So I'm driving down the road today, when the brake pedal becomes really hard to push. I hear a hissing sound coming from the floorboard area each time I press the brake. After getting past the initial hard-to-push stage, the brake pedal goes down further, but not to the floor, and stops the truck, though very slowly. I have to plan ahead when I need to stop, as it isn't possible to stop quickly. The brakes made no noises recently, and no lights are on in the dash area. I don't feel any grinding, which would indicate the brake pads are gone.

I'm going to pull a wheel tomorrow and check the pads and rotors. I checked the fluid yesterday before the issue started and it was fine. I'll check it again tomorrow.

Ideas as to what this could be? Anything else I should check?

Thanks,

WG

 

Hey man, ... sorry to hear.

I would first check the basics, ... Fluid, Leaks(in the cab above your feet) from the master, .....but if you're hearing a hissing sound from the floorboard area, .... You might wanna check the booster, via the troubleshooting section. VERY RARE, especially with what I believe is in yours, a dual diaphragm booster, 1" Master....

I would start with 'what you can see' and then go from there....(Troubleshooting in the Manual, testing Booster, Master, Pedal Play symptoms. I would think if the pedal is freezing up, then relieving, ..... one of those two is giving up the ghost.)

 

Step on the brake pedal and then start the truck, does the pedal go down a bit? If not, the brake booster isn't doing its job (ruptured diaphragm most likely). The hissing from the floor boards is also a big tell-tale sign, the booster gets atmospheric pressure from inside the cab (rubber accordian boot surrounding the brake pushrod). 2 years ago the diaphragm popped in my '88 - not fun since I was 4 hrs from home and towing my 3,000 lb mini-backhoe through the Appalachians -

 

Wow! The same thing is happening with my truck. I checked prices on 1sttoyotaparts and....~$800!! And thats $300 off dealer price!

 

$217 for the dual diaphragm at NAPA with a lifetime warranty - for such a simple item, go aftermarket
https://www.napaonline.com/Catalog/C...+50070+2070026

 

corax,
I did a search right after I found out the OEM price and checked out Napa. I've always tried to stay Toyota, but at this point, not gonna do it! I don't think I'll have this truck another 18 years.

 

Corax, I tried the brake test you mentioned abpve. No matter what I do, ignition off or on, the brake pedal will not move very much. It never sinks to the floor since this problem developed. I checked the fluid reservoir/master cylinder- it does not appear to be leaking. I didn't see any fluid in the cab either. I haven't pulled off a wheel to check the pads/rotors yet, but will do so while I have the truck in the garage. Their condition does not seem to affect the apparent need for a new brake booster.

Since I'll have to take off the master cylinder to get at the brake booster, should I replace the master cylinder too while it's apart? I have 204,000 miles on the Yota odometer, and believe the master cylinder to be original. The master cylinder costs $56, the brake booster $250. I'll check with Napa, as they seem to be cheaper than the other parts stores I called. As I'm facing a possible layoff in the near future, I'm trying to balance saving money on unnecessary repairs with not having to tear into the same parts twice. I recognize this is just a personal preference, and it isn't absolutely necessary to change the MC, but since I already will be removing the master cylinder, should I put a new one in? Or is this a waste of money on a part unlikely to fail? It's no big deal, just looking for some free input. Thanks for helping me diagnose the issue!

Toyo4x4, what will you do?

Wiseguy

 

Going down to Napa tomorrow and get Part Number: NBB 532776. Seem like they have one in stock.
Maybe this will fix the slightly rough idle, too, since its tied into the vacuum.

 

Toyo4x4,

I was wondering if you Plan to replace the master cylinder while it is off the 4runner.

Thanks,

Wiseguy

 

No need to replace the master cylinder if the pedal position remains constant under pressure - hold pedal down with a constant force with engine on or off. If pedal slowly goes to the floor, then there is a leak and it needs to be replaced, otherwise leave it alone. It is not really a wear item.

I would consider the bone yard replacement booster. Although they can go bad, its rare. Honestly, I would rather have a used OE booster than a new reman in most cases...especially with your uncertain financial future. Should be $40 or less at a yard.

 

From what I've just read above I don't need to replace it. I've been driving around today (carefully) and the brake pedal does not depress as though it has a leak.

 

Thanks, guys. I think I'll leave the master cylinder alone and look for a junkyard brake booster as suggested. For ~ $40 vs. $220, it's worth the gamble.

 

FWIW - test the booster before you remove it. A few quick checks should tell you for sure:

1. With the engine off pump the pedal until its completely hard. Start the engine and note two things: (as already mentioned above) did the pedal soften at all? Second, after a say 10 seconds of idle does the pedal feel any better.

2. The second thing to check is if vacuum is getting to the booster. There is a plastic check valve on the vacuum line going from the manifold to the booster side. Carefully wiggle/twist the check valve to momentarily break the seal on the hose on the booster side. If you hear a hissing, you are getting vacuum to the booster. If not, check the engine side (probably not a booster problem). Go from there.

If #1 is NO and #2 is YES on the booster side, you have pretty much confirmed your booster is FUBAR.

Good luck.

 

AngryBob pretty much hit it with the "previously loved" part suggestion. Most used parts will carry some kind of warranty, even if it's only 30 days. If you can, find a "U-Pull-It" or "Pick-A-Part" type junkyard where you can wrench off your own parts - there's plenty of money to be saved going that route. FWIW, a few years ago I snagged a master cylinder out of a junkyard (looked clean, so I guessed it wasn't very old) and its still perfectly fine.

Oh yeah, I'll second (or third?) that there's no need to replace the master cylinder if its OK right now.

 

So I finally decided to tackle the replacement of my brake booster. Halfway through, this happened:
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So, I gave up for tonight, until I buy some REAL wrenches later this week. I'll probably go with Craftsman, as I've only once had a tool they made fail (socket wrench), and they replaced it for free.

I snapped it while trying to loosen the clevis retaining nut (not the pin) under the dash, which attaches to the old brake booster.

 

Will cranking my 4runner with the master cylinder removed damage anything? I'm only cranking it to keep the battery charged, and will not touch the brake pedal or attempt to move the vehicle. I'll get around to finishing the repairs if my job ever slows down...

 

Won't hurt a thing.

 

Thanks. That's what I thought, but it's free to ask and good to be certain.