Dual Master Cylinders?

[jaybee]

Has anyone tried using a unit like this one?  http://www.fabquest.com/wilwood/wilwood-pedal-mc-s-valves/wilwood-super-pedal-dual-master-brake-pedal-assembly.html

I've been doing some playing in a brake design spreadsheet. No surprise that when you take front brakes from here, back brakes from there it's easy to sub-optimize the setup. Adjustable proportioning valves work well, but of course the first solution is just one solution...maybe it's the best one, maybe not, or maybe it's situational.

Plugging this unit into the spreadsheet brings the pedal effort way down, eliminating the need for a booster. The adjustable balance bar eliminates the proportioning valve. When you add up the combined cost of pedal, a dual m/c, booster, and proportioning valve it's pretty cost-competitive.

Seems like a pretty good way to go...but if I've missed something it isn't even close to the first time.

[wayne petty]

that is designed to use a rotating cable with a big knob for the driver to adjust brake bias on the track..  so they can come into pits without locking up one set of wheels over the other when the gas tank is empty.. and still have full braking with a full tank..

selecting brake calipers with 2/3rd of the piston diameter and 1/3rd the diameter on the rear... if the tire sizes and corner weights are  within reason.

if you are running rear drums.. there are various diameters of wheel cylinders to adjust the rear bias for different body weights.. even with the 3/4" gm snap ring retained wheel cylinders.. 86 S10 blazer 2 wheel drive is a larger bore to increase rear braking when full size calipers are used on the front..   rear shoe widths and diameters of the drums are also available..

i am probably wrong ...  lets see what the RRT members say..

big tires in the rear.. front runners the other end. make for really serious brake bias issues..

[jaybee]

Here is some information about balance bar operation and adjustment.  http://www.wilwood.com/TechTip/TechPedalTip.aspx

[jaybee]

Hmmm, I guess there's no experience with such a setup, or perhaps no interest. That either means it's just not the way things are usually done (which I admit is true) or it has negatives I'm not seeing.

[unklian]

I built one, LONG time ago.
Lots of time, no money. :cry:

Worked very well.

[enjenjo]

A diamond studded Rolex tells time, as does a $.99 cent digital watch, but beyond the bling, both of them do an adequate job.

I've used that type of brake pedal and master cylinder setup on race cars for the adjustability, tires, and track conditions can change enough to justify it. Most hot rods don't need that range of adjustability.

A lot of hot rods have so much more tire on the rear that it is difficult to lock the rear tires at all.

If the tires are reasonably close in size, adjusting with wheel cylinder/caliper sizes, or brake pad compound generally gets it close enough.

[tom36]

[Author    
enjenjo    

"A diamond studded Rolex tells time, as does a $.99 cent digital watch, but beyond the bling, both of them do an adequate job."


Hey, I like that! Can I borrow it?      Tom...

[enjenjo]

[Author    
enjenjo    

"A diamond studded Rolex tells time, as does a $.99 cent digital watch, but beyond the bling, both of them do an adequate job."


Hey, I like that! Can I borrow it?      Tom...

fine with me.

[jaybee]

I totally get it on the adjustability. No street car needs that as an ongoing thing, but it could help get things dialed in. It's pretty stuff, but when you add up the cost of all the components in a conventional power brake system it looks comparable.

You make an extremely valid point that you don't need the fancy expensive bits to make a cool car.

[unklian]

I totally get it on the adjustability.
No street car needs that as an ongoing thing,
but it could help get things dialed in.

Like a lot of adjustable stuff, once it was set correctly,
that is it. It never moves again. But it IS "correct".

[river1]

I totally get it on the adjustability.
No street car needs that as an ongoing thing,
but it could help get things dialed in.

Like a lot of adjustable stuff, once it was set correctly,
that is it. It never moves again. But it IS "correct".

I wish that was true with my BELT  

[416Ford]

New postPosted: January 15 2015    Post subject:   Reply with quote
local to me costco $1.77.9
local to me fry's (kroger) $1.79.9
_________________
Most people have a higher than average number of legs.

You need to stop eating Kroger fry's all the time.

_________________
Most people have a higher than average number of legs.

[wayne petty]

i was waiting to hear more info on the vehicle..

i was thinking that either the pedal ratio is increased.. or the master cylinder bores are smaller so the pedal effort matches a power brake system.  so actually YES.. that design will remove the need for a power brake booster..  could they actually have different sized master cylinders for either side. if you have significantly different brake bias needs.

proportioning valves only limit /reduce pressure to the back wheels.. reducing rear bias if you cut down on the pressure  but can only increase rear brake bias if you release the reduction  by adjusting the other way..

there is also built into the brake safety valve a SHUT OFF.. that if one side looses pressure the spool/piston moves toward that side and blocks the flow preventing the master cylinder from loosing all of the fluid.. it also turns on the BRAKE warning light on the dash.. but this is well known..

the reason i keep replying is i don't want your front brakes locking up way before the rears.. or the rears locking up way before the fronts.. it is just not safe for you as a car driver but also not safe for other people out there.. if something screws up . you could be held legally in civil court.

my former boss was a ASC president for a while out here and he described several mechanics who had injunctions on them preventing them from doing anything brake related on cars..  that was in the 1960s'  there seem to be too many ruthless hungry legal eagles now a days anyway..


trying NOT to be rude.. just trying to help..

[jaybee]

I've been meaning to come back to this for a couple of days.

Yes, the key to this unit is an increased pedal ratio of 7:1. I don't think they could get away with this except for the dual masters. Figure in a conventional single the piston has to move far enough to push all the wheel cylinders. In a conventional dual m/c it moves the rear piston to the drum or caliper, then hydraulic pressure transfers to the front piston and it also has to move far enough to apply pressure at the wheels.

This setup moves both the m/c's about the same distance, which is less than in either of the other setups. Also, it does use a smaller m/c for the rear wheels than the front, making it more optimal that way as well.

[PeterR]

The suggestion that dual cylinders reduce pedal effort has been around for years, however analysis of the mechanics of the system reveals it simply is not true.