pendrag

Our 1999 V6 4WD 4Runner with ABS has suddenly developed a braking problem (I'm "assuming" suddenly, because it's my wife's daily driver, not mine, and she only mentioned it the other day). You cand stand on the brakes and they just gradually slow down the car. There is still more or less normal pressure on the brake pedal. The ABS doesn't come on. The problem begins with the first brake attempt of the day and doesn't improve with pumping the brakes.

It feels like something's pushing on the rear of the car, or as if you're braking downhill with a heavy load. What little stopping power you get seems to be evenly and smoothly applied; there's just not nearly enough! My pregnant wife discovered this by applying her brakes and coasting right through an intersection; thank God there was no oncoming traffic.


Things I checked:

• Brake fluid was at correct level and had been flushed with Valvoline DOT 3 & 4 Synthetic fluid about 15 months ago. I went ahead and re-flushed the system with a motive bleeder, again using Valvoline DOT 3 & 4 Synthetic. The old fluid was a slightly darker yellow, but wasn't very bad.
  
• Checked brake lines for obvious leaks - none found.
  
• Parking brake was non-functional and bell cranks were both frozen.
  
• I did the FSM operating check and air tightness checks on the brake booster. Operating checks came out ok, but in the second air tightness check (depress pedal while engine on, turn off, observe if reserve distance changes) the brake pedal pushes up when engine turns off.
  
• There is strong vacuum going into the brake booster.
  
• The ABS and brake indicator lights are off.
  
• No grinding (or other sound) coming from the discs.
  
• When I stand on the brakes while going down a gravel road, the ABS didn't activate, but I got a few short, intermittent "grinding" sensations/sounds coming up through the brake pedal. This wasn't the normal ABS vibration.

I'm going to fix the bellcranks next, but what else should I be checking out on the brake system? I'm kind of thinking maybe the parking brake was frozen, leading to non-functional rear drums, leading to the front brakes taking the full load, then glazing...sound like a reasonable hypothesis? Thanks!

brokedown1

Possibly you have a bad proportioning valve, or both wheel cylinders are stuck, but not likely at the same time. Pull the drums off and you should be able to put a little pressure on the pedal to see if the shoes all move freely. Also, I assume, you checked to see that there is no fluid leaking onto any of the drums of discs? You could also have a rear hose check-valving on you. If you are not familiar with that problem, it's where the hose degrades inside, and can have a little flap that stops the flow of fluid when the brakes are applied. Just some thoughts, good luck.

tantacoma

DONT LET YOUR WIFE DRIVE THIS UNTIL FIXED.

I have no experience with ABS, but will chime in. Read at your own risk .
Could be a bad ABS wheel sensor.

Have you checked the brake pads and shoes? The grinding sounds could be due to completely worn linings.

One 'get around' is to temporarily disable the ABS by pulling the appropriate fuse. Here is a snippet from an old thread on a different Toyota Tundra forum:

DRCOFFEE

What you described sound like a vacuum check valve problem. I had that happen in december when it was cold out. The check valve is on the vac assist drum on the firewall. By the brake resevoir. Remove it and soak it with WD40 inside the valve. What I did was fill it with WD40 and then work the valve around for a minute with a small screwdriver on the plunger. Just dont damage the seal around the sides of it. The WD40 is a thin lubricant which is safe on most rubber items and is a water dispersant. A new one is $40 so its worth a try to free up the valve.

If the valve is good then the booster is defective and the diaphram is probably shot.

The ABS will only activate if you can get the brakes to lock up and stop the wheels from turning.

tantacoma

Good advice from DRCOFFEE here.

There are several in-cab tests you can do, to see if the booster/checkvalve is working right. This one works on most, if not all, Toyotas:

DRCOFFEE

WTF?!

Does anybody ever come back with the results of their problem? It drives me nuts when someone comes asking for help and then disappears leaving the question unanswered. Forum members can learn from your problem today, tomorrow, next week, or next year.

pendrag

Sorry I took so long to return. I got caught up with work, but I've been working on the 4runner the last few days. Here's what I've been up to:

My bellcranks were completely frozen up with rust. I removed them, stripped them down to bare metal with a wire wheel, painted them, lubed the crap out of them, and reinstalled.

The brake shoes were extremely worn, unevenly so. One had a spot where it was down to about 1/64" and chipping on the edge. I replaced the brake shoes.

When I replaced the shoes and bellcranks, I removed the cables from the bellcranks and adjusted them to about 0.025" (spec is 0.016" to 0.031"). When I reinstalled the cables, the bellcranks were pulling back too far, so I've been playing with the cable slack adjuster. I thought I had it about right, but the parking brake is still not engaging. It's clicking about 13 times (to full extension) but it's not stopping the car. I think I may have not adjusted the brakes far enough, so I'll try that again.

I bled the brakes again tonight after finishing (I thought) with the drums, but stopping is still soft. I haven't checked the booster/checkvalve yet, as I've been working on those drums for starters. It's raining now, so I'm done for the night.

So anyway, I'm still around, still working on this. I'll keep the thread updated as I try various things. Thanks!

DRCOFFEE

The way I was taught to set the rear shoes is to tighten the shoes enough to get the drums on. Then tighten the star wheel until the wheel cant spin. Now to get the shoes in the right position, pump the brakes 2 or 3 times. Go back down and set the star wheel so that the wheel only spins one revolution when you spin the wheel. After that the parking brake will adjust the brakes. Remember to only pump the brakes if all the drums and calipers are on.

Once the brakes are set properly, go back and setup the parking brake bellcranks. If you do the parking brake first the brakes may not be set correctly

pendrag

Thanks, I'll give that a go. When I did them earlier, I just tightened the star wheel until I could just hear the shoes kissing the drum.

Is it okay to tighten the star wheel by actuating the bell crank manually? I found that was easier than messing around with a brake spoon through the rear port.

DRCOFFEE

I wouldnt. You need to know the star wheel is moving and theres no guarantee using the bellcrank. I just use a stubby flat screwdriver and rotate the wheel every few click. Pumping the brakes centers the shoes on the drum with force but only do it after using the star wheel to get it touching the drum or you can pop the wheel cylinders out. You may know that but a casual reader may not be aware.

pendrag

I just got back from a trip out of town, so I haven't had much time to work on this the last four or five days. I tried the 'tighten the star wheel until the wheel won't spin, pump brakes, and then back off the star wheel' idea, right before I left. I had a hard time getting the star wheel loose again from the access port, and I gave up at one point and just decided to pull the wheel off. Unfortunately, that was when I broke my security lug nut socket, so I'm going to probably bring the truck by somewhere and get them to remove the security lugs. I did finally end up getting the adjustment looser, after I tried a different pick and worked at the star wheel through the rear port for a while longer.

Also, the battery died while I was out of town, so I'm going to have to jump it tonight.

More as it develops...

pendrag

I swapped out the vacuum line to be sure it wasn't blocked, first of all. Then I pulled the check valve out. The valve seemed to work fine. With the engine on, I'm getting strong vacuum out of the engine. I blew into the check valve from the engine side and it closed up; when I blew into it from the booster side, I got air flow coming out. I connected the valve to just the engine (without reinstalling it into the booster), and the valve had strong suction, so I believe I can rule it out as the problem. It did seem a bit loose at the grommet to the booster, so there is potential for leakage there. I'll replace the grommet next chance I get and see if there's improvement.




Results from the FSM brake booster tests:
1. OPERATING CHECK
(a) Depress the brake pedal several times with the engine
off and check that there is no change in the pedal
reserve distance.


No change in reserve distance apparent.


(b) Depress the brake pedal and start the engine. If the
pedal goes down slightly, operation is normal.


Pedal goes down slightly.


2. AIR TIGHTNESS CHECK
(a) Start the engine and stop it after 1 or 2 minutes.
Depress the brake pedal several times slowly.
If the pedal goes down farthest the 1st time, but
gradually rises after the 2nd or 3rd time, the booster is
air tight.

Goes down easy the first time, then presents resistance on subsequent pushes and travels shorter distance.


(b) Depress the brake pedal while the engine is running,
and stop the engine with the pedal depressed. If there
is no change in the pedal reserve travel after holding
the pedal for 30 seconds, the booster is air tight.


When I turn off the 4runner, the pedal immediately pushes up against my foot and wants to rise up.




If I turn off the engine with my foot off the brakes, then press the brake pedal with the engine off, I hear a hiss coming from somewhere near the booster. Here's a youtube clip I made of the sound. It only occurs on the first pedal press. The pedal is pressed first at 6 seconds into the video, then you can hear the pedal being pressed several more times.




Finally, just wanted to note that I adjusted the brake pedal travel today since it was low.

pendrag

Any opinions?

pendrag

Update - I replaced the brake booster and bench bled and reinstalled the old master cylinder. Then I bled the brakes again. When I test drove it, the brakes were very strong again (I squealed the brakes in the driveway going only a few mph). They felt almost too strong. Then I gave it a test drive around the block.

The brakes seemed to be working ok, but when I got back from the test drive, parked, and then decided to drive it again, the truck wouldn't move easily. It felt like the brakes were applied, even though I wasn't pressing the pedal and the parking brake was down.

Thinking I might have over adjusted the brakes, I backed off them to the point that the parking brake didn't work. I then drove back and forth in the driveway, pumping the brakes and applying the parking brake to the point that I hoped I'd adjusted the brakes enough. I took it for another test drive, and the brakes got tighter and tighter, to the point that I was giving it a fair bit of gas just to get back down the block to my house again. The front brakes feel warm to the touch, but the rear brakes feel cool to the touch. Also, the parking brake isn't engaging.

So, what's up with that? I'm worn out, but I'd really, really appreciate some guidance on this, because I'm feeling really discouraged about this project.

pendrag

Hi, after a busy weekend, I'm back. I loosened the rear drum brake adjustment. Next, I checked out the brake pedal adjustment and the pedal was down too low, due to me not threading on far enough the U-shaped linkage 'yoke' that connects the push rod to the brake pedal. I re-adjusted the brake pedal and thought I'd finally fixed things. The brakes were a tad softer than before (more like they should be) and the truck drove ok. I also went back and readjusted the parking brake.

After I drove it across town, I started noticing that there was an intermittent vibration coming from the rear, which I could feel though the parking brake handle when I applied the parking brake while in motion. It felt like the vibration came for a while, then left for a while. I noticed it at high speeds 70+ and lower ones (45 mph). I think what might be going on is the rear brakes intermittently starting to drag, then loosening back up. The vibration, I think, is coming from the drum needing to be turned. I don't notice the vibration through the pedal, when braking; I'll just be driving down the road and the truck will begin vibrating and it will get worse and worse, then die off. Jerking the parking brake handle didn't do anything to 'loosen' it when it was vibrating. When I stopped, I smelled hot brakes coming from the rear wheels.

So, any ideas now? Thanks guys!!

stophammertime

Checking in for the same problem - I'll be posting up the resolution when I find time to knock it out this weekend.

pendrag

stophammertime, please do come back and let us know what it was. I'm looking forward to your post! Also, I like your user handle. :-)

J2F42C

I'd get the drums turned (not at your local auto parts store), then make sure your E-brake is working correctly including the bellcranks before putting them back on.

You may have a bad rear cylinder(s) that made need replacing. But start with the drums first.