Doesn't stop worth a Darn

[old66tiger]

I finally got my ride back on the road and am shaking out some of the bugs. New 461 Pontiac roller motor with solid rollers. This baby moves. unfortunately, my new Wilwood brakes are not stopping it like i thought they would. I have the 12.2 rotors with dynalite 4-piston calipers all of the way around. I have a 1969 corvette master (1.125" bore) and an adjustable prop valve in line with the rears. I have a 9" factory single booster. The brakes have been bleed to death. The pedal is rock hard. I am getting about 10.5 - 11" of vacuum at idle. The last motor had 13" of vacuum with the 9" and 4-wheel drum and would just about put you through the windshield at 40 mph or less. This isn't even close.



Please offer up some advice before i go dumping $$$ into a dual diaphragm booster, electric vacuum motors or vacuum canisters. Actually, I would like to run a dual 7" if possible but I understand that it is all about the entire package. Manual brakes is an option only if I don't have to put my foot through the floor to stop.

Thanks...Bob

[a67]

I finally got my ride back on the road and am shaking out some of the bugs. New 461 Pontiac roller motor with solid rollers. This baby moves. unfortunately, my new Wilwood brakes are not stopping it like i thought they would. I have the 12.2 rotors with dynalite 4-piston calipers all of the way around. I have a 1969 corvette master (1.125" bore) and an adjustable prop valve in line with the rears. I have a 9" factory single booster. The brakes have been bleed to death. The pedal is rock hard. I am getting about 10.5 - 11" of vacuum at idle. The last motor had 13" of vacuum with the 9" and 4-wheel drum and would just about put you through the windshield at 40 mph or less. This isn't even close.

Please offer up some advice before i go dumping $$$ into a dual diaphragm booster, electric vacuum motors or vacuum canisters. Actually, I would like to run a dual 7" if possible but I understand that it is all about the entire package.

Thanks...Bob

Yup, sounds about right...

You know, there is a ton of information on braking systems at your fingertips...

And I've always wondered why states allow absolutely stock antique vehicles on the street with no yearly inspection. But once a vehicle is modified (antique or not) they need yearly inspection.

Bob.

[ProdigyCustoms]

10.5 to 11 is no where near enough vacuum for any booster. And a 7" single or dual will be even worse. Your going to have to either tune a lot of vacuum into it, or go hydroboost, or go manual. But 11" vacuum will never do it.

[old66tiger]

Frank, let's talk when you have time. I need a solution to this problem. E-mail sent. Thanks...

[old66tiger]

Who here has 4-wheel manual and what is it like compared to power 4-wheel drum? The disc brakes were supposed to be an improvement over drum.

[GRNOVA]

I run a 4 wheel manual disc setup in my Nova woks great you really get a feel for the car in my opinion. I run a blower and only have 10 lbs of vacuum. I also have 4 piston Wilwood calipers front and back 11" in front and 12" on rear. Plus once I swapped to softer pads it made a huge difference! Good Luck!

[ProdigyCustoms]

Having a power booster and not enough vacuum is worse then having no booster at all. Wilwood brakes are designed as manual brakes. But I remember our conversations and that is a big car, I would look at a Hydroboost for the kind of brake pedal your looking for.

[68sixspeed]

Also you have way to big of a master cyl- you should be <1" bore master cyl typically for these cars. If you don't want to go hydraboost, you may get away with a dual diaphram 9" booster, smaller bore master cylinder, and a vacuum tank with a check valve. When you are driving around at rpm and get off the gas you'll build a lot more than 11" of vacuum. Another option to help a vacuum setup is an electric vacuum pump, but that alone won't fix your combo imo without dealing with the booster size and master cyl size. FYI, I run a 9" dual booster, 15/16 bore master cyl, tank, no electric pump (I had an electric pump with the prev. 358" motor in the car) -Dan

[wmhjr]

Who here has 4-wheel manual and what is it like compared to power 4-wheel drum? The disc brakes were supposed to be an improvement over drum.

I've got a '66 GTO vert w/Wilwood 12.2" 4 pistons all around and a Wilwood 7/8" bore master. My pedal is firm and responsive. I just put more aggressive pads on and have not bedded them in yet. The brakes are not as aggressive as I want yet but they are very good. I have not yet measured what pressure I'm generating but plan to do that over the next couple weeks. I think after bedding my pads in mine will be about perfect for me.

[ssealeycpa]

I had a similar problem with my 69 Chevelle (396 with high duration flat tappet cam = not enough vacuum) I ran a SSBC vacuum pump which I HATED. It was loud and cycled on and off all the time. I changed motors and am now running a hydraulic Roller cam (.631 lift and 255 degrees duration @ .050"). I am running a Mighty Demon 850 CFM carb with only one port for the PCV so I had to plumb a port from the intake which goes to a vacuum canister w/ check valve and then to an "original" style power brake booster. I was getting 13-14 inches of vacuum and it works fine now. I was attributing the increase in vacuum to the new roller cam profile. Double check that your PCV is not leaking (I capped every vacuum source when I started tracking my stuff down). Bottom line that I want to share with you is to not run a vacuum pump!

[critter]

Just curious about something. Did anything in the installation instructions reccomend moving the brake rod mounting point up an inch or so on the pedal arm? When I did the rear disc/1LE brakes on my TA most everyone agreed that it had to be moved up for 4 wheel disk. I didn't do a before and after so I can't say if it was really needed but that's where I have mine. I drilled it and made sure the angle wasn't off enough to create a bind.

[wmhjr]

All I know is that stock pedals had two holes - lower for power brake setups and upper for manual. You're supposed to use the upper hole to get the right pedal ratio if you switch to manual, but that's all I know.

[silver69camaro]

Who here has 4-wheel manual and what is it like compared to power 4-wheel drum? The disc brakes were supposed to be an improvement over drum.

I've run both setups you mention, and to me adding a power booster to 4-wheel drums doesn't really make it stop better. It just takes less effort at the foot, but I do remember the brakes fading more often (which is typical for drums).

It's not that discs are supposed to be better, they are better.

[Wilwood Tech]

Common contributors to "hard pedal, won't stop" issues are an oversized master cylinder bore and/or inadequate pedal lever ratio. Another contributing factor is the “aggressiveness” of the pad. Disc brakes require approximately 900-1200 PSI at the front caliper for effective functioning. Additionally, Vacuum boosters require 17 to 18 inches of vacuum for optimum performance . We recommend that you use a Pressure Gauge to measure your pressure at the caliper. If you are not generating the required pressure, we recommend increasing your pedal ratio, and or going to a smaller bore master cylinder. In cars with motors that have lot of cam, a manual system seems to be preferred by most our customers. The piston bore size(s) of your calipers and your pedal ratio determines the appropriate master cylinder bore size. A good starting point with a properly balanced system is 7/8" bores with a 6:1 pedal ratio. Good luck!