Won't stop over 110 mph!
 

I have finally sorted out a 1995 FMII turbo Miata that I drove at Road Atlanta this weekend. The car is seriously fast and handles great but any attempt to stop at speeds over 110 mph results in a firm pedal but no stop! I'm running Carbotech pads which worked great before the car was turbocharged.

Before I dump a bunch of cash on a big brake kits do any of you have some suggestions.

Thanks

George S.

Um, WAT?

Did you drive it to the track and did it stop on the way home? What Carbotech pads are you using now? ABS? Bone stock? Prop valve? What fluid are you using? Thermal shielding on the master cylinder and brake line? Heat shield for the turbo? GIVE MORE DATAS!

I'm guessing you cooked the hell out of your master cylinder and brake lines with all the fresh heat the downpipe is dumping into the engine compartment.

It stops fine at any speed under 110 mph, street or track.

Carbotech XP10 Front Brake Pads and Carbotech XP8 Rear Brake Pads.

No ABS.

SS brake lines, stock rotors and calipers.

No proportioning valve (stock).

ATE Super Blue Racing Brake Fluid.

Heat shield on turbo and air intake only.

My diagnosis is the brake pads and rotors are over heating.

Firm pedal is either overheated pads or positive pressure in the brake booster. If you're on XP8/10/12s, make sure you still have a working check valve in the hose from the brake booster to the intake manifold (the OEM hose has one, if you didn't change it). If you're on 1521s, you need a pad upgrade.

To be honest, if you continue to do track days with a turbo system, you need a Wilwood-based BBK. Stock brakes are not adequate, regardless of pads or ducting.

I thought that a big brake kit would be needed. I don't have any ducting and still have the back plates in place but if I have to spend another $450 for new Carbotech pads and rotors I guess I should just bite the bullet and install ducting to a big brake kit.

The Version 4 BBK offered by Good-Win Racing looks real solid. It appears to offer more features than what Flyin Miata offers at a lower price.

Any thoughts here.

I'm biased, but if you can fit it under your wheels, there's no better option than my 11.75" kit. Low rotor costs and excellent pedal feel. Combine it with OEM Sport rear brakes.

Trackspeed Engineering 11.75" BBK

I don't track, but I have the TSE BBK and sport rears and it's the most amazing pedal feel in the world. Absolutely glorious.

In for replacing check valve. I'm guessing the sustained boost getting up to 110 is getting past a leaky valve.

Great call on the potential leaking check valve. Braking hard after a short straight I would get a hard pedal with little braking force and then suddenly a lock up. I guess the lock up was occurring after the master cylinder was finally seeing some vacuum from the manifold off boost.

I'll track down a replacement check valve and spring for some big brakes.

Thanks folks.

I can say that, if budget is not a major hindrance, the full TSE BBPK* (Big Boy Pants Kit) is pretty stellar. I finally got to run mine recently and the pedal feel, consistency, and stopping power are silly.

Full disclosure: I have never driven another Miata with another BBK, so I can't comment on relative performance.


* TSE 11.75" front brake kit, TSE ducting, M-Tuned rear adaptors, Sport rear rotors, Hawk DTC-60 pads

I'd put Wilwoods in the rear as well, Flyin' Miata has a kit that would go well with the TSE front setup.

I just got through installing the 11" front from 949 and the 10" rear from FM, but my car will always remain NA, and the lowest weight was the priority.

I'm running something similar to the 949 Wilwood 11" kit w/TSE ducting and non-sport rears and non sport master/booster/prop. So far, its all kinds of win.

It's been said many times: 11.75" TSE Kit w/prop valve + M-Tuned/Sport Rear Rotor + Sport booster & Master + ducts = bestest brakes.

I've got the M-Tuned brackets and sport booster/master in the garage should I need to upgrade beyond my current setup.

^If you're getting serious, I'd go with Wilwoods in the rear too. This is what I put on the rear, but with Carbotechs.

Flyin' Miata : Chassis : Big brake kits : Flyin` Miata four piston rear brake upgrade - track

TSE was supposed to have something for the rears awhile ago, but I couldn't wait any longer.

Quite honestly, the FM Wilwood rear seems like overkill, plus expensive. There are a lot of guys running the M-Tuned/Sport rears without issue so I tend to stick with and recommend what has been proven to work. I mean, maybe it'll let you get away with changing pads/rotors once a year or something for the average HPDE enthusiast but ROI on that seems excessive. Seems to me that $500 would be better spent on time behind the wheel.

Hell, maybe I'm wrong and its the best thing evar. FM does tend to put out a solid product so I wouldn't expect them to slack on something like this. :dunno:

The FM rears seem best suited for guys with dual purpose cars that want quick pad changes at the track and a working parking brake Monday through Friday. Of course Wilwood peeking out behind all 4 corners makes some good bling for folks that can't let their laptimes do the talking.

I will own up to being slow. I figured if I was taking +2 on brakes, might as well go as light as possible.

Excellent point. If you are taking points for brakes, you might as well do anything/everything allowed since most CCRs are '+x for non-OEM brakes'. The weight savings is significant.

There is a non-parking brake version of the FM rears. $100 cheaper too.

Yeah but then you have to come up with your own solution for a parking brake, like the JR dragster calipers and connecting another hydro master to the stock ebrake cable, or using some mechanical caliper. Too much work, press the easy button. Unless your car doesnt go on the street and isnt required by the rules to have a redundant braking system (I don't see why kind of psychopathic, uninsurable rules would let you do that).

I went for the non-parking brake route.

I think Keith mentioned the parking brake is basically there for rules compliance (SCCA) and will hold the car on a slight incline.

If you actually use the car on the street, the Wilwoods don't make much sense. The weight savings are there but the lack of an e-brake function is a big deal for a street car. Use Sport rears or 1.8 calipers on an adapter bracket. For a race car that's looking for every pound, pull the e-brake cables and switch to Wilwoods. There's a group of guys in the middle who autocross and need an e-brake for legality, and for those guys, the e-brake Wilwoods make sense. I won't lose sleep over not selling those kits, though. Our goal was a niche kit that was the lightest possible rear brake setup (hence our decision to do 1.8 rotors and not Sport rotors), and e-brake functionality was never in the cards.

Still working on ours (sorry for not returning those emails, Buddy). Other projects have gotten in the way but it's still happening. Our proprietary 2-piece rotors will shave another ~1.5lbs total, reduce heat transfer to the hub, and work with FM's kit (for those of you who couldn't wait).

Pretty sure NASA PT/TT rules don't require parking brakes (under no-points modifications: http://www.nasaproracing.com/rules/time_trial_rules.pdf) . I know spec e30s don't either. NASA autocross X class allows parking brake removal, etc.

Not too far fetched not to have an e-brake on a track only car.

Weird. Its one of those rules the insurance companies would require, even if it would be a tad silly to think you could save your ass with just the e-brake on a track in the event of a primary brake failure.

The most direct comparision we have to the "Version 4" BBK from Goodwin is our Stage 1 kit with the proportioning valve deleted. Of course, I think you should run the prop valve as that'll make a bigger difference to your braking than anything else. We use the Wilwood Spec 37 rotors in front, which I think are as good as anything else on the market.

The FM kit with a deleted prop valve would be $945, which is $650 less than the Goodwin kit. If you want the prop valve, it's $995. So I'm not seeing the "lower price". For the price of the Goodwin kit, I can hook you up with rear Wilwoods and 6 piston front Dynapros.

The Wilwood rears add more bite in the back with a larger piston area and have a larger pad. They're a good upgrade. The stiff calipers help contribute to a really nice pedal feel, and the bigger pistons mean you can actually get some rear bias.

On my track car, I find the parking brake most useful when I'm loading on the trailer. I'd never expect a parking brake to be helpful on the track in the case of a failure. Ever tried to stop a car at speed using the parking brake? It's entertaining and educational and ineffective.

Back to the original question - as noted, a firm pedal but no stop is usually pads. I'm assuming you only hit 110 mph at one point on this track, so it could be a matter of cooking everything in the turns before that point. It might be worth doing a straight line test with cool brakes, and to check the booster you could also lift off a little bit before you hit the brakes to ensure you've got vacuum. As Savington noted, make sure that check valve is in the line to the booster.

No brakes after long sustained on boost straightaway is either overheated pads or your check valve is leaking and you are getting boost instead of vacuum in your power brake booster.

One of the reasons I would like to design a system without a vacuum booster. More consistent pedal effort in not relying on a constant vacuum charge in the booster.

.

You're giving me bad thoughts about making a bracket and adapter to run 2 wilwood masters and a balance bar in the stock location rather than putting the new booster and master setup I have. Dammit, I already know what the setup will look like, and how much more awesome it will be. Dammit.

I would fix the problem 1st before throwing $$ at it. spec miatas hit 119mph at Road america & they are heavy and use stock brakes. FP / EP miatas are lighter / faster & use stock brakes. The FP miatas are over 130 mph and they use the dinky 1.6 brakes.

racers may bitch about them, but I've never heard about a complete failure under race conditions (and I'm talking about NA cars with less than 200 hp). It would be a safety issue and then no one would run them. Big power, then yeah beef it up

I suspect your pads are glazed. I had a similar situation on a PTB MSM (on stock sport brakes) - turns out the customer bedded them in during a rain race and then wondered why the car wouldn't stop. Pad surface was mirror finish.

Kendall

Most of the well preped EP/FP miatas I have seen don't use a booster. Better more consistant brake feel. They also dont need to scrub near as much speed to enter a turn compared to the small amount faster they are top speed than your typical HPDE car so caliper and rotor size dosn't need to be increased. The method they use to go faster is to not use as much brake rather than just add more power for the straight.

just trying to make a point (the stock brakes are not shit & you dont need to spend thousands of dollars or you die) - and I'm sure the FP guys would go to bigger brakes if they could, but that's the class equalizer. OP needs to fix his brakes before chucking $$ at it (especially if its in the check valve / MC area). Still there are cars (2400# spec miatas on DOT tires with no brake cooling) that make the stock brakes work.

KJ

The issue isn't so much about weight, as it is about speed. 110mph isn't significant in that its not beyond a stock miata. In this case, I agree the OP needs to sort out why he is losing brakes at a specific speed (which it seems the suggestion for the check value is pretty close), but I don't think its a bad idea for him to upgrade his brakes. an FMII turbo car is a whole other beast compared to a spec miata or even a mazdaspeed.

The only thing I think you are missing is that weight is not as big a factor in braking as speed. Maybe you are not, but you seem very focused on the heavier miatas as justification that the stock brakes work (and work well), but that rule doesn't apply the same way when you are running 100+hp more. Just keep in mind that velocity is squared in the kinetic energy equation, while weight is not.

100+hp over stock, and 2300-2500lbs in street trim.

I aint arguing, just trying to help. The MSM I built was at the very top of the PTB points system & couldn't take the points for brakes - it was my job to make them work. sport brakes, ducted, with a manual prop valve worked excellent on 2350# car with almost 300 ft-lb of torque (unless the pads are glazed).

It being nasa, we tuned it with an effective torque curve to be under the max HP limit for the power / weight - but have a shit ton of torque everywhere else (and it was very much 100+ HP over stock). Maps looked crazy maximizing the area under the curve. Customer spent tens of thousand of dollars to make the car fit in the rules.

Anyway, blah blah thread jack. I'm not against big brake kits, but a car going 110 mph probably doesn't need them.

<-- Has a massive BBK on a car with 100 WHP.

https://www.miataturbo.net/attachmen...ine=1383156658

OP, fix the acute problem with your current system and then make a new thread discussing BBK options. [/thread]

:2cents:

Fixed.

:bowrofl:














Me too.

Wilwoods on all 4 corners.