No brakes - I'm out of ideas

[Dreadl0ck]

My 69 roadrunner is disc brake converted using a SSBC brake system and some aftermarket GM booster.

On my way home from this weeks cruise I noticed when it was time to exit the freeway that the brake pedal went all the way down without any brakes applying. So I pumped it a couple of times and got enough brakes to safely slow the car down to make the exit.

Drove about 1/2 mile down the road to my house, braked to make the turn into my driveway - same thing. Pedal goes all the way down, pump pump pump pump - some brakes applied.

Checked the pads to see if they were worn to the extent that it would allow for air to get into the system when applying brakes. Nope - pads looks fine.
First thing I checked was the level in the cylinder - seemed fine to me - about mid
Bled the brakes at a diagonal patter - fresh fluid came out directly

So now I'm out of ideas - I've checked for leaks or moisture around fittings and hoses - but it looks dandy fine to me. My idea is that the seal inside the cylinder might have gone bad - but that's a long shot. Or isn't it?

Either I tear it down - Or I buy a new cylinder / booster combo that actually belongs on this car (The kit that SSBC sends out seems to be some GM kind)

How do I know which ones fit my cars and my brakes? I looked at Willwoods cylinders but they don't seem to have any boosters. Can anyone find the part numbers needed to replace my old stuff? (Another problem with the booster I have - is that it's impossible to find a grommet between the check valve from vacuum pump and the booster. It's IMPOSSIBLE to make it stick...) I don't know how many grommets I've picked up from inside the booster. That's another reason why I'm looking at other stuff.

Someone - help?

 

[440roadrunner]

I really cannot help you but it certainly sounds to me like the master cylinder has gone away

I assume that this happened suddenly, and that you had good brakes up 'til then.

This thing rear disc or drum? Self adjuster on the rear? Pads are not going to wear down magically and cause that.

 

[Dreadl0ck]

Yea, it happen suddenly - I was exiting the area where we had races / cruising and all was good - drove home and on the exit - BAM bo brakes.

Today when I tested it in the garage (engine off just pressing the pedal without any vacuum hooked up to the booster which should give me rock hard pedal) it actually felt like it was applying the brakes. I'm going to take it out for a spin this week to see how it behaves before I start to tear things down.

What I noticed though: The seal on the reservoir looked a bit shabby - but that wouldn't cause this right?

Car is disc brake converted with brakes from SSBC

 

[Yatzee]

Believe me you are not alone on this issue after doing a disk brake conversion. Your problem will boil down to either not having enough volume of brake fluid to actuate all four corners of the braking system or little to no assist to get to the pressure you need for good application. Things you need to consider are: the bore and stroke of the master cylinder which determines the volume, the pedal ratio which determines the stroke of the master ( again volume) and the amount of vacuum you have to enable the booster to go to full stroke if necessary. I'd call SSBC and have a chat. If you run drums out back, residual valves will ensure the shoes stay out closer to the drums without dragging or else you'll have to adjust the shoes close to the drums. It takes a lot of volume of brake fluid to get the shoes out to contact the drums even though the cylinders are a small bore. Buying a combo master/booster does not always resolve braking issues of this type unless all other calculations are taken into consideration. Usually poor stroke distance and pedal ratio are evident if the pedal goes right to the floor before the master has reached the end of it's forward stroke. You'll have to do some research online and with SSBC to come to any concrete conclusions lest you'll be throwing good money away. Determine the output volume of the master at full stroke ( you may need to go to 1" bore), determine the travel required to get to full stroke ( you can do this by depressing the master's piston while in a vice), determine the full travel of the pin on the brake pedal arm while it's disconnected ( you may have to move the pin up or down or buy a proper lenght push rod to get to the measurement previously found by depressing the master cylinder piston) and draw your conclusions from there. Pedal firmness is determined by the pedal ratio and booster performance which depends on it's size and the amount and volume of vacuum present. I pulled my hair out trying to get sastisfactory braking and finally went to hydra boost and have never looked back. Good luck!

 

[440roadrunner]

............ Your problem will boil down to either not having enough volume of brake fluid to actuate all four corners of the braking system........... bore and stroke of the master cylinder .......... the pedal ratio which determines the stroke of the master ( again volume)

Uh...........whut?

So you don't think that the fact that he's been successfully DRIVING the car with good brakes counts? Maybe one of us misunderstood something fundamental here?

So let's ask the OP to clarify? How long has the system been "as installed," how long / how far have you been driving it and how did it operate up to the failure?

In other words is this a component failure or a system DESIGN failure?

 

[Dreadl0ck]

Well, weird part is that the brakes has been working really good for about a year - even when I left my house they worked - hell they worked after blasting the car into the 12s at the track. But just disappeared. So even if I totally hear you with the explanation about the mechanics of brake systems - it's weird that they were there one minute and gone the next.

Car has discs all around. One theory we're working with is that the problem came after an extended period of really hot idling and that the headers which sits just under the reservoir heated the fluid to it's boiling point - thus introducing air into the system. Could that be something to work with?

 

[Yatzee]

It would seem I've got the wrong impression of exactly what the problem was, as he was asking about purchasing new parts. Boiling the brake fluid would have happened a long time ago as would the problem. Could be the booster, could be the vacuum pump, could be the master - have to test all three thoroughly for proper operation as the problem just suddenly appeared. I wouldn't speculate which component is at fault, that would have to be determined. What I do know is that I installed an SSBC system on my car, swapped out three different boosters, two master cylinders, two proportioning valves and brake pads twice and never really got that "safe" feeling of braking hard at 60 m.p.h. The calipers they sell are actually from an early GM Corvette so I would suppose that if you used components from that model car, you'd have exactly the braking that Corvettes had back in their day. Make sense?

 

[OSDart]

Change the MC. And use the Mopar booster/MC combination.

 

[440roadrunner]

I don't know how a booster could cause a pedal to go to the floor. A failed booster SHOULD just "lose boost." Bad master. Thas' my story, I'm stickin to it LOL

 

[Bb70charger500]

I'd have to agree with bad master. Are you running a stock mopar booster? I just bought my 4 wheel disc brake conversion and the dealer switch out the wilwood master with a diff style because there's been problems or something like that ,anyways it was fairly cheap master and it bolts right up to a stock booster . I can get a picture of it tomorrow and see if there's a part number for it .

 

[Dennis H]

Or get advice from Barney Rubble. I say Master.

 

[Derwud]

How long have you had this conversion on your car? Biggest question you have to answer, where did the brake fluid go? You say after loosing the brakes the M/S fluid level was about "mid". The only reason for it to be "mid" is Pads worn down or a leak. Pull the master and see if the seal at the booster is wet.. But replace the Master and make sure you get a large reservoir 4 wheel disc M/C..

 

[Dreadl0ck]

Well - can anyone direct me to a combo of booster/MC that would work with my SSBC brakes? I get really frustrated from reading the specs - there's a zillion combos.

What it looks like now (before I cleaned up the cable mess)

 

[dryheat]

I would suspect a sudden loss of brake pedal indicates a failed master cylinder.

For my own education ... What in the world is that braided hose feeding your booster? It's going to a strange area in which to draw vacuum from.

 

[Dreadl0ck]

The cam doesn't produce enough vacuum to power the booster, so there's an electrical vacuum pump mounted under the battery tray

Here's a view of it (before I cleaned up all the cables and removed the fake braided hoses