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mikes55
01-19-2017, 02:03 PM
I'm thing about taking off the power brake booster on my 55 chevy because the pedal is hard and it will not lock up the brakes due to not enough vacuum. I have wildwood disc brakes front and rear and would like to hear from a few tri five owners with front and rear disc brakes and what size bore wildwood master cylinder yall are using and the rod location on the pedal for manual brakes or how the same 4 wheel disc brakes are working with the power brake setup. any help would be greatly appreciated.

markm
01-19-2017, 02:13 PM
That is why many guys with power steering use a hydra boost instead of a vacuum boost to assist brakes. I remember almost hitting my parents mailbox 40 years ago after installing a big cam in my 67 Camaro. Low vacuum really adversely affected what had been very good power brakes.

chevynut
01-19-2017, 02:13 PM
Why don't you try removing the booster and using your existing master cylinder first, to see if it works? What size bore does it have now? If you go with a smaller master cylinder bore, you're going to get more pedal travel. If you move the pivot down to get less pedal travel, it's going to take more force to stop. Brakes are kind of a balancing act.

I would go with a Hydroboost and forget it. I sell adapters for them. :)

Rick_L
01-19-2017, 02:34 PM
I think you need to start with a 7/8" or 15/16" bore master cylinder. You need to go back to the stock pedal ratio if you have changed it. (That's the only natural way it goes together anyway.)

Trying it without the booster but with the same master cylinder will be a waste of time. That's essentially what you have now.

chevynut
01-19-2017, 03:44 PM
I always thought that power brakes with a non-working booster made the brakes worse than without the booster. Not sure why that would be the case, but on some cars it's hard to push the pedal down at all. Or so it seems.

Rick_L
01-19-2017, 04:39 PM
It's pretty simple, pedal ratio and master cylinder size.

mikes55
01-19-2017, 04:58 PM
wouldn't want to go that route

mikes55
01-19-2017, 05:00 PM
wouldn't want to go that routwe

mikes55
01-19-2017, 05:02 PM
what is the ratio on a stock brake system

mikes55
01-19-2017, 05:03 PM
what is the ratio on a stock brake pedal

Rick_L
01-19-2017, 05:58 PM
.Stock pedal ratio is 6:1.

If the master cylinder is at stock height, the pushrod will be level and the clevis will line up with the original hole in the brake pedal arm and you'll have the 6:1 ratio.

If you re-drilled a new clevis hole 1" down from the original, you'll have a 4:1 ratio. It's usually used with angled vacuum booster mount. 6:1 ratio means you have 50% more pedal travel but 50% more line pressure than 4:1. You need a pretty hefty booster to make up for that. Or conversely, if the booster is dead or limited vacuum, you have to push real hard!

You didn't mention what booster or master cylinder you have. Usually the Wilwood calipers need a smaller master cylinder than the typical GM calipers used in conversions, so you may need a smaller master cylinder if it was sized for GM calipers.

If you feel you really need boost or a shorter pedal travel, as already suggested a hydroboost is the answer, especially if you already have power steering.

mikes55
01-21-2017, 07:54 AM
do you know what is a factory ratio for a 55 chevy

markm
01-21-2017, 08:04 AM
do you know what is a factory ratio for a 55 chevy

Read Ricks last post he told you.

mikes55
01-21-2017, 08:06 AM
looks like you are pretty familer with this. yes I did have the CPP conversion and I called and it is a 1/18 bore master cylinder I have now. I called wildwood and they suggest a 15/16 bore if I go manual with the 6:1 ratio would be what I need. do you believe that combination would be just as good as power. in Bowling Green the last 2 years most of the cars had nanual brakes. I am also running a 7'' booster because of valve cover clearance.

chevynut
01-21-2017, 08:10 AM
I personally don't think you'll ever get manual brakes to perform as good as power brakes. If you could, car manufacturers would be doing it. I also think most of the guys using manual brakes are doing it for looks, not performance. A big vacuum booster is ugly, takes up lots of room, and often interferes with the engine. A hydroboost is better in that respect, but it's still "ugly" in a way. They work great though, if you have power steering. IMO the best looking boosters are the ones ABS Power Brakes sells...they're electric and look like a regular master cylinder. They're expensive but you see them on high end builds and you might actually be seeing that on those "manual brake" cars.

markm
01-21-2017, 08:18 AM
I personally don't think you'll ever get manual brakes to perform as good as power brakes. If you could, car manufacturers would be doing it. I also think most of the guys using manual brakes are doing it for looks, not performance. A big vacuum booster is ugly, takes up lots of room, and often interferes with the engine. A hydroboost is better in that respect, but it's still "ugly" in a way. They work great though, if you have power steering. IMO the best looking boosters are the ones ABS Power Brakes sells...they're electric and look like a regular master cylinder. They're expensive but you see them on high end builds and you might actually be seeing that on those "manual brake" cars.

I agree with most of this and would add that the bigger the cam the trickier it is to get good performance with a vac. booster. It is possible to get good stopping without power assist, my 56 is an example of this, while my 55 has issues that I am addressing.

BamaNomad
01-21-2017, 08:27 AM
The only thing a booster does is reduce the driver's pedal effort; it does not affect the actual brakes, or the car's 'braking ability' at all. If the driver has enough leg strength and control to depress the brake pedal to achieve the braking required, then he doesn't need a 'power booster'.

chevynut
01-21-2017, 03:32 PM
The only thing a booster does is reduce the driver's pedal effort; it does not affect the actual brakes, or the car's 'braking ability' at all. If the driver has enough leg strength and control to depress the brake pedal to achieve the braking required, then he doesn't need a 'power booster'.

Well you could say that about power steering too...if your arms are strong enough manual steering is fine. So are crank windows. :D

If you can generate enough line pressure with your leg you're going to get the same braking as the same line pressure with a booster. The difference is the amount of force on the brake pedal....it's a lot less with power assist. It's not just about having enough strength, it's about comfort and effort to brake the car. I can't think of one new car that doesn't have power steering or power brakes.

Sure manual brakes can work if you want to work 2-4 times as hard pushing the pedal. Also, as you move to a smaller master cylinder the pedal travel increases. There is a pretty cool device I saw from ECI (I think) that helps take up the pedal travel and reduce the brake pedal travel. It has a stepped piston arrangement.

BamaNomad
01-21-2017, 11:53 PM
Well you could say that about power steering too...if your arms are strong enough manual steering is fine. So are crank windows. :D
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Absolutely... all that is true.. :) My first new car was a special order 1970 Roadrunner, 4-speed, Hemi suspension, F60-15 Polyglas GT tires, drum brakes all the way around, and NO Power Steering or Brakes... It was me and the car, and I loved it.. :) ... I did have to use a little 'go pedal for 'rear steer' when needing to make sharp turns at no/low speeds... :)