Brake issues, might tie everything together

Well, that was... inconclusive.  Why am I not surprised?  The Frog and his intermittent taunting.

Brake vacuum line is puling 20 to 21 inches at idle, fluctuates pretty rapidly but never leaves that range.  I don't have a helper, couldn't test a quick throttle blip and I don't think it would tell me anything, would it?

The booster check valve resists pressure, but I only used my mouth to try to push air into it; I don't know what it can take so I didn't want to use compressed air, but I learned that I can push almost 2 PSI by mouth before all the colors start changing and everything starts turning red, so I learned something pretty useless today.  LOL.  I nearly blew a cheek out pushing on the booster check valve, but didn't seem to be pushing anything at all.  This may have been an inadequate test.

Brake pedal gets plenty hard when pumped two or three times when engine off, then depresses about 3/4 inch when I start it up.

Depressing brake when engine on, then turning it off, I can maintain brake pedal position indefinitely.

It might just be confirmation bias, but after farting around with it, it seems like my idle is now about 50 rpm lower than previously but I may just be having a bad idle time.  By the way, when I run it with the brake vacuum disconnected, The Frog gets all sad and sickly.  That idle is far worse than the normal "poor idle" I have been talking about.  What I am talking about, it just drops engine speed down to about 600 or 650 rpm and seems like it is just slightly sputtering in a slightly bouncy way.  Same kind of thing as when the vacuum is open, but subtle; not painful, pathetic and sad.

Yeah, so... WTF?  If I were getting intermittent "catastrophic" engine vacuum issues, shouldn't I also have noticed the engine briefly running like crap during one of these booster failure incidents?  That has never happened -- all three times it was just stiff brake pedal and no boost, but the engine is just humming along fine.  It has happened once shortly after startup, and twice when the engine was well-warmed.  After soiling myself while getting the car stopped or slowed with a hard, grindy brake pedal (no boost), I pump the brake a time or two and my boost returns like nothing is wrong.  The brakes themselves still work fine without boost.

Also checked for hot rear discs.  Barely warm, so they are not dragging, but that's my parking brake thread.

FWIW I had my brake booster go all silly twice in quick succession. Once I come back to my car a few hours later and the pedal is rock hard. Next day the same thing happens. That was about 2 years ago now and it hasn't happened since. 

The first thing I would do is flush the brake fluid out completely. Then I would replace it with Toyota red brake fluid and observe.  I had issues like this in the cold and it was caused by using racing brake fluid for over a year.  

I agree with Dev, this could be, at least in part, due to whatever brake fluid is in the system right now. Just last week I bled the clutch on my Acura after having extremely intermittent shifting issues. For the past 6 weeks, once or twice a week it would become really hard to shift for a few minutes, then work as before, no restart, or anything other than pressing on to the next stop sign or light. It hasn't happened since the bleed, no air bubbles were observed escaping, and overall clutch engagement is much smoother (and I thought the shudder was just a side effect of stage 1.5 clutch and light flywheel) than before. High performance DOT4 looked terrible coming out, it was in there for 19 months. Should probably bleed the brakes too now that I think of it...

Thanks.  Just did that a few weeks ago in Round 1.  The first time this happened was December 13.  I took it to my mechanic shortly thereafter and had him flush the brakes.  He showed me the old stuff that they had flushed out and it looked like maple syrup, pale brown and clear of any haze, like... new motor oil.

It was replaced with low-viscosity DOT4 which has seemed identical in performance to the previous fluid so far.

Posted by: @marsrock7

I agree with Dev, this could be, at least in part, due to whatever brake fluid is in the system right now. Just last week I bled the clutch on my Acura after having extremely intermittent shifting issues. For the past 6 weeks, once or twice a week it would become really hard to shift for a few minutes, then work as before, no restart, or anything other than pressing on to the next stop sign or light. It hasn't happened since the bleed, no air bubbles were observed escaping, and overall clutch engagement is much smoother (and I thought the shudder was just a side effect of stage 1.5 clutch and light flywheel) than before. High performance DOT4 looked terrible coming out, it was in there for 19 months. Should probably bleed the brakes too now that I think of it...

The  problem is with Dot 4 fluid.  I come to find out that it’s too viscous in cold weather and once it takes in a little moisture it then behaves badly in systems that are designed for Dot 3 only. I had the same clutch issues and so has my local Spyder  friend I split a case of racing brake fluid which was idiotic on my part.  
This made me realize there  is a lot of garbage information on the internet and car forums.  There is a good  article by Stoptech that mentions staying with Dot 3 if your car was designed with dot 3.  

The reason I say to use only Toyota is because it is formulated specifically for the rubber seals.  They have a special lubricant the other fluids don’t. 

I haven't looked at the lids in the MR2, but I know for a fact that my TSX does say DOT3 or DOT4 for both clutch and brakes... I guess the lifespan of DOT4 is just shorter and it acts differently from old DOT3 once it's reached that point.

Posted by: @marsrock7

I haven't looked at the lids in the MR2, but I know for a fact that my TSX does say DOT3 or DOT4 for both clutch and brakes... I guess the lifespan of DOT4 is just shorter and it acts differently from old DOT3 once it's reached that point.

   I believe it says Dot 3 fluid only.  I had a debate on this a good while back after presenting my evidence and I was in the minority of opinion. The best rebuttal was it says that but you can use DOT 4 and it was only advisory.   I then found some Toyota vehicles that listed DOT3 or DOT4 and still some were not buying the logic because people are stupid and don't trust when the manufactures say only it means only.  I was stupid to believe internet car forums when the problem is far more complex that I have no business agreeing with blind assumptions by others when what I should do is trust the manufacture until there are reported problems with the manufacture  fluids.   

Apparently those that used the wrong brake fluid for some models of Toyotas had their master cylinder fail and Toyota determined that the reason for the failure was not using their brand of Toyota fluid which has a lubricant in the formulation that without it caused the rubber to dry out.  Although our cars were not listed in the TSB it made me think there are a lot of unknowns that we should not be messing with.  Toyota DOT3 fluid is made for heavy duty use like towing and it is my belief  that its overkill even for the track.  No one ever has claimed to have made the Toyota red experience  fade even on the track that prompted them to have to upgrade the fluid.  The people that upgrade the fluid are those that do it thinking there is problem without any evidence.  First feel the fade and then upgrade, nobody does this. 

@dev

Well, I bought the dot4 out of disregard for toyota fluid advice so that's on me, but also because I was planning to do the flush myself. Yet I wimped out with other stuff to do in mid-late-December, restoring those silly wheels, holiday traveling, stuff.  Maybe I might get the chance to flush them again sooner than I like.

But my understanding is that moisture causes spongy brakes.  And although it has happened only in the rain and three times is not a trend, but I had not heard that the moisture also migrates in and out.  The Frog's brakes have been fine in colder weather than those days, too.

I know we don't like to diagnose over the internet, and I totally agree, but these discussion still get me in the ballpark, and I like to learn by discussion, so I appreciate all the advice. Just working my way down the troubleshooting list.

I suppose that intermittent failures in the booster and/or check valve are still on the table.  Not much left to test before I have to start swapping parts. Check valve is 35 bucks, master cylinder is a couple hundred, booster is almost six Benjamin.  Hmm, what order should I do this in???

Posted by: @nottamiata

@dev

Well, I bought the dot4 out of disregard for toyota fluid advice so that's on me, but also because I was planning to do the flush myself. Yet I wimped out with other stuff to do in mid-late-December, restoring those silly wheels, holiday traveling, stuff.  Maybe I might get the chance to flush them again sooner than I like.

But my understanding is that moisture causes spongy brakes.  And although it has happened only in the rain and three times is not a trend, but I had not heard that the moisture also migrates in and out.  The Frog's brakes have been fine in colder weather than those days, too.

I know we don't like to diagnose over the internet, and I totally agree, but these discussion still get me in the ballpark, and I like to learn by discussion, so I appreciate all the advice. Just working my way down the troubleshooting list.

I suppose that intermittent failures in the booster and/or check valve are still on the table.  Not much left to test before I have to start swapping parts. Check valve is 35 bucks, master cylinder is a couple hundred, booster is almost six Benjamin.  Hmm, what order should I do this in???

Flush the brake fluid first.  Incompatible brake fluid can do weird things.  In my case it gave me the kind of symptoms you have experienced in the cold.  For other Toyota it caused issues with the master cylinders rubber seals.  Some cars have had severe abs issues due to the viscosity in the cold.  Sponginess is just one of many symptoms. With incompatible anything you don’t know what you are going to get. At some point it’s very difficult for enthusiasts to speculate so it’s just better to follow directions on the cap. 

I plan to do this in the next week or two. Need to get the fluid. But I do want to rule out vacuum leaks since I am having mild engine trouble too.

My boost is degrading now, and my low idle issue is getting a bit worse in terms of frequency, but the symptom us the same: idles at about 675 rpm, and a bit rough, as you would expect from idling 10% too low.  I'm becoming more convinced that it is a vacuum leak, but not willing to wager any doughnuts yet.  The engine pulls 20 to 21 inches of vacuum, but it fluctuates in that range pretty rapidly, as measured at the brake booster vacuum (disconnected from booster check valve).

At idle, the engine sometimes runs normally, and is more frequently dropping to 675 rpms for a few seconds.  Sometimes it recovers, sometimes not.  It never stalls or gets worse.  Diagnostic tool reads -80 kPa.  When I measure the vacuum at the end of the brake booster line (at the booster end), the vacuum bounces rapidly between 20 and 21 inches.  Is that normal?

Here's what I've tried:

I installed a shutoff valve and tee between the brake booster check valve and the engine vacuum to perform some tests.  The teed line has the booster check valve on one end and the vacuum gauge on the other.  Standard splice to measure the line vacuum: I can cut the engine vacuum with the valve.  After getting 20 inches of vacuum in the line, I cut off the valve.  The booster maintained 20 inches of vacuum in the line after I sealed it up.  This means one of two things: either the check valve does release pressure toward the engine properly, or it is blocked completely.  However, pumping the brake pedal when the line is still sealed off does allow pressure into the exit line, because the vacuum falls to about 12 inches (and keeps going to zero after a couple more pumps) which means the check valve does allow movement toward the engine vacuum.

This does not test whether the check valve maintains the vacuum in the other direction, however, since I have sealed the normal exit.  However, since I know the check valve flows "out" correctly, and the pressure does not change unless I push the brake, I feel pretty confident that the booster is not leaking and allowing atmospheric pressure into the vacuum chamber. This tells me the vacuum chamber is working, and it "excludes" the check valve since I know it is allowing exit.

So all that remains is testing whether the check valve prevents backflow.  Otherwise, I will assume that there is an engine vacuum leak elsewhere (could stil lbe inthe brake booster line, but I am eliminating the brake booster and check valve first and working my way toward the engine.  I realize it might not be in the brake vacuum at all.  Ther could be more than one issue also.

One more clue I have here: when I use the valve to shut off the vacuum right between the check valve and the brake booster line, the engine still low-idles.  So isolating the brake vacuum entirely does not fix that.  This makes me suspect vacuum issues elsewhere in the system, at a minimum.  IN fact, they are more likely, since I am pretty sure ther is no pressure leak originating at the booster.  Hoo boy, I can't wait to try to fiddle around behind the engine...

But in order to test the check valve negatively, I am going out to buy a cheapo $6 inline check valve in a little bit.  I will install that between the engine and existing check valve, leaving both valves in the line.  If adding that extra valve solves the stiff pedal issue, then I know the problem is the booster check valve.  Cute little $6 diagnostic tool, maybe.  If it solves the booster issue but not the other vacuum issues, then I know the real booster check valve is bad and I probably also have another leak.  If it does not solve the brake issue at all, then I scratch my head and assume that the booster is bad?  That just doesn't make sense given the other tests.  I suppose it could be the master cylinder from there, but then what about the low idle...?

So: is that vacuum bounce normal or a sign of a problem?  It stays rigidly between 20 and 21 inches, and seems the same at smooth idle or rough.  It's lower vacuum values and not as bouncy when I rev it, but when idling the bounce behavior and the 20-21 range is identical at 750-normal as well as 675-low.  What does normal look like / how steady should the needle be?  I'm such a newb, I haven't even figured out which hard pipe is the engine-end of the booster line yet but I'll be working my way back.  If I could stop dropping a Benjamin on tools every weekend, I might be able to afford a repair manual!

Yup.  I knew it.  Brake booster check valve is bad. 

The temporary one fixed the brakes.  Warm engine still idled rough immediately after the install, intermittently, which was discouraging.  But after I got back from a quick trip around the block to test the brakes -- keeping some moderately high rpms going 25mph in 2nd gear -- when I got back home, there were no more rpm drops sitting in the driveway.  It just hummed along at about 780.  If anything, that's a tiny bit higher than it has normally been, but just slightly.  I wonder if the ECU is learning.

I definitely need a new check valve, regardless of other potential leaks.  Hopefully it won't be a PIA to get the new one seated and sealed in the booster can; I'm kinda "over" this issue now. Looks dead simple, though.  I've never taken the front beauty collar off, hopefully that's dead simple too.  But yeah, I still have to circle back to address the sticky parking brake cables, so this is getting old now.  Learned a lot, ready to move on.

I think I finally got a break this time.  I got the $30 fix instead of the $560 one, but it is a bit too soon to say for sure about anything other than the check valve.  Will see how it idles for a few days.  But hey, I got some long-overdue ramps and a few more tools and materials to add to the workshop.  The check valve was $13, not 6, but still well worth it.  Might not be a bad idea to just have 2 of them in there all the time.

Nope.  I didn't know it.  Still having issues.  Rained very hard yesterday, got a new behavior.  Similar to the first event, started car after it sat in heavy rain for 8 solid hours. leaving work, there is a short sharp decline with a stop sign at the bottom, maybe 15 feel long.  Quick bump to the brakes and the ABS went off.  WTF???

Oh boy, here we go...  Another ABS event occurred again about 15 seconds later when I tested the brakes.  Then a wee bit squishy for a bump or two, really slight, but definitely abnormal.  Then they worked again as normal, so I shrugged and drove home, swearing and vowing not to drive it again inthe rain until I flush the fluid.

Took it really easy on the way home, regretted using the highway, didn't die.  Rush hour was over and I had the good fortune of being given space.  Amazing what happens when you go the speed limit and no higher..  Once again, after the 12 minutes of 3500ish RPM, no brakes.  I was expecting hard but workable.  No, this time it was hard, but the brakes also felt "glossed", like not as much pressure on the pads themselves.  F*CK... first time it really got truly concerning.  Had plenty of time to engine brake and so forth, and the brakes had returned somewhat, so I was not saying my last goodbye, but still...

Dropped out of gear and let it idle to get some vacuum while I coasted to the exit ready to engine brake and pull the parking brake.  Fortune smiled upon me again, but I kinda knew it would becasue I was getting vacuum.  I have always been able to get the pistons to push, but the pedal has just been weird.  Gawd Dangit this has to be vacuum related or contaminated/wrong fluid. 

I have been scouring forums. Bimmer Bois are talking about water in the brake booster.  But they are talking about a clogged drain, and I don't think our booster has a drain?  Then again, condensation is inevitable, so I would have thought that a booster could very well collect water.  Does our have a drain?

Again, for me, this only happens during the rain and a booster full of liquid, water or brake fluid, would be a continuous problem.  This is 5/5 events that only occur during HEAVY rain, and has happened nearly every heavy rain we get.  Yesterday was not cold, but the humidity was 100% and the temp was gradually falling.  I've also noticed a propensity for this to happen inthe afternoon, not th emorning.  Hypothesis there is that the booster, line, or whatever is filling with vapor in the morning, condensing during the day, and trying to murder me on the way home.

This is why I keep coming back to vacuum, or at least refuse to give it up as a contributor.  I absolutely do not rule out incompatible brake fluid either.  I am scouring the stealerships today to find some genuine Toyot Red DOT 3.  BIL is slated to come over this weekend and pump while I scuttle around under the car.  He has automotive skills so he can keep me honest  too, but I'm doing the work.

However, I cannot get past the 100% correlation to heavy rain.  I know brake fluid absorbs water.  I started having this problem before this last fluid change.  The fluid may have made it worse, but it was happening with the old fluid.  I have no idea what the hell fluid was in it before, but it looked pale brown when my mechanic showed me the old stuff.

I changed my struts in August. I briefly considered whether I screwed up an ABS sensor, but that install went really well and I dont recall any Oh S moments with the sensors or cables.  Symptoms seem unlikely too.  But I would like to know how weird braking triggers the ABS now anyway.  Yes, yes, abs kicks in when it "detects a wheel is slipping".  Great, but I'd like to know exactly how it "detects".  Yes, sensors, uh, huh, but what is the LOGIC?

It is apparently not the check valve on the booster.  "Replacing" it by inlining another one did help, though, I think.  Or, could have been coincidence.  My new one arrived in the mail.  Sigh, might be more wasted money.  I am going to install it anyway.  Will drop a well-tethered wick down there to see if it is holding water.

Is there a drain on our booster for letting liquid out?

Can brake fluid (the whole fluid side of the hydraulic system) only act up based on very high external humidity, then immediately start behaving again when the air dries out?

Can water from super-damp ambient air somehow get sucked into a vacuum line and cause the immediate onset of symptoms and immediate relief when the humidity changes back to drier air? 

Could there be water migrating directly into the vacuum system while the thing sits parked in the rain for several hours before the events (seems terribly unlikely, but could happen to a cracked hose)?

As above, but applies to the brake booster only being dysfunctional during high humidity?

I'm really looking forward to at least having the fluid flushed.  More so to getting past the issue altogether.  This is untenable.

Didn't see it mentioned earlier so I will go ahead and ask. Did you replace the grommet with the check valve or just the check valve?

Hold old was the "motor oil" like brake fluid that you had flushed previously? It shouldn't have been that color. The fluid could be building up moisture in it due to a bad seal on the MC cap. That or the color is due to the decay of the seals inside the MC itself. If you have the test strips I recommend testing the fluid to see how contaminated it is before moving on.

On a side note Ford is recalling some master cylinders because of DOT3 had an odd reaction with zinc valves in the HCU's that would cause braking issues.