!!87 4runner brakes occasionally lock. new booster??
03-11-2010, 01:40 PM
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!!87 4runner brakes occasionally lock. new booster??
Hello fellow YotaTechs.
I purchased an 87 4runner about a month ago. I live in alma, co. Which is at an elevation of 10600ft. The vehicle was only used for off road prior to my purchase. I now use it as a daily driver. The master cylinder had been replaced before i purchesed it because they said the from brakes would occasionally lock up. I had no lock up issues for a few weeks then one day after a long idle they locked up mid driving slowly gaining more pressure, and the pedal would be stiff as could be with no give. i pulled over and allowed to cool down for 30 mins and the brakes were free of pressure, allowing me to drive again. This problem persisted every few days, then soon became a daily problem. to avoid the cool down period I would jump out and bleed the brakes, a burst of steam would come out then brake fluid after being bleed the truck was driveable again. Yesterday i had this occur over 10 times which is unusual for 1 day. After my brakes caught fire the 10th time they locked up I removed the vaccume hose to the booster and drove the remaining 20 miles home with no power assist or problems. It has new pads and I replaced 1 bad caliper. What I would like to know is do i need a new brake booster or is this caused by something else? Any feedback would be greatly apppriceated thanks for taking the time to read this and hopefully help.
I purchased an 87 4runner about a month ago. I live in alma, co. Which is at an elevation of 10600ft. The vehicle was only used for off road prior to my purchase. I now use it as a daily driver. The master cylinder had been replaced before i purchesed it because they said the from brakes would occasionally lock up. I had no lock up issues for a few weeks then one day after a long idle they locked up mid driving slowly gaining more pressure, and the pedal would be stiff as could be with no give. i pulled over and allowed to cool down for 30 mins and the brakes were free of pressure, allowing me to drive again. This problem persisted every few days, then soon became a daily problem. to avoid the cool down period I would jump out and bleed the brakes, a burst of steam would come out then brake fluid after being bleed the truck was driveable again. Yesterday i had this occur over 10 times which is unusual for 1 day. After my brakes caught fire the 10th time they locked up I removed the vaccume hose to the booster and drove the remaining 20 miles home with no power assist or problems. It has new pads and I replaced 1 bad caliper. What I would like to know is do i need a new brake booster or is this caused by something else? Any feedback would be greatly apppriceated thanks for taking the time to read this and hopefully help.
03-11-2010, 03:35 PM
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After my shock, and doing a little looking, it sounds like the front calipers are getting over heated from the front pads dragging on the rotors. The heat in the calipers is in turn heating the brake fluid causing it to expand, as all heated fluids do, and causing the pistons to place even more pressure on the pads, and on the rotors, thereby causing more heat.......
Perhaps a rebuild of the calipers is in order?
Caveat here: I have never had this problem and am only flinging ideas hoping to hit the mark.
Perhaps a rebuild of the calipers is in order?
Caveat here: I have never had this problem and am only flinging ideas hoping to hit the mark.
03-11-2010, 08:23 PM
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Check your booster, since you were able to drive without problems when it was disconnected. Does the pedal move when you start the truck and when you turn off the truck?
Next, check/replace the bearings when you pull the calipers. If your rig has only been off-road, there is a good chance the bearings are bad from contaminates . I had bearings go out and boil the brake fluid, but I lost breaking power slowly. And of course the fluid went bad. This all happened over a stretch of time, month or so.
Next, check/replace the bearings when you pull the calipers. If your rig has only been off-road, there is a good chance the bearings are bad from contaminates . I had bearings go out and boil the brake fluid, but I lost breaking power slowly. And of course the fluid went bad. This all happened over a stretch of time, month or so.
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