Braking issue

[Mike94ZLT1]

Hey guys, about two years ago I had to replace the front calipers on my 2002 QX4 because one of them was starting to seize up. I replaced both front front calipers, rotors, and of course new pads. About two weeks ago my front passenger caliper started seizing again, so I pulled the front apart to replace the calipers, pads, and rotors AGAIN. I did notice that the passenger side caliper was glazed pretty bad as well, and I am wondering if there was/is something else causing these calipers to prematurely fail. What else should I be looking at? Booster? Master cylinder? Proportioning valve?

[VStar650CL]

Did you flush the fluid when the first one seized? Brake fluid is hygrophyllic (moisture-loving) and most cases of seized pistons are from humidity gradually invading the fluid.

[Mike94ZLT1]

Did you flush the fluid when the first one seized? Brake fluid is hygrophyllic (moisture-loving) and most cases of seized pistons are from humidity gradually invading the fluid.

No sir I did not, I will take it to my buddy's shop and have them do it tomorrow. I would also like to note that the brake pedal feels soft now, but after you hit the brakes a few times it firms up. Does that seem like air in the lines?

[VStar650CL]

Yep, that could certainly be air. Could also be booster vacuum, does the brake effort increase when the pedal gets hard? If the stopping power decreases with a hard pedal then it means the pedal is firming because the booster is losing boost. Could also be seals in the master cylinder, see if the pedal heads for the floor when you hold constant pressure on it for a minute or so. If it does, the seals in the master are leaky and allowing fluid to bypass.

[Mike94ZLT1]

The pedal doesn't get hard like the booster failed, it just firms up a bit. It feels like air in the lines to me. I will drive it around shortly and report back. Hoping that just flushing all the brake fluid will fix it!

[AlanAZ]

Somewhat germane: I flushed the brake fluid in my QX4 with Bosch Dot 5.1 (ESI6-32N) over a year ago, and got the firmest brake pedal that I can remember. While more expensive than my previous go-to brake fluid (Valvoline Dot 3/4, $9 vs. $14 for the Bosch), it is considerably less hydrophilic, with a 3 year recommended service interval vs. 2 years. It should remain better for longer, and flushing less often is a time or cost saving. And being LV (low-viscosity), ABS function is reportedly quicker and smoother, particularly in low temps, not that I have had an occasion to see this in action in dry, hot Phoenix. I have since then used it an couple of Lexus SUVs with similarly excellent brake pedal feel results.

[Buzzman]

This might seem a little bit "out there" but I have had it happen to an older car I had:
One of the front calipers appeared to be stuck in (piston not retracting), resulting in hot brakes and serious premature wear on the pads.
Turned out the caliper was actually OK. It was the short rubber brake line that was the problem.
It had deteriorated, and had collapsed internally. This prevented the brake fluid from backing out when the pedal was released, leaving the piston pushed in.
Might be something to check on your Q.