dlx111

So i posted before about braking problems I had, that turned out to be the wrong brake booster in the car. So i have an o reilly unit in there now the correct one and the brakes work but im still suspecting theres something going on. What Ive been getting on and off for the last couple months is an inconsistent change in pedal feel. What I mean is one day i can be driving and the pedal will get really stiff with high engagement then later on it will return to normal, then the next day it can feel a little mushier than normal for awhile then return to what I would consider normal pedal feel. I was suspecting the booster was going bad when I felt the pedal get stiff but like I said the pedal feel returned to normal. I also tried the recommended booster tests and to the best of my ability it held vacuum through them all. I also just bought a new check valve and OEM one not the cheap autozone ones, and booster vacuum lines are brand new too. Still the same thing. So im thinking is there another source of vacuum that could be screwing it up or maybe the booster is somewhat defective?

Krauthammer

Did you bleed your brakes correctly?

TomCat39

^^This. To do this you may even need to bench bleed the master cylinder.

Just to make you aware if you are not already, there is a specific order to the wheel to bleed. It runs in an X pattern but I don't recall off the top of my head which wheel is first or which is third. You may wish to check your FSM.

dlx111

yeah bled them recently and always follow the order. Master Cylinder was bench bled when first installed and havent touched it since. The brake fluid was a little dirty which led me to believe maybe there was a leak but I dont lose brake fluid at all

TomCat39

I would try bleeding again. It really sounds like you got a bubble sitting in the line somewhere.

dlx111

If you were to have air in the MC wouldnt it work its way our of the system eventually?

Krauthammer

it's a closed system. unless you have a leak, which is another problem in itself

TomCat39

I wasn't thinking a bench bleed personally.
I was thinking catch it when the brake pedal is rock solid, then do the regular bleed procedure at the wheels.
When the brake pedal goes solid, that usually means the bubble is past the piston area and will get pushed out the lines.

dlx111

Is there normally supposed to be any idle fluctuation when depressing and letting off the pedal? My idle goes up when i let off my pedal

Krauthammer

Sounds like a possible vacuum leak.

TomCat39

That's normal. When you use the brakes it increases vacuum demand.

If you sit and pump the brakes you can bring your idle almost up to 1500 rpm from 750. You can keep it going just by continuing the pumping.
You have to remember the booster operates off of vacuum.

dlx111

Ok cus i was still suspecting a vacuum leak but like i said the booster seems to hold vacuum with all the tests so i guess ill try bleeding the crap out of my brakes again.

mk378

Having good vacuum applied to the booster all the time, but sometimes no power brake action would suggest the booster is not working all the time.

Air in the brake lines causes the pedal to go down lower than normal along with poor stopping performance. And that will be consistent every time you press the pedal.

TomCat39

If the booster was the problem, would the pedal feel mushy like an air bubble at times?

I was under the impression it would still feel solid but no power assist so significantly reduce braking performance?

dlx111

when i roll down my driveway with my car off(no vacuum) i hit the brake and its super solid and little braking power

TomCat39

Based on what mk378 was saying, if it was air in the system it would allegedly be consistent, not sporadic like you are experiencing. I just have not heard of booster issues causing mushy pedal, that's typically associated with air.

My thought is the air bubble has made it to the proportioning valve and sitting in the back lines. When applying brakes, the first and most force is typically the front brakes so unless you are hammering the brakes, I was thinking you could potentially not feel the air bubble if it was not really activating the rears from mild braking.

However, this was purely speculation.

dlx111

Yeah idk then. Ever since my OEM booster went out my brakes have never been the same. They used to be super strong and consistent and now they're mostly crap. These reman units must be built like crap or something. Would a failing MC have any contribution to the pedal changing?

TomCat39

When you changed the booster, did you use the special honda tool to align the pushrod gap of the booster and the master cylinder?

You might have play in the push rod.

dlx111

Nope never knew that was a thing. Ive adjusted the pedal to pushrod engagement before, when i put this one in i made sure the clearance wasnt too close because the last booster i put in my brakes weren’t letting go.

TomCat39

Yeah a failing MC could contribute to the whole problem.

dlx111

Though i would be seeing some kind of loss of brake fluid though from my MC reservoir right? It always stays at the same level so i know theres no leakage in the system

TomCat39

I can't answer that. I've never taken an MC apart to wrap my head around it's operation. I suspect you may be right but it would be purely a guess.

Crashmaster91

When the seals go bad inside the master cylinder, the fluid can move around them, instead of into the system like they should. When this happens, there might not be a leak, but the pedal will feel mushy. This however is usually pretty consistant, but the seal could sometimes help push the fluid through.
My friends went out while on the freeway off ramp, but worked flawlessly in stop and go traffic 5 minutes prior. I almost had to pay for a detailing to clean the seat. Changing the MC might not be a bad option, but make sure that you bench bleed it and ensure there are no bubbles, or you will have more problems

dlx111

Wanted to update this, have not bled brakes. plan to but havent yet. But yesterday driving my pedal went from its pretty normal high engagement to engaging almost at the bottom like the booster went out. I still had powered brakes but the pedal travel changed dramatically. Then today starting the car up and driving to work its back to normal....

mk378

If the booster stops working, you will have to press much harder on the pedal to stop the car. But it would still go down about the same amount, just not easily.

Pedal sometimes goes down more than normal is likely what @crashmaster91 said, an internal leak in the master cylinder. This is especially true if you can pump the pedal and have it "catch" and work normally on the second pump (Don't keep driving like that though, because at some point it won't).