snofrandy None
June 7, 2010 12:09 p.m.

Hi, I'm looking to purchase a 1996 Miata and I was close to buying it, but I couldn't figure out what's wrong with the brakes.

When I try slamming the brakes to test it, it takes quite a bit of effort, like it doesn't have power. Same thing with regular braking. I have to extract a bit more effort to make the car stop.

Another problem is that it makes a thud thud thud sound that gradually gets slower as the car gets slower. This only happens when the brakes are hot already (not when I started driving the car).

From my personal knowledge, i don't think it's the master cylinder because the pedal doesn't go all the way down to the floor when i press it. Also, the brake pedal goes back up after pressing it.

This is the only think that's keeping me from buying the car. Basically, my own safety.

What's you guy's opinion on this?

Thank you!

psteav Reader
June 7, 2010 12:15 p.m.

Gonna take a wild guess and say you've got a bad power brake booster? Sometimes the vacuum diaphragm in those can rupture, which basically leaves you with manual brakes that are really high-effort. IIRC, it's because the master cylinder piston is sized differently for manual brakes as opposed to power.

As for the thud-thud-thud, does it sound like a warped rotor? Does the steering wheel shake when it does it? Don't know why that would only happen when hot, though.

WilberM3 Reader
June 7, 2010 12:23 p.m.

ive heard something like the thud sound on a hot set of brakes at the track if there's some pad material left on the rotor, you might see an outline on the rotor of the pad. just something to check out. if thats the case rotors ought to fix it.

does sound like a bad booster on the pedal effort.

snofrandy New Reader
June 7, 2010 12:25 p.m.

hi psteav. as for the thud-thud-, the wheel doesn't vibrate when I press on the brakes so i don't think the rotors are warped.

so one possible is brake booster. Is there a test I can do for that to know it's still working w/o me disassembling it first?

triumph5 New Reader
June 7, 2010 3:03 p.m.

In reply to snofrandy:

Do this only where you have lots of room. Disconnect and plug the vacuum line to the brake booster. If the braking is the same, you've got a shot booster. Did this on my Protege, and not only discovered the booster was shot but first I found there was a hole in the bake booster line. Replaced the line; no change. I replaced the booster, problem solved. Thudding? Did the car sit for any time? Possible flat spot on a tire. Sometimes by simply driving the car for a half hour, warming the tire, it'll go away. Otherwise the tire may simply be shot..

racerfink Reader
June 7, 2010 5:04 p.m.

I left the shim clips out the last time I replaced the brakes on my '90, and it makes quite a loud clicking noise when I apply the brakes. Wouldn't call it a thud though.

Also, on both my '90's, I've had a problem with the fixed caliper slide (not the bolt) on the right rear being bent. Wore pads out quickly on that corner, and definitely took more effort to stop the car

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