Rear breaks lock up on hard stop

I have a 1997 SR5 4runner that I've recently bought. New to Toyota and absolutely love it!! Except it tries to pull a Burt Reynolds when you brake hard. The back end losses control. I can feel the front pulsate when I'm around 20mph. It always throws the back to the right and I'm facing oncoming traffic. I have pulled both abs sensors in the back and both are fine, passenger rear had metallic matter but wiped off and nothing changed. I adjusted the rear drums and nothing changed. My axle seals are not leaking and I have new shoes and hardware. It stops great with no concern until you need to stop NOW then it tries to kill you. Any help would be AMAZING!!!

 

Rear breaks lock up on hard stop

Rear brakes lock up on hard stop

Which one is correct?

 

Cycle some new fluid through it by bleeding. My ABS sensors have been broke for over ten years but still stops evenly...

 

Did yours lock as well? And I will definitely try that

 

I have never in over twenty years had a brake problem. I kind of like it without anti-lock. Come up to a stop and the darn brake pedal starts lifting and it doesn’t stop. Helps in snow though I don’t see much here and try to avoid driving in it now...

 

And they have never squeaked...

 

I'm new to abs brakes. I would believe that it shouldn't lock like it is tho. Mine dont squeak either. It locks up like it does in warm dry conditions

 

Your front pulsing are due to bad front rotors.

Are you sure both rear brakes lock?

Lockups are often dues to rear brake cylinders and badly adjusted or faulty e-brake cables.

Edit: I see you said you had all new hardware. I deleted a bunch.

-Mike

 

I just read a post that an old brake line can deteriorate inside and cause a delayed release of fluid...maybe that is it?

If you have put on quality parts and didn't mess up the rebuild...then try a new brake line?

Since it spins to the right...wouldn't that mean the passenger side is locking up?

 

Lol...I also read another post about troubleshooting this.

If you can get it to happen in a CONTROLLED environment, jack up the rear, verify the brake is locked, release the bleeder valve and if the wheel unlocks...it's a hydraulic problem.

 

Grit from wear and corrosion can build up inside the brake cylinders. This can cause the pistons to get stuck enough in the cylinders that the return spring cannot overcome the friction (this can also happen in the master cylinder). It can also cause the pistons to skew in the cylinders and cause very odd wear. Rust, dirt and crud can also build up on the sliding surfaces of the brake caliper which can cause them to not release (this is easily seen by uneven pad wear).

One function of brake fluid is to absorb moisture in order to prevent corrosion in the lines and pistons. At some point it can absorb enough moisture (water) that, under the heat of heavy braking, it can boil. This can cause the brakes to lock up. Replace brake fluid periodically (not sure of the best interval, but it’s more related to time and environment rather than miles).

Probably best to take “old reliable” to a brake place and have them go through the whole system. Spending $$ now to have things taken care of properly is better than spending $$$$$$ when they fail and cause collateral damage.

Just a note. Stand there and watch the mechanic. Make sure you stay out of their way and don’t ask a lot of questions. You’ll probably have to stand just outside the roll up door for liability insurance issues. Even if you’re not mechanically inclined, they won’t know that, but they’ll be more conscientious of what they’re doing because you’re watching, and will more likely invite you in to show you stuff as they do the work.

 

I have pulled both drums, pads have even wear and they lock every time I stop hard. Not just every once in a while, every time. I do use the e brake often but even after I adjusted, cleaned and resurfaced the shoes the drums to where they needed to be I took it up my road (hadn't set e brake yet) I was an idiot and decided to stomp on the brakes at 45 and almost rolled it. I have bleed brakes today, all except driver rear I will need a new nipple. And i dont feel any pulsating until a hard brake, around town is smooth.

 

I am not new to brakes and have worked on many, but am new to abs. Planning on replacing both wheel cylinders and rear brake hoses. Wouldn't hurt with the fact that it has almost 309,000 miles on it

 

If it seems to brake normally at normal speeds and normal conditions, it may not need to be utilizing the ABS capabilities because none of the tires are loosing traction. However, under heavy braking, when the nose dives and the rear wheels start to loose traction and slide, the ABS needs to do something to correct for the loss of traction. The controller figures out what’s happening based on input pulse frequencies from all the sensors and reacts in what it thinks is an appropriate response by reducing pressure at the wheel(s) it thinks is starting to skid (spinning slower than the other wheels). If the controller is getting bad information from one or more of the sensors (intermittent or none), it will react based on the data it sees which may be inappropriate for the actual conditions (garbage in, garbage out). The controller may also have problems adjusting the pressures to individual wheels due to internal problems or problems with the hydraulics (sluggish valve or actuator, bad hydraulic line, ?). Your scenario seems to indicate that when the rear wheels start loosing traction, ABS, for some reason, does not release some pressure on the rear wheels to allow them regain traction (a sliding tire has no directional stability), and somehow thinks the front left wheel is sliding (even though it may not be) so it releases some pressure which allows it to roll easier. Couple that with that ABS may also think that the right front tire is braking normally so it doesn’t change anything, and “presto”, the truck is spinning to the right.

This may sound crazy, but it almost seems like a couple of sensor wires or brake lines are crossed somewhere so that ABS is confused as to what reality actually is, or its response is being directed to the wrong wheels.

There may be some ABS codes available through the diagnostic port.

 

I have looked at all sensors on each wheel, none have been tampered with until I removed and wiped each contact off. It appears my abs unit has been removed and reinstalled making me believe this has been happening befor I got the vehicle. I will start cheapest starting with new wheel cylinders and rubber lines. Would it be worth pulling the abs fuse? Seeing if that's what's causing me to lose control?

 

Check as much of the sensor wires from the wheels to the controller as you can. Look for chafing, frayed wire or bad, loose, or corroded connector contacts.

If the ABS controller was removed and replaced, that opens up some possibilities. If the ABS is a rebuilt unit, it could be defective, or it was installed incorrectly and there’s a greater possibility that lines or sensor input could have been switched. I’ve never messed with ABS units, so I don’t know what kind of identifiers are on the unit to indicate which line goes where or how to identify which line is which (I guess you could trace them to find out). An official Toyota Service Manual would probably tell you (the manual for my 2003 Tacoma is two volumes, each about 2” thick).

 

Well looks like I'll have to invest in a manual then. Definitely worth the look to see if any lines are switched

 

Get the official one from Toyota. They may have to order it.

 

Will look into it

 

I would just disconnect the ABS sensors and fuse. If the ABS pump is not working and you still have the issue, it shouldn't be the ABS pump.

My understanding of ABS was that it was more to release pressure out of the system. It's got to be a rare thing for the pump to add pressure.

 

I’m not sure about OPs 1997, but my 5th gen uses ABS as a method of traction control for limited slip functionality. The ABS actually applies positive pressure to individual calipers to to prevent wheel slippage.

 

Good to know, I was not aware that could be the case.

I think for third gen, Trac Control was only for 2001-2002? I know my 2002 has it. There are lots of web pages on how to disable it.