The other night I almost rear-ended someone with my Civic when my front brakes locked up with moderate pressure in a light drizzle, and today I had to bear on them pretty good on a dry day and again they locked up and almost wore my poor tires a flat spot. My entire brake system is stock and the last thing I did to them several months ago was put in new front pads and resurfaced the rotors and put everything back together nicely with molykote on all the rubbing surfaces. No ABS, so I suspect the proportioning valve or the master cylinder, neither of which has seen any maintenance during the car's life. The valve is a bear to get to and requires that I undo 6 fittings in a tight location and would run me over $100 to replace so my first thought would be to take it apart and clean it and put it back together and bleed the system. I'm not sure how to determine if the master cylinder is at fault. I did do a full system flush with new fluid a year or so ago. I would expect the rears to lock up way before the front in any case, but that's not what's going on. Any ideas? Thanks for the help!

 

Does the ABS indicator come on when this happens? Barring the indicator not working, the ABS indicator would come on when this happens if something is wrong with that system. An easy way to check if the indicator is working is the ABS indicator should come on for 2 seconds after you turn the ignition on.

A hard pedal is indicative of a bad booster but, we'll get into that if you tell us the ABS indicator isn't coming on.

 

Thx for the reply. It's an LX so there is no ABS : (

 

abbreviated diagnostic tree:

1. Drive until the brakes drag or the pedal gets hard.

2. With the engine running, raise the vehicle and spin the wheels by hand.

Is there brake drag at any of the wheels?

YES- step 3

NO- Look for other causes of hard pedal.

3. Turn the engine off, pump the brake pedal to deplete the vacuum in the booster, then spin the wheels again for brake drag.

Is there brake drag at any wheel?

YES- step 4

NO- Replace the brake booster.

4. Without removing the brake lines, unbolt and separate the master cylinder from the booster, then spin the wheels for brake drag again.

Is there brake drag?

YES- step 5

NO- Check the brake pedal position switch adjustment and pedal free play. If OK, adjust the booster pushrod.

5. Loosen the hydraulic lines at the master cylinder, then spin the wheels for brake drag.

Is there any brake drag?

YES- step 6

NO- replace the master cylinder

6. Loosen the bleed screws at each caliper and wheel cylinder, then spin for brake drag again.

Is there any brake drag?

YES-Repair the caliper or wheel cylinder at the wheel(s) with brake drag.

NO- Look for a bulging master cylinder cap seal, discolored or contaminated brake fluid in the master cylinder, or damaged brake lines. Replace any damaged items. If all of these items are OK, replace the proportioning valve.

 

Well I should be able to figure something out after doing all that. Thanks for the thorough procedure. It makes sense to check those items piecemeal. I'll do that in the next few days and see what I find...