Why are my calipers sticking?

[Mark]

On my daily driver, I changed my front calipers (from a '77 bronco), in February and installed H-boost at the same time. Everything has been fine all summer, but the last couple of days, it seems, when the front end warms up after a bit of driving (probably 10 miles or so) my calipers will start to drag and stick. I made it back to the office and by the time I go home, they should cool down enough for me to get home.
My hubs are hot to touch, my calipers are too hot to touch, the brake lines at the master cylinder are cool. The master is warm and the H-boost is very warm (a little hot). Has anyone experienced this before?

Are my calipers engaging when the hub warms up?

Is my hydroboost push rod pushing forward when the powersteering fluid warms up thus engaging my brakes?

Any thoughts?

I guess I need to troubleshoot right when I get home while everything is hot.

 

[gearida]

You may have corrosion in the caliper piston. Do both sides get hot or only one? I have had the rubber brake lines at the calipers act like one way check valves, they let fluid go through to the caliper but not release pressure thus holding the calipers on. I know some guys will clamp the rubber hose when removing calipers and this will distort the inside of the hose, even if the outside looks good. I would not think that the lines would get hot. The temp comes from the pads and rotors and not the fluid, generally. When your brakes are cool jack the truck up and spin the tires, while rotating have someone hit the brakes and see if when released the wheel is free or still has fluid pressure. Then crack the line at the caliper and see if it is free wheeling then. My two cents.

 

[Kenny]

What master cylinder are you using? If you're using the stock drum master, did you remove the residual pressure valve? If it's still there, I'm wondering if it might cause enough pressure to slightly engage your front calipers which is making them hot over time.

If it's not that, maybe your pedal to hydroboost pushrod is a hair too long.....thus making it barely engage the brakes all the time?

Anyway, I think you're on the right track with trouble shooting it when it's hot. Put it up on jack stands, and have a buddy push and pull on your pedal while you spin the wheels.

 

[bronko69er]

My hydroboost runs hot too, I prolly could use a bigger fluid cooler (just running a stock one).
I figured it was normal though.

 

[john74]

make sure the contact area where the pads ride on the caliper are clean and rust free, they should move freely without any pressure on them

 

[Mark]

Thanks for the replies and advice!

OK, made it home, and as anticipated, both front hubs too hot, felt brake drag increase as I approached home base. Pulled into the Bronco garage portal, jacked up the front end, could not turn the front wheels by hand, actually had to give quite an effort.

Pulled the wheels off, yes, calipers squeezed tight onto both rotors.

Popped the hood, as soon as I loosened the master cylinder from the H-boost the calipers released.

Looks like I have a pushrod issue between the H-boost and MC.

Back to experimenting with proper length, I guess.

Why is heat being an issue though?


BTW the master cylinder was new when installed in February (stock '77 MC front disc application).

 

[Mark]

Shortened the pushrod between the MC and HB by about 5/16".
I get more pedal travel (feels more natural) and everything seems ok, but I need to give it a more thorough test driving stop and go in town.

I'll report back so that someone with a similar problem may learn.

 

[Pa PITT]

Well keep us posted ...I hope your on the correct track ....but I was going to say look at your calipers if they have steel pistons in them then move on ...but if they have the plastic ....phenoflik ...well that is not even close to being spell correct ....less say "hoof "material pistons made out of this stuff will wear and turn side ways in the hole ...just another bad ideal by some mfg. When I had my parts store I finally got to where I'd not stock the plastic pistons calipers ....When they turn side ways they lock up ....Now watch someone that wasn't the problem ....Well I bet I replaced 50 set w/steel and never any steel ones ....
Keep us posted ....

 

[mr incredible]

what happens is the front brakes are staying engaged just a bit , causing the heat ,, and then it is transfering to the calliper , and actually heating the fluid in the lines , causing the fluid to swell ,, locking the brakes after a bit of time ,,, as it cools down ,, it will release ...

i deal with this in the motorcycle industry all of the time ,, due to brake fluid contamination ,from moisture ,,,, not nescessarilly the same issue ,, but close ,,, 69 er ,, you might try changing out your fliid ,,, might cool it down a bit ,,,

 

[Mark]

what happens is the front brakes are staying engaged just a bit , causing the heat ,, and then it is transfering to the calliper , and actually heating the fluid in the lines , causing the fluid to swell ,, locking the brakes after a bit of time ,,, as it cools down ,, it will release ...

That makes sense.

Pappitt, I cannot remember if they're steel or plastic, but next time I change 'em, I'll make sure to get the steel ones.

 

[TOFIC]

Your Hboost should be a little warm. As fluid is constantly moving through the unit to get to the PS box this would be normal.
I believe you are on the right track but I would be a little suspicious of that master. The reason I say this is you said it was fine for about 9 months ( your first posting) and now it pops up??? Sorry, not selling me on the HBoost with that statement, once they work, they work period. I would look at that master or check the lines to the front brakes, notably the one that feeds the fronts. Has it been banged and is now pinched causing pressure?? Again not the Hboost it is something else - - - have you changed ANYTHING on the front end in the last little while?? new tires maybe?? wheels?? rotors?? maybe gone wheeling and got a little wild and hit something with the front end??
See my point??
TOFIC

 

[Hazegray]

I'd suspect the rubber brake lines. My buddy had a Chebby truck that had disk brake calipers that wouldn't release (smoked the grease right out of the bearings). We took one brake line off, and sure enough, completely swollen on the inside. Put new ones on..problem went away.

 

[Mark]

Your Hboost should be a little warm. As fluid is constantly moving through the unit to get to the PS box this would be normal.
I believe you are on the right track but I would be a little suspicious of that master. The reason I say this is you said it was fine for about 9 months ( your first posting) and now it pops up??? Sorry, not selling me on the HBoost with that statement, once they work, they work period. I would look at that master or check the lines to the front brakes, notably the one that feeds the fronts. Has it been banged and is now pinched causing pressure?? Again not the Hboost it is something else - - - have you changed ANYTHING on the front end in the last little while?? new tires maybe?? wheels?? rotors?? maybe gone wheeling and got a little wild and hit something with the front end??
See my point??
TOFIC

I agree, it is not the H-boost.
As I posted, as soon as I loosened the master cylinder from the H-boost the calipers released.
The master is only 6 months old.
Looks like I have a pushrod issue between the H-boost and MC. I think my brakes were slightly engaging like oldwinghunter described.
Last night I shortened the pushrod by about 5/16" and that gave me substantially more pedal travel. I am assuming that in the cold weather the problem wasn't noticeable and became an issue when the air temps increased making it harder for everything to cool down.

 

[TOFIC]

I would say the 5/16 of an inch is a bit much. Mine works well with 25 thousands of an inch of freeplay. This amount is the recommended slack for the Hydroboost units in a GM application. I hate to admit it, but it works for all installs.
TOFIC

 

[Mark]

I would say the 5/16 of an inch is a bit much. Mine works well with 25 thousands of an inch of freeplay. This amount is the recommended slack for the Hydroboost units in a GM application. I hate to admit it, but it works for all installs.
TOFIC

How are you measuring "freeplay"?
It's impossible to determine if 5/16" is too much if you don't know how much it was too long before trimming. You may be right, but it feels much better.
I wasn't able to drive it yesterday (top off and raining), but I intend to give it a good workout today.
Thanks for the insight.

 

[airman]

Mark, is your brake pressure warning light operational and if so did it come on during this event?

 

[Mark]

Mark, is your brake pressure warning light operational and if so did it come on during this event?

Jeff, it is wired up and it's supposed to light up briefly upon startup, but it does not, so I'm assuming it is not operational and did not during the event. I guess that would be a good time for it to actually tell me something.

I heard before the function of the light, but I must have forgotten...

Anyhoot, I've been driving the piss out of the Bronco since shortening the push rod and no reoccurrence - brakes feel great, stops on a penny, no drag, hubs are actually cool to touch - problem solved, happy ending. ;D

 

[airman]

Actually since I got so far into my brakes I know too much. I look at that light everytime I start. The light tells you that you have a difference in pressure between the front and the back brake curcuit. In you case I bet it would have been on without your foot on the brake because it seems you had some pressure at the front and none at the back. Thats what I had and your thread helped me out a bunch. Thanks.

You may have a bad bulb. Its easy to change and is basically the same bulb as the ones in the gauge cluster.

 

[Mark]

You may have a bad bulb. Its easy to change and is basically the same bulb as the ones in the gauge cluster.

Thanks - I'll try changing it - it's my anal goal to have every light working.