Topic: front brakes keeping locking up

[4wheelworks]

my 1994 4runner, the front brakes will lock up and not release pressure until you take the cap off the master cylinder,   it has new calipers, master cyl, front brake lines, a good used booster, back brakes are working fine,  pedal will get rock hard,  any ideas will help,

[zippo]

Could be a DOA master cylinder?

[crazykooter]

Both front tires lock up ?   Tho normally master cylinders dont cause locking like this unless the plunger inside is sticking or air in the lines.  If it was sticking then the brake peddle would have a lot of play in it when the brakes lock up.   Poss that your getting sort of a vapor lock on the brakes.   Does it do it under light braking or just harder braking ?   Take a few mins and a quart of brake fluid and flush the whole brake system.   There is a bleeder on the bottom of the master as well. 

[Rocksurfer]

Had this happen on my 86 turbo, it was the plunger as stated. It would get stuck and not release for around 5 min. I took the MS back and got another one and everything was fine, on a side note they did give me the wrong MS for a 22re instead of a 22ret they are different.

[4wheelworks [OP]]

on thew search for a good used brake booster/ master cylinder combo  who has one, how much and thanks for the help!

[Burl]

I was having a similar issue with mine, apparently a 1 inch bore ms is not compatible with 4cyl calipers.

[79coyotefrg]

I was having a similar issue with mine, apparently a 1 inch bore ms is not compatible with 4cyl calipers.

yes they are, ive been running the one inch bore sold by Marlin for about 2 1/2 years.  unless the master you have is one equipped with ABS.

[Burl]

That's weird because when I brought my rig into your guys store I was told to upgrade to the v6 calipers and vented and slotted rotors.  That seemed to fix the front brakes locking up.  Idk maybe was justa fluke but the 4 cyl calipers with the ms I purchased from marlin was a bad combo but what i've got now works great.

[crazykooter]

I ran V6 master and a dual booster with stock 1st gen truck calipers for a while and never had an issue.  Only reason I upgraded to v6 calipers was due to the ifs hub swap with fj80 rotors.  Only did that to make the front end wider without spacers.

[kneedownnate]

I put a 1" mc on my first gen with no other mods and I have absolutely no feedback, just a very hard pedal that barely moves.  I could lock up the brakes if I didn't get used to it, so maybe that's why yours were locking up