300zx front brakes keep locking up

[Azazel703]

I have 1990 300zx and the front brakes keep locking up ive replaced the master cylinder front brake caliber the front brake lines from the caliber to where it goes back into the engine bay but none of this has help it

[Pablo808]

If it's the caliper that's locking, tap it with a hammer and see if it releases.
If not, use a 10mm or whatever size it is to loosen the bleeder on the caliper and see if it releases.
Sounds weird to lock up when you changed the lines, Master and caliper.
Is there a line that you think you've missed?

[Azazel703]

Ive have replaced all the lines just the ones on the passanger side because that the side that locks up the driver side just drags. If i open the bleeder the caliper frees up

[NolimitZ32]

If the caliper piston moves freely when you release pressure then its either your master or you have junk in the line somewhere that is blocking up the flow of fluid back toward the reservoir when you release the brake.

[ca18det_boy]

Did you adjust the rod on the back of the master cylinder that hooks up to your brake pedal? Something is telling me the lock nut came loose, and now your rod is out of adjustment causing a locking situation.

[Ace2cool]

+1 to all said above, plus the fact that my calipers had to be rebuilt. Had some rust on the pistons and mine were seized. Pretty simple procedure if you've got a decent technical know-how and an air hose. Don't lose the O-ring between the two halves of the calipers.

[Azazel703]

Ive replaced the calipers. And used an air compressor to blow thur the front brake lines and that didnt help they seem to start to lock up with me just driveing not pressing the brake

[Ace2cool]

I'd say the MC is improperly adjusted then. Not returning all the way so not letting fluid back into the reservoir.

[Pablo808]

Ive replaced the calipers. And used an air compressor to blow thur the front brake lines and that didnt help they seem to start to lock up with me just driveing not pressing the brake

Here's a link on how to adjust the master cylinder pushrod.
https://static.speedwaymotors.com/pdf/916-31939.pdf

If the pushrod for the MC is too far out, your brakes aren't going to return back in.
What I can think of right now since you did say you cleaned out your lines.

Best luck to you. Return back with your progress.

[amc49]

X2, there is a very small port in there called the compensation port that MUST be open at full brake off and m/c piston all the way back. It allows fluid to drain back when it heats up from brake use and not flowing back then begins to lock the brakes simply driving the car as most brake pads barely touch to rub and heat up even not being used. The piston rod going into back of the m/c needs maybe 1/16" of clearance to make sure that port stays open all the time when the brake pedal is released.

[Azazel703]

I adjusted the push rod and now the brakes doesnt feel like they are locking up but after driveing it like 5 miles the front wheels are so hot you cant touch the rim

[amc49]

Maybe not enough. If one side only is doing it not the M/C.