How many inches of vacuum should a new brake booster hold if it's good?

So today while looking for vacuum leaks I tested the vacuum booster diaphram. I found that the MAX vacuum it will hold is 15 inches before it leaks into my hand operated vacuum tester. The tester can do 25 inches no problem if the vac line is plugged. The air plenum can pull 21 inches at idle, so there is a constant leak which is reducing the vacuum in the air plenum and may be causing some of my fast idle problem as well. Anyone have help/advice? Fixes? I don't think this is normal? Opinions?

Another crazy thing I found today- I'm getting ready for a compression test to see if I need an engine or try to fix this one. 285.000 miles! Anyway- while removing the spark plugs I found that they were all "loose" like they were installed, but never torqued down! I would estimate about 2-3 foot pounds of force on the 3/8's short ratchet was all it took to loosen all 6 plugs! None of the crush washers had been compressed, so good thing I found these before they went flying.

 

I think I have a similar problem. Do you have any codes right now?

 

If the diaphragm in the booster has a leak, the only thing you can do is replace it. That would definitely be a cause or contribution to a high idle.

Spark plugs should be 13 ft-lbs, I like to use just a smidge of anti-seize to keep galvanic corrosion at bay.

 

If the booster is leaking vacuum then its time to replace it.

 

I can hear a sort of hiss when I step on the brake. Is that the brake booster?

 

I think I have a similar issue, I can bleed all my brakes and have great pressure until I start the truck, then the pedal goes soft. When I pump while the truck is running I think im hearing air. I have no brake fluid leaking anywhere, I have also bled the master cylinder and the d block.

 

Off a 4Runner but it is the same...

 

There are some easy 1min booster test videos online
Let everyone know results

 

Yeah. If you hear hissing or sucking when you press the brakes, it's time to start shopping for a new booster. Whatever you end up getting, I recommend hitting it with a couple coats of black paint before installing.

 

No codes yet, but the scanner at the mechanic said the engine was running lean, and to look for a vacuum leak. I am 99% sure I have a leaking brake booster. My test vacuum pump will pull 25 inches but the most it will pull on the vac hose hooked to the one way valve is 7 inches, any further pumping does not increase the vacuum reading, so I have to assume that there is a leak inside the brake booster and it's fast enough that it probably reduces the total vacuum seen by the intake plenum by some percentage. Not only that, but anyone driving this vehicle may not be ready for the lack of stopping power that could result. So I ordered the new brake booster yesterday from Amazon that says it is a direct replacement for the Toyota part number

Good info and now in the process of replacing the brake booster when it arrives. Hopefully that will make a difference! It was not easy to remove and it won't be much fun to re install and bleed all the brakes either, but I wanted to avoid taking a chance of kinking one or more of the brake lines, so there was no choice but to disconnect the master cylinder for this operation.

 

Why the black paint? what about the gasket between the master cylinder and the front of the booster? That stock one was not much more than notebook paper so I don't think it was doing much in the way of sealing things up.

 

Unfortunately I did not drive the truck in that condition as it really required more brake force than I was comfortable with to drive it. Also, the fast idle was trying to make the truck run at about 45 miles an hour which is a bit unnerving at a stop light with no real stopping power due to the vacuum leaks.

If you buy a vacuum tester at Harbor Freight you can test your brake booster with the engine shut off. just hook it directly to the hose leading to the air plenum and see if it is holding a solid 20 + inches of vacuum. There might be some condition of the brake pedal where a good vacuum exists and other positions where it is absent. I cannot determine for you if any of these conditions are correct or incorrect, but I do know that my booster will leak into the output hose at any vacuum above 7 inches and the engine will pull 21 inches at idle, so this brake booster is leaking at anything above 7 inches and that is un acceptable to me with my high idle speed problem, so I am going to replace mine out of caution (23 years old and 285,000 miles) and my test results. Good luck and let us know what you find out!

 

No codes yet as I did not have a scanner at the very brief time I was driving it. Now that I have a scanner (blue Driver) I will try and get the codes if I still have problems after the replacement of the brake booster which should be closely related to the fast idle problem I am experiencing. But if the brake booster does not cure the fast idle loss of vacuum then the same codes should still exist and I will let everyone know what they are as soon as I do a full scan. However, the scanner can not pinpoint which branch of the vacuum operated system is causing the overall low vacuum situation. it only knows there is a "lean" condition because of the systems that it can directly monitor but it does not have sensors to monitor absolute vacuum levels over most of the system.

 

Sorry to still be asking the same question, but can somebody with good brakes do a quick check with a vacuum tester and tell me if your booster will hold a vacuum with the engine shut off? I can't find a Chinese made one that will hold ANY vacuum. May have to resort to a used one from the junkyard!

 

My "Centric" aftermarket booster doesn't hold vacuum for more than a few seconds after the engine is shut off. It's very disappointing to not have an OEM option anymore.

 

Nice to have a reply! I think that few seconds is about average. But my concern is that none of my Chinese copy brake boosters from AMAZON can even establish an inch of vacuum on my Mityvac gauge, so I sent them all back. The next one I try will be from NAPA but it too will get the vacuum test on the bench to see if it will establish a vacuum before I install it. I would think that the gauge would show something besides zero if the diaphram in the booster was holding a vacuum, but this is not my area of expertise and I can't find anyone who really knows the subject well.

You do have an OEM option but it will be about 600.00 for a Toyota booster. By the Way- Toyota had two versions of boosters they used in the 01 Tacoma. You need to check your build date and take the VIN number and door sticker pics to the store and have them verify which part number you need. The Napa booster will run you about 200 bucks after you turn in your core.

 

I never got any real codes as you suggested, just a fast idle 1500-2000 depending on how bad the vacuum leak was at the time. My OBD2 sensor connector was badly corroded so none of the scanners could really communicate because of the bad connection. I finally sprayed the OBD2 connector with some AC50 a couple of times and eventually my new Blue Driver could communicate, but never gave me a code for the fast idle problem, so i returned it for a refund. The check engine light was still intermittant at the time as well which is pretty frustrating as well. Since then, I have found a few questionable vac hoses and replaced them which really helped the vec readings at idle, but only if I had my brake booster dis-connected from the air plenum. Now the question is can I find a brake booster that can hold a vacuum above 20 inches or better with just my hand operated Mityvac 8000. ?? Could be that the Mityvac does not have the capacity to test a 10 inch diameter brake booster? at least I'm getting tired of pumping the handle waiting for the needle to move off of zero!

 

In theory, couldn't you attach the vacuum hoses in the engine bay before installing the booster, the fire up the engine as a pre-test?