99 xj. my left front brake siezed up on me. so i installed a brand new caliper and rotor but that did not solve the problem in fact its even worse. tire just dragged. so im assuming that after i apply brake pressure, the brake fluid is not able to return to the master cylinder. this is only affecting the left front. so i followed the brake line to a unit just beside the master cylinder. all the lines go into here but the LF line only has a small brass fitting befor it. is this a one way valve??? could it be my problem?? help im stuck and so is my brake.

Proportioning valve? It doesn't have ABS does it? Number cause of a siezed caliper is moisture, when is the last time you flushed the fluid? Are you sure the flex hose is not collapased?

no abs. brand new caliper still siezed on. i bled the brakes fine so the line should be ok. not sure what to do next?

With the caliper released,and no pedal pressure, of you crack the line at the porp valve are you getting pressure? As in a release of back pressure?

When you got the new caliper did you get the right one? There are two different sizes. There is a composite size and a cast size. The problem is many of the composite rotors look like the cast ones. The best way of telling which size to get is to put both rotors side by side. I forget which one is taller, but the "hat" is higher on one then the other. If you put the wrong size on it can rub and scrape on the inside of the rim and on the outside of the caliper.

All the above advise is assuming that you have verified that the unit bearings and u joints are free from defect or damage and free wheel smoothly?

The rubber brake lines can collapse internally and act like a one way check valve, allows fluid in but doesn't let it return. They are like $8 each, replace both sides.

X2, sounds like the hose is the problem, hoses are not that cheap where I'm at , but either way....you need one

Had the same thing happen but with a GM vehicle. New caliper kept seizing even though I could bleed it. Replaced the line and all was fine..

it is a steel braided brake line that came with the lift and is only 3 months old. my original caliper siezed up out of nowhere while driving on the highway. so i replaced it. new caliper still siezed but i can turn the wheel if i release pressure from bleed screw. i will try loosening brake line at the proportioning valve and see if i get any back pressure there. if so should i replace the whole unit??? or like i said. there is an extra fitting (not sure what it is) on this line only, in between line and valve.

Take a pic, the extra part could be a adapter for the line.

Ill try and get back at it tomorrow. Just signed up to this forum. And just found the app. So far so good. I appreciate the help.

It still could be the brake hose, new does not always mean good. Swap the left and right hoses and see if the right caliper siezes.

Since it has done it with several different calipers, I would take a real hard look at the master cylinder.

Could be the piston in there is not returning fully to rest.

If that was the case both calipers would be siezed. There are only two lines that come out of the master cylinder, one for the front brakes and one for the rear brakes. A master cylinder piston hanging up would not effect only one caliper.