[crm318]

I just received a brand new brake booster from Ames this evening. Out of curiosity, I applied vacuum to the check valve (with my mouth and a vacuum hose) and there was no resistance and a loud air leak sound from the pushrod/black grommet area. I sealed the recession off with duct tape and tried it again. It held and concaved the tape. I tore the tape off and it leaked down through the grommet. Do y'all think it's bad? The reason for the replacement is because last weekend, after hard braking, the engine almost died. My brake pedal is stiff and my AFR gauge doesn't even register a reading (shoots past 18.0 after start up). I figured this had to be it, even though the one on the car is only 3 years old. Does the master cylinder form an air tight seal when bolted on?

[crm318]

I broke the master cylinder from the old booster and see a ton of corrosion and rust and no o-ring. It seems if there was one installed on the new booster, that may solve the problem. That is a brand new master cylinder on the car and an o-ring from a corvette master cylinder in the pic.

[Goatracer1]

You shouldn't need an o-ring on the master cylinder. I have been working on GM cars for 50 years and have never seen one. In fact if the master leaks fluid it will run out between the cylinder and the booster. The rubber seal between the push rod and the booster shell seals it. Without the master bolted up that seal may leak.

[crm318]

Well I talked to Ames and the manufacturer of the booster and the both agreed it was defective. They are sending out a replacement, no question asked. It's always great working with Ames.

[mgarblik]

When you get your new one, here is a good test. Pull the vacuum hose off your regular daily driver with a vacuum booster and put a union in the hose to 3' of 3/8" vacuum hose. Start the car and charge your new booster with vacuum. Exercise the pushrod a couple times. It should move forward with minimal effort to prove the booster is working. Now shut the engine off and push the pushrod in again. You should get 1 to 2 easy pushes and then it should get very stiff. This proves the booster was really working. Now start the engine again and charge the new booster. Shut the engine off and carefully remove the vacuum hose only, not the check valve. Set the booster aside for a couple days. After a few days, push the rod and you should get at least 1 boosted push before it gets hard. That proves there are no vacuum leaks. If it passes, put it on. If it fails, well you have another defective Chinese booster.

[vertigto]

Curious...who is the manufacturer of the booster in question?

[crm318]

I'll have to give it a shot. The supplier to Ames is a company called MBM.

[mgarblik]

Originally Posted by crm318

I'll have to give it a shot. The supplier to Ames is a company called MBM.

MBM has their own web site. I looked around there some. They are very careful in their wording about what they are and what they do. They are not clear about being an actual manufacturer or basically a warehouse facility and distribution center for import brake parts. Just not clear to me. They use allot of red, white and blue lettering on the site but do not specifically say where the products are designed, engineered or manufactured. They make a big deal out of being located in Ashville, NC and how beautiful it is. But since there is zero info listed about "Made in USA" anywhere on the site, you just have to assume they are an importer and distribution center. The few USA manufacturers left like to advertise that fact and make sure customers know that fact. Not shroud the origin of the parts in some cloak of secrecy. I would test booster #2 no matter where it was made.

[crm318]

Well, booster #2 did the same thing. Applied vacuum and could hear leak down at the master cylinder grommet. Any suggestions for well known brake component suppliers? I was thinking of giving inline tube a call.

[Scarebird]

Originally Posted by crm318

Any suggestions for well known brake component suppliers? I was thinking of giving inline tube a call.

Tuff Stuff.

Originally Posted by mgarblik

MBM has their own web site. I looked around there some. They are very careful in their wording about what they are and what they do...

Johnny has all his stuff make in China.

[vertigto]

I would not recommend Right Stuff/RPUI.

[mgarblik]

Originally Posted by crm318

Well, booster #2 did the same thing. Applied vacuum and could hear leak down at the master cylinder grommet. Any suggestions for well known brake component suppliers? I was thinking of giving inline tube a call.

Very disappointed to hear this. Now we know where NOT to buy a brake booster. I would also be interested to know where one that functions correctly could be purchased. They simply need to be sealed air/vacuum tight. It's really not rocket science. We were teaching booster overhaul at my school until the early 2000's because dealership techs were expected to do this at the dealer level. Then GM stopped providing service parts for them. Once removed from the car the overhaul could be performed in 30-45 minutes on a single and a little over an hour for a tandem model. Pretty simple stuff. You do need a few special tools.

[Shiny]

Originally Posted by Goatracer1

.....Without the master bolted up that seal may leak.

Originally Posted by mgarblik

When you get your new one, here is a good test. Pull the vacuum hose off your regular daily driver with a vacuum booster and put a union in the hose to 3' of 3/8" vacuum hose. Start the car and charge your new booster with vacuum. Exercise the pushrod a couple times. It should move forward with minimal effort to prove the booster is working. Now shut the engine off and push the pushrod in again. You should get 1 to 2 easy pushes and then it should get very stiff. This proves the booster was really working. Now start the engine again and charge the new booster. Shut the engine off and carefully remove the vacuum hose only, not the check valve. Set the booster aside for a couple days. After a few days, push the rod and you should get at least 1 boosted push before it gets hard. That proves there are no vacuum leaks. If it passes, put it on. If it fails, well you have another defective Chinese booster.

These two seem a little different, might help (at least me) to know if the unit can be tested without having it bolted to a master.

Mike

[george kujanski]

Call me crazy, but if the internal diaphagm moves when the MC rod is depressed, the space behind the diaphagm (driver side) increases in volume. air has to get in there to fill the space. When the MC rod is released, the air behind the diaphagm is then pushed out.

The important thing is that the vacuum side of the diaphagm should not leak.

This make sense??

george

[mgarblik]

Originally Posted by Shiny

These two seem a little different, might help (at least me) to know if the unit can be tested without having it bolted to a master.

Mike

I have never found it to be necessary to have a MC involved in testing a vacuum booster. At least from 1963 forward. 1962 and older models, some of the boosters had the MC piston as an integral part of the assembly, meaning the piston stays with the booster when removed. The fact that the OP hears air rushing around in the driver side of the booster without application, indicates the air valve is either missing parts or defective as produced in China. The boosters we rebuilt in my classes were usually done on a Friday, charged with vacuum and put on a shelf with the students name. On the following Monday the student was asked to push the rod inward in front of me. If it still had vacuum in the chamber the rod would power assist and move easily and they would get a passing grade. If the rod was super hard, the vacuum had leaked out and they got a failing grade and a chance to do it over correctly. We called it quality control. I wonder if these replacements are checked with vacuum at all or just slapped together and thrown in a container ship?

[Shiny]

Thanks Mike

I never would have guessed a booster would be capable of holding a vacuum for days.

Apparently it also surprised some of your students!

Mike

[mgarblik]

Originally Posted by george kujanski

Call me crazy, but if the internal diaphagm moves when the MC rod is depressed, the space behind the diaphagm (driver side) increases in volume. air has to get in there to fill the space. When the MC rod is released, the air behind the diaphagm is then pushed out.

The important thing is that the vacuum side of the diaphagm should not leak.

This make sense??

george

Exactly. The passenger compartment side where the rod attaches to the pedal has an air valve and reaction disc, When pushed, air from the passenger compartment enters the booster through the air valve to take up the space. If he is hearing hissing without application, the diaphragm is leaking, or the air valve is is somehow allowing vacuum through it.

[highway star]

From shop manual: Test Power Brake Booster:
If the pedal feels "hard" while the engine is running, the booster isn't operating correctly. If you suspect the booster is defective, do not attempt to disassemble or repair the power booster. Doing so is unsafe and will void your warranty.
Test 1
1. With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the booster is working properly.
Test 2
1. Run the engine a couple of minutes.
2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.
Test 3
1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight.

Of course there is the option to have it rebuilt & replated.