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Brake booster delete

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Old Mar 15, 2012, 09:25 AM   #1
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Brake booster delete

Something Ive been doing for a while has been driving my car with the vacuum line disconnected from the booster. This doesnt provide the best solution to the idea of boosterless braking, and potentially vacuum eliminating antilag type functions that I am trying to accomplish. So I too the booster out and made some basic measurements on a pieces of scrap aluminum. This is not machine shop quality but with a bandsaw, drill press, tap and hole saw I made this.

Im going to use a 15/16's master cylinder unless I find that this decrease isnt enough. Its actually from my impreza l swap which never got completed. 4 channel, and the evo brake reservior fits right on top of it. The brake lines are routed a touch different from the cylinder but thats all easy stuff.

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Old Mar 16, 2012, 07:50 AM   #2
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This seems like a BAD idea.
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Old Mar 16, 2012, 08:04 AM   #3
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Manual brakes have been around forever. No biggie, if he can drive around with the vacuum hose detached he already knows how the pedal feel changes. Manual brakes aren't for everyone and can be a pita sometimes. The pedal is more consistent and has a more direct feel but in return takes more pedal pressure to stop.
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Old Mar 16, 2012, 09:15 AM   #4
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Especially before i was working without a mechanical advantage .. im dropping .125" dia off my my cylinder so it will help some from where i was before. Buschur sells a kit for 500 that does this. Granted ita cnc and a new unit with complete everything
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Old Mar 16, 2012, 01:22 PM   #5
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I'm going brake boosterless myself. I thought about making a mount myself and just buying the Wilwood master cylinder, but I wanted something that looked professionally done since it is in plain sight once I pop the hood.
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Old Mar 16, 2012, 09:35 PM   #6
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Im into function over form and performance over cost... Usually I have to make something work, then go back and make a pretty version. I just got a free lathe though, and I have a lot of other tools at my disposal. Im learning and eventually my stuff will be machine shop quality, or atleast a lot better.

The aluminium was scrap, and the MC is leftover from my impreza l > RSti widebody. I actually will have this set up for a hydraulic handbrake too! Bought a few necessary pieces from a speed shop today.
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Old Mar 16, 2012, 11:24 PM   #7
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Drives: 05 WW Evo VIII RS, 1996 INFINITI I30 (DD)

A RS can lock its front wheels easily but by disabling the brake booster does it make that problem go away or does it still lock?

BTW, was that your main motivation for disabling your power brakes on your Evo?
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Old Mar 17, 2012, 06:39 AM   #8
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Quote:
Originally Posted by deylag View Post
A RS can lock its front wheels easily but by disabling the brake booster does it make that problem go away or does it still lock?

BTW, was that your main motivation for disabling your power brakes on your Evo?
Simplicity of function, and anticipation of some form of antilag in the near future. Also desire to clean up the engine bay. David Buschur noted that he would lock the brakes up easily with power brakes, and that this modifiation helped him regain control in emergency stops.
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Old Mar 17, 2012, 06:22 PM   #9
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Have you looking into increasing your pedal ratio?
Normally non assisted brake systems have high pedal ratios.
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Old Mar 17, 2012, 08:55 PM   #10
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yes, hence the 15/16;ths
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Old Mar 17, 2012, 11:18 PM   #11
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Quote:
Originally Posted by 211ratsbud View Post
yes, hence the 15/16;ths
? I think you misunderstand what 15/16 MC is and what a pedal ratio is, totally different dude. Because you don't have any assist you need to increase the pedal ratio significantly, adversely this will increase your pedal travel, and normally you counter it with actually increasing the MC size... I do this for a living.

Assisted brakes use pedal ratios 2.5-3.1 generally, unassisted are like 4.5-7.0
Often times the servo ratio in the booster is somewhere 6-10 on most passenger vehicles...since you take that away you try to make it up with the pedal... that is the correct method to achieve what you are doing.
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Old Mar 18, 2012, 08:29 AM   #12
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A smaller mc wont increase pedal stroke and modulation?
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Old Mar 18, 2012, 09:41 AM   #13
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Quote:
Originally Posted by 211ratsbud View Post
A smaller mc wont increase pedal stroke and modulation?
Just some general info:
Every time you release the brake pedal the pistons will roll back into the caliper, every caliper is different depending on the type of piston seal and piston material etc... but generally like ~0.25mm. You'll find that every piston does this, so taking into consideration every piston area you'll get a fixed volume that needs to be made up in order to give any brake torque every time you apply the brake.


A smaller MC will increase pedal stroke because you need to displace the same amount of fluid volume (since you didn't change your corner brakes), because the cylinder is smaller in diameter, you'll need to increase stroke to make up the same volume. Its true that a smaller MC will also provide high brake gain because of higher brake line pressures for the same given amount of pedal force (given same pedal ratio)... but removing a booster and trying to make up for it primarily with the MC is generally the wrong direction.

Pedal stroke is completely a subjective personal opinion, sportier brake systems have reduced strokes by nature, but its not necessary...although it helps when you start getting a spongy pedal on a track day, long stroke escalates the bad feeling.

You are at a positive by removing the entire booster and putting in such a large stiffener plate, you are losing the dead stroke of the booster by a few mm's and the deflection of the fire wall combined.

Hope that sheds some light
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Old Mar 18, 2012, 10:47 AM   #14
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Well, I did redrill the brake pedal pivot point up, but i cannot tell how much pushrod deflection is acceptable. Is the piston in the cylidner compromised greatly by moderate angles of deflection from the rod?

I will use the stock MC if i can.

https://secure.buschurracing.com/cat...faf51b8959d01e

They just use a smaller sized cylinder..

Last edited by 211ratsbud; Mar 18, 2012 at 10:51 AM.
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Old Mar 18, 2012, 01:30 PM   #15
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Brake systems are all about balance, there is no such thing as the perfect system. Reducing the size will help with deleting the booster as it increases the brake gain. You judge if the stroke is too much, more stroke seems better than providing a huge increase in force from your leg.

I'm just giving you the advice if we were to redesign a brake system which had a conventional booster to delete it, we would change the pedal ratio and backwards calculate what the MC size should be to keep a similar stroke.

Perhaps you should find out what size Buschur used for their system I didn't see it mentioned, only that the stock RS MC was no good. Is the RS and GSR/MR MC the same size I wonder....
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