'00 Taco, Sudden intermittent hard brake pedal?

2000 Tacoma SR5 Xtracab/ 2.4L/ 5 speed/ 4x2/ no ABS/ 169K miles

Just a couple days ago I noticed my brake pedal randomly had a different feel to it while I was driving around. After 8+ years I know how the pedal should feel when I hit it, but out of nowhere it was harder than usual, like it had lost some of its power assist. On the next application of the brakes it felt normal.
Randomly it goes from a "normal" feel to this "stiff" feel where it has to be pushed harder to get the usual brake response, and may or may not do it the next time. It has done this the past couple of around-town trips, and I'm not sure what to suspect.
Earlier today I performed the brake booster check with the 4 tests outlined in the shop manual (Haynes not the FSM,) and it passed. I checked the line from the manifold to the booster, as I had already replaced it years ago. It wasn't in great shape so I replaced it with a new line and clamps, but it made no difference. It almost seems like a failing brake booster, although I've never had one fail before. The truck is running great with no CEL or obvious vacuum leaks.
The master cylinder was replaced several years ago, and has worked fine since. The fluid is fresh and topped up, with no apparent leaks; within the past year, give or take, I replaced the front pads and rotors along with the front wheel bearings. The old pads were worn evenly, the calipers showed no signs of leaks or failure, and the slides etc all got cleaned and a fresh coat of hi-temp grease. They've had no issues since.
I was going to change the rear shoes this past fall, but stopped for 2 reasons: even though they've been on there awhile, the new shoes didn't have much more meat than the old, and the brake shoes I ordered didn't seem to be the right ones anyway (Bosch BS505's.)
I had one side done, but the new shoes seemed "taller" and caused difficulty reinstalling the drum, even with the adjuster maxed. Despite triple checking and getting assurance those were the right shoes I still don't think they're right, but Idk... all that to say the old shoes went back on and adjusted in fine, and the parking brake works perfectly fine as well. Nothing was hanging up then, and no leaks from the wheel cylinders. This was months ago, and there were no issues till now, so I don't suspect that has anything to do with it.
The issue really feels like the exact opposite of a master cylinder going bad. Where that causes the pedal to go spongy, this is causing the opposite effect.
Any suggestions on my next step?

 

Sounds like brake booster to me.

 

Ty MechanicJon. I think so too, but I hate to throw parts at it without knowing. Or at least being fairly certain... the cheapest reman is $150 on Rockauto.
What would cause the booster to fail intermittently, but still pass the checks?

 

Other than use and age a leaky brake master cylinder into the booster will rot the diaphragm.

 

Thanks glamisman. Afaik the master cylinder isn't leaking, but wear and tear gets my vote. They don't look that bad to change. I just wanted to make sure there wasn't something else I could do before I swapped it out.

 

I had hoped I found the fix and would be able to post a helpful solution. Unfortunately I only have more questions...
I wanted to rule out the more simple causes of this problem 1st before throwing a whole booster at it. Remans are $250+, new are $300+, and a local guy with a Tacoma graveyard said $80 for a used unit, no guarantee.
I checked the booster check valve 1st to see if it may be sticking. I unhooked the line from the intake and popped the valve out of the booster. When checked, it moved freely when air was applied to either side. It may be worth mentioning no air escaped when I took the check valve out of the booster or unhooked the line from the intake. I thought maybe still the valve or the grommet was faulty, and went ahead and got a new universal check valve and grommet from O'reilly's. The new valve didn't fit, but the new grommet did.
Since the old valve moved freely I reinstalled it with the new grommet, and immediately noticed a change in the pedal feel. It was still firm but not hard to depress like it was, and stayed consistent every time I hit the pedal. I took it as a win.
But after a couple days I couldn't convince myself that the brakes felt like they should. The pedal is still too hard, even though the braking response seemed better since the grommet was replaced. I've been driving my other car more since I'm leary of the brakes on the truck atm. Yesterday I got a chance to dig into it a little more and here's the twist, and the more questions part:
I wondered if bleeding the system would help, even though it didn't seem warranted because the pedal isn't soft or spongy, and the level of fluid in the reservoir hasn't dropped. I started to bleed them down anyway, thinking it couldn't hurt, only to find out there's no fluid going to either back wheel. Starting at the rear right, the 1st pumps of the pedal and cracking open of the bleeder netted a dribble of fluid. Next 2-3 times, nothing. Next time less of a dribble, then nothing. I removed the bleeder valve completely, and still only a dribble from the wheel cylinder. I moved on to the left rear, and same exact thing. I tried for an hour in vain before running out of daylight. I haven't tried to bleed the rear proportioning valve or the fronts yet, but I can confirm the fronts will lock up when "panic stopping" from 20 MPH, since they are obviously doing all the work.
I have not yet disconnected either rear line further up to see if fluid is getting thru from the master, which I think would be the next logical step. But now I don't know what to suspect. Seems whatever is preventing the back brakes from working is more than likely the cause of the hard pedal, but that wouldn't be the master cylinder... would it? The master was replaced 7-8 years ago. As I said it hasn't apparently lost any fluid. I guess it could be faulty, but I've never had one fail before that caused a hard pedal, only the soft or to-the-floor pedal. The booster wouldn't cause this...right? Hard pedal, yes, but not blocking fluid...no?
TIA for any help.

 

Have you checked your front pads ?

I have had pads get twisted on the pins enough to hang up and cause a hard brake pedal.

Mine progressed to the point the pedal was hard all the time.

Good Luck !

 

Thank you for your reply Bivouac. The pads and rotors were replaced within the past year, slides were greased, all that. Nothing at all was unusal at that time. I have not specifically pulled the caliper or anything to recheck the front brakes, but recently had the front wheels off and everything looked as it should.
I haven't had any trouble out of them, or the brakes in general, save for a new master several years ago, till this showed up with the hard pedal a few weeks ago, combined with now finding the fluid not getting to the back brakes.

 

I didn’t do this…..until other members told me

need to bleed LSPV bleed screw just like the r & l bleed screws on calipers/drums

after I did this, discovered LSPV failed
(Only running 100% front brake bias)

with searching/help here
Now have $45 LSPV delete
4 wheel black marks now

 

Another possible is a crushed Brake line.

Good Luck finding the problem!

 

Ty ControlCar. I am going to replace my worn out Craftsman 3 ton jack with a new one from Harbor Freight tomorrow, then this will be my next step. Hopefully the LSPV hasn't failed...how do you know if it has?
Sorry for the obvious question, but could removing the booster check valve have created the need to bleed the LSPV?
I'll check it out and post back.

Ty. Refreshing the rubber brake lines on all corners is definitely on the short to-do list.
They're cheap and easy enough, and it's time anyway. I'm going to inspect all the lines again while I'm at tomorrow.

 

About 10 or 12 yrs ago i had the exact same problem, hard pedal no pressure to rear brakes, when i got it trouble shot to the LSPV and found out they cost about $300.....hell no. I disassembled the LSPV and cleaned it out....it was nasty. Since then i change fluid every 2 years with full bleed at ALL 5 locations.
To this day i am still running original booster, master cylinder, LSPV and wheel cylinders however i did the Tundra front upgrade a couple of years ago truck stops like a cat on shag carpet.
IMO this is all due to lack of brake system maintenance and not bleeding at LSPV.

 

Automan
How I knew LSPV failed, 2 things
-when I got taco from prior owner, had invoice for new front/rear brakes. While doing front bearings, I saw that the front pads were half life and top edge of pads were peeling off like a curly Q. Never seen before. I inspected rear drums….zero wear. I chalked up to wrong size pads installed and replaced front pads
-after replacing the 3 27yr old rubber lines, I could not got the life of me bleed the rear corners…..kept getting bubbles.
After going through $18 of b fluid, I gravity bled rear as best as I could

returned here and ‘found out’ about this known-to-fail LSPV
Went on how to delete

 

For those of you still following along, the LSPV apparently was the culprit. I dug into it yesterday after checking over all the hoses and hard lines, and started with bleeding it, then all 4 corners, and then returned to the beginning and did it all over again. For good measure, and because it was time, I went ahead and drained and bled the clutch master/slave cylinder, and also replaced a torn rack and pinion boot that I noticed when I last changed the oil.
It took some time to get the valve to bleed but then it went smoothly. The brakes now feel and stop exactly like they should.
I got virtually no air or anything suspicious out of it, just used fluid. I was not suspecting it at all, since this is the 4th time in 8 years I've refreshed the fluid and completely bled both hydraulic systems.
Thank you both for the info about the LSPV delete mod, I was not aware of it but I will be checking into it.
BTW ControlCar I am running those same KYB's. I put them on a couple of years ago, and love the difference they made.
In the same spirit of this post but slightly off point, has anyone used Bosch BS505 rear brake shoes for a 5-lug, 2WD application? I mentioned this farther up as an aside, but I ordered these last fall, and I couldn't make them work. The looked to be the same size as the old shoes, but once installed the drum would not go back on, not with any amount of adjusting or coercing. They seemed to be too "tall" to fit the drum over, but everything I looked up, including Bosch's own site, said they are a direct fit.
Thank you very much to everyone who chimed in to help!

 

A firm Automan!

hit me up if you want Q answers to that delete job

pretty easy job
The worst part was bleeding brakes for the 3rd freaking time!
Need to fabricate a small bracket for the manual bias controller (able to use same bolts and bolts holes that the LSPV uses in frame

 

A firm automan is a happy automan!
But unfortunately the problem persists...
It was normal for a couple days, then back to sometimes normal, sometimes too firm a pedal. I presume this is what a failing LSPV does.
I'll be looking it up myself, as well, but I'd take that information on the delete mod when you are able, ControlCar. I am going to wind up replacing the LSPV or doing the delete but I have got to get this taken care of.