The brakes on my 4Runner lock up after I drive it for about 10-15 minutes. When I start the truck cold or if it sits for a little bit, I have no issues.

I have replaced my brake booster, brake master cylinder, front brake pads, anti-rattle clips, front brake rotors, front wheel bearings, and front wheel bearing races. I have adjusted the brake pedal.

I bled the whole brake system (except the LSPV in the rear) until the fluid came out completely clean. I figured that forgetting to bleed the LSPV could have been the issue, I rebled the brakes again starting from the LSPV. I went LSPV, driver's side rear, passenger's side rear, passenger's side front, and driver's side front. There was some air in the lines the second time I bled the brakes.

The problem was slightly alleviated from the second time I bled the breaks, but they continue to tighten, just not completely lock up.

Am I missing something when I am bleeding the brakes or do I need to bleed them more? I know ideally I should replace the front calipers and do the rear brakes too, but I'd rather not drop the money right now if I can fix it by working with what I have.

 

kind of sounds like the caliper pistons are rusted and "sticking" in the caliper bores ..


.

 

Replace the rubber brake lines. They can swell internally and cause brake lock up.

 

Before you start replacing parts, try to figure out where it is happening. It might be as simple as touching a wheel after you drive for a few minutes; the one that burns the hell out of your hand is the one.

It probably has nothing to do with bleeding; with your foot off the brake any expansion in the brake system pushes fluid back into the master cylinder (unless the master cylinder is toast). Air in the system should produce a very noticeable "spongy" pedal.

Like thralldad, I had a bad flex brake line (on an S-10). It didn't cause the brakes to lock up, but to not apply. But I think he's right that it could cause your problem. But you should be able to see it easily in the slightly more worn pad, or the very hot wheel. If you still want to check before replacing it, use your c-clamp on the piston, just like you were replacing the pads. If compressing the piston is difficult, replace the flex line.

 

Did you adjust the brake booster when you replaced it? 4runners have an adjustable rod between booster and master cylinder. I had the same problem on my 95' and .050 thousandths of an inch makes a huge difference. I'm not talking about adjusting the pedal, guaranteed its the booster adjustment. Don't spend the money on brake hoses or anything else like I did before you try adjusting this. Mine worked fine when cold then a mile or two down the road the brakes would drag almost to the point of complete stoppage. Hope this helps!

 

As scope says, figure out first which one(s) are locking up. Make sure you check the rear brakes. My son reworked his rear brakes, adjusted the star wheel too tight in order to make the e-brake work, and had exactly the symptoms you are describing. After he drove it 5-10 miles the brakes would heat up, expand, and essentially lock the rear wheels.

While the rear brakes are self-adjusting when you pull the e-brake, they can only get tighter, never looser. Once they're too tight, they'll stay that way until you loosen the star wheel by hand.

 

Yes, I did adjust that rod and it did help, but they still lock up. That's actually what I meant by adjusting the pedal, I just didn't know how to best phrase it.

Thanks for input on the flexible brake lines. I totally forgot that could be an issue. I'll more than likely just replace those since they're probably shot after 30 years. I'll take it for a drive and try to figure out which brake is giving me the issue. If after the brakes lines are done and the front is still giving me issues, I'll go ahead and replace the calipers. I'm trying to hold off on doing the rear until summer time (poor college student).

More input is welcome!

 

Figure out just what brakes are locking up!!!

Much easier to figure out the problem at that point.

Does your Emergency brake work like it should??

 

I dont know if you fiXed already but...
This thread help a lot if someone else played with the self adjust...
https://www.yotatech.com/forums/f116...l#post52255842