Brake Booster Advice

[KO KO]

Aloha,

In 2015, at 236,xxx miles, I had my power brake booster replaced with a new OEM booster. Now, I'm at 272,xxx miles and am experiencing intermittent hard brakes. I followed the FSM operation check, and it appears to be the booster.

Results:
1.
a. Depressing the brake pedal several times with the engine off results in a very hard brake pedal. I'm not sure what it means by check that there's no change in the pedal reserve.
b. The pedal will go down slightly upon staring the engine intermittently.

2.
a. Depress brake pedal first time it's fine. Rather than a gradual rise from the 2nd to the 3rd, it's immediately very hard to depress, and pedal travel is equally minimal on 2nd and 3rd depression.
b. When I depress the brake pedal & hold, then turn off the vehicle, a pressure can be felt building behind the pedal, pushing against my foot. I don't know that the pedal reserve travel changed since I used my foot to keep the pedal fully depressed.


Any tips on how to proceed? There isn't even 40k miles on this booster. Maybe that's not what's failing? If it is, then I'm inclined to say I don't want to pay for OEM that's giving me cheap aftermarket lifespan.

 

[enox]

Start with a bleed and see if you have air in the system, also do you have abs?

 

[KO KO]

Yes, I do have ABS

 

[enox]

Hard to say, your booster should not have gone out by now..

My brakes will feel hard when I overhear them, the fluid boils and creates bubbles. Then bleed the system at each caliper, then they get back to responsive.

I like to bleed them with a clear tube, then I can watch the bubbles come out and see when the fluid is clean and new.

I also saw a huge improvement with removing the ABS module.

Next time I bleed and change the brake fluid I'll use a racing fluid which will have a higher boiling temp and won't create bubbles.

 

[KO KO]

Hmmm... ok. I’m not exactly in the NW with that heat wave. It’s hotter in Seattle right now than Las Vegas. Still yet, locally, car batteries have been crapping out more than normal all month according to the roadside assistance guy (mine included, less than 3 years old).

THANKS!

 

[enox]

Yeah try it, you don't have to have a heatwave to cook the fluid either. It can be from excessive braking or heavily loaded, long down hill ie pulling a trailer, riding the brakes going down if off road on a long steep downhill.

Quite a few methods of boiling the fluid.

Hope that helps, report back and lemme know!

 

[richmondbob]

Hmmm... ok. I’m not exactly in the NW with that heat wave. It’s hotter in Seattle right now than Las Vegas.

Damn, dude. I'm in that heat wave and am looking at my brakes now, too.

 

[smritte]

Now, I'm at 272,xxx miles and am experiencing intermittent hard brakes.

Air wont cause this. The booster "system" will as well as something in the vacuum system. That doesn't mean the booster is bad. I have seen OE parts fail prematurely though. The booster may have been new but how many years did it sit after it was made. Never say cant happen, prove it didn't.

1. Vacuum at the booster. "if" for some reason you have a leak this could cause it. If the leak only happens when something torques or is another item on the same vacuum line having an issue, this could make it intermittent. Do a vacuum test.
Small leak will be more noticeable on acceleration not coasting to a stop.

2. Check Valve issue. These normally just fail. They can crack and leak. Normally you have no reserve if they fail. Start vehicle, run for a few seconds. Shut off and wait several min's and press pedal. If the pedal is hard, check valve or booster diaphragm. Normal reserve is 2-4 pumps before pedal firms up.

3. Check booster for internal leak. This can be obvious or not, hopefully it is easy. Start car. At idle depress the brake about 2-3 inch's and hold. Leaking booster diaphragm's will normally hiss. What's happening here is, one side of the rubber diaphragm has vacuum and the other air. They should stay separate. Any real leak, you hear the air "hissing" to the vacuum side.

The vacuum hose is pretty big and any cracking should be easy to spot. I have seen low vacuum due to anything under the hood with a hose to it.

Unfortunately, you said the magic word, "intermittent". That makes things a bit harder. I believe I hit all the booster test points.

 

[KO KO]

Air wont cause this. The booster "system" will as well as something in the vacuum system. That doesn't mean the booster is bad. I have seen OE parts fail prematurely though. The booster may have been new but how many years did it sit after it was made. Never say cant happen, prove it didn't.

1. Vacuum at the booster. "if" for some reason you have a leak this could cause it. If the leak only happens when something torques or is another item on the same vacuum line having an issue, this could make it intermittent. Do a vacuum test.
Small leak will be more noticeable on acceleration not coasting to a stop.

2. Check Valve issue. These normally just fail. They can crack and leak. Normally you have no reserve if they fail. Start vehicle, run for a few seconds. Shut off and wait several min's and press pedal. If the pedal is hard, check valve or booster diaphragm. Normal reserve is 2-4 pumps before pedal firms up.

3. Check booster for internal leak. This can be obvious or not, hopefully it is easy. Start car. At idle depress the brake about 2-3 inch's and hold. Leaking booster diaphragm's will normally hiss. What's happening here is, one side of the rubber diaphragm has vacuum and the other air. They should stay separate. Any real leak, you hear the air "hissing" to the vacuum side.

The vacuum hose is pretty big and any cracking should be easy to spot. I have seen low vacuum due to anything under the hood with a hose to it.

Unfortunately, you said the magic word, "intermittent". That makes things a bit harder. I believe I hit all the booster test points.

Disclaimer: I only started working on the vehicle myself this year (outside of oil changes). Bear with me and my learning brain.

1. I'm not sure what you mean about doing a vacuum test. I followed the procedure in the FSM. Is that not the test that I have pictured above that you are referring to? Can you explain how to do a vacuum test while accelerating?

2. Pedal is intermittently hard on first pump. Should it be soft the first pump, it is consistently hard on the second pump.

3. If I'm parked, idling, and depress the brake & hold, there is a hissing sound (intermittently). When there is a hissing sound, the brake will go from soft to hard, and will push back on my foot.

Vacuum hose appears to be ok and without cracks.

I noticed that when the brakes are acting up, I can still brake seemingly fine. I just have to press the pedal much harder.

 

[SNLC]

I have seen plenty of boosters fail that give intermittent hard brakes before they finally fail completely. My last 80 had that issue until I put in a new booster, it also got progressively worse over 2-3 months until it finally failed.

Cheers

 

[cody c]

He wants you to check the vacuum system is working properly.

it sounds like you have one of two problems, one being the diaphragm of the booster leaking, or not enough vacuum generated to work the booster.

increasing idle (throttle) creates more vacuum. A vacuum gauge would help identify if it is that component of the system.

get a vacuum gauge, tee it into the line and see what it tells you. You could also check the gauge with it blocked off from the booster to help identify if there is a leak.

you could baseline to see how much boost is produced at idle and say 3000 rpm or something, then pinch the line near the booster and see if it’s the same (without working the brakes) if it is substantially different you may have a leak at the booster.

that is also a few bucks to find an electric vacuum pump, but if you had one handy it would be easier to locate the leak, you might be able to hear it, or find the source with smoke, like a cigarette or incense burning or something

if you had an electric vacuum pump you could swap it in and see if the brakes act differently with the engine off, this would also tell you if there is a vacuum issue.

if course you could just swap the booster too and you’d know if the brakes got better that was likely the issue, but that is expensive and for a part that should probably be good as long as it wasn’t damaged during instal or was a rebuilt part or something

 

[smritte]

Sorry was at work on break when I posted. Some of these things I explain better in person than typing it out.

1. I'm not sure what you mean about doing a vacuum test. I followed the procedure in the FSM. Is that not the test that I have pictured above that you are referring to? Can you explain how to do a vacuum test while accelerating?

You need a vacuum gauge. Test it at idle. Beg borrow or buy one and install it in a port just to see what it is. I would like to see 16 inch of vacuum or higher. Boosters like high vacuum. They will work (kind of) as low as 10 inch but that's pushing it. Doo a random U-tube search on testing an engine with a vacuum gauge. Its very simple and a very good diagnostic tool for quite a few things.
The acceleration comment wasn't complete. I totally missed writing vacuum drops on acceleration. It should not be part of this test, disregard it.

2. Pedal is intermittently hard on first pump. Should it be soft the first pump, it is consistently hard on the second pump.

This is a big clue. This points at a leak from the check valve to the booster. Could be both.

3. If I'm parked, idling, and depress the brake & hold, there is a hissing sound (intermittently). When there is a hissing sound, the brake will go from soft to hard, and will push back on my foot.

There should be no hissing here at all. Your loosing vacuum in the booster.

Booster should hold vacuum. I have parked my Cruiser, jumped in 3 days later and had 2 pumps of soft pedal.
As I mentioned earlier common cause here is, check valve, booster. The hissing condemns the booster. It never hurts to replace the check valve when you do the booster. They really shouldn't have a 20 year life span.

I'll try to dig up my cut away of a booster so you could see what's going on.

 

[LandLocked93]

Was this done with the OEM booster install?

80 Series 1FZ Brake Vacuum kit

80 Series 1FZ Brake Vacuum kit (BVK-1)

absolute-wits-end.com

Speaking to the metal bit specifically.

 

[KO KO]

Okie dokies. To Harbor Freight tomorrow for a gauge. I did indeed find a video & it even demonstrated how to test the valve to at least attempt to eliminate (or not) that component. I did change out a couple vacuum lines when I put in new spark plugs & wires about a week & a half ago. I'm going to do it to at least test the system. If it's the booster, well, ok then. Since it's the most expensive part, I will at least go through everything else just in case.

Was this done with the OEM booster install?

80 Series 1FZ Brake Vacuum kit

80 Series 1FZ Brake Vacuum kit (BVK-1)

absolute-wits-end.com

Speaking to the metal bit specifically.

I don't know. My service records don't indicate anything beyond the booster itself being replaced. I was just looking at it (5 min ago) and the rubber is fairly pliable. Considering the pliability of some of the other hoses in my engine bay, it seems likely that at least the hose was swapped out 6 years ago.

 

[LandLocked93]

If the current booster was truly new-OEM (not fake or NOS) and nothing outside the booster was replaced at install, assume the booster good imo until you rule out everything else. Go from the check valve out.
Isolate to dominate.

 

[enox]

Well...this just happened and my brakes became extremely hard.

 

[pedwards]

^ yeah, that will def make your brakes hard.

that's your check valve, and the line that connects is the vaccuum line. without constant vaccum your booster has no way to generate any power to assist your braking. Replacement check valves are available. i would recommend replacing it before replacing your booster, it much easier.

in the short term, i think it would be fine to glue it back together with some epoxy. but that's not a long term solution, considering the check valve is a pretty cheap part.

 

[enox]

Fortunately the booster has (2) extra check valves not being used. So I swapped to a good one and now it's all working again.

 

[Dave 2000]

Booster leak or one way valve leak, run engine and turn off in a quiet place you will almost certainly hear it. It is possible the hose from the manifold is collapsing preventing full vacuum, but that would be rare but worth checking.

Regards

Dave

 

[enox]

Booster leak or one way valve leak, run engine and turn off in a quiet place you will almost certainly hear it. It is possible the hose from the manifold is collapsing preventing full vacuum, but that would be rare but worth checking.

Regards

Dave

Yes, that had a hose on it which the nipple broke off so I swapped to a good one.

Hose looked good