I'm not having much luck getting help at yotatech, so I thought I'd come over here and see if y'all could give me some advice about my 1999 4Runner (ABS, 4x4). I'll try and be succint, but I've been working on this for a while.



Briefly, I started with two problems: (1) a hard pedal and weak braking and (2) bellcranks were frozen with corrosion. I removed the bellcranks, refurbished and painted them, and reinstalled with a new set of shoes (old shoes were unevenly worn, with one down to 1/64"). I inspected all the connections, replaced the vacuum line to the booster, and bled the brakes.

So, still chasing the weak braking, I tested the booster according to the FSM. Results of each test are listed below, but long story short, I decided to replace the brake booster.

I replaced the booster and bench bled and reinstalled the original master cylinder. Current Problem: The brakes came back super strong and responsive, but when I test drove it around the block, the brakes increasingly started to drag. I parked it a few minutes, then tried to do another test drive; the brakes were engaged so hard, I could barely get it to move.

Thinking I'd over adjusted the rear brakes, I popped them off and adjusted them so loose that the parking brake didn't engage. Then I backed-and-forthed in the driveway while cranking on the parking brake to hopefully adjust them right. I test drove it again and the brakes started dragging increasingly hard, enough I barely made it back home. The front brakes were warm and the rears were cool.

So this went on until 11:30 pm, and I'm now discouraged and exhausted (upper 90s here today). I could use some expert advice and I'm hoping y'all can help me figure out what to do next.



BELOW is a bunch of stuff I've already done/checked, which you might find useful to know.



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. Whooshing sound on first pedal press with engine off.

(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.

Things I checked:

• Brake fluid was at correct level and was flushed with Valvoline DOT 3 & 4 synthetic fluid 15 months ago. I re-flushed the system with a motive bleeder, same fluid. The old fluid was a slightly darker than new but wasn't very bad.
  
• Checked brake lines for obvious leaks - none found. Flexible lines are nearing the point they need replacing.
  
• Parking brake was non-functional and parking brake bellcranks were both frozen. I refurbished and replaced bellcranks.
  
• Old booster had a good check valve and vacuum is going to the booster.
  
• I measured the clearance between the booster push rod and the master cylinder using a vernier caliper and adjusted them to be as close to 0 as I could.
  
• I bench bled the master cylinder, holding my fingers against the line ports and pushing the piston with a punch. I bled the rest of the system with a motive bleeder after reinstalling the booster.
  
• The new booster install was fine, but I worried about doing damage while cramming the booster into place. The linkage between the booster and the brake pedal was very tight. I'd previously adjusted the brake pedal travel distance according to the FSM.

so fronts are dragging..... could the pistons be seized causing the vehicle to think its being stopped?

does it pull to one side?

could something be wrong with a valve in the master cyl not letting the fluid to flow back through the line (the opposite way) after its forced down the line towards the caliper making the vehicle stop.

were both front brakes hot after test drive?

EDIT: you said you adjusted the brake peddle according to spec. could that be off pushing so hard on the master cyl and not having enough room to return back to its original place so that the pressure is taken on the brake lines to the calipers?

Comments inserted above.

thanks. keep me informed, ill check back in the morning to see if anyone else has commented. sleep on you thoughts and see if anything comes to you.

hopefully we have converted you over to T4R.org for good. haha welcome!

I think if that were the case, it wouldn't be "ok" at first and then get progressively worse.

That's a tough situation to be in, I've been in the car business a long time and don't really have much advice to give ya. I'd be stumped too.

With the rears being cool, I'd start looking there. Usually they need to be warm to very warm to the touch.

Loosed the star adjuster enough and pull off the drums. Look to see if they may be warped, or had grooves cut into them, causing the shoes to bind against them. You may need to have them resurfaced. Also physically check the motion of the E-brake on both sides.

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!!

hmmm...on your recent issue with the rear brakes, you may wanna check your slave cylinder in the drums if they're heating up so much you can smell em. is there any gear oil bleeding in the drums? seems like the vibration started AFTER you messed with the drums so I'd go back to what you did exactly and double check it. sometimes the simplest overlooks can cause something like this. not sure about the rest of your brake troubles, very weird. as much as I'd hate to, I'd go back through every lil step.
Good luck man.

Yes, I agree I'm likely the cause of the vibration. I'm wondering if it has something to do with either my drum adjustment or perhaps the drum being out of whack / warped somehow.

I had to work on my other 4runner's front brakes today, to put on new pads and rotors, and I'm happy to say that THAT job actually went off without a hitch. I needed that.

My wife's due in 23 days, so I've REALLY got to get the drum brakes figured out soon!