NEED HELP Brake pressure lowers with outside temp I


Did rotors and pads in April because I noticed grooves.
By end of May grooves were back in front rotors

Also hear slight rubbing of pads first 5 minutes of driving

Temps affect brake pedal pressure as follows

90+ rubbing noise very stiff pedal
80+ intermittent rubbing good pressure
70s good pressure noise only in the first 5 minutes
60s low pressure at first then fine after a while of running rubbing noise first five
50s no pressure from front pads only rear pedal goes to floor

There doesn't seem to be pulling to a certain side when braking so sticking pads just be both sides

Grooves on both front rotors both sides

Truck leaks no fluids what so ever

Reservoir is full no drainage or leaking

Did not bleed brakes when pads changed

The problem is localised to the front brakes only.
Both sides pretty evenly
The truck seemed like it may have sat over grass fora while noticed rust but not enough to think flood so I assume parked over grass for prolonged period of time
Rear rotors had been just don't before I bought the truck works fine.

My thoughts on the culprit is

Bad/dirty/rusty/torn boot front calipers

Possible bad front brake lines


You mean the slides on the bracket and not the piston itself correct? I was thinking the bleed job as a start. The fluid is still clear. Not dirty at all. But then I was thinking maybe it got moisture in it?


Well-Known Member
Yes the bracket slides. You could check if the caliper is freely compressable. also just because the fluid in the reservoir is clear does not mean the fluid in the lines is. The previous owner may have added fluid do the reservoir at some point or something on the brake system was changed and they improperly bled it.


Silver Supporter
I agree with @coolasice. If the brake fluid is dark, I would drain and fill the brake fluid until it's clear. Brake fluid absorbs water and that could be a big part of the temp and pressure issues you're having. Make sure you are using DOT3 fluid to refill the master cylinder.


Yea I am going to try that this weekend. As I was mentally working through the problem last night I realized that all the heat generated from them being sticky in the hot temps must have created a pretty good gas bubble that as the temps dropped probably turned into moisture in the line.


Silver Supporter
A full bleed is not that hard, depending on your knowledge and tools. There are Speed Bleeders, and there are self bleeding Vacuum Pumps, in both pneumatic and hand operated. Lots of youtube video's on both kinds. I have speed bleeders on my Acadia and love them. Easy to bleed by myself, but you absolutely need to be sure that the master cylinder is constantly topped off with fresh brake fluid or you risk incorporating air right back into the system...which will cause brake pedal fade *and many other safety issues.

Any amount of water/condensation in brake fluid is bad. It can cause your brakes to feel squishy at times, no matter what the weather conditions are, but especially bad when it's hot! Not going to get into the the scientific's of it, but you should really start with a clean brake fluid change. And try not to leave the brake fluid container open too long or the cap off of the master cylinder too long since brake fluid naturally absorbs condensation/humidity from the air. Remember, it's just bad for it.

If you still feel a brake pedal fade after a fluid change, you may want to look into purchasing a new master cylinder. They don't always leak on the outside when there's a problem. There are internal seals that can go bad and cause your pedal to fade, and it will never show signs of a leak on the outside.

As for your rotors;
- First, check the slide guides as mentioned a few posts above.
- Check the face of the brake pads for debris that may have embedded themselves into the pads (small rocks, sand, gravel, etc) and either remove them or buy new pads. Sounds a bit excessive, but it can happen and gouge your rotors pretty bad.
- Check the pistons inside of the calipers to see if the seals are bad and if the pistons move back/forth freely (as mentioned above also). If they're binding up, that can and will cause all kinds of issues that you're mentioning. A rebuild or complete replacement may be needed.

First and foremost (in my opinion) is to buy a few large containers of new brake fluid and flush out the whole system. Start with bleeding the rear passenger caliper, then bleed the rear driver's side caliper, then front passenger and finish with the front driver's side. Basically, start bleeding each caliper that is furthest away from the master cylinder, and work your way closer to it. And be sure to not let the fluid go too low in the master cylinder or you'll have to start all over again.

Speed bleeders:

Bleeding brakes (by yourself) with a Mityvac Vacuum Pump. These pumps can sometimes be rented at your local auto parts stores. Usually free of charge to rent, but you'll naturally have to leave a deposit:

You can also have someone sit in the vehicle as you're bleeding each wheel to press on the brake pedal, just be sure to fully close the bleeder screw before the brake pedal is released, or it'll suck air back into the lines.


Silver Supporter
Speed bleeders are great because you can literally loosen each one up, then sit in the car to manually press the brake pedal to bleed yourself. Once you let off of the pedal, the speed bleeder(s) automatically close and do not allow air back into the system. Once flushed, you simply tighten them back down, re-assemble everything, then sit back and and grab a beer.

You CAN open all of them at once to bleed all four calipers at the same time, but you'll be wasting a lot of new fluid that's closest to the master cylinder. Your call though...

I can't stress this enough though;
Be sure to keep the fluid level topped off in the master cylinder as you're bleeding the lines!!

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