A fresh new year bump to a timeless thread.
I've owned my 03 with the "small" brakes since 2011. I now have about 180k miles on the old gal and she has big heavy tires and wheels along with the body armor, bumper, and winch to lug around. Although she sits in the garage 80% of the time now, I figured it was time I rebuild the brakes as the front pads were giving an audible indication they were low and as far as I can tell, the fluid looked original.
I rebuilt all of my factory calipers, had the rotors turned, and picked up new pads before reassembling. During that time the reservoir stayed topped off and I plugged the lines as best as I could to prevent much air from making it into the system.
Having a 1999 Lexus GS it operates like our 4runners in terms of the electronic motor that pressurizes a reservoir. I never could get the pedal feel I wanted in my Lexus after a rebuild on the brakes earlier last year, so I took it to Lexus, and despite it being a hefty bill, the brakes felt better than they ever had since owning that car.
So - equipped with this experience and knowledge, I didn't bother with anymore than bleeding the calipers a bit for safety before dropping the 4Runner at Toyota to do the fluid flush and bleed process properly.
Upon getting the truck back, I didn't feel great about the feel of the pedal. It felt okay - probably similar to how it felt before I did the brake job, if even that good. Compared to my Lexus, the pedal feels like garbage. I drove around for probably 15 miles trying to see if the pedal feel would improve. It didn't. I've had some experience in the Lexus, (before I had the MC bled properly) after letting the car sit overnight, the pedal would feel better in the morning. Not the case with the 4Runner. In fact, I cannot get the front wheels to lock in a hard brake in a strait line (33" BFG tires). To me this is inadequate at best, and closer to dangerous. It feels to me that the pedal stroke is far too long before I get good contact between rotors and pads and I never feel a firmness I get with the Lexus. I called the dealer and spoke to the service advisor about it. He told me the procedure with the tool would have completely flushed the system and gotten the air out of the lines and brake master cylinder completely. And then said maybe it's something else in the brake system - frozen caliper, failing BMC, etc. None of it really adds up and I feel either there's still air in the system or (as difficult as it is to believe) the pedal is and will always be just this mushy.
A couple of observations:
I've driven a GX470 with stock sized tires - as I understand it these all came with the "large" brakes - and the brakes feel SOOOO much better and more powerful than mine. I've also spent a fair amount of seat time in an 07 FJ Cruiser - also, as I understand it, these came with the larger brakes - and 33" BFG tires. Like the GX, I was very surprised how much better those brakes felt than mine.
Is it that the small caliper / rotor brake systems just feel lousy compared to the larger ones? Based on science and physics, the larger brakes should only be more effective at resisting fade by absorbing more heat energy and should have no bearing on pedal feel, as it's the same master cylinder that's doing the work on the pistons that should be responsible for the "feel". I considered the 5th gen brake upgrade, but dismissed it due to the relatively minimal difference I'd expect in performance.
I've noticed, as others have stated, following the engagement of the ABS the brake pedal will get firmness and the stroke will be reduced. I'm not sure why this happens exactly, but for a period of time (maybe minutes, maybe the remainder of the drive) the pedal feels great - like I wish it did all the time. I'm trying to rationalize what is happening. Obviously the solenoid(s) for the ABS system is actuating. Is an air pocket being released resulting in the better pedal feel and brake performance? And if so, where is it going? It seems based on my experience that a day later - after the car sits for a spell, this improved pedal feel vanishes, and the old mushy feel is back. If it's going into the lines, maybe doing a line bleed / flush directly after would be good? Would engaging ATRAC actuate the same solenoid(s)? Curious - as winter weather is here - maybe after a little skiff of snow, would it be worth getting out and engaging ATRAC and / or ABS, and then pulling back to the garage and trying to bleed out any air that escaped the master cylinder via the calipers before it runs back up to its nest?
Here's a video of the BMC firing up with the key on after sitting in my garage 2+ days. I'm a little surprised at how high the fluid rises in the reservoir when not pressurized. In the back of my mind I wonder if air voids are what are getting compressed as the fluid draws down. Curious if others have a similar occurrence - honestly I never really noticed before.
2003 4Runner Master Cylinder - YouTube
All this to say, I suppose I'll ask my spouse to help, and do some bleeding from each caliper, but I still am trying to find a solution for triggering the solenoid in an attempt to purge it of any air pockets that may have formed over time and somehow not gotten flushed with the dealers' service.
hwell:
