# switching to non-vacuum brake master cylinder?



## cruisin (Jun 3, 2009)

dtbaker said:


> planning for my next conversion.... I am considering eliminating the vacuum assist on the brake master cylinder just to simplify and reduce the cost of the build a little. The standard Gast/Thomas pump+reservoir+vac switch work fine, but take a fair amount of space, time, and money to install. I was looking at aftermarket master cylinders from 'race' places like Wilwood the other day, and it got me thinking that it might be cost effective to switch the master cyl to a non-vacuum one.... but I don't really know what to look for in making acceptable braking performance while minimizing the pedal pressure after giving up vacuum assist.
> 
> In my case, the vacuum assist is 'marginal' anyway... living at 7000' de-rates the max vacuum I can get from a Gast/Thomas (about 13" for good cycle time) to the point where it is only semi-assisting me anyway!
> 
> ...


You may want to consider replacing the master cyclinder with a non power type and using AC with regen. I havent used my disk brakes since converting as all of the braking down to about 2 mph is by regen. Of course if you need to do a panic stop you will need to have additional braking power.


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## dtbaker (Jan 5, 2008)

cruisin said:


> You may want to consider replacing the master cyclinder with a non power type


uuuhhh, yeah, that why I started the thread. I want to know more about how to maximize the stopping power without vacuum assist, or changing the pedal if possible. Any specific recommendations for master cyl that can be used?




cruisin said:


> and using AC with regen.


uuuhhh, nope. switching to AC is not something I am likely to consider.


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## DavidDymaxion (Dec 1, 2008)

You might be able to adapt a master cylinder from a car that does not have power brakes. Another thought is larger brake cylinders would have the same effect as a smaller master cylinder bore -- maybe a high performance model of the car would have larger brake cylinder bores.

Another thought is high performance brake pads. I put Hawk HPS pads in my gasser. With the old brakes I could push with all my might to stop quickly, but no skid or antilocks kicking in. With the Hawk HPS pads, about 1/2 effort will skid the fronts or kick in the rear antilocks -- it was a huge improvement.

Castrol SRF brake fluid has very low compressibility. When I put it in my car the pedal was incredibly firm -- it would go down just so far and no further. If you do something to increase the pedal travel this could be a way to get some of it back.

Many cars will flex the firewall under hard braking -- if your car does that additional bracing could also help you get back some pedal travel.

I haven't tried this, but some folks say braided brake lines don't swell as much, and make for a firmer pedal -- this could be yet another way to reclaim some pedal travel.

You really want some brake pedal travel in reserve. Pad knockback or hot brake fluid can cause the pedal to sag and braking to occur closer to the floor.


dtbaker said:


> uuuhhh, yeah, that why I started the thread. I want to know more about how to maximize the stopping power without vacuum assist, or changing the pedal if possible. Any specific recommendations for master cyl that can be used? ...


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## Duncan (Dec 8, 2008)

Hi Dtbaker,

How heavy is your car? - small cars didn't use to have power brakes, that said there is a trade off between pedal movement and system pressure at a given pedal force.

Be careful of pads that give more braking - they could be OK BUT they may not work when hot - racing pads (for high temperatures) are notoriously weak until they are up to temperature


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## dtbaker (Jan 5, 2008)

The car is just a little Suzuki Swift. Stock ICE is 1900#, Lithium build is 2000#. I don't really want to go to the expense of racing calipers in front and then have to add a balancer for drums in back.... I was just contemplating an inexpensive swap of the master for $100 or less as an alternative to the typical vacuum pump+switch.


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## piotrsko (Dec 9, 2007)

back to the Original (?) question: brake force applied to the wheel cylinders is a function of piston area in sq inches times pedal travel times pedal force. more or less ( I can play a rocket scientist on TV) the reason most cars have assist is because most of the world now lacks exercise and cannot produce more than 50 lbs of force on the brake pedal. as an example: 50 lbs applied to a 1 sq inch pedal that didn't move much is about 50 psi. move the pedal 2 inches and you have, I think, 100 psi. move a smaller piston more for the same volume and you have the same pressure. In my case Fords come with either a 3/4 piston or a 5/8 one. the 5/8 will need about 6" of travel instead of about 3 1/2 for the boosted 3/4. If you really need I can get out one of my 60's era auto books and get the exact formulae for calculating theoretical line pressures. back in the day... you also had to consider mechanical advantages in placement of the rod and what class lever you were using, generally 2 or 3.


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## Roy Von Rogers (Mar 21, 2009)

If you want mechanical braking go to drum brakes, we old timers were using those long before girlymen power brakes came along, if you want to use mechanical on disk's, you better have an Arnold type leg...lol

Roy


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## dtbaker (Jan 5, 2008)

piotrsko said:


> back to the Original (?) question: brake force applied to the wheel cylinders is a function of piston area in sq inches times pedal travel times pedal force. more or less ( I can play a rocket scientist on TV) the reason most cars have assist is because most of the world now lacks exercise and cannot produce more than 50 lbs of force on the brake pedal. as an example: 50 lbs applied to a 1 sq inch pedal that didn't move much is about 50 psi. move the pedal 2 inches and you have, I think, 100 psi. move a smaller piston more for the same volume and you have the same pressure. In my case Fords come with either a 3/4 piston or a 5/8 one. the 5/8 will need about 6" of travel instead of about 3 1/2 for the boosted 3/4. If you really need I can get out one of my 60's era auto books and get the exact formulae for calculating theoretical line pressures. back in the day... you also had to consider mechanical advantages in placement of the rod and what class lever you were using, generally 2 or 3.


some of this I would agree with.. other stuff not so much. hydraulic fluid is basically NOT compressible, so other than the tiny travel in calipers, and tiny expansion in soft lines, there is very little 'travel' as fr as I can tell... just boils down to psi applied to master divided out to psi applied to wheels.

given that in an existing system with a balance between front disc an rear drum, the only real variable in replacing a vacuum assist master with a non-vacuum assist is whether the appropriately smaller bore master is available, with enough travel to take up the slack....

so.... question remains... given a 'normal' small car with moderate OEM vacuum power assist, is there a specific Wilwood or other replacement manual master that would give similar psi with similar effort, and no changes to pedal or calipers?


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## DavidDymaxion (Dec 1, 2008)

Good point, you don't want a pure race pad, as it won't work well until hot, which won't happen in street driving.

The pads I cited, Hawk HPS ("High Performance Street") work great in regular driving and give full braking right off the bat. I got pad fade only once the track, but I have a 3600+ lb car+driver with undersized brakes. All my other track brake problems have been due to brake fluid, not the pads.

If your pedal is firm, but the car isn't stopping, it's the pads. If the pedal is too low and/or spongy, that's brake fluid.

Most disk brake cars are too hard to stop without power assist, but my lighter sports cars, Pontiac Fiero and Porsche 911, I have been able to stop OK without power assist (more effort on average, but less effort for a max power stop than my power assisted brakes gasser).


Duncan said:


> ... Be careful of pads that give more braking - they could be OK BUT they may not work when hot - racing pads (for high temperatures) are notoriously weak until they are up to temperature


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## EVfun (Mar 14, 2010)

dtbaker said:


> The car is just a little Suzuki Swift. Stock ICE is 1900#, Lithium build is 2000#. I don't really want to go to the expense of racing calipers in front and then have to add a balancer for drums in back.... I was just contemplating an inexpensive swap of the master for $100 or less as an alternative to the typical vacuum pump+switch.


I would think such a light car could easily do without power assist. For a first, low speed, test you can just try disconnecting the vacuum line on a regular Metro and see how it feels. The booster has a spring that makes braking force harder than it would be with the booster removed. If the force is acceptable it would be up to you to fabricate a firewall adapter to attach the master cylinder without a brake booster (if needed) and a new pushrod of the correct length. You may want to see if any state regulations limit your ability to change the braking system. 

You can move the pivot point to increase leverage but it is usually a more involved change. When you increase the leverage you need to make sure that you can still apply the brakes in the event of a 1/2 brake hydraulic failure. The increased leverage means you move less brake fluid before the pedal hits the floor. High leverage manual brakes where easier to build when single circuit braking systems where legal.


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## piotrsko (Dec 9, 2007)

if there is a manual version master cyl available, it will bolt up to the existing firewall holes for the booster. It should be also correctly sized for pedal travel and bore.

I like roy's girlie man comment


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## dtbaker (Jan 5, 2008)

EVfun said:


> I would think such a light car could easily do without power assist. For a first, low speed, test you can just try disconnecting the vacuum line on a regular Metro and see how it feels.



It is very doable without vacuum for me (having bulging quads capable of hundreds of pounds in leg press!), but borderline for 15 yr old daughter who will be driving car soon. seems like if I can find a master cyl with one size smaller bore, it *should* be great. just asking to see if anyone else already has.


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## mizlplix (May 1, 2011)

Some disk brake calipers are designed from the start to use a power assist and can not be converted to non-power(manual) brakes. Been there twice.

It is the linkage design AND caliper piston size that is the problem. Once you get to a small enough piston in the master cylinder to have a reasonable pedal effort, the single stroke fluid volume transfer is not sufficient to move the caliper piston far enough to overcome the pad preplay and apply a stopping force, making it necessary to pump the pedal at least once. (Whew)

A slightly larger M/C bore reduces the pedal movement, but increases the effort to stop the car......a designed in need for a power boost of some type. 

Both times I had to change out the calipers to some with a smaller piston because the linkage could not be altered to make it work the other way. Otherwise I could have just increased the pedal arm length with the bigger piston and been there. 

1/16" bore size steps seem to be a standard.

The car I have now uses a M/C bore of 1/8" smaller than the powered M/C bore.

I hope it gets you in the ball park.

Miz


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## Duncan (Dec 8, 2008)

Hi Dtbaker,

On most cars the brake pedal "box" just unbolts, it may be relatively easy to unbolt the pedal box and move the pivot point.

Most cars use hanging pedals with the pivot point up above the master cylinder and the foot pad below it,

Move the pivot point down lower (closer to the master cylinder) - 6 mm (1/4 inch) will probably make a huge difference,

Get another pedal box from a scrappers to play with


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## dtbaker (Jan 5, 2008)

I sent in a detailed email to Wilwood asking for some guidance, but haven't heard back from them yet. It is sounding like chances are fair if I can find a master cyl with a 1/8" smaller bore, and enough volume, that this might work.

I would be that Wilwood would have a matched set of master and calipers that would be fine, BUT...

If I'd have to swap out the calipers, then it starts not making sense cost wise... it would start costing more than going with the usual vacuum pump setup. I will continue to poke, and may just try a slightly smaller master bore regardless to see how it feels.

Does anyone know what the master brake cyl bore size in a a stock 1997 Suzuki Swift IS?


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## piotrsko (Dec 9, 2007)

has anybody used the vacuum set up in a ford F 250 series? all diesels and some v8's and v10's. I know they pull enough vacuum to run the auto hubs, and a/c, and should be really cheap at the wrecker yards.


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## EVfun (Mar 14, 2010)

You bring up a good point. Diesels vehicles with vacuum assist brakes have a vacuum pump somewhere because there is no engine vacuum. Almost every newer vehicle has vacuum assist brakes. There should be a number of pump options out there at the local auto wrecker.


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## ElectriCar (Jun 15, 2008)

Look in my "upgrade to Calb" thread for explanation of how I converted my S10 ~3300lb to manual. I picked up the parts from a wrecked 85 S10 with manual brakes. My original MC piston dia. was 1.25" and extremely hard to push without vacuum. The manual MC was 1" but had I believe 1/2" longer stroke. Had to mod the brake pedal also for more leverage and it's still pretty hard to stop fast but normal driving is ok, harder than manual but you'll adapt.

Since stroke and diameter combine for volume, the smaller diameter reduces resistance and volume but the longer stroke makes up for it. I did a pretty good write up on my truck conversion with photos. Also I have 4 wheel disc brakes since replacing the axle with an S10 Blazer rear.


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## dtbaker (Jan 5, 2008)

after initial conversations with Wilwood tech support, it is not looking like a non-vacuum switch will save much if any money... since the Swift did not come with a 'boosterless' version, there is no stock switch to go find in junkyard.

There ARE manual cylinders available from Wilwood and aftermarket, but a tandem cyl, plus proportioning valve to tune front/back adds up to around $300 if new parts.

Key info is that the Swift has two outlets to front, and one outlet that goes to a funky splitter looking thing that assume is what is the 'modern' way to retain either front or rear brakes if one line pops somewhere. This means that it would be best/safest to have a 'tandem' master, and the bore size needs to be probably either .700, or .875 to give low enough pedal effort.

There are LOTS of old 60s cars that have completely manual brakes, and available new master cylinders for under $100 with .700, .750, .875 dia... but only single outlet. So I'm not positive a single cyl can move enough fluid to take up the slack, especially considering the rear brakes are drum. I may still try it, but it is looking like it would require adding some kind of splitter/proportioning valve to attempt to balance front/rear brakes


.... and may not save much if any time or money over the usual vacuum pump setup.


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## EVfun (Mar 14, 2010)

Single or duel cylinder is not the issue when moving fluid. Single circuit brakes where prohibited after 1966 because if a single part of the hydraulic circuit fails brakes are completely lost. The duel piston designs keep brakes on 2 wheels after a failure. 

You need a master cylinder with a slightly smaller bore than stock. Then you need to make sure the pedal doesn't go to the floor if one bleeder valve (simulating a failure) is open.


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## ElectriCar (Jun 15, 2008)

My brake system uses the same valve on the vacuum boosted brakes. Only changed the MC and that's it. Chevrolet calls it a "Combination Valve". It basically has a shuttle valve inside which switches the rear line hydraulics off if you lose pressure on the rear brake line. I think it does the same to the front in the same situation. 

What I found in my area is general mechanics don't know squatolla about brakes other than how to replace pads & rotors. If that or the MC doesn't fix it they're lost.

I think I would have spent the $300 if I had to if that's what it took to get rid of that gawd awful compressor running every other time I stopped!

But do your due diligence on brake systems and you may not need anything other than the MC from Wilwood. Maybe Wilwood tech support can help if you've not talked to them yet.


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## gsmith191145 (May 1, 2011)

My car has a station wagon master cylinder which was larger than the original master cylinder. Also if you want to control your brake pedal pressure you can install an adjustable metering block to set the percentage back to front.


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## mizlplix (May 1, 2011)

A sad fact of life is that Wilwood has poor (none) customer assistance. How can I say that? 40+ years of racecar building. I had to learn the hard (costly) way. They do not, will not recommend M/C bore sizes either.

1. Measure old M/C bore. Select any M/C that will bolt up to your mount and is 1/8" smaller in the bore.

2. Speedway motors has every necessary fitting (metric/american) to adapt, resize, invert or twin to get you hooked up. Their tech people are awesome. They ship within hours of ordering.

3. An adjustable proportioning block will only adjust front/rear percentages to compensate for adverse weight distribution or brake cylinder/caliper mismatch.

Sorry, but a combination valve does not shut off the flow to anything. The shuttle piston presses a switch and lights a bulb on your dash and sez "BRAKE" indicating a failure (which you already know because you are running through the intersection).

Although on some GM vehicles they do incorporate a fixed bias adjuster to set the braking balance (a bandaid supplied by engineers who do not want to pour more money into the car build).

Sorry if I sound harsh. It was not meant to. Brake systems have always been a mix-n-match game, unless someone has done the cut and try and sells the complete kit.

Miz


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## ElectriCar (Jun 15, 2008)

Come to think of it I believe the combination valve doesn't block off the section with the fluid loss. I thought it did for a long time but found it was acted that way because the MC plunger couldn't retract fully after I did the conversion causing the rear section to not reload with fluid when we tried to bleed the system. Eventually the front brakes would build pressure but not the rear so I thought it was because the rear had too much air in it and I couldn't get it out. Because of this the valve kicked in and the light came on. Not until I found the problem and fixed it did the valve recenter.


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## dtbaker (Jan 5, 2008)

mizlplix said:


> A sad fact of life is that Wilwood has poor (none) customer assistance.


I have to agree... several emails, no response. tel call, non-commital and not much help. Also very expensive!



mizlplix said:


> 1. Measure old M/C bore. Select any M/C that will bolt up to your mount and is 1/8" smaller in the bore.


this is about what several other sources are saying, so sounds like a good idea. I spent a while poking thru RockAuto.com looking for a 3/4" bore tandem with horizontal bolts.... and found a couple with two outlets, but none matching my three. Also new tandems are pretty expensive even from rockauto. It would give me an idea of what to look for in a junkyard though.



mizlplix said:


> 2. Speedway motors has every necessary fitting (metric/american) to adapt, resize, invert or twin to get you hooked up. Their tech people are awesome. They ship within hours of ordering.


good to know and I am adding to my bookmarks!


Another lead I got was to contact people at whitepost.com about the cost of sleeving the master.... they specialize in sleeving/restore of old hydraulics when the replacements are not readily available. Sounds good, but I haven't heard back yet. If this works I could just use the original master, and either leave the booster un-vacuumed, or remove and add spacers, or remove completely and re-bend the brakelines to hit the new outlet locations.


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## piotrsko (Dec 9, 2007)

you could probably resleeve it yourself, I don't recall any holes/notches except for the refill ports. You could match drill through the existing ports, and the holes for where the brake lines exit.. seamless tube, do a mild hone after it is pushed and drilled. Most of aircraft supply houses have precision tube you can buy in 1 ft lengths.

The other thing would be to go to say a bendix online catalog and see what they have that cross references with what your specs turn out to be.


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