Sticky Front Calipers
 

OK guys, I'm stuck! Please help me out.

A couple of weeks after replacing my front pads and rear shoes, both of my front calipers started to drag. Both sides are dragging about the same.

So far I have:
- Removed the calipers and greased up the pins and slides
- Replaced both front calipers
- Replaced the master cylinder
- Flushed the entire system (with base bleeding)
- Taken apart the combination valve
- Made sure fluid freely passes back from the calipers to the master cylinder
- Measured the Hydro booster rod stick out length which appears to be ok (about 15MM from flush)
- Scanned back thought the last 10 billion threads to find a similar reference

I'm suspecting the problem must be in the hydro booster so I am about to:
- Check to make sure the return line is not plugged or internally broken
- Flush the power steering fluid

If this doesn't fix it I will probably have to replace the hydro booster which costs big bucks! Can anyone think of something I have missed.

Any help would be appreciated!

Forgot to add my Sig....
 

[duhhh] Sorry, new member.....Rob

I assume that you know that the pads are supposed to drag a little bit?
They don't retract away from the rotor but rest on it, otherwise you would have a low pedal.
You should be able to spin the tire easily while the truck is jacked but still hear rubbing.

I think you have done way more than most of have. What are the symptoms? What are you hearing that makes you think its dragging too much?

Thanks for the response guys.

I'll try to describe the symptoms a little more precisely.

When I drive off, the truck feels like it's hooked up to an elastic tow strap. It needs to rev up to about 2000 rpm before it starts moving but then suddenly "releases" as though the strap broke.

I know it's the front brakes because I put it up on 4 jack stands and reproduced the problem by putting it in 4wd in the air. I "drive" it a bit and then push the brakes and release them. I stop the engine, take it out of 4wd, get out, and then try to turn the tires by hand . The rears are free but I can barely turn the fronts. I then take the wheels off and try to push the pistons back in the calipers and they are way stiff.

Thoughts?

Never had anything like that. When you installed the new breaks did you open the bleader valve when pushing the piston back or let it flow backi into the system? I have not done the brakes on my truck but on my other vehicles it is recomended to open the bleader and let the fluid purge out until the piston is pushed in all the way. This is to keep contaminents out of the system. I would keep bleeding the brakes and if you have a pressure bleeder that would event be better. The wife gets kind of POed when she has to pump and hold. HA HA.

Good point. When I changed the pads my fluid was quite dirty and I did push it back through the system. Thats why I changed the master cylinder, took apart the combination valve, and replaced all the fluid. I suspected that I pushed something yucky back through the system.

Even though I basically have a new break system from the hydro booster forward, I still don't get complete pressure release. I think I just need to continue into the booster.
Rob

I've seen brake hoses not let pressure return from the calipers.

Yeah, I've heard of this too Smokin. Because both sides are sticking the same I have a hard time thinking that both soft lines went bad the at once.

Do any of you guys know if it is possible to have the rear system hold the master cylinder from returning, thus keeping pressure on the front?

Kinda' grabbin' at staws here but....

I wouldn't have such a hard time believing those hoses are both bad. I've seen it a few times as I was a GM dealer master technician a few years back. They've both been there for the some amount of turns and miles most likely! The inside layer will get a bubble under it after a pin hole or crack starts, blocking fluid flow.

Mine did have a somewhat similar problem last winter, I only had the truck about 2 weeks, the caliper slides seized and warped both rotors severely. The weird part was that it didn't behave they way most vehicles do with warped rotors, made a strange noise when the outside temps. were below 20 F otherwise drove ok.

You have convinced me to give it a try. I'll buy a hose and swap one side to see if it has an effect. It's a cheap test compared to the booster!
Thanks Smokin'

Worn front bearings can cause the rotor to tilt causing drag.

I have had to replace sliders and pins to solve similiar situation, then onto the hoses next. Goodluck,,Rick

You can rule out the hydroboost as a problem. It will not maintain any system pressure after you release the pedal, and even if the linkage is too tight both the front and rear brakes will be locked.

You indicate you took apart the combination valve, but that is where I would look for the trouble if you are not getting error codes from your antilock controller. Have someone press and release the brakes while you are watching the combination valve. If the pin on the front does not fully extend and then retract with the pedal, you have your problem located.

The other thing to check is an air bubble in the line between the combination valve and the front calipers themselves. That will cause pressurization on just that circuit. I am not familiar with the term "base bleeding," but if you have not used a power bleeder and pushed all new fluid through the master cylinder and out each front caliper (and rear wheel cylinder) so there is absolutely no trapped bubbles I would try that if the combination valve is good.

That sounds more like a rear shoe problem..... to me anyways.