# using sticky brake pads instead of vacuum booster



## dtbaker (Jan 5, 2008)

I finally got a set of Carbotech front brake pads with the stickiest compound (AX6) in hopes that I could use just the pad upgrade and skip the vacuum pump to booster in my next build. Installed 2 days ago, got them seated with vacuum still in place, and today turned off the pump to see how they did without booster.

preliminary results are that the pads ARE way stickier than OEM.... almost too much with vacuum and a bit of squeal under low pressure braking as predicted. After turning off vacuum pump it FEELS like there is some internal spring in the booster that takes a fair amount of pressure to overcome. Net is that it is pretty drivable, better than with OEM pads, but probably too stiff for a comfortable drive by 'the wife or daughter' without vacuum to the booster.

so...... sticky pads do not seem to be enough to avoid a vacuum system in my preliminary evaluation.

The alternative for SOME vehicles is to switch to a boosterless master (with a slightly smaller bore diameter) that may be from an earlier version of the vehicle. But in my case, there never was a boosterless version, and the master has 3 outlets which don't match any old boosterless master I have been able to find, which would require significant brakeline work to re-route and maybe re-balance.... which I am not seeing as a good alternative. So, back to the vacuum system.


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## EVfun (Mar 14, 2010)

dtbaker said:


> After turning off vacuum pump it FEELS like there is some internal spring in the booster that takes a fair amount of pressure to overcome.


There is, the booster has a fairly stiff return spring that you wouldn't have with manual brakes.


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## GizmoEV (Nov 28, 2009)

Thanks for posting your results. Are you going to try to remove the booster to eliminate the spring and see how it feels?


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## dtbaker (Jan 5, 2008)

EVfun said:


> There is, the booster has a fairly stiff return spring that you wouldn't have with manual brakes.




hhhhmmmm, so in the interest of science, I am willing to try to remove/bypass the spring to see if it then feels drivable without vacuum if it can be done without TOO much expense/time.... any specifics on how I might best do this? 

If I remove the booster, I am guessing it would take a standoff adapter to position the master back where I don't have to mess with brakelines. Is there any way to remove the return spring and leave the booster physically in place?


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## EVfun (Mar 14, 2010)

I've heard of a brake booster being gutted but I've never taken one apart. There is a diagram showing the basic structure at the top of this page. Click the image on the right near the top of the page for a larger internal view.


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## Rational (Nov 26, 2011)

tradeoffs, tradeoffs, . . .
this cost/benefit/risk tradeoff seems to be 
a one time cost + maintenance for a booster 
vs.
repurchasing pads + rotors 

from 
http://en.wikipedia.org/wiki/Brake_lining

"The dynamic friction coefficient "µ" for most standard brake pads is usually in the range of 0.35 to 0.42. This means that a force of 1000 Newtons (or pounds) on the pad will give a resulting brake force close to 400 Newtons (or pounds). There are some racing pads that have a very high µ of 0.55 to 0.62 with excellent high temperature behaviour. These pads have high iron content and will usually outperform any other pad used with iron discs. Unfortunately nothing comes for free, and these high µ pads wear fast and also wear down the discs at a rather fast rate. However they are a very cost effective alternative to more exotic/expensive materials."


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## hamsterpower (Oct 13, 2009)

One thing to keep in mind is brake pads that are designed to handle high temps, are NOT designed for low temps and likely will not help for gentle stops. In fact these "High Performance pads" often only work HOT and are much worse in normal driving.


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## WarpedOne (Jun 26, 2009)

Whate about a bit longer brake pedal?


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## dtbaker (Jan 5, 2008)

hamsterpower said:


> One thing to keep in mind is brake pads that are designed to handle high temps, are NOT designed for low temps and likely will not help for gentle stops. In fact these "High Performance pads" often only work HOT and are much worse in normal driving.



this particular compound ( carbotech's AX6 ) is formulated to maximize cold stops for short course autocross and street performance. Generates a fair amount of dust, squeals a little but stops significantly better than OEM even when cold.... expensive too ($150-ish), but cheaper than the usual vacuum setup.


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## dtbaker (Jan 5, 2008)

WarpedOne said:


> Whate about a bit longer brake pedal?


I looked at both a longer pedal, and changing the pivot for better leverage. The pivot in the Swift would be a real challenge to change; and take more time and money than vacuum. 

Making the pedal longer would put the contact lower than the ball of foot when heel is on the mat, and while it MIGHT help I think it would have to be lengthened by several inches to make much difference, and the 'feel' of having the brake pedal contact under the arch of your foot gets kindof weird.


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## WarpedOne (Jun 26, 2009)

> and while it MIGHT help I think it would have to be lengthened by several inches to make much difference


Brake pedal is about 10" long and there is about 2" between pivot and brake cylinder. 
1 additional inch would increase braking force for 10%. Not much but some


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## Rational (Nov 26, 2011)

You know, if you modify the brakes and there is an accident the insurance co. will blame you even if it's not your fault. 
'Burden of Proof' means nothing when dealing with politically-connected companies.


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## dtbaker (Jan 5, 2008)

Rational said:


> You know, if you modify the brakes and there is an accident the insurance co. will blame you even if it's not your fault.
> 'Burden of Proof' means nothing when dealing with politically-connected companies.


I doubt any traffic accident would trigger a forensic investigation as to the modifications made to the car. The most obvious change being an electric motor might draw attention if it stuck on and all fail-safes failed.... but I can hardly imagine them looking for or finding minor mods to anything.


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## dtbaker (Jan 5, 2008)

WarpedOne said:


> Brake pedal is about 10" long and there is about 2" between pivot and brake cylinder.
> 1 additional inch would increase braking force for 10%. Not much but some



by the 'feel' of it currently, I think that whatever return spring is inside that booster is adding more than 10% of the pedal pressure required. If it is halfway easy to get to, I might try removing the spring just to see if it makes the feel more drivable.

otherwise I would sadly conclude that the pedal pressure is a bit high for *most* people's comfort without the vacuum assist even with the sticky pads.


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> Thanks for posting your results. Are you going to try to remove the booster to eliminate the spring and see how it feels?



has anyone pulled a booster apart? is the spring buried internally, or maybe somewhere I can unhook it?

otherwise I could consider pulling the booster OUT and adding a spacer to maintain the master location so that no changes are needed to brakelines for now....

comments?


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## WarpedOne (Jun 26, 2009)

> If it is halfway easy to get to, I might try removing the spring just to see if it makes the feel more drivable.


I'd be surprised if removing it doesn't significantly improve braking force.
The system is designed to work OK when there is vacuum, there is almost no attention to performance without vacuum in modern brake designs.

I'd suggest you remove it completely and do it in most failsafe way. You can also replace brake discs with biggest that still fit your car. Cars with different engines typically come with differently sized discs.


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## piotrsko (Dec 9, 2007)

newest series of comments: brake pedal is, I believe, a class 3 lever which essentially means if you need more force, you move the working point up towards the pivot to get more leverage/force.

The pedal assembly isn't all that hard to pull, just annoying and cumbersome. The dealers have to replace the plastic bearings for "squeaky" pedals. Some even mount to the firewall. I pulled out and swapped the one on my ranger to add the clutch pedal.

if you can get your hands on another pedal rod out of a wrecked car, just cut it down to the length you need and bolt the mc directly to the firewall. worst case you make an adapter plate. the length calc should be about 3/4 inch out from the firewall.


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## dtbaker (Jan 5, 2008)

piotrsko said:


> The pedal assembly isn't all that hard to pull, just annoying and cumbersome.



the pedal assy in a Swift looks like it would be a real bear to pull.... and need to be done at the time when the ICE is out, before all the conversion stuff is installed. there is not a lot of room to work with and the pedals wrap around the steering column. There is not enough 'meat' on the lever arm to drill a higher pivot hole, so it would require fab of a whole new hanger, fab of a standoff or removal of the booster and changing brakelines, or dismantling the booster to get at the return spring which I don't know about yet.... 

the alternatives so far end up to be far more time and expense than going with the regular vacuum system.

I am exploring alternatives to find possible solutions that would take less time to install and cost less than the typical vacuum pump/switch/reservoir. I think it is POSSIBLE to refab a pedal assy, but would be more time, money, and trouble than electric vacuum.

If it turns out to be easy to remove the return spring from the booster, then that plus sticky pads MIGHT be an easy and cost effective alternative.


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## ChristianThomas (Nov 29, 2011)

Remember that the area of the master cylinder piston changes dramatically with small changes in diameter. Check w an old guy at a salvage yard to find a manual master cylinder w a similar brake line arrangement. Even a couple millimeter difference in diameter could give a major boost in braking.

To regain some of the volume lost to the smaller bore, upgrade your brake flex lines to stainless steel jacketed ones. The reduced ballooning gives a great feel to breaking and results in less fluid necessary for any particular brake force.


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## dtbaker (Jan 5, 2008)

ChristianThomas said:


> Remember that the area of the master cylinder piston changes dramatically with small changes in diameter. Check w an old guy at a salvage yard to find a manual master cylinder w a similar brake line arrangement. Even a couple millimeter difference in diameter could give a major boost in braking.
> 
> To regain some of the volume lost to the smaller bore, upgrade your brake flex lines to stainless steel jacketed ones. The reduced ballooning gives a great feel to breaking and results in less fluid necessary for any particular brake force.



yes, the stock dia is 13/16, and I have looked in vain for a 3/4 with matching outlets (to minimize brakeline re-routing). Once you get in that deep and look at the time to switch out the masters and expense of the master plus re-plumbing brakelines, the cost of adding the typical vacuum pump/switch is close to a wash. If there were a bolt-up change it might be worth it.

or.... it is turns out to be easy to remove the heavy return spring inside the brake booster that MIGHT make enough difference when used w/ sticky pads leaving the stock master in place.


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## PhantomPholly (Aug 20, 2008)

First things first - rather than gut the booster, I would make adapters and simply bypass the whole device, plugging the holes in case you decide to hook it up again later.

My airplane had a gross weight of 1,800 pounds and had to stop using simple toe brakes. No problems braking from 120mph, but I believe the secret was that the disk had nearly the same diameter as the wheel. 

With typical car brakes you have the problem that the disk is usually about 1/3 the diameter of the wheel. Your brake booster overcomes this by providing torque multiplication to the friction area to overcome torque division due to the smallness of the rotor.

But all is not lost. You might try a different master cylinder, one which requires more movement of the pedal to accomplish the same amount of caliper compression. On aircraft they are located behind the pedals and have an integral reservoir. Here is one manufacturer - whole assembly around $100 and simple enough you might be able to jerry-rig it in place.


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## dtbaker (Jan 5, 2008)

...thought I would post a followup on the use of carbotech brake pads in my quest to avoid a vacuum power brake system.

The carbotechs DO have significantly more stopping power, but not enough to get by with an un-modified power brake return spring fighting your pedal push without the vacuum assist.

Additionally, they squeal like crazy, they wear out FAST, like in 5000 miles or less, generate LOTS of dust (blackens rims in less than 100 miles), and some of that dust is your rotors which get eaten alive by these pads! I saw probably .020-.030 rotor wear in less than 5000 miles of use.

...so, for racing these pads might be great for max stopping power. For normal street use I would not recommend going this route.


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## GizmoEV (Nov 28, 2009)

Thanks for the update. I was thinking about getting some made for my Gizmo but I think I'll pass since they wear the rotors so fast. Gizmo rotors are paper thin to begin with so I don't want to wear them out faster! I'm glad I have regen on this rig.


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## tinkeringgreg (Mar 27, 2008)

Look at where the lines go from the master cylinder. One should go to the rear brakes and the other two should go to the front brakes. then if you look at the maser cylinder closely you will see that both front lines go into the same pumping chamber.
You should be able to connect both front lines together with a proper tee fitting and then feed that from the front output of a manual master cylinder. Keep in mind if there is a proportioning valve in the brake circuit it has to stay or your front/rear brake balance will be off. 

hope this helps Greg


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## dtbaker (Jan 5, 2008)

tinkeringgreg said:


> Look at where the lines go from the master cylinder. One should go to the rear brakes and the other two should go to the front brakes. then if you look at the maser cylinder closely you will see that both front lines go into the same pumping chamber.
> You should be able to connect both front lines together with a proper tee fitting and then feed that from the front output of a manual master cylinder. Keep in mind if there is a proportioning valve in the brake circuit it has to stay or your front/rear brake balance will be off.
> 
> hope this helps Greg


this doesn't really help.... I looked at lots of options, conversion to a manual master being one. My specific vehicle never had a manual master, so it would be a conversion to something generic with smaller bore, hoping to retain enough travel, and require re-plumbing. 

My specific vehicle has three lines out of the master, so at a minimum I'd have to re-plumb at least the first lengths of brakeline to the respective connections.

My conclusion at the moment is that the cost/time required to replace the stock master+booster with a manual tandem, re-balance, and re-plumb brakelines outweighs the cost of sticking with the defacto standard electric vacuum pump and stock master+booster.


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