THSCC Forums

Jim,

I don't know what your braking problem is, but since you are in Mod, can't you do something with master cylinder diameters or caliper piston sizes or even an adjustable proportioning valve? In regard to pads: I've run Hawk HPS and HP+ pads on my Formula Ford. The HPS pads are great (no dust and very easy to modulate). The HP+ pads had a higher coefficient of friction (less pedal pressure needed) and I actually didn't like them since on my very lightweight car the front brakes locked up too easily. However, they may be what you need to get more rear braking. The do dust a lot, however.

Dick

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Dick Rasmussen

FS 50 2018 Mustang GT

Thanks very much for the input Dick.

I’m think I’m just fighting the fairly typical early Miata braking issues. The stock proportioning valve tends to be heavily biased towards the front and on top of that, the early Miatas tend to lock up the right front brake before anything else. With a stiff suspension, I think the situation is only compounded. I thought my braking performance was suffering due to the previous owner’s choice of rotors and pads but after putting a good set on the car a few weeks ago, I realized there are other issues. I believe the right-front lockup deal is mostly a weight bias issue and nobody I’ve seen has come up with a satisfactory solution.

I did recently service all my calipers (which are stock) and they seemed to be in great shape. I replaced all the seals and slider pins so I’m pretty sure there isn’t anything left to gain in performance there. The car does stop decently but just not as hard as I would like. Compared to ABS equipped Miatas I’ve ridden in, my braking performance definitely seems weak. Some of that may be an illusion since I wasn’t driving and the other Miatas had stock suspensions which caused a lot more nose dive. Scott Johnson recently drove the car and noted that the brakes seemed a little weak but I guess it could be hard to judge since it accelerates decently pushing braking points further back than most cars.

I’ve heard of a few people putting a Wilwood adjustable valve in place of the stock one but they wind up running it at full bias towards the rear and still don’t get enough rear braking. One relatively cheap and easy solution people have found is to use the stock proportioning valve from the ABS equipped Miatas as they tend to be a little bit more biased towards the rear. I’m hoping that I can find one from a junkyard over the winter. How this compares with the Wilwood solution, I have no idea. Other than being much easier to install… I may wind up trying both at some point.

If that doesn’t help, I will probably try the pad biasing as well. I’ve heard good things about the Hawk pads but couldn’t remember which pad was “stickier” than the other. If you’ve ever seen my car, you’d know I’m not too worried about brake dust. I also have a set of big rear rotors from the new Miatas I could try as a possible solution but it will limit my wheel choice (no 13” ones, that’s for sure).

Unfortunately, most of my information was gleaned from various message boards. While I’ve always been careful to “know the source”, you never know what other factors are at work. That’s another reason I’d like to attend some bigger events next year-- hopefully I can meet some other fellow Miata drivers that are facing the same issues and chat with them.

Jim

Jim,

I used to have a similar front/rear problem with my Datsun 260Z. In Stock trim the high ride height caused more weight transfer to the front. Combine this with the soft suspension allowing the rear wheels to go to lots of positive camber and I would get early rear wheel lock up, especially when trying to trail brake. I went to "softer/grippier" front pads and got more braking out of the fronts before the rears locked up. When I lowered/stiffened the car for street prepared, I went back to the harder fronts. Be careful with mixing compounds. If the rears are heat sensitive by being a higher performance pad, you may end up with too much rear brake in a street/traffic situation after driving awhile. As I recall, however, the Hawk HPS's and the HP+'s didn't seem to change coefficients as they got warmer . . . but how hot could they get on a formula ford in an autocross. A funny story from my 260Z days: I tried one brake compound (a "street" compound) that was so sensitive to pad temp that the car would pull after a few easy stops to the side with the tighter wheel bearings due to slightly more pad drag. You better believe I spent a lot of time trying to figure that out!

In regard to your right front brake lockup have you tried weight jacking (assuming there is no sway bar or other preload)? You might check corner weights (with driver) to see if the right front is significantly lighter than the left front. If so put some sort of shim (or crank up the spring perch) in either or both the right front or left rear. This can compensate for too much left side weight. Also, what are the camber angles? Even if they are the same, the heavier loaded side may be less sensitive. Finally, make sure the lock up isn't driver or course induced. If you are turning even slightly to the right, you might be unloading the right front.

Dick

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Dick Rasmussen

FS 50 2018 Mustang GT