Brake booster delete - mounting plate

manga_blue · Postby **manga_blue** » Mon Nov 23, 2015 1:59 pm

This looks really good! A word of caution though ... I had a Fiat 124 unboosted. Over time the higher forces from the pedal cracked the firewall, to the point where I busted out a whole slab of firewall and drove the brake and clutch masters into the engine bay. Fortunately that happened from clutch force in a fast 2-3 shift, not under braking.

I know the MX5 is no Fiat but I'd check the integrity of the firewall in that area and be conservative about any mods you make to it.

madjak · Postby **madjak** » Mon Nov 23, 2015 3:54 pm

manga_blue wrote:This looks really good! A word of caution though ... I had a Fiat 124 unboosted. Over time the higher forces from the pedal cracked the firewall, to the point where I busted out a whole slab of firewall and drove the brake and clutch masters into the engine bay. Fortunately that happened from clutch force in a fast 2-3 shift, not under braking.

I know the MX5 is no Fiat but I'd check the integrity of the firewall in that area and be conservative about any mods you make to it.

Thanks for the advice... As with all my brake mods, I'll be checking these frequently for signs of fatigue. Also, before I head out on the track I'll be applying as much force as I can to the pedal to see how much everything deflects. The last thing I want is a brake failure on track!

I have reinforced the pedal box itself as well as pedal pivot for the pedal but nothing on the firewall yet. I will probably make up a brace that either goes across from the base of the masters to the strut or triangulate down to the chassis rail to stop the firewall flex. I could also brace it back to my under dash roll cage bar. I will be putting lots more force on the pedal which applies directly into the firewall. It isn't the thickest material there in the first place and it already flexes with the standard setup.

There is really only one way to find out!

manga_blue · Postby **manga_blue** » Mon Nov 23, 2015 4:09 pm

I'd say that taking all the flex out would be a very good move. Flex is what did the Fiat in.

Without boost you could be putting 10 to 15 Kgs force on the pedal. Depending on your stroke ratio that translates to 40 to 90 Kgs on the firewall. It's probably only 10 max when it's boosted.

3gress · Postby **3gress** » Mon Nov 23, 2015 4:16 pm

While you're at it, brace the throttle bracket against the firewall also. I noticed you fixed the crack that was starting in the metal, similar to where mine tore.
I throw a pic up for you to see how i had a little stand-off welded on .

madjak · Postby **madjak** » Mon Nov 23, 2015 4:20 pm

The pedal ratio is currently the same as stock at 4:1, however I will be putting a lot more force on it to stop the car without the booster. Nothing broke / bent when I disconnected the booster and I think I was putting a lot more force than 10-15kg... more like 60-70kg I think! It's hard to tell how much load you're applying when you're hurtling towards a corner at 180kph and you stand on it. Not only does the pedal get your leg pushing on it, but all your body weight transfers into it as well.

Fatigue will be the issue if there is flex. I might even run the next event with a GoPro in the engine bay to see how much everything is moving around.

Actually thinking about it... May as well just get it braced now. No point mucking around given it helps stock brakes and if anything will help this more.

madjak · Postby **madjak** » Mon Nov 23, 2015 4:23 pm

3gress wrote:While you're at it, brace the throttle bracket against the firewall also. I noticed you fixed the crack that was starting in the metal, similar to where mine tore.
I throw a pic up for you to see how i had a little stand-off welded on .

Nice spotting and guess what... I've already done just that, though mine is an offcut of 20x20 SHS. I figured I was just heavy on the pedal but maybe its a common problem.

madjak · Postby **madjak** » Tue Nov 24, 2015 1:32 am

http://i292.photobucket.com/albums/mm7/Madjak/MX5/20151123_214017_zps9cwyygmt.jpg

http://i292.photobucket.com/albums/mm7/Madjak/MX5/20151123_214027_zpsifrslx1g.jpg

I don't have enough 1/8" npt to m10 fittings to connect it all up. I'm going to get the existing front brake lines modified to -3an hard fittings. Nearly there now.

madjak · Postby **madjak** » Mon Nov 30, 2015 4:48 pm

My brake system is now all installed. I had massive problems bleeding the system, trying manual bleeding, pressure bleeding, priming the masters... all the time with brake fluid going everywhere! After hours of mucking around I debugged the pressure to find out there was an air bubble in one of the front calipers. Once I got that out, everything worked fine.

The balance bar I chose has stoppers so that you can't get too greater angle on the bar itself. This is so that if you lose a circuit you still get full brakes on the other. This stop however makes it extremely hard to bleed air bubbles out of one circuit as you don't get full pedal travel on that line. Also the fluid moving through the system is half as much so the velocity of the bleed is slower. This makes pulling out air bubbles really tough. So, if you ever have to bleed balance bar brakes, check each corner first and step through the bleed process. It helps if you have 3 people.

This is it almost finished. The front brakes lines weren't yet installed... ahhh the room!

The pedal feels awesome! It feels nice and solid with only a little pedal movement. Tapping the brakes gives me the expected brake response, without the massive hit from the booster. I'm hitting 1000PSI on both the front and rear systems with a concerted push on the pedal. From my past logging I know around 700-800 is needed when on the track with hot tires and pads.

I'm a little concerned still that there is too much rear bias with the masters I have chosen. 5/8th front, 0.7" rear. I run an offset plate on the rear caliper so it's moved out to fit the 11.44" wilwood rotors. This probably gives the rear of my car more bias than others here. It's hard to tell on the street bit I think I'm still locking the rears first. I'll take it for another drive tonight and try and get the pads up to temp.

madjak · Postby **madjak** » Tue Dec 01, 2015 1:46 pm

I took the car for a longer drive last night... the brakes work great. With the bias dialed all the way front I can lock the fronts easily, and the opposite locks the rears. Pedal effort isn't as hard as I was expecting given I'm keeping the 4:1 ratio especially once the pads have a little bit of temp and the rust was worn off the rotors.

Does anyone want to try the booster delete and keep the existing master? I will get a bracket waterjet cut and sent across. My only concerns with this option is that there may be too much pedal movement. It will really only suit cars with very solid pads that don't have a lot of give. I would also suggest that this isn't done on a road vehicle.

Installation will be:
1) unbolt pedal box from under the dash, remove brake booster
2) remove some metal at the top of the pedal box to clear master dust boot, drill a hole in the pedal at the required point. (25mm higher than existing hole)
3) remove some metal from the firewall to clear the master (half circle)
4) install block-off plate, install existing master (will need to hand bend the brake lines a little)
5) measure and modify an existing bolt to be the new push rod and install
6) bolt it all up and test.

gslender · Postby **gslender** » Wed Dec 02, 2015 10:09 am

madjak wrote:Does anyone want to try the booster delete and keep the existing master? I will get a bracket waterjet cut and sent across. My only concerns with this option is that there may be too much pedal movement. It will really only suit cars with very solid pads that don't have a lot of give. I would also suggest that this isn't done on a road vehicle.

Happy to give it a try. What do you need from me? Cash, beer, love ???

madjak · Postby **madjak** » Wed Dec 02, 2015 1:17 pm

I'll just add it to my next run of bits I get made... probably not until Jan though. Given it's just a blanking plate, I'll post it over to you and you can try it. The mods would be reversible if you didn't like the end outcome... the only thing is your firewall will need to be permanently modified to clear the master cylinder in the new location.

You could actually try it without the blanking plate and add it in later if it all works.

project.r.racing · Postby **project.r.racing** » Wed Dec 02, 2015 2:10 pm

Oh I could try this in another car of mine. The applications for motorkhana/autocross is great. The ability to control the rear pressure is awesome. No more handbrakies.

gslender · Postby **gslender** » Wed Dec 02, 2015 4:20 pm

madjak wrote:I'll just add it to my next run of bits I get made... probably not until Jan though. Given it's just a blanking plate, I'll post it over to you and you can try it. The mods would be reversible if you didn't like the end outcome... the only thing is your firewall will need to be permanently modified to clear the master cylinder in the new location.

You could actually try it without the blanking plate and add it in later if it all works.

Sounds fine to me... my brake setup looks like this right now... so it would be great to try this and if it works I'll enjoy the extra space too!