I've had this 99 4runner for a week and a half, and just about have most of its issues sorted out. It has 216k mile....2WD auto, limited.

The next issue to tackle is the lack of braking. I initially read and thought i had diagnosed a bad power booster (or low vac pressure) but vac pressure is fine and I've replaced the booster with a new aftermarket one first, then a used OEM unit. With virtually no change.

I initially get decent power assist on the first time I push the pedal. After that each push has less and less braking but the pedal doesn't go to the floor. It seems to build and hold pressure.

Wondering if it could be the master cyl or needs bleeding? etc.?

 

Not sure what to think, are you sure the front calipers aren't totally seized up and not able to clamp down on the rotors?
maybe the check valve in the vacuum line to the booster is stuck or put in backwards.
maybe the vacuum line is collapsing.

 

The caliper check and bleeding is my next move. The booster check valve is good. I've tested it.

Honestly, you get one good boost assist pedal push, but even it won't put you into the windshield. Its like I"m towing a 6000lb trailer. But not like i have zero brakes either?....I have a 1970 f100 with four drums so i know what "no brakes" feels like and its not that.

 

You can test the effectiveness of the brakes (sort of) by lifting the front end and having a helper hit the brakes while you try to spin the tires. This could help rule out seized calipers.

You can also try to bleed the front brakes. You may have collapsed lines. If so, when you open the bleeders under pressure you get a really slow flow instead of the powerful squirt. Bleeding the brakes will give you an indication of contaminants in the system. If coca-cola dribbles out, you can feel confident you’ll be replacing some parts or rebuilding your calipers because they have internal rust.

You can test the vacuum assist brake booster. in an empty parking lot get up to about 15mph and apply the brakes and see how long it takes to stop and the feel. Now disconnect the vacuum line to the boost and do the same thing. (You may have to plug the vacuum line or the truck will run poorly but don’t worry this is temporary) If the run without the vacuum line does change the way the truck stops you know that the booster isn’t doing what it’s supposed to.

 

ok...Here's what I've found so far.

I did the parking lot brake test with and without the booster vacuum tube attached and the booster is definitely helping. The next thing I did was to feel each rear brake drum to see if they were even hot and as soon as i touched the drivers rear drum i noticed it was covered in grease....so i pulled the wheel and drum and as expected, found an axle seal that failed...... I've had this in the past on my tundra and it basically had no affect on braking so not sure this I contributing that much to my braking issue. Either way I'll fix that today and then start bleeding each wheel.

 

axle seal leak?

 

yes without a doubt

 

Axle seals are pretty common on 3rd gens. If you’re doing it yourself, check for a groove in the collar of the axle. There was a thread a while back by @aowRS that talked about flipping the seals or not driving them in all the way or something (memory is a bit fuzzy about a several year old post) to prevent future leaks. If you search around you should find it.

 

Quite often the axle seal leaks are caused by the differential's breather getting clogged. When you replace the axle seal and brake shoes, pull the diff breather and make certain it's clean, and air is free to move through it both ways.

I just got my axle seals replaced at the dealer. He found the breather was completely clogged. That's why the seals leaked. They replaced the brake shoes and springs on both sides, and bled the brakes, including the LSPV (don't forget that when bleeding the brakes!). My mechanic recently replaced the front brake calipers and discs, so I essentially have all new brakes. The rear brake shoes DID make a biiiiig difference in braking. Yes, the new parts on the front made a difference, buuut the rear really made a difference.
I'm strongly considering getting some diff breather extensions to make them A) easier to ensure the stay unclogged and 2) clean them if they DO get clogged, somehow.

Have fun! I personally HATE doing rear brake shoes. They are a PITA, even with the special brake tool...
Pat☺

 

Yeah LSPV. Friend had bleeded his brakes and still had an issue. My friend took the advice of a hack. Friend was told I was full it. Months later I saw my friend and he said turns out I right about it. I had learned on the forums.

Breather, I always extend mine up to the fuel fill neck test them at that time. i just push air through them

 

so on the braking issue.....

does a bad master cylinder make sense at this point?

 

There is a possibility that it's the issue, but it sucks to put new parts in and find out it was wasted effort/money.
If you have eliminated all other possibilities like making absolutely sure the LSPV is properly bled and the rod isn't bent I would say that would be a logical next step.
You might try disconnecting the LSPV rod first and tying it up to the bottom of the truck and see if that makes a difference.

 

I, personally, take the LSPV's bar off the axle, then move it up and down through it's range while bleeding the LSPV. It seems to help break the crud loose that builds up in the LSPV, and lets it come out with the fluid as it comes out of the LSPV during bleeding.

Good luck!
Pat☺

 

Heres the update from this weekend. I found out that i Don't have LSVP on this 4runner (it has ABS). So i was able to find a local guy parting out a 2000 4runner and got the booster and master cyl from him and replaced mine. Bleed all of the breaks and STILL have the same issue......

What's left except the ABS unit/pump?

 

Calipers

 

Ok....time for an update on this ongoing issue.....

Since last post I have: new master cylinder followed by a two-person brake bleed....x2. Replaced the Booster again with a know good unit, tested the front calipers to make sure they're actually clamping, adjusted the rear brake shoes out (probably slightly past perfect just to make sure)... and finally replaced the ABS pump and bled that.

STILL I'm getting close to normal powered pedal feel on the first initial pressing but anything immediately after that feels manual. or unpowered. Until I drive another block or two and the cycle continues. Even though my vacuum pressure is showing adequate I have to think maybe it's dropping off sharply after each initial pedal press???

I'm stuck here. Please let me know what i can check/try....

thanks.

 

What is after the mc/booster? Rod?, Hose?, check valve? check the hose end to end, the check valve, the connections too for vac leaks under pressure.
Sounds similar to my last brake job, the mech showed me where the right rear wheel cylinder seal was going, the lip was deteriorating, looked fine at first sight, replaced with new Aisin's, yep, made a difference.
Another truck had the booster replaced years ago and never felt right, wrong rod in new booster lol, tiny bit too short.
Pins on a caliper one time were rough, replaced those n lubed...yep.
Good luck