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Manual brake setups


wvumtnbkr
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I'm thinking about getting rid of my brake booster.  Anybody have pros and cons for doing so?

 

Anybody running manual brakes?  How did you determine master cylinder size?

 

How is pedal feel and modulation?

 

Any info is appreciated!

 

1987 mazda rx7

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Been running manual brakes since the 1UZ swap. The whole team loves it. Go to chasebays.com and see if they make a kit for the RX7. You can buy that or use the Wilwood MC in their pictures and buy it on Summit for $85. Only real downside, besides a slightly higher pedal force, is the lack of dual cyclinder (front/rear). You can get dual cylinders but the singles are cheaper and work well. I run a doubly banjo bolt out of MC to the stock prop valve. Made the plate from some scrap steel (1/8"ish think).

 

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LOL< I was gonna post to check with @IPF Racing - beat me to it.

Love how everyone helps each other on here (while the pundits say this forum is only for whiners...)

edit: I'm looking to do the same thing, but I too would like a dual circuit setup.

Edited by mcoppola
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Reverse hanging pedal set. At least 6:1 ratio. Wilwood or tilton attach plate to dash bar. If using Turbo II calipers I would start with 3 3/4” masters. If pedal travels to far for your taste go to a 7/8” for fronts. Remove the whole pedal colum mess from the rx7. Changing the masters to Taylor the pedal feel is the way to go. Made this change to old car and it was best setup. Always run a two circuit brake system 

Edited by TimS
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46 minutes ago, wvumtnbkr said:

I'm thinking about getting rid of my brake booster.  Anybody have pros and cons for doing so?

 

Anybody running manual brakes?  How did you determine master cylinder size?

 

How is pedal feel and modulation?

 

Any info is appreciated!

 

1987 mazda rx7

 

Klaatu was manual brakes

Pros: Better feel, better modulation, easier to left foot brake
Cons: Increased force required 

 

We just made a rod to push the OE MC using the pedal linkage.

Edited by red0
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6 minutes ago, TimS said:

Reverse hanging pedal set. Wilwood or tilton attach plate to dash bar. If using Turbo II calipers I would start with 3 3/4” masters. If pedal travels to far for your taste go to a 7/8” for fronts. Remove the whole pedal colum mess from the rx7. Changing the masters to Taylor the pedal feel is the way to go. Made this change to old car and it was best setup. Always run a two circuit brake system 

 

Its money, but this is what I'm aiming for as long as theres money left in the budget once the cage is done.  Might stay stock for a while until we can develop the platform a little.

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20 hours ago, SonsOfIrony said:

 

Its money, but this is what I'm aiming for as long as theres money left in the budget once the cage is done.  Might stay stock for a while until we can develop the platform a little.

You have a brembo car?

 

Stock 20+ yr old Infiniti master w/abs running rock auto china z33 brembo copies, a bit over boosted, works good enough, never felt the need to rip it out to do better.

 

Edited by Team Infiniti
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If it works I wouldn’t change a thing. I had problems with low vacuum and erratic boost when I changed from a turbo engine to NA ( huge port on that brigeport 13b). I will say once the manual brakes were setup it was great. 

Using the oem pedal will give you a bad pedal ratio and make the effort very high, like when booster doesn’t work. 

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52 minutes ago, Team Infiniti said:

You have a brembo car?

 

Stock 20+ yr old Infiniti master w/abs running rock auto china z33 brembo copies, a bit over boosted but works good enough to never feel the need to rip it all out trying to do better.

 

 

Yes, Brembo car.  I tried to send you a PM, but it wouldn't let me.  I got a question for you, but don't want to clutter this thread.

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2 hours ago, wvumtnbkr said:

Hmmm.  Might be time for some math....

I think I see what you might be thinking here. If you figure out what you're pressure on the pads need to be, you can then back into how much pedal pressure there needs to be. If I were you, I might spend some time looking at how you could change where on the pedal the master cylinder is attached. You could also just make the pedal longer so you have more leverage.  It might be easier to change the brake pressure by changing that than putting a different master cylinder in. Then again it might take a lot of work to re-engineer the brake pedal in your car.

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5 minutes ago, The Aero Man said:

I think I see what you might be thinking here. If you figure out what you're pressure on the pads need to be, you can then back into how much pedal pressure there needs to be. If I were you, I might spend some time looking at how you could change where on the pedal the master cylinder is attached. You could also just make the pedal longer so you have more leverage.  It might be easier to change the brake pressure by changing that than putting a different master cylinder in. Then again it might take a lot of work to re-engineer the brake pedal in your car.

I have an angle grinder and a welder and I'm not afraid to use them...  keeping the replaceable parts stock might be beneficial....

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1 hour ago, scottyk said:

You building something special because the platform has already been developed 

 

Not sure I'd call 1 A/T car that shares the same chassis, that I've only ever heard about second hand but never seen, "developed".  Not in the same way the E30 or Miata have been refined. 

 

Not saying the Z that has raced with CC is't fast or competitive, it's just an unknown quantity to me.

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20 hours ago, wvumtnbkr said:

I'm thinking about getting rid of my brake booster.  Anybody have pros and cons for doing so?

 

Anybody running manual brakes?  How did you determine master cylinder size?

 

How is pedal feel and modulation?

 

Any info is appreciated!

 

1987 mazda rx7

 

Lookup the math or get one of us to build a calculator for you. You are basically calculating the wheel torque required to bring the wheels to slip (max force limit) at 1-1.2 G (calculating the vertical force on front vs rear wheels and multiplying that by an assumed mu of 1-1.2). This torque goes through the caliper to master cylinder area size difference as a multiplier, and your pedal ratio is a multiplier. 

 

A pedal force of 100-200 is reasonable. Above that you will most likely have drivers complain that the effort wears them out over time. 

 

Most vacuum booster have an assist ratio of 1.5-2:1. If you like your current pedal force, you will need to make the pedal ratio 1.5 times better, or usually people make the master cylinder bore AREA 1.5 times smaller. I bet you have some room to go on pedal effort, so you might want to start at 25 to 50% more mechanical advantage in the master bore area\caliper bore area, pedal ratio, etc. 

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14 minutes ago, Black Magic said:

 

Lookup the math or get one of us to build a calculator for you. You are basically calculating the wheel torque required to bring the wheels to slip (max force limit) at 1-1.2 G (calculating the vertical force on front vs rear wheels and multiplying that by an assumed mu of 1-1.2). This torque goes through the caliper to master cylinder area size difference as a multiplier, and your pedal ratio is a multiplier. 

 

A pedal force of 100-200 is reasonable. Above that you will most likely have drivers complain that the effort wears them out over time. 

 

Most vacuum booster have an assist ratio of 1.5-2:1. If you like your current pedal force, you will need to make the pedal ratio 1.5 times better, or usually people make the master cylinder bore AREA 1.5 times smaller. I bet you have some room to go on pedal effort, so you might want to start at 25 to 50% more mechanical advantage in the master bore area\caliper bore area, pedal ratio, etc. 

 

We did not increase the mechanical advantage at all on our mechanical brakes, and the force did wear us out. I would have gone with 2x mechanical advantage if given a choice. 

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Here's a reasonable primer for the math:

https://www.knowyourparts.com/technical-resources/brakes-and-brake-components/from-pedal-to-pads-brake-systems-explained/

 

Here's the WIlwood chart showing their pad compound friction coefficients:

https://www.wilwood.com/BrakePads/BrakePadsApp

 

I have power brakes and power steering in the Fiero and power brakes with manual steering in the Civic. The Fiero has very good feel and is noticably less work to drive than the much lighter Civic, especially when the g-loading gets up there. One of my regular drivers finds the steering in the Civic wears him out more in one stint than the Fiero does in two and has requested that I convert the Civic to power steering. 

 

No cons from any of my drivers about the power brakes in the Civic, pedal is consistent and height has been adjusted for good heel and toe.

 

Edited by mender
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1 hour ago, red0 said:

 

We did not increase the mechanical advantage at all on our mechanical brakes, and the force did wear us out. I would have gone with 2x mechanical advantage if given a choice. 

 

Did you increase caliper piston size/count or even rotor diameter at the same time?  Increasing piston size will act the same as decreasing master size.

 

On the turbo rally cars, the standard practice at the club level is to keep the same master size, but move the actuator rod approximately 1" closer to the pivot on the brake pedal when deleting the booster.  Many of the "OTS" booster delete adapters place the the master 1" high to maintain near ideal actuator rod angle.

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A well setup pedal box is worth 1 sec on most tracks for me.  Willwood and tilton can give you MC recommendations based on pedal feel you are looking for.  I have experienced 2 booster failures so far while racing champcar.  The car I run (SC300), new MC's are expensive and rebuilds are suspect at best.  For the left foot brakers, they may find the pedal to be inconsistent due to lack of vacuum. 

 

DDR Racing Celica took a few attempts to get the feel correct but his car has some of the best braking feel and easiest heel-toe that I have experienced.  We haven't converted over yet mainly due to worry about ABS but am looking to make the leap to a pedal set sometime in the future.  Pros, less weight, better placement, ease of adjustability, true brake bias.  Cons, Cost, setup time, complexity. 

 

Good luck, and as always great info from the members.

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I believe you are less likely to flatspot the tires; yes because the brakes are easier to modulate but also I swear that when you lockup and lift they release quicker. This could be a tire thing too, as I notice if you lockup an RS4 it flatspots, toyos, both yokohamas, and Z3s do not flatspot easily. 

Interested to see if anyone else has found the same with manual brakes.

Edited by wd6681
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2 hours ago, Hurljohn said:

For the left foot brakers, they may find the pedal to be inconsistent due to lack of vacuum. 

 

 

 

You may have that backwards, or I'm misreading.  The lack of consistent pedal feel is one of the primary reasons to ditch a vacuum booster which can vary it's assist wily based on throttle inputs, and engine RPM.  That's why a booster delete is so popular among the stage Rally teams.

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4 hours ago, SonsOfIrony said:

 

You may have that backwards, or I'm misreading.  The lack of consistent pedal feel is one of the primary reasons to ditch a vacuum booster which can vary it's assist wily based on throttle inputs, and engine RPM.  That's why a booster delete is so popular among the stage Rally teams.

That is what trying to convey.  

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