Brakes

Question: I have an 03 Ford Expedition and I have been experiencing pulsating in the steering wheel, I have turned the front rotors twice and in no time they are back the same way. So, I replaced both the front rotors and calibers, and its still not right. When I was bleeding the whole brake system, I noticed that the rear did not bleed like the front did, the pedal did not go all the way down. My question is what determines the amount of pressure that goes to the front verses the rear? I think that my problem is that the rear brakes are not being applied enough, thus causing the front to work harder and get hotter than normal, causing them to warp easier.

 

Answer:

There is a proportioning valve ( or sometimes called a modulator valve
) which in modern vehicles is usually combined with the ABS functions.
It should be located immediately after the master cylinder and is
usually an aluminum block. Your brake system should apply more
pressure to the front brakes, which is where most of the braking
occurs. You can test function of the proportioning valve by doing a
low speed panic test and see if the front or rear brakes lock up
first. Do it in an empty parking lot and have someone watch from a
distance to see which wheels lock up. With ABS, it wont be easy to
see. I would say 20 - 30mph would be all the faster you would want to
go. Again, be careful, make sure the parking lot is empty.

When you replaced your rotors, did you tighten the lug nuts with a
torque wrench? Improper torquing of the lug nuts can cause rotor
warpage over time.

Question:

I own a 96 Chevy Cavalier and the breaks are bad, the pads are still good, we removed the air from the line, and it has great vacuum what else could be wrong?

 

Answer:

The master cylinder could be bad. How did you remove the air from the lines? With modern ABS systems, its usually best to use a pressurized or vacuum bleeder to make sure all the air is out. The old crack the bleeder and have a buddy push the pedal does not work as well as it used to. I would take it to a shop that has the proper bleeding equipment and have them get all the air out, if its still bad, then its more than likely the master cylinder.

Question:

Hey Kevin,

I have a 2001 Audi A4 Quattro and I recently changed the rear pads. I bought Wagner brake pads which where the more expensive of the choices and now have a persistent squealing noise from the right rear pads. which occurs while driving and goes away when I brake and comes right back when I let off the brakes. I tried to sand the calipers and applied never seize and special spray lube but nothing seemed to work. Any suggestions would be great.

 

Answer:

When you changed the pads, did you screw in the caliper pistons, or just use a clamp to push the piston back in? On the Audis the piston must be screwed back into the caliper. Its possible there is not enough room for the pads to back off the rotor, it may be rubbing while the brakes are not applied. Also I dont know what you sanded on the caliper, but you may have damaged the caliper depending on how much and where you sanded it down. As with any brake job, cleaning the calipers and rotors is critical to no squeaks and should only be done with a spray on brake cleaner. ( no abrasives !)

Question:

Engine runs rough like missing on excelleration but when you apply the breaks the engine runs smooth for a moment. I am getting a code of egr low vaccume but have replaced the egr valve already.

Answer:

The code tells all. The EGR valve does not create vacuum, the engine
does, so the low vacuum code at the EGR valve is not pointing to a bad
EGR valve, but rather a low vacuum signal to the valve. Typically the
only way to have low vacuum, is to have a leak somewhere. The
improvement in engine performance when you apply the brakes tells me
that you brake booster is most likely the culprit when it comes to the
vacuum leak. Not typically a DIY project, your best bet would be to
take the vehicle to the dealer and have them confirm the diagnosis and
replace the brake booster.

It is common to hear some minor squeeking from your brakes, but do you know when it's too much? Brake dust can build up and cause some squeeking. Keeping your wheels and brakes clean can help, but sometimes it's unavoidable. Have your pads checked at all services (oil changes, tires, etc) and you should not have any problems. If you hear grinding or squeeking even when you are not using the brakes, get to your mechanic and have it checked out. Learn more about your brakes... Kevin