Like the title says. My car had been sitting since last July, and I can't for the life of me figure out why the fronts won't lock. I have good pedal and no leaks. The rotors had rust on them, so I got them cut down. Bench bled and installed a new master cylinder. The idiot light came on, but thats because its sensing after the adjustable prop valve. After bumping up the rear pressure I can lock the rears and idiot light doesn't come on. I took the caliper off and slid plywood in between pads and it clamped tightly and made the wood crackle.

The only other thing I can think of is, while it sat I removed the booster to paint back there. Maybe its on its way out?

 

Why would you want to lock the fronts anyways? If the tires stop rolling (locked up) you lose steering control.

The goal is to have maximum braking but without lockup.

 

Well they don't stop hard like they used to. I don't want to lock them, but I want them to be able to lock. It means they're working right.

 

Have you bedded the front pads in? With turning the rotors you may want to sand the faces of the front pads along with the contact areas of the rotors. Use some emery cloth of about 180 grit. Use a circular motion on the pad & rotor faces.

Then run them through a bedding procedure. Can get that info from a site such as Brembo, StopTech, or Wilwood.

{edit} I just wanted to clarify the sanding. This is BY HAND, no power tools. A sanding block is helpful. The pads should have a uniform appearance to them after sanding.

When sanding the rotors, sand just enough to put a nice swirl pattern into the surface. You are not trying to remove material, just placing a non-directional roughness to them. This also helps knock down the ridges left by the cutting tool. {/edit}

RBob.

 

Considering weight transfer during stopping.....Rears should lock way before fronts anyways.

Just because a brake locks up, it doesn't mean it is working right. Working yes, but not working right.

 

out of my own curiosity, if you had adjustable capability front to rear, wouldnt you want them to lock at the same point though? If the rears lock before the front, then you are gaining nothing from the rears, but are also loosing braking force in the front. Am I correct or am I thinking completely wrong on this?

 

To be honest, you (almost) never want the rears to lock

Rear brakes that are locked will put the rear of the vehicle leading the front of the vehicle.

A proportioning valve is more then a pressure reducing device. A proper one has a knee in the pressure curve. This knee has to be adjusted so that as the brakes are more heavily used, the pressure is reduced further at the proper point.

This is because heavy use of the brakes shifts weight forward. Unloading the rear tires, which requires less clamping of the rear brakes. Otherwise they lock and the car swaps ends...

RBob.

 

I tried bedding but it didn't get me anywhere. I remember when I first bed them the car stopped much harder. I'm thinking maybe my booster is on its way out. Maybe its giving me pressure, but not enough.

My brakes were niiice before this. Had the rears bite without locking up.