Brake Booster Delete
 

I hate the brake booster. Because of the cams in my car, I get really inconsistent braking when blipping down through the gears... I can actually feel the assist coming and going, and beside that, the pedal feels numb.

So I ran the last few events to test the brakes with the booster line removed and whilst the brake pedal requires lots more force, the brake pedal is far more linear and I can feel the brakes working through the pedal. Once used to the additional pressure required, brake modulation is far better. I immediately found that I could brake later and deeper into the corners and my times dropped a bit.

I've pulled out the pedal box and removed the booster entirely. As part of doing this I figured I may as well go for an adjustable bias and dual masters. Here are some pics of my pedal box mod:

https://www.miataturbo.net/attachmen...ine=1447841576

https://www.miataturbo.net/attachmen...ine=1447841576

https://www.miataturbo.net/attachmen...ine=1447841576

https://www.miataturbo.net/attachmen...ine=1447841576

Some additional bracing is required on the pedal box to strengthen it after being modified. I've sized the master cylinders at 5/8" for the front, 0.7" for the rear so they are slightly smaller than the stock dual master from my car which was 7/8" will give me some extra brake ratio. Initially I'm keeping the stock pedal ratio of 4:1 but will probably need to increase this to 5:1 - 6:1 by dropping the top pivot a little. We'll see how it feels once it's in the car. With the booster still present but the vacuum line remove, there is a lot of resistance the pedal box adds, so maybe with it gone it might be fine.

So far the mods have been extremely simple, retaining the original mounting points on the pedal box. The biggest hassle is getting all the brake lines connected which I'm going to do via a single custom distribution box that will have 1/8" ports in, 1/8" ports for brake sensors and 1/8" ports out for the various lines.

I'll report back in a few weeks when I've raced with this setup.

Pimpy

I'm considering something similar. Dual master setup is nice. Vacuum brakes feel crappy with big cams.

Brake distribution block complete. The pedal is all braced and mounted in the car. Just need to connect the stock brake lines to the bottom 1/8" NPT ports. I'll upload some pics of it installed later today.

https://www.miataturbo.net/attachmen...ine=1448144875

https://www.miataturbo.net/attachmen...ine=1448144875

Not the same for the LHD cars, but the removal of the brake booster lets you fit in longer trumpets on the ITBs... Not that I run them. Still having some extra space and less weight on this side of the engine bay is always nice.

https://www.miataturbo.net/attachmen...ine=1448245527

Even better, you own a Mazdaspeed B Spec car. Going all out with a pressure sensor too. I'm surprised this isn't getting more attention.

I picked up these 1000psi pressure sensors for $30 each from ebay and installed them in the existing lines a few months ago to log the fluctuating pressure with the booster. I logged the pressures by trying to keep the pedal pressure even as I blipped the throttle whilst I was dropping down gears. There wasn't a lot of point though because I could feel the pedal moving under my foot anyway so I'm not sure how even the pressure was... Still you can see in the logs a high initial brake pressure, followed by dips and spikes as I blipped the throttle. Regardless the booster wasn't helping and had to go...

I wouldn't rely that the readings are calibrated, but it's great for logging and comparing setups. It will be good to check them when the dual masters are in to make sure I'm hitting the same pressure points as I was prior to removing the booster. It will also be good to log the brake bias I'm running at future events.

The car is a 1989 Eunos Roadster B-spec imported from Japan... All the B-spec stuff has been replaced over time with only the badges left on the car. I ended up moving all the running gear into a new chassis and selling it off.

Those $30 sensors are awesome. I just ordered a couple for oil and fuel pressure.

I checked my oil and fuel pressure ones against an accurate gauge and they did read about 5-8 psi higher throughout the pressure range, so be a little careful using them. I use mine for logging so I'm more interested in changes rather than actual values.

The 1000 PSI ones are a little tricky to find... Search for "1000 PSI pressure transducer" on ebay

The same place I bought my 0-100psi had 0-1000 I believe.

I'll try and get an accurate gauge to check against. I'm going to be using them for warning.

I use them for the engine protection in the ECU and data logging. I have a separate standalone Longacre gauge for oil pressure which includes a 3 stage warning light. It's against this gauge that I can see the difference in pressure but it's also the same difference against a mechanical fuel pressure gauge to these cheaper sensors so I figure they all read a little high.

That's my plan, logging and warning lights. I have a mechanical fuel gauge I'll compare it to, but I guess I could also adjust the readings in the ECU.

Maybe they just need to be calibrated differently in the ecu? What values are you using.

I just use the listed 0.5v for 0 PSI and 4.5v for highest PSI rating (100 or 1000PSI) and linear in between. It would be easy to re-calibrate in the ECU but I'd need a better master gauge to base it from. I haven't been bothered to mess with them as I'm not relying on accurate values but maybe it's worth doing just to know which gauge / sensor is right. I trust the Longacre gauge more but it reads lower than both the ebay sensor and an Autometer electronic gauge. Maybe it's the one that is low, I doubt it though.

It's a bit like tire pressure gauges. Mine reads different to others, but I know what pressures work for me and as long as I use my gauge it's all good.

If you do check them, please report back what you found as I'd be interested how accurate they are.

Interesting. I'll ask around at work and see if we have any lab grade pressure measurement stuff. I'll let you know what I find out.

this makes my pants tight. :likecat::likecat:

It would have been nice to remote mount the reservoirs up in the cowl area at the base of the windscreen but they are too tall to fit. I might look around for a 3-way reservoir that will fit up top.

I used flexible lines to connect the masters to my distribution block, its just easier to get everything to fit right. I don't have enough 1/8" NPT to 10mm fittings to hook up all three lines and I can't find anything locally to join metric and imperial brake fittings so I'll get the lines modified at a brake place. In the longer term I would like to run flexible lines so I can route the LHD brake line away from the headers. For now some heat wrap will do it.

https://www.miataturbo.net/attachmen...ine=1448331481

https://www.miataturbo.net/attachmen...ine=1448331481

Update:

I've finished the installation with everything hooked up and working. I had some major dramas bleeding the system. To bleed a balance bar setup you really need 3 people or a pressure bleeder. Even still a bubble of air must have been trapped in one of the front calipers and it took several goes and lots of mess to get it bleed properly.

I've taken the car for a drive and the pedal feel is awesome. Very firm pedal, not much movement but a nice linear feel to the brakes. I can actually feel the feedback through the pedal for the first time. With the bias bar wound full lock in either direction I can easily lock the front or rear brakes. The bias bar I've used is designed to allow only a certain amount of angle so that if I loose a circuit the other circuit is still effective. This is what made the bleeding difficult.

I'm running the car this weekend at the local race track so I'll report back on how I found the brakes at race pace.

Total materials required:
5/8" (0.625") master for front
0.7" master for rear - may be different based on caliper and rotor size
Balance bar (2.5 - 3")
Balance bar remote adjuster
Ally block off plate (make it yourself from offcuts)
28mm hole saw for drilling into firewall and pedal box
Welding some bracing on the pedal box
Modify the existing lines to fit to the new masters.

Approx costs: $300-450 USD depending on masters and fittings etc.

There is also an option for doing just a booster delete. This would involve moving the master upwards 30mm to mount to the existing holes and drilling a new hole 25mm higher in the pedal for the clevis. The hole in the firewall would need to be raised with a block off plate covering the rest, and the pedal box would require some minor mods to fit. It would certainly be cheaper however I'm unsure how much it would increase the pedal travel due to the higher pedal ratio. That would depend on how effectively you can bleed your brakes and the pads you run.

and then....

The brakes work great on track. Nice even and progressive feel. It took me a while to get used to the extra pedal force required on the initial application but after a few laps I was used to it.

I think I would prefer slightly more pedal ratio as the force to stop on race rubber is fairly high. I'll try it at a few more events first but maybe I'll move the pivot to 5:1 instead of 4:1.

We see 5.75:1 as a common pedal ratio. You'll notice that immediately.

Just a quick update on this... I'm still running the stock pedal ratio and I'm used to it now, in fact I think the pedal feel is awesome. It works fine on 245 Hoosiers with some aero and I still have spare brake capability if I want to lock them so I don't see an issue on a high downforce big grip setip. I have pulled the dash and checked all the steelwork to make sure it's all holding up to the higher pedal forces and all the welds looks good. It was one of my bigger concerns of modifying the stock peddle box.

I've just upgraded to a hydraulic handbrake and Wilwood rear calipers but I have yet to run the car with them on yet. I'm still waiting for new pads to rock up. The Wilwoods move the brake bias to the rear a bit so I'm going to adjust the sizing of the masters to balance it out.

The best thing about my brake setup is I can jump in the car and hit the brakes on that first corner with cold pads, tyres etc and I know what the car will do. With the booster, I used to stress about that first corner and take it overly easy so that I could get a gauge on how much the brakes would bite but now I don't even think about it. Some of the street events I've been running are extremely unforgiving with big concrete barriers on all corners. One lockup and you're in the wall so having predictable brakes helps.

One thing people never consider is adding a vacuum pump to retain the brake booster with larger cams. When you drop in vacuum due to the cams, if you added a vacuum pump either set to PWM through a stand alone or just full time on with key on.

Vacuum pumps can be had for super cheap from many cars in the junk yard. New Chevy trucks also have a belt driven vacuum pump that could easily be mounted and setup for a miata engine.

I like your set up though and I am glad it is working for you. I'll have to weigh all my options when it comes time for me to upgrade my brakes before I do a setup like yours.

The easiest solution is to run a 2L storage tank in between the pcv and booster. It would have enough volume to buffer the dips and surges in vacuum.

I must admit it was a great feeling to toss that rusty booster in the bin though. That's almost enough reason in itself.

I was just thinking about this just this morning.

I just installed some more aggressive brake pads and now it is very easy to lock up and the pedal feel doesn't really give any hint that it's about to happen. I am wondering if this will help that.

Also experienced some inconsistent pedal feel at my last event before the brake upgrade and wondering if that booster check valve is failing.

Ideally for motorsport you don't want pads with bite. A lot of the so called racer pads have very high bite which feels great to a new driver as it gives some immediate feedback to hitting that pedal. You actually want a nice smooth application of friction when hitting that pedal so you are shocking the tyre as little as possible. OGracing has an excellent write up in his brakes thread.

You can try installing a volume in the brake booster vacuum line but really that will only help if you have real big cams or ITB's. You can make a buffer volume cheaply by using a short length of PVC plumbing pipe, glue some end caps on either side and tap in some hose nipples. But really for you the first port of call should be to check the PCV valve. You can buy some cheap aluminium ball bearing valves that you just put into the hose rather than using the stock PCV. Second is to make sure the booster isn't faulty. Mine was 25 years old and rusty which might have been half my problems.

That seems likely to me. AIUI, boosters don't let air in (or "release vacuum") until you let off the pedal, so in theory a properly functioning booster with a working one-way valve in the booster line shouldn't really care if the manifold vacuum is wavering during a single braking event.

--Ian

Yeah... My symptoms were that I could feel the brake pedal moving as I blipped the throttle. So I could feel the gain and loss of assistance as I went down through the gears under brakes. I also found the very first application of the brake would give me more assist and then rapid brake applications immediately after would reduce in effectiveness. It was fairly painful... so I got rid of the problem altogether.

Brilliant, you've come back to update just in time! :D:D:D
I've just got basically the same brake booster delete,
Mazda MX5 Brake Bias Servo Replacement Pedal Box Kit ? Hydraulic Dual Cylinder [KIT A] - Pedal Boxes, Bias / Servo replacement, Mazda, MX5 - www.compbrake.com

stock pivot has a delicious firm brake pedal. on stock 93 1.8 calipers, rotors, though, so weak as piss :D
put a new hole at 60mm from pedal pivot, bit more pedal travel, but still far to hard to get any sort of hard braking.
Threshold braking feels absolutely great, so communicative, but its almost a 1 rep max for little me haha.

will be putting on braided lines next week, so should firm up a bit hopefully. My main mission goal here is to have a very solid pedal, maybe 1- 1.5" of travel to full lockup, but i can compromise :(

What calipers n rotors are ya running?

Cheers :D

If you change pedal ratio you ideally need to firm up everything in the brake system so that you don't get a spongy pedal. You need braided lines, low compressible pads and to bleed the system well. I run Ferodo DS Uno pads which have a low compressibility.

Up front I'm running Wilwood 11.75" rotors with Radial Mount Dynapros (Mini Cooper S kit)
On the rear I'm running Wilwood 11.44" solid rotors with stock NA6 caliper (to be replaced with Dynalite rotors once I make up the second offset bracket)

Thanks for the reply :)
​​​​​​May hold off on the braided lines for a moment, seen some kits which have them included.
Was checking out the fedoros yesterday, have you tried the ds2500? Wondering if the the Uno's won't be very effective till their warmed up? Car will be being tracked, but some fast roads or popping over to mates house... Don't want to have to curb-stomp it.

Sorry should have asked before; 15" wheels? I hear some fit for 11.75, some don't.

Thanks again

I've run DS3000s and they are great on a race track but you need to get them hot. First corner and they will either lock or not stop. I also chewed through rotors and pads in 6 events.

DSUnos stop well from cold and don't change much as they heat up. I've now done 30 events on them with the same rotors and they still have some left. I had to cut them by hand to fit the rear stick calipers though.

My brakes just fit into Kosei 15s and 949 15s fine.

Hi Madjak,

i sent you a PM

Thanks for sharing this mod!

I'm also running ITBs and had been thinking about dual master setups, but I wanted to copy how you retained OEM pedal geometry while I test it out.

I wasn't happy with how much the pedal mount had to be cut, so I built my own mount and changed the pedal ratio to 5.5:1, while leaving the position and actual pedal stock. With a brace that runs to the underdash mount and some gas pedal surgery, it's now stiffer than stock. It's 1/8" plate, since I never want to worry about braking my breaks :)

https://cimg0.ibsrv.net/gimg/www.mia...1c96153d75.jpg
https://cimg1.ibsrv.net/gimg/www.mia...0224c4dab3.jpg

I see someone found the dimple die set.

Master Cylinder Wear!
 

I can't tell from the OP post whether there is a "pivot" on the pedal arm attachment, but because the pedal apply point actually swings through an arc during your brake apply you really need to allow the rod pushing on your master cylinder to move a bit up and down.

If you dont do this then over time the side loads of a "stiff" rod (get it?) will cause your pistons and seals to mash against the casting of the master cylinder and eventually they will wear and you will not generate enough brake pressure. That's not a great situation to be in so I wanted to put that info out there.

Madjak's setup has the exact same set of components and degrees of freedom as 99% of dual master pedals in race cars: a spherical bearing bias bar in a tube with clevises on each end.

There is no need to add any extra pivots, but it is important to play with pushrod lengths to make sure the geometry is as good as possible.

Reviving a Thread for a Good Cause
 

Reviving this thread because I recently went through this, and have some feedback. First things first, however - massive thank you to Madjak! Without your thread I wouldn't have a general guide to follow and would be blind the entire way.

Next, I'd like to update the BOM with the exact parts I used:
Wilwood 340-1757 Balance Bar Assembly
Wilwood 340-4990 Remote Brake Bias Adjuster Cable
Wilwood 260-6087 .625" Bore Compact Master Cylinder
Wilwood 260-6088 .700" Bore Compact Master Cylinder
uxcell 38mm Carbide Hole Cutter, TCT Hole Saws for 5mm Stainless Steel Sheet Metal

Notice the holesaw is 38mm - you could get away with 36mm, but the 28mm not helpful at all.

Some pics (take special note to the horrible welds):
Attachment 232534
Attachment 232535
Attachment 232536

dude, fucking thank you!!!
thanks for posting all the parts!!

Glad I could help! One thing to note, you may end up with different cylinder bore sizes depending on your caliper choice and piston sizing. Feel free to report back with feedback!

so i'm about to purchase this. i see you mentioned a remote bias adjuster but did not list which adjuster you went with.
what did you end up installing?

Looks like he's been banned for being a former vendor. Typical IB things.

The 340-1757 balance bar is the adjuster, and the 340-4990 remote adjuster cable attaches directly to it.

Bias adjustment is done by rotating the threaded balance bar which changes the pivot point and changes how the force is divided between the front and rear masters. You don't need a hydraulic bias adjuster like what normal miatas run.

so i did my version, although i felt like the balance bar was too lose, so i 3d printer a 7mm spacer, still allows it to move around but it doens't flop all over the place.
also, i may have sized my front cylinder wrong.....
i also need ideas on a remote reservoir to feed the dual setup.



https://i.ibb.co/dfpqvgZ/0-D870-CAD-...59-1-105-c.jpg
https://i.ibb.co/XygrdyK/544-C77-D1-...DD-1-105-c.jpg
https://i.ibb.co/9hdwjxH/5375-E677-4...55-1-105-c.jpg


https://i.ibb.co/zsdfLrs/6-F4-FA02-C...DC9928-F22.jpg

The balance bar is supposed to have some wiggle to it. Wilwood recommends using 2 quarters to set the gap (1/8”). They have a good video on how to set it up

keeping this thread alive, this is how far ive gone.
i did a plate in aluminum to close the ugly hole, powder-coated wrinkle black (its what was on the gun at the time)

now, i am replacing all the ugly hardline with stainless braided lines for a cleaner look.
i may hide them inside the firewall.
https://i.ibb.co/4dM8JS6/IMG-5141.jpg
https://i.ibb.co/0CDgTjc/IMG-5140.jpg
https://i.ibb.co/C9bL4qn/IMG-5139.jpg
https://i.ibb.co/P16YX4s/IMG-5137.jpg
upload image by url

looking good! I’d love to know what stainless brake lines you go with. I’ve been throwing that idea around myself and haven’t decided yet. Nice work getting the 323(?) clutch master to fit. I have one sitting in a box but haven’t attempted to make use of it

oh these are actually wilwood masters, all three of them.

the lines, im using some i purchased from amazon.
i figured out the fittings and all.

so, after the setup and bleding, i feel like the car doens't brake enough. i know it would will be hard to press, but i cna't even lock up the tires no matter how hard i step on the brakes.


can someone confirm this?

0.7 for the rear calipers
0.625 for the front...or do i have them backwards?

I've built a bias pedalbox for my '91 Eunos (Mx5) but wanted to keep a sensible pedal feel, this I did by altering the pedal ratio:loser:

standard Mazda pedal ratio is to suit a servo-assisted system so doesnt lend itself for 'keep-fit' braking!

this was done by cutting the pedal and hortening it to achieve the desired ratio and repositioning the pivot-point in the pedalbox to suit...
there was aditional work as I wanted to recreate the origonal pedal-pad 'swing' and allow the ballancebar to 'swing' in as gentle an arc as possible so the cylinder pushrods didn't 'bind' when entering the cylinder...

I cannot remember the measurements and dimensions - they are written somewhere but....




some details in my M5's thread...
https://mighty5s.com/post/45038/thread

Attachment 232539
the evolution of pedals (top standard)

Attachment 232540
test-assembly in the 'dummy' bulkhead (cut from a scrap bodyshell)

Attachment 232541
how the cylinders are mounted.

.625" front
.7" rear

Attachment 232542
another view, can see the plumbing, I've used self-assembled braided hose and running the front passanger as well as the rear in through the bulkhead with the passanger side re emerging above the innerwing to run to the wheelarch.

^^work in progress so as yet untested:inout:

Rich.

hmm, wow. thats a lot of work.
imma have to build a pedal fro scratch!
fuck me...

ok, i'll give that a try.

so i guess the piston sizes are correct, you didn't make meniton on what size goes to back and rear.

was a bit of work but worthwhile;)

I strted by drawing the pedal's 'swing' on paper, fixed the pivot and pencil on the footpad. then with my desired ratio drew the diferent swing - I 'doglegged' the pedal to correct the swing and redrilled the pivot-point lower & foreward on the pedalbox to account for this (the origonal pivot hole position is visable on the strengthening sideplate I welded onto the modified pedalbox)

Attachment 232537

sorta:rofl:

Attachment 232538
:bigtu:

Rich.