Not PT but disk brake problems.....

[Olav]

My dd Chevy Tahoe 2002 have a issue with the rear brakes. I changed all 4 rotors and pads, handbrake linings and backing plates. Replaced the long brake line on top of frame to rear. Bleed the brakes. Guide pins on calipers is lubricated and calipers are moving free . Now the rear brakes is not loosing pressure when I drive. They are hot and almost block the wheels ? This happens after 5 min driving.
I have a few teories regarding this.

1: Rear brake hose is not letting fluid return. Collapsed inside ? I had same issue a few years ago on a Caprice -90 when i mixed DOT 5.1 and DOT 4 brake fluid. Why is the brake hose collapsing ?



2: When I put every thing together there was hardly enough clearance between rotor an pads to mount together. Is the rotor getting so hot it grows wider and starts to brake ?


After 5 min the wheels are free but i don't know if the rotor gets colder or fluids returns ?

Any comments ?

Olav

[Apogee]

Olav, it could be caused by either of the ideas you mentioned, so I think you're on the right track. That said, I would crack the bleeder screw when the brakes aren't releasing to see if that releases the caliper. If it does, then you have a hydraulic issue in the form of residual pressure in the system which could be caused by a variety of things, including a damaged hose. If it doesn't, then you have a mechanical issue which could be as simple as overly thick pads and/or rotors, either of which would be an relatively easy fix IMO.

Tobin
KORE3

[Olav]

Tobin; Here in Norway 1/4" brake lines are no easy fix. The workshop that made my brake kine used 6mm instead of 1/4" line. Could 0.35mm smaller line cause this. The new line is CuNi and the inner ID is smaller !
They didn't tell me this so ! had to put it on the car while i was repairng it.

Have you heard about the problems with mixing DOT4 and DOT5.1 fluids. I friend of mine who is a mec. supervisor at the local GM dealer says this is not uncommon on Isuziu vehicles....


Olav

[Apogee]

The line size difference is so small, it shouldn't matter one way or the other so long as the fluid velocity doesn't get to the point that cavitation becomes an issue, and that would be a whole different set of issues/symptoms.

As for mixing DOT3/4/5.1 fluids, I've never had or heard of any issue with doing so as long as they're all glycol-ether based fluids. It will certainly de-rate the higher temp fluids, but that shouldn't impact the release characteristics of the calipers.

Tobin
KORE3

[Olav]

Thanks! I have ordered brake the hose and hopefully it will be OK...