Should I be able to lock my brakes up? Miata content

 At our last autocross event, the finish line was at the end of an area where you can pick up a lot of speed. Many cars that day nearly blew the stop box, and everybody was really on the brakes, including me.

But throughout the day I noticed that I could not lock up my brakes. And I was really on them. I have gone through my braking system last year, currently have stock rotors that came with the car. Stoptech street performance pads, front and back. And fresh fluid. No leaks anywhere I can see. And I did swap out the rear calipers for rebuilt ones. The old ones were leaking. I’m only running 195/60r14 federal ss595’s. 

I have two thoughts: flex lines are flexin’ like hulk hogan. Or the pads just aren’t hot enough to lock yet. 

One abstract idea: these rotor came with the car, maybe they are at the minimum rotor thickness and the calipers can’t squeeze hard enough? 

Any help is appreciated. 1997 miata. Base. 

I am assuming no ABS.

Yes, you should be able to lock up at least the fronts. If street pads won't lock the wheels when cold, they're not street pads. On thin rotors, the piston will simply protrude further from the caliper. Go too thin and you'll eject the piston - that's when things get interesting.

Step 1: did you bed the new brake pads? It's amazing what a difference that makes.

Step 2: have you lubricated the slider pins on the front calipers?

It would've taken a mighty stomp to lock up my old RX-2.  Solid discs front, drums rear, no power assist.  Opposite end of the spectrum was the '76 Cutlass.  It would lock if you tapped the brakes a little too quickly.

Pretty easy for me to believe that the heat at the end of a run would be causing some fade.  Maybe a more aggressive pad?

Keith Tanner said:

I am assuming no ABS.

Yes, you should be able to lock up at least the fronts. If street pads won't lock the wheels when cold, they're not street pads. On thin rotors, the piston will simply protrude further from the caliper. Go too thin and you'll eject the piston - that's when things get interesting.

Step 1: did you bed the new brake pads? It's amazing what a difference that makes.

Step 2: have you lubricated the slider pins on the front calipers?

 

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These, and the rear equivalent.  No ABS. I lubed the slider pins.  And performed the break in procedure as stop tech says too. Even during the bed in process, I never once got them to lock up. Then again, I only do autocross and spirit of driving. So I never get these brakes hot enough to really cook them. I did not figured that I would have to, considering they are supposedly a street pad. 

 I specifically went with the stop tech because they were recommended on several forum searches as the autocross pad to have 

Oh, and thank you to whoever fixed my title grammatical error. Siri sucks

Getting them hot enough to cook them is the purpose of bedding - you need to get the pads hot and keep them hot so they can transfer a layer of material to the  rotors. If they're not smelly, it's not enough. You don't need to get street pads as hot as competition pads to bed them, but you do need to get them hot. You also don't want to lock the wheels while bedding as then you'll end up with a big chunk of material transfer and pulsating brakes.

I don't have direct experience with the Stoptechs, but any pad that cannot lock the tires from a cold stop cannot be called a street pad like I said. I think you've got something else going on.

In reply to Keith Tanner :

 How plausible is the flex line theory voiced earlier? 

Shouldn't be enough flex to stop you from locking up. That's a lot of flex.

Alright. It’s a nice hot day today. I’ll take her out to this abandoned road I know and try rebedding them. They’ve been on there for a year though, so it’s doubtful there is anything to transfer. If that doesn’t work I might go for a new master. The pedal feels great. Just won’t lock. 

As long as you have pad left, there is something to transfer. Cars that see a lot of really mellow street use will benefit from the occasional re-bed if they're asked to do performance work.

Sticky tires might overload the braking capacity.

In reply to iceracer :

Not sure if federal ss595 counts as “sticky”. Lol

While your out on that open road see if you can get the wheels to lock up.

If there is a gravel road near you try there or bring a few gallons of water to said abandoned road and pour water on the road. Try braking at about 10mph and see what's what.

Keith Tanner said:

Getting them hot enough to cook them is the purpose of bedding - you need to get the pads hot and keep them hot so they can transfer a layer of material to the  rotors. If they're not smelly, it's not enough. You don't need to get street pads as hot as competition pads to bed them, but you do need to get them hot. You also don't want to lock the wheels while bedding as then you'll end up with a big chunk of material transfer and pulsating brakes.

What is interesting about your post is that, I generally abide by the "brake and cool, brake and cool, and when you can taste the brake pad in the air, stop braking and just drive home normally" school of bedding.  And locking up the brakes is NEVER an issue.  I generally have to two-foot it in order to get the brakes hot enough to get niffy.

I don't have direct experience with the Stoptechs, but any pad that cannot lock the tires from a cold stop cannot be called a street pad like I said. I think you've got something else going on.

I have never had any car, ever, that could lock up the brakes (or engage the ABS) on smooth dry pavement.  Ever.  Not even teh R with the 330mm Brembos that lives on winter tires.  (And while its brake pads definitely do not work when it is near freezing and raining hard, they also don't tolerate heat very much either, I can get them to fade to uselessness in only three 80-40 whoadowns on country roads)

My current RX-7 was close, in that when autocrossing on BFG Sport Comps, braking deep into a corner I would have to trail brake slightly to prevent rear axle hop as the speed came down through 25mph or so.  I don't think that really counts.

iceracer said:

Sticky tires might overload the braking capacity.

I doubt it. I'm just running 1.8L brakes with the milder Hawk pads on 225 width Nexen N Fera SUR4Gs and it'll lock the fronts up. People flat-spotted the E36 M3 out of my 225 Rivals with Porterfield R4S pads too

You don't have to go fast to bed your brakes. all you need to do is start applying the brake and then apply throttle you can do this all at 15 miles an hour. when they stink stop. repeat as necessary. We used to bed the brakes on a Formula Vee and a GT-1 class car in the pits with this method.

Have you checked your brake booster or vacuum line and connections to it? Not getting full braking force can be due to power brake booster issues. 

I suppose that it's relevant to ask the question, how's it stop?

Your ultimate braking capacity is determined by the traction from your tires. All the braking system can do is fail to take advantage of it. It needs to strong enough to take you past that traction limit so you get right up to the edge. Not able to lock up the brakes means you do not have enough brake torque at your disposal and you’re leaving performance on the table. 

My bedding recommendations are based on the Stoptech white papers, ironically.

Doesn’t a failing booster give weird pedal feel? It’s been a while. 

Knurled. said:

I have never had any car, ever, that could lock up the brakes (or engage the ABS) on smooth dry pavement. 

The only way that's a true statement is if you were never trying to lock them up. Sure there's lots of cars that, if you ease in to the brakes and get the weight transferred, become very hard to lock up. But accelerate up to 45mph and then plant your foot to the floor on the brake pedal as if it was the throttle in a Miata and 99.9% of all cars with functional brake systems are going to lock up or hit abs at least for a moment.

I don’t think I’ve driven a car that couldn’t lock it’s brakes or trigger ABS on even the grippiest pavement. Even my AWD cars could, even with the drivetrain trying to prevent the front from locking. Newer cars are really easy, as many will apply more braking than requested if the brake pedal is applied quickly. I guess many drivers don’t brake hard enough during a panic stop, so today’s cars sense a panic stop and add extra braking. 

Keith Tanner said:

Doesn’t a failing booster give weird pedal feel? It’s been a while. 

Depends on how dead it is.  One that's all the way gone just feels like it takes a ton more force to stop the car. :)

I'm inclined to agree with Knurled here.  I think many (most?) cars without ABS were designed to have just enough brake torque to lock with a mighty stomp.  Factor in less than ideal conditions and a bit of fade, and you're not locking up unless you get two feet on the pedal and stand on it.

dps214 said:

Knurled. said:

I have never had any car, ever, that could lock up the brakes (or engage the ABS) on smooth dry pavement. 

The only way that's a true statement is if you were never trying to lock them up. Sure there's lots of cars that, if you ease in to the brakes and get the weight transferred, become very hard to lock up. But accelerate up to 45mph and then plant your foot to the floor on the brake pedal as if it was the throttle in a Miata and 99.9% of all cars with functional brake systems are going to lock up or hit abs at least for a moment.

That doesn't really count though, does it?  That's like complaining about having poor traction if you do a clutch dump, or poor handling if you just twist the steering wheel without setting the chassis first.  It's not the car's shortcomings, it's driver error.

My dad had a track day/autocross/daily ‘91 Miata.  The brakes felt terrible the few times I drove it.  We bled and bled and bled the brakes more times than I could count, with no improvement.  Somebody suggested taking the street/track pads out and replacing them with something softer, and it made a HUGE difference.