HELP. No brakes after conversion Parts replaced 2 times.

[66fasty]

How's it going? I did a Stock GM a-body disk brake upgrade on my 65 Skylark(Originally manual 4-wheel drum) With a power brake kit from cpp. I bench bled the master, put everything on bled it multiple time and I couldn't get a pedal. Tried a new master, no pedal. I'm pulling about 13" of vacuum But the pedal feels like the bleeders are open no hard at all. I have to get this out of my dads house ASAP.

2 new masters, 2 new proportioning valves, added residual valves, new calipers. Only thing I remember is that the caliper brackets had to be tweaked to even bolt up. Could this be the problem?
Thanks,
Phil

[mc84_zz4]

How is the engagement with the pedal lever? There may not be enough travel to engage the master Cyl... JMO from 10,000 feet

[66fasty]

Its a power booster set-up so the rod isn't really adjustable. The travel is normal its just a really soft pedal. Anyone in the San Bernardino area want to look at it? haha

[mc84_zz4]

On another forum, similar situation, but they got a brand new dead booster (not from CPP).
I had never heard of that before, nor do I know how to test for that, maybe someone may chime in on that (?)
I bet you're sick of smelling brake fluid.

[Apogee]

Bad booster typcially gives a hard pedal in my experience. Do you have the front calipers installed on the wrong sides with the bleeders incorrectly oriented?

Tobin
KORE3

[6'9"Witha69]

And 13" vacuum @ idle? That is really low (too low) for vacuum assist brakes. Have you tried gravity bleeding prior to standard bleeding?

[MonzaRacer]

OK do you have lines swapped and also are the rear drums still on,? if so they need to have a slight drag (2 hands) while turning.
The master cylinder needs the large section ran to the front brakes, As for 13" of vacuum heck most boosters are rated at 15" so its not that low.
Try this, one turn loose on each fitting at master cylinder, have a person push down see fluid only(ie no spitting) tighten them, pedal up, one turn each(this is give or take as line needs to slide in and out a tiny bit)pedal operator, pushes down, hold tighten lines.
With brakes adjusted, pump pedal 3 times, open right rear bleeder, do this several times, checking master cylinder (small section) for level after every 2 or 3 bleeds.
After right rear is bleed the left shouldnt require much.
Then bleed right front, then left.
This should get pretty much every bit of air out.
MAKE darn sure your front brakes are coming out of the larger portion of the Mastercylinder.
you should not need any vacuum assist for this, brakes MAY feel spongy till car rolls few times to settle brakes. I see this with our Pep Boys (where Iwork) brakes, they feel crappy till rub a few times.
Also it depends on the pads as some will feel like absolute crap till you roll them and stop couple of times as the grinding of the pad at manufacture leaves heavier grooves.
Also you can use the open bleeder, push down,hold, close bleeder, let pedal up, open bleeder, etc. BUT remember this moves LOTS fluid so watch master cylinder.
Good luck, ask if I have confused you.
Lee Abel
AFTERMARKET PERFORMANCE

[MonzaRacer]

Oh yeah just though of something, if this is an upgrade type setup, try this, make a block of wood fit all calipers at same time, between either pads or calipers without pads in, then try the pedal, if you get a firm pedal you may have adapter issues holding calipers crooked and the setup is flexing. We have been seeing some brake issues with improper rotors, bent caliper brackets ,front/rear/left/right swapped and even some wrong calipers too.

[66fasty]

Ok, It still has drums on the rear. New wheel cylinders and shoes, adjusted so they're dragging. Bleeders are pointing up on the calipers. I did notice that while my dad was pumping the brakes the front caliper brackets do flex and like I said we had to hammer and tweak the brackets to get them to line up. The brakes only work if I'm driving and I hold the rpms up (poss giving more vacuum?) and try to brake quickly. I'm at a loss on this. My dad's tired of working on it and I just want to drive the thing! It's been sitting for about 6 years(only get to work on it about once a month if that) because of this haha, sad but true

[sebtarta]

Did you check to see if you have a leak somewhere?

An air bubble could cause this too.

[66fasty]

Yea I've looked for leaks multiple times, the only thing I can think of is that we have a few unions on there that could have leaks(letting air in) or maybe our hand bent lines are letting air in somewhere. I'm going to order some prebent lines for it as a last resort.

[SoCal Cruzer]

Don't forget that the Power booster pushrod attaches to the brake pedal at a different hole (lower) than the Non-power set-up. This assures proper pedal geometry/action. Don't know if this is your problem, but I thought I'd point this out since you did a non-power to power conversion as well and is often overlooked..

[66fasty]

Nope, got that changed too. Its almost time to take it to a shop and let them handle it, instead of throwing more money at it. But its only worth 1500 so its hard for me to get the lady to justify it lol.

[MonzaRacer]

put blocks in place of rotor with calipers off, if its firm your looking at some parts wrong/out of alignment.
Can you get some pics of your set up.
Cause if it has a caliper bracket then caliper bolts to it then your parts may be wrong ir installed wrong OR they are flexing too much.
Had a car the other day at work, other tech put new calipers on, turned out get wrong caliper, ordered from new supplier and tada we had pedal, the wrong on was bolting on but the flex was taking up all brake pressure.

[66fasty]

I have these brackets.
http://cgi.ebay.com/ebaymotors/1964-65-66-67-68-69-72-GM-A-BODY-BRAKE-CALIPER-BRACKETS_W0QQitemZ260353071461QQcmdZViewItemQQptZM otors_Car_Truck_Parts_Accessories?hash=item3c9e409 965#ht_3107wt_939

[JRouche]

Frustrating as hell huh?? You at least didnt do what I did. I had the front calipers swapped, left for right and well you know. I was bleeding for days, no peddle. Finally got a clue and swapped them.

Im thinking 13" of vacuum is fine. But thats besides the point. You bleed the brakes with the engine off. I didnt catch if you had a solid pedal after bleeding, with the engine off? If you did, if it was solid then thats good!! You bled the system.

Where is the soft pedal? Engine off or on with a vacuum?

And I wouldnt worry about leaks. If you are not pushing fluid out then you definitely are not pulling air in. The hydraulic force being applied during compression is magnitudes above atmospheric pressure. If yer not pushing fluids you are not pulling air. No leak.

Im gonna assume you have no pedal during the bleeding process, engine off, no vacuum applied.

In that case (engine on, vacuum applied, more force) I can only say the master cylinder is bypassing fluid. Thats if you are following correct bleeding procedures.

Starting at the back, only cracking the bleeder slightly, making sure to not pull air in through the bleeder threads. A tight connection of the tube on the bleeder so its not sucking air. Pumping the brakes slowly and consistently to drive the column of fluid out the bleeder. It will take some time for a MC removable. Small line, to get that bubble from the MC to the rear will take some fluid. I have had to refill the MC twice before I got that big push of air bubbles out to the far rear brake cylinder. And then even after I got that major bubble out it still took another filling to get the other rear cylinder to wash out. Then the fronts took a refill to do both. Thats where the large containers of brake fluid come into play..

So if you went through all of that. And you have a solid pedal with the engine off. its solid..

Now!!! If you already did all that and then fired up the engine. Pulling a vacuum on the booster and the pedal sinks I would be surprised.

The booster wont allow any additional movement. Its a safety thing. It doesnt allow, or I should say create any additional slack in the rod. It just helps to push the physical connection of the rod.

Im not sure where you are getting the soft pedal. Engine on or off. But if you havent pushed a quart of fluid through the lines yet I would keep pushing fluid. Thats assuming you dont get a solid pedal with the engine off.

If you arent losing fluid at any joints, and you have taken up the slack on the rear cylinders (drum brakes) I would keep pushing fluids. If you have already gone through a quart of fluid then I would be looking at the adjustments for the rear drum cylinders. If they are moving too much they will take up alot of pedal.

And as far as the front brackets go. If they flex (which they should not) then that will give a soft feel, but not too much. The pads will pull a mis-aligned caliper into position. Say the caliper is cocked sideways from the rotor. But that will be a soft pedal with boost applied (engine on) but not alot of travel engine off. You cant bend the bracket that much without boost. Engine off force on the pedal will still feel pretty high. And not much travel of the pedal.

If you have run a quart of fluid through the lines and its still sinking then I would be looking at the rear drum cylinders for the movement.. JR

[66fasty]

The pedal is solid when the engine is off. When the engine starts it gets VERY soft feels like your stepping on a bean bag chair or something. And I get no braking power unless I jam the pedal down or give it gas at the same time as Breaking. Another problem I had was when we switched proportioning valves the new one was leaking out of the brass screw on the front. I'm going to borrow my friends vacuum bleeder and leave it on each wheel for 15 min each or a full bottle. Not sure what else to do at this point.

[jtm311]

I just had this problem on my upgrade 2 days of dealing with it. It turns out that the pro valve was bad. Try bleeding them without it in. I would say 13 vacuum is to low. I think you need at least 18.

John

[tumper93]

What type booster is it? If is one of the small diameterswhich are dual diaphram then you most likely have one of the bladders not sealing and it causes this type of problem, if the other were not sealing you would have the hard pedal like others have stated. The duals can drive you nuts with their faults sometimes

[JRouche]

What type booster is it? If is one of the small diameterswhich are dual diaphram then you most likely have one of the bladders not sealing and it causes this type of problem, if the other were not sealing you would have the hard pedal like others have stated. The duals can drive you nuts with their faults sometimes

Hmm? I dont get that. A bad booster will give you a hard pedal and no brakes. Not a soft pedal after the vacuum is applied.

The only thing the booster does is give you more help to push the pedal (the rod). A bad booster wont take a solid pedal (engine off) then make it soft.

An over boosted MC will give you a soft pedal. But it will also give you some very touchy brakes. Hard to modulate. Too much braking, but not a lack of braking.

Remember, the brake pedal is firmly attached to the rod. And the rod seats in the MC piston. Its all a solid connection. Its a safety issue, thats why they build it like that. If you loose vacuum you will still have limited braking. Just gotta stand on it to get it stopped. JR

[tumper93]

On a dual diaphram booster you have (2) diaphrams, one on atmosphere side and one on vacuum side and depending on which leaks wil depend on how the booster will react. Trust me I have run into this before over the 20 years I have been at a chevrolet dealership and sometimes it will bite you thinking it "should" do this or that. If it were a single diaphram you have vacuum on one side and atmospheric pressure on the other and it will be a hard petal if it doesn't seal. Hope I explained that in a way that is understandable.

[JRouche]

On a dual diaphram booster you have (2) diaphrams, one on atmosphere side and one on vacuum side and depending on which leaks wil depend on how the booster will react. Trust me I have run into this before over the 20 years I have been at a chevrolet dealership and sometimes it will bite you thinking it "should" do this or that. If it were a single diaphram you have vacuum on one side and atmospheric pressure on the other and it will be a hard petal if it doesn't seal. Hope I explained that in a way that is understandable.

Ok, school is in. For ME :) Im gonna learn something here.

The impression I got from 66fasty is he had no pedal with vacuum applied. But a hard pedal without vacuum.


Tried a new master, no pedal. I'm pulling about 13" of vacuum But the pedal feels like the bleeders are open no hard at all.

I trust yout technical knowledge, Im not a mechanic, new to the game.

But I just dont see any way for the pedal to feel loose just by applying vacuum unless there is a bleeding issue. The additional force provided with boost will compress an air pocket easier than just the master cylinder (no boost).

Dual diaphragm or single, they all still have a solid rod that connects the pedal to the MC. A faulty booster will always give a stiffer pedal with less braking and more effort. No matter where the leak.

Im not trying to say you are wrong. I would love to see the mechanics behind your idea though. I know you have seen it before. Im just trying to get my head around it being a faulty booster. Im just trying to learn here :) Ive seen some weird things before, and in the end they are usually explainable. Im sure this is another one..... JR

[Skip Fix]

My 81 TA dual booster works fine with even down to 10-11". Below that got a little iffy at idle.

[66fasty]

ok, i have a single diaphragm 11" booster. very hard pedal with car off, very very soft pedal with the car on and no brakes unless i jam the pedal fast. thinking it has a very small leak somewhere and we're just not seeing it because the fluid is clear. going to go bacl over it AGAIN and see what i can come up with.

[JRouche]

ok, i have a single diaphragm 11" booster. very hard pedal with car off, very very soft pedal with the car on and no brakes unless i jam the pedal fast. thinking it has a very small leak somewhere and we're just not seeing it because the fluid is clear. going to go bacl over it AGAIN and see what i can come up with.

Ok.. I have one more idea. Besides bleeding it with a vacuum pump or pressurized MC cap ( use both and they work) how bout this. Bleed it with the vacuum applied to the booster, engine running. Have the pedal person push firmly and quickly. The added force on the MC rod may help to push out an air pocket if that is your problem. Make sure to stay clear of the hose that you have connected to the bleeder, you do have a hose on there right? Otherwise there will be a big blast of fluid straight out of the bleeder, big mess.

I still see it as a BIG air pocket thats not being dislodged. Could be in one of the wheel cylinders. Just a thought. Stop buy, we can hook it up the vacuum and pull ALL of the crap out.. JR

[mrn2obelvedere]

I have a couple of points to add here.

1)If you've ever wondered how power brakes really work then go here. Its an interesting read even if you already understand: http://auto.howstuffworks.com/auto-parts/brakes/brake-types/power-brake.htm

2)I am of the opinion that you have air in your system somewhere or something is inappropriately sized.

3)Leaks are easy to detect. Feel around the connection in question. Is there brake fluid on your hands? Look at the connection, does it look wet?

4)Is your master cylinder appropriately sized to your calipers? I am not sure about the specifics of your swap, but one thing is for sure, a drum brake system will have smaller pistons at the master cylinder than a disc system. If you have a drum brake MC then you might not be pushing the volume necessary to actuate the pistons at the calipers, and no amount of bleeding will get you the pedal you are looking to get.

5) Forget about the vacuum booster for now. If your brakes are properly bled and the components match, then when the car is off the pedal should feel rock hard (not firm, rock hard), with the car on your pedal should feel firm.