A year ago, summer, hot day, I was driving down an 8-ish% grade for about 1/2 mile through a residential area and by the time I reached the bottom of the hill, the brake pedal was rock hard and there were no signs of stopping. I feathered the brakes and e-brake until I was able to miraculously manage to reach a stop. Scary stuff.

I bled the brake fluid with the Nanocom, and did a power bleed to cycle the ABS unit and replaced the pads with Akebono pads. I didn't encounter a driving situation quite like that hill since, and also didn't have brake issues until yesterday...

So, same sort of situation, steep grade, hot summer day, and by the time I reached the end of a 1/2-ish mile descent (relying very little on the brakes to manage speed, btw) I reached the bottom and BARELY came to a stop in time before reaching an intersection. Brake pedal was rock hard and brakes had essentially no power in them. Felt like I was going to snap the pedal arm off.

What the heck is going on? This isn't OK. Both times I was alone, but normally it's my wife driving around with our 8-month-old.

The ABS block is new. The system is bled very well. The brakes are EBS slotted and drilled rotors (previous owner install, I'm not the biggest fan). That doesn't leave much left. Are the rotors really a possible culprit? What about the pads? Should I roll with something softer, like OEM LR? Is the brake booster an issue to consider?

 

Have you purged and replaced your brake fluid. Could be the booster or a vacuum issue, brakes normally fade with heat but very uncommon in normal driving with disc brakes.

Here is a good read to explain the vacuum issue https://www.classiccarrestorationclu...d-brake-pedal/

 

Yep, brake fluid purged and replaced fully.

I have a spare booster I can throw on there and see if the problem changes.

 

Your foot is something to consider... It's good practice to go down those hills in the lowest reasonable gear, use the transmission to keep at or below the speed limit... DO NOT keep your foot on the brake all the way down.

 

Something is wrong. Your wife and baby are in danger. I would look at everything calipers pads rotors etc. There is no way your brake fluid would boil or be so hot that quick.

even if you had the cheapest pads and rotors that should not happen.

 

To me it sounds like there is no or very little vacuum.

 

Kind of where I'm left thinking too. I'm going to replace the booster and will report back with whether or not that solved the issue.

 

Agreed. Combed through the entire system and rebuilt the calipers with new seals, rotors are true and aren't worn, pads are new. I'm suspecting a vacuum issue. I'm going to run a vacuum test and check it out tomorrow.

 

Yep, I'm pretty dumb in most areas of life but going downhill in a truck without working the brakes too hard is one thing I'm OK at, which is why this brake behavior is so strange at first glance.

 

I'm going with rotors on this one. Back in my BMW track days there was a weird condition when gas build up between the pads and rotor would create a hard pedal and barley slow the car. It was scary as you described. Harder pedal pressure would do nothing. It was related to heat build up and off gassing from the pad material getting trapped. It was usually progressive with heat but if I remember could also come on suddenly and randomly braking in a corner, etc. The worse I ever experienced it was with drilled rotors. Which are supposed to help ironically. Hard core track guys would not use drilled or slotted rotors and said they were for show. I would think if it was vacuum or booster related harder pedal pressure would help as you would be manually braking at that point.