Do I need power brakes?

[GRNOVA]

Just wondering if I can just remove the booster on the brakes and have manual brakes? Is the the correct way to achieve manual brakes or do I need to buy a new master cylinder? I want to get this car ready fot GGJoilet.

[parsonsj]

Yes, you can. But the pedal ratio and master cylinder diameters will be wrong. See if there is a different pushrod location (up higher on the pedal) to fix the pedal ratio, and consider Wilwood's (pn 260-8555) tandem master cylinder.

jp

[Vegas69]

I'd stick with power if it works with your motor and it's a mainly street driver.

[GRNOVA]

That is my problem I am only pulling 10 lbs of vacuum at idle! I need brakes.

[Vegas69]

What do you intend to do with the car?

[GRNOVA]

Auto- cross

[Vegas69]

Manual brakes may work out fine then.....I don't care for mine all that much on the street but they are good for mashing on the pedal in a race.

[GRNOVA]

Dang cell phones. I was on the phone with Jeff from Wilwood Tech and we were just about to start measuring for Pedal ratios and the phone went dead and I lost him:machine::machine::machine: Anyway I tried to call him bach and he is gone for the week!!! How do you measure pedal ratios. This was for a new master cylinder to cange over to manual brakes.

[yellow heap]

I have manual disk's(fr & rear)on the Heap-drive it to work every day and take it on fishin trips often(to other states and countries sometimes)-love them as they can give a VERY nice pedal feel.
For the most part all you need is a master cylinder with a smaller bore(1 in. is popular) and move the push rod to the upper hole if there is one or drill it-you may also need a new(or fabed)push rod depending on what master you run
Pedal ratio is the ratio from the pedal to the push rod compared to the pivot to push rod

[The WidowMaker]

How do you measure pedal ratios.

and i tried to convince my parents that i didnt need math......... ive used math more on this project than anything else.

you need to find the ratio of the two contact points (where the pushrod connects, and where your foot contacts the pad).

a 6:1 just means that you move your foot 6" for 1" of pushrod travel. so, if you have 8" from the pivot to the pedal, then the pushrod needs to be 1.3333" from the pivot.

8/6=1.3333 where the 8 is the length and the 6 is your ratio and 1.3333 is the pushrod.

somebody correct me if im missing the question...

Tim

[GRNOVA]

Ok my pedal ratio can be adjusted to 6:1. Now my other question is I just got off the phone with Wilwood and they told me to buy the 7/8" mc 260-9439. Does this sound good for my application? 4 piston front and rear calipers.

[Yoda4561]

Definately do it the right way, don't just pull the booster off. I lost my power booster on my 4wheel drum equipped 72 cutlass once and figured "ahh hell, I got strong legs, will be fine for a quick trip to the grocery store". I damn near rear ended another car pulling into a parking lot through a deep puddle from a rainstorm the night before. Going about 10mph and standing on those brakes (really, I was pushing so hard I was out of my seat) and it felt like I had no brakes at all. If the entrance to the parking lot wasn't a slight upward incline I probably would have hit them. When dry or going a bit faster they were fine, but when those drums got wet and the brakes were cold, good luck stopping. Power brakes give a huge boost to braking force, because of that power setups don't have any real mechanical leverage to speak of, when you go manual your pedal ratio and master cylinders need to be set up to provide that additional leverage by themselves.

[parsonsj]

7/8 Master sounds right. That's where I'd start.

jp

[gearheads78]

I love my manual brakes. 77 Malibu master with C6 front brakes and LS1 rear.

[Bryce]

i have a 15/16 bore manual MC with disc front and drum back. It works great.

[GRNOVA]

JP, and everyone
Thanks for the replys, helped me out alot.
Ordered a Wilwood 7/8" it will be here tomorrow.

[6'9"Witha69]

I run the 7/8" Wilwood Master as well. Feels damn good.

[GRNOVA]

Ok, just picked up my Wilwood MC.

I pulled everything out of the car and am trying to understand this some may think I am beating a dead horse.
But I am still alittle confused.
Here is my set up.
Am I figuring this right for a manual brake set up?
https://static1.pt-content.com/images/noimg.gif

[GRNOVA]

pedal moves 5 3/4" till pedal hit the floor. Piston bottoms out at 6"

[GRNOVA]

Can anyone tell me if this is correct before i install it in the car?

[parsonsj]

Tim,

I can't tell from your drawing... but if your pedal moves 5.75" and the pushrod moves 1.2" then your overall ratio is 4.8. And that's gonna take some muscle to move.

Pedal ratio is length of pedal swing-arm (pedal pivot to center of pedal pad) divided by the length from pedal pivot to the pushrod mount. And you haven't given us those numbers. Your 90 degree swing thing looks cool, but we need more information about how that works to give you an answer.

jp

[The WidowMaker]

im not seeing some info. you need the length of the pedal from the top pivot (you state 12"), and the distance from that same pivot to where the pushrod connects (i dont see that part). that would be your ratio. if your pedal is 12" as you state, then your pushrod needs to connect to the pedal at 2" in order to get the 6:1 ratio.

Tim

[GRNOVA]

Ok, I just measured from the pivot piont to the connecting rod and it is 2"

[GRNOVA]

Is this what your looking for?
https://static1.pt-content.com/images/noimg.gif

[parsonsj]

Yes. That's a 6:1 pedal. You should be good to go if your swing arm is 1:1.

jp

[GRNOVA]

Ok, took the car out for a spin ckecked the brakes and they will stop the car. The only thing is that I cannot lock up the tires. I drove the car for a good 15 minutes stepping on the brakes going abot 30mph jamming on the brakes but cannot lock up the tires. Is this normal? I am using a wilwood adjustable prop. valve and it is set all the way to increse on the rear.

[The WidowMaker]

my thought is that you should be able to lock them up with a quick full jab of the pedal. air in the lines? ive had issues with that in the past and it always led back to a little air.

it may be safer not being able to lock them up in a panic stop, but i dont think there is any way you could gauge whether you are now right at the cusp before lockup. i would think that there is a little braking power left.

Tim

[Rick Dorion]

This has been helpful to me in coming up with a system:

http://www.hotrodheaven.com/tech/brakes/brakes4.htm

[1969CamaroRS]

Hydroboost is always another option for a vacuum challenged motor.

[GRNOVA]

Thanks for the link.

Just went through and bled them again not really any air pedal feels good little hard but stopped the car good. Just a thought ,I am running 20's out back with 12.19 in rotors could this be a factor?

Is there some kind of gauge that I can hook up to check pressure. If so where does it go and second where do you get it?

[parsonsj]

20 in. wheels will most definitely affect braking performance.

And you're on the right track: we need to know what sort of line pressure your calipers are seeing. Wilwood has brake caliper gauges, where you hook the gauge into the caliper bleed port. Have a buddy stand on the brakes, and get a reading. You should see "explode the brakes" pressures in the 1000-1200 PSI range.

jp

[parsonsj]

Here's a link:

http://www.wilwood.com/Start/Products/006-MasterCylinders/014-PG/index.asp

[GRNOVA]

Thanks John,

Just ordered it will pick it up at 3:00 today.

Question: Does it matter which bleeder I put this in top... bottom

Again thanks for all your help on this matter.

[6'9"Witha69]

Go top. Bottom will drip and let air in, resulting in having to bleed again. Top works best. It is not recommended to bleed from the bottom either. They are only there to make them universal left to right.

[GRNOVA]

Just checked it is 900psi

[GRNOVA]

I just noticed that the line running to the brakes from front to back is a 1/4" should I change this to 3/16? once it hits the rear ir is 3/16

[GRNOVA]

My bad Just the rubber hose is 1/4" So both rears are 900 PSI

[parsonsj]

900 psi isn't too bad. You ought to be able to lock 'em up at that kind of pressure.

What pressure do you have at the front caliper in the same situation?

jp

[GRNOVA]

I need to get some kind of extension for the fronts the pressure guage it will not tighten up enough it hits the top of the caliper.