing to check. If you are wondering if the valve is stuck open, check the pin that turns out. Grab an ohm meter and set it to 1000 ohms. If the pin is connected to ground, it is stuck wide open and generally wont allow fluid flow to the rear port.
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