random locking front brake

vehicle: 2001 DC v6 4x4

Helping a buddy troubleshoot his super weird brake issue. Brake lockup up randomly once every other week to 2-3 times a day. There's no consistency.

Issue: when the vehicle is slowing to a complete stop but before coming to a complete stop and not even applying that much pressure to the pedal, seemed like you suddenly slam on the brake hard. Other time, once you come to a complete stop and wait for the light to turn green and go, the rear tire will spin as if someone chock the front tire. Issue also occur when you come to a complete stop, shut off the vehicle and at a later time while trying to drive off, the rear tire will spin as if the front tire is chock.

Note: the brake pedal will return to the original position (up) when brake lock occurs with and without the engine being on. No fluid leak.

What's been changed:
-new ABS pump (issue still occur)
-unplug ABS motor (issue still occur)
-new power brake booster (issue still occur)
-new L&R front brake caliper (issue still occur)
-Front brake line are SS and only few years old

Maybe a sticking brake master cylinder? Just don't seem right how the MC can cause this intermediate issue. We bench test the MC and the internal spring/piston return to normal position every time.

 

Piston in the caliper?

With all those items replaced, could be a good time to replace the calipers and move up to Tundra brakes.

 

Here's a write up by @turbodb if you guys decide to go down that route -

https://adventuretaco.com/new-to-me-tires-and-a-tundra-brake-upgrade/

 

replace your brake hoses

 

He don't need TBU.

So even after new caliper (L&R) as mention in the original post, the piston are bad, lol? Is that what you're saying?

 

Didn't catch the new caliper; disregard said post.

Hoses are a good suggestion as stated above. Who's to say gunk didn't get stuck in there or something.

 

The front brake lines stainless steel, manufactured by Crown and maybe 1.5 yards old. I doubt they'll be the issue. If they're factory rubber, I would understand.

 

Orginal fluid were clear prior to bleeding. Nothing is clog in the line from what I know. When we replaced the caliper, fluid drops consistently. We manual bleed the system and the pressure from ever crack is the same and fluid came out perfectly fine. We even vacuum the entire system after manual bleeding.

 

there is the possibility that the master cylinder spool valve(s) are binding... it is pretty rare but it does happen if the fluid is so bad that the bore/spool valve is corroded. If you look at the diagram you will see the 2 spool valves separated by a spring in the middle... I would look at your lines to see if the forward lines go to the problem brake. It is easy to disassemble to verify but usually a new master cylinder is the "fix". If you do replace the master cylinder be careful of the seal that sits in the brake booster... damaging this causes a vacuum leak that is bear to find if you don't know it is there. If it still happens the next step is dealing with ABS... when people start having problems there that they usually disable it as it is expensive to fix.

 

Will have him look at the MC. As far as the ABS, another unit was put in and the issue still exist. We then unplug the ABS motor and that didn't fix it as well. We now know the ABS is not the issue to began with.

We originally thought the PBB was the issue by not releasing the pressure from the MC but after installing a reman unit, the issue still exist. Same for the brake caliper, lol.

 

very odd so I am going to ask a odd question... could he have installed the caliper(s) on the wrong side, i.e. with the bleed ports on the bottom? I am not even sure that it can be done on a Tacoma but you never know.

 

Maybe bad front spindles bearings?

 

When we changed the caliper, they spin freely on the lift. With tire on, there's no play/wobble. Even when driving, they make no noise.

 

I don't have any suggestions, except to say Brake gremlins suck big time.

 

I was about to suggest that as well... my old tacoma was on dropped spindles and bagged... I think I torqued one of the bearings too much one day I was driving and one bearing seized locked up front right pulled my whole truck right thankfully no accidents were caused

 

But these front wheel bearing are pressed fit into the hub/spindle and the only thing pushing against them is the cv and 34mm nut. But they're not seized, I would understand if they stop spinning after the lock up.

I suggested he change the MC, will find out if that fix the issue.

 

Big time. I was sure it was the PBB or ABS pump but it wasn't.

 

Do you have an update on what the problem was. I am having the same issues on my 1995 Tacoma. With new booster, front calipers, and rubber lines.

 

***UPDATE***

@ThatPurpletacoma

Changed the master cylinder as a PM and issue still occurred. We end up adjusting the travel limit on the power brake booster. That solved the issue.

Might want to check that.

 

Ok I will have to go try that.