I just did the tundra brake upgrade on my 99 4runner. Everything went well and I bled the brakes after I was done until there was no more air bubbles coming out.

After putting everything together and going for a drive, my brake pedal is quite soft. I bled the brakes again but still had the same issue.

Took it to a mechanic to bleed it for me since I thought I didn't do it properly. Still had the same issue. The mechanic also pointed out that the truck dips forward a lot when braking, suggesting the rear brakes aren't doing much but I think that was the case before I did the brake upgrade as well.

I asked him to keep the car for another day and check out the rear brakes and fix the soft pedal.

He didn't get a chance to look at it yet but he thinks my master cylinder is bad and is not providing enough pressure to the rear brakes.
I didn't think this was likely since it was working fine the day before until I did the brake upgrade. He said I likely damaged the seals in the master cylinder when bleeding the brakes because my friend was pushing the brake pedal too hard.

Is this even possible or likely? Any ideas what to do here? I don't want to buy a new master cylinder when to me it doesn't seem like that's it.

i may be wrong but the rear brakes are drum brakes and it seems more likely to me with the extra added breaking upfront that the rears just need to be adjusted to lock at the same time as the front, you could have a master cylinder issue becuase of the soft pedal feeling your talking about, it's tough to say without having a look at it, but i would have started with adjusting the rear brakes before going the master cylinder route

Thanks, I did adjust the rear brakes about a month ago and have barely driven it since then so I don't think they just need to be adjusted but I can check this again.

Even if they are not adjusted, why would that cause the pedal to be soft? Shouldn't it just mean longer pedal travel if anything? Also they wouldn't have gone out of adjustment from upgrading the front brakes I wouldn't think.

well i could be wrong on this, but the way i'm looking at is you've increased the braking resistance on the front end by quite a bit, meaning the front tundra brakes are now doing a unproportionate large part of the braking, that was just in reference to the nose diving effect your getting now.

as for the soft pedal, yeah i don;t know about that it does seem like a master cylinder problem but then again it could be becuase that by the time the back brakes kick in the fronts have pretty much already stopped the car so it makes the pedal feel soft since your only apply 50% of the weight you had to to get the truck to stop, this is all speculation on my part.

more or less just thinking aloud, i can;t see it being much of aything else, either a simple adjustment,master cyclinder, or air in the system from somewhere else....

You could still have air in the ABS system which will cause soft brakes, standard bleeding will not remove it. I just had to fix this on my 4runner. In order to push the air out you need to activate the ABS system, I used a dirt road. Afterwords bleed them like normal and I did the process 1 more time and it was corrected. Hope this helps.

Did your mechanic actually take off the drums and visually check the rear brakes? It's common for these to puke rear diff oil through the seals. It's also common for these to have crappy master cylinders causing a spongy pedal.

No he did not. I did read about this axle seal issue and I just tried to take the drums off to check myself but can't get them off. They get loose but are still stuck somehow. I'm guessing the shoes are grooved into the drum but I'm not able to back off the star adjuster (it seems to only go one way to tighten the brakes?) Is there a trick to this?

For the master cylinder, what are the chances it went bad at the same time as I changed the front brakes? I don't believe in crazy coincidences like that unless it's like my mechanic said and I broke the seals when bleeding the brakes myself by having my friend push the brake pedal too hard.

I'm in a bit of a rush to get this fixed since I'm gonna be pulling a trailer across canada (about 2,700 miles) at the end of the month and need good brakes. I'm thinking of just letting the mechanic throw parts at it

How many clicks does your e-brake take to hold the car? This is the first way to check if the rear is adjusted properly (most manuals say 5-7 clicks to HOLD the truck).

Air in the ABS system is the next likely problem. That is what I had told Yukon when he had a similar problem. I didn't realize that the ABS could be bled by just making it activate, but it seems to have worked for him. I would try this before letting the mechanic try anything (that can get expensive fast). After activating the ABS a few times, fully re-bleed the brakes and see what that does for you.

I doubt you did anything to the master cylinder. Based on the 3 or 4 I've replaced over the years, I not sure it is even possible to damage them by pushing the pedal too hard.

Takes 8 clicks to hold the car on a slight slope (just tried right now). However, I think the parking brake cable needs to be adjusted too as there's some slack in it as I don't feel any resistance until the 4th click.

As for the air in the ABS system. Is there no way to bleed this without engaging it? I live in the middle of a big city and there isn't a dirt road for probably a 30 min drive at least and it doesn't look like it's gonna snow /ice anytime soon...

Sounds like you might need to slightly adjust your drum brakes. If you did the Tundra mod yourself, it should be pretty easy. Chock the fronts well, then jack the rear end up so both tires are off the ground. Remove the little dust cover on the back of the drum housing, and use a brake spoon to turn the star adjuster (lots easier than using a screwdriver). Turn them so that you get the slightest bit of drag on the tire when you turn it. Be careful though, as it is easy to go too far (and the adjusters have a one-way ratchet). You are better off going a little bit under than too much.

No other easy way that I know of to bleed ABS.

At times, the drums will stick to the hubs from all of the caked on dust and rust. You may need to take a mallet and do some pounding to loosen them up in order to get them off. Some drums have a couple of threaded holes in them around the lug nut area to use as push-offs. You just have to have the correct sized bolt (I'm not sure if our trucks have these, but I don't seem to recall any the couple of times I've had my drums off).

Also, I just had a "Duh!" moment. I can't believe I didn't ask this before: Did you properly bed the news brake pads???

I think it's just the slack in the parking brake cable. I did adjust the rear brakes again earlier today and they're already to the point where the wheel almost doesn't make a full turn when I spin it. I also think I went too far on the right wheel by accident. You say it's one way ratchet which seems to be the case since I couldn't turn the adjuster the other way. How do I back the pads off a bit then since it's one way?

As for bedding the brake pads, no I didn't do that yet since I didn't get a chance to as I immediately noticed the pedal was too soft when I took it out for the first drive after doing the brakes. This shouldn't cause a soft pedal though should it? Poor braking performance sure, but not a soft pedal?

I was editing my post when you replied. I put in some info on how to get the drums off. Unless you can lift the ratchet piece off of the star wheel somehow, the only way to back them off is to get the drum off. To do it through the port in the back, you would have to look in and see if you can see the ratchet piece, then you'd have to push it toward the drum to lift it off of the star wheel.

I'm about to do the Tundra mod myself (ordered parts yesterday), and I seem to recall in my research that many people had a spongy pedal feel until they bedded the new pads.

Thanks, I did get the drums loose off the hub (I can wiggle them around a bit with my hand) but they are still stuck which I think are the shoes sticking to the inside of the drum? Seems the only way to get them loose is to back off the pads using the adjuster but if I can only back them off after taking the drum off well... catch 22.

I didn't see any ratchet piece when I was looking in through the hole when I was adjust the brakes earlier today, although it's hard to see anything in there.

I think I'm gonna bring it to another mechanic tomorrow who's a friend of mine. Didn't really want to since it's a far drive but I don't really have the time to try and fix this myself.

Thanks for all the replies.

Found a decent pic of the inside of the drum:


It's from a recent axle seal replacement thread.

You can see how the adjuster (the ratchet part) sits on the star wheel. This might help you to lift them off and back the adjusters off a little. Sometimes the shoes can groove into the drums enough that they are a PITA to get off. Also, I seem to recall reading that if you set the parking brake, it lifts the adjusters off of the star wheel so you can back them off (this may not be correct though, and I can't recall the exact layout of the part myself).

I can't tell, is it sitting on top or below the star wheel? I.E. do I need to lift it up or push it down to release the wheel?