Rotors getting VERY hot

[55trucker]

I have an ongoing problem of the rotors getting hot. Almost too hot to touch. master cylinder and a bleed job.

When you replaced the master & the booster did you alter the booster push rod at all? It IS adjustable, if by chance the replacement master & new booster has placed the cylinder piston closer to that push-rod that may be your issue, there is now an interference contact & the master piston cannot retract to it's proper *at rest* position.

 

[Eddo Rogue]

Are the pads worn evenly? Your calipers might be the issue.

 

[8thTon]

I cannot press the brake pedal most mornings until engine is running, thus creating vacuum to the booster, which would lead me to believe the booster/check valve was losing vacuum.

This just sounds normal - until it has vacuum it provides no assist, so it's hard to press the pedal. Unless it's much more extreme than normal.

I'm guessing you have air in the lines - air is compressible and will expand when warm, which applies the brakes slightly. That causes drag and heating.

But three lefts do.

Three is more than enough to screw anything up.

 

[Eddo Rogue]

This just sounds normal - until it has vacuum it provides no assist, so it's hard to press the pedal. Unless it's much more extreme than normal.

I'm guessing you have air in the lines - air is compressible and will expand when warm, which applies the brakes slightly. That causes drag and heating.


Three is more than enough to screw anything up.

+1 air in the lines. bleeding in some fresh brake fluid wouldn't be a bad idea. Maybe some high temp stuff.

 

[NebRanger]

Did some running around this morning, was able to move the pedal before starting the truck, (so it had vacuum) so hopefully that issue has been resolved. Checked rotors for heat, just by hand until I get ahold of a temp gun, but they are signifigantly cooler than they have been. Now I wish I had taken a temp of them prior. Cool enough that I can leave my fingers on them for a few seconds, so much better. It still has a pretty short pedal stroke, and pretty abrupt braking. No frost this morning so no stuck brakes, or its possible that could be resolved also.
I appreciate all the responses.

 

[NebRanger]

were the old pads worn evenly?
did you replace just the calipers or calipers & brackets?
if just calipers did you clean & lube the slider pins?

how about the rear brakes, warm or cool?

jack the front up, engine off.
spin the wheels, too much resistance?
engine still off, hit brakes. wheel stops immediately?
release brakes, wheel releases immediately?

repeat with engine running.


if you think there is residual pressure in the lines try opening a bleeder. does the fluid run out or squirt out?
does the wheel turn easier with a bleeder open?

are the pads so tight in the brackets that they can't move?

for testing purposes you can disable the ABS by disconnecting the connector(s) at the front of the frame. follow the cables.

you mentioned rotors and hubs separately, 4WD? (shouldn't matter)

pjtoledo
The old pads were evenly worn
Just calipers, cleaned and lubed along with pins, always
rear brakes are cool
I generally crack open the bleeders before getting pedal pressure, just to make sure they crack open before applying pedal pressure. No surge of fluid.
yes, rotors and hubs seperately, 4wd
Thanks for the input

 

[NebRanger]

When you replaced the master & the booster did you alter the booster push rod at all? It IS adjustable, if by chance the replacement master & new booster has placed the cylinder piston closer to that push-rod that may be your issue, there is now an interference contact & the master piston cannot retract to it's proper *at rest* position.

That was my initial thought also, measured the master and booster and made adjustment to the booster rod, set it at about .025 free play. I was rather disappointed when I pulled the old booster out because it measured almost the same.
Thanks for the reply

 

[NebRanger]

This just sounds normal - until it has vacuum it provides no assist, so it's hard to press the pedal. Unless it's much more extreme than normal.

I'm guessing you have air in the lines - air is compressible and will expand when warm, which applies the brakes slightly. That causes drag and heating.


Three is more than enough to screw anything up.

I have not had this issue until recently, if the check valve is working properly, shouldn't the booster hold vacuum?
I suppose air is a possibility, I have done 2 complete bleeds in the last month, replacing and removing the master cyl, and have only seen what I would say is normal air from the removal and replacement of the master. Have used right at a quart each time and bleed each corner well after seeing any air. I would rather bleed longer than not, as brake fluid is cheap.
Thanks for the input.

 

[8thTon]

I have not had this issue until recently, if the check valve is working properly, shouldn't the booster hold vacuum?
I suppose air is a possibility, I have done 2 complete bleeds in the last month, replacing and removing the master cyl, and have only seen what I would say is normal air from the removal and replacement of the master. Have used right at a quart each time and bleed each corner well after seeing any air. I would rather bleed longer than not, as brake fluid is cheap.
Thanks for the input.

No check valve is perfect, and to be useful it only needs to hold for minutes, not for hours overnight. A tiny leak would not matter much. I've certainly felt the brake pedal fall as the truck is started before.

 

[NebRanger]

No check valve is perfect, and to be useful it only needs to hold for minutes, not for hours overnight. A tiny leak would not matter much. I've certainly felt the brake pedal fall as the truck is started before.

Fair enough, mine has just not done it until recently.
Thanks

 

[Uncle Gump]

No check valve is perfect, and to be useful it only needs to hold for minutes, not for hours overnight. A tiny leak would not matter much. I've certainly felt the brake pedal fall as the truck is started before.

My truck didn't move for two days... Booster still had vacuum.

 

[8thTon]

My truck didn't move for two days... Booster still had vacuum.

Yeah, they can do that too. But if it had the tiniest of leaks, say just enough to leak down in 2 hrs, what would it matter? Even if it had no check valve at all it would not cause the brakes to get hot, you'd just have random and variable brake assist. It'd be weird but not match the original symptom.

 

[Uncle Gump]

Yeah, they can do that too. But if it had the tiniest of leaks, say just enough to leak down in 2 hrs, what would it matter? Even if it had no check valve at all it would not cause the brakes to get hot, you'd just have random and variable brake assist. It'd be weird but not match the original symptom.

No check valve would be really bad news if the engine quit and you needed brakes... its foolish to tell people you don't need the check valve.

I never said anything about the booster causing a sticky brake... I specifically said it sounded like two different issues he was looking at.

 

[8thTon]

No check valve would be really bad news if the engine quit and you needed brakes... its foolish to tell people you don't need the check valve.

I never said anything about the booster causing a sticky brake... I specifically said it sounded like two different issues he was looking at.

Who the hell ever told anyone they don't need a check valve?

 

[Uncle Gump]

No check valve is perfect, and to be useful it only needs to hold for minutes, not for hours overnight. A tiny leak would not matter much. I've certainly felt the brake pedal fall as the truck is started before.

Yeah, they can do that too. But if it had the tiniest of leaks, say just enough to leak down in 2 hrs, what would it matter? Even if it had no check valve at all it would not cause the brakes to get hot, you'd just have random and variable brake assist. It'd be weird but not match the original symptom.

Who the hell ever told anyone they don't need a check valve?

I went back and read again... while you didn't actually say to take it out... you don't need it. You do say if it leaks a little... no big deal.

Pretty much everything related to your brakes is a big deal... and the OP asked if it should hold vacuum in the booster. The short answer is YES. Not if it doesn't it's OK.

OP... if that new booster won't hold a vacuum... I would buy a new check valve... cheap insurance.