I am bleeding in my new brake system. It is Wilwood front/rear disc with their tandem master. Few hard lines twisted when removing so I just ended up making new hardlines for the whole car. Today I was supposed to bleed the brakes for the first time but I am experiencing a suction/hissing/whistling nose coming from my power booster everytime I depress the pedal. I pumped and pumped and pumped and it would won't create vacuum to get fluid in the lines.

I looked it up and I am getting "Leaking brake booster diaphragm". Is this correct? Is it from mismatched parts (Wilwood master with my original 11" power booster) or did the power booster just happen to fail?

I do not want to put more money into the brakes. It's been a challenge but if needed I may end up removing the power booster and go manual. Any advice or suggestions here? It is a 1.12 bore which was recommended by Wilwood for power brakes. It may be too large for manual.

 

Sounds as if the booster just failed.

 

Damn, thats odd, it was working fine before I started working on changing out the rear brakes. I think I will just drop $90 on a new one from flea bay and not waste any time.

 

Did you change the booster or master cylinder? Usually a failed booster makes the pedal hard.

 

Everything was changed except the brake booster

 

Look at the area where the plunger of the booster goes into the master cylinder. Make sure the mating is correct not a short pin into the long pin master. Did you bench bleed the master cylinder? If not you may never get the air out of the brake lines.

 

The master came with a pin you use if using a booster. It does make contact with the rod. I did bench bleed it before I installed it on the car. The master came with the bleeder kit and I bled all the air out on a vice.

 

As Eric suggested, ensure the pin is properly seating against the master cylinder push rod. I think there's only like ~1/16" tolerance. It certainly needs the correct adjustment. Sometimes you can validate a faulty brake booster by having the engine running and applying pressure to the brake pedal. If the engine stalls misfires it sometimes can be a brake booster seal failure. I'm suspecting an incorrectly adjusted brake booster-to-MC push rod pin. Did you follow any particular procedure for brake booster pin to MC adjustment? I posted one on here some time ago I can try to find in case you didn't follow any specific instructions.

 

There's really nothing too fancy about this "tool" - you can easily fashion it yourself to get the proper depth. Also, here's a link to a small test to perform for the brake booster. Read down through the page
Test Power Brake Booster

 

I did not adjust anything, I just used the pin that they included for power boosters and bolted it up so you are most likely correct.

Thank you. I have a 3d printer, I can make that tool in a couple hours. I will give that a shot and see how it goes. How do I bring out the pedal rod if needed? Would I need to disconnect it from the pedal? Same as the video shows?

 

If you didn't remove the pedal linkage there is no reason to disconnect the pedal linkage to adjust the brake booster push rod. I believe your push rod can be adjusted from the window between the MC and the brake booster? What car is this? I'm assuming a '68 cutlass from your other posts, but it's always best to state what you're working on. There's an off-chance you might not have an adjusting window between the MC & the brake booster on your car in which case some of the earlier models I think used shims. The pedal rod you're referring to is not the same thing as the brake booster push rod. The brake booster push rod sits between the brake pedal rod and the MC push rod inside the brake booster (vacuum cylinder). Hopefully you have the '68 CSM which demonstrates how to adjust the brake booster push rod.

I would suggest you do perform that test I provided in the previous link to demonstrate the brake booster is capable of holding a vacuum and is tight. I'd suggest you perform the several tests outlined to ensure you have a tight brake booster before you go too far. I'd hate to see you have a bad brake booster, faulty vacuum line or brake booster check valve. Those tests are simple and easy to perform.

 

Yes, 68 Cutlass Supreme. I do have the service manual which I will look at. I will go over all the tests on that link as well later this evening. I think I have enough info to figure out if the booster went back. I will let you know if I have any issues beyond that. Thanks again.

 

Sometimes a visualization of the testing is appropriate. The first one he conducts contains two parts: (1) Testing the check valve & (2) Holding vacuum. HTH

 

Thanks for the link. I think the booster just failed. Check valve was working fine, when I held the pedal after shutting off the engine it started to depress right away, when I held the pedal and turn the engine off, it didnt move at all. I can hear a vacuum leak from the booster when the car is running. I pulled the master and used the tool I printed and with the rod pin that Wilwood included, it lined up literally exact so that everything points to failed booster.

Thanks for the suggestions, advice and links. I learned a few things today.

Here is the tool I printed, luckily I was able to find the file online for free already someone had made.

 

Since my last post, I replaced the brake booster and everything went well. I am having a new issue. Once I shut the car off I can hear a really high pitch whine coming from the booster for around 10-15 seconds and then it stop. Is the diaphragm bad?

 

During the time after you turn the car off (the 10-15 seconds you stated), place your foot on the brake during the whining. Does the whining stop when you press the brake pedal?

 

The check valve could be suspect. The brake booster (diaphragm) should be able to hold a vacuum for a period of time after the engine is shut down - maintaining a vacuum inside the booster. Air (vacuum) should not be escaping through the check valve or around the check valve. The check valve is a one-way valve allowing air to be pulled from the booster but not into the booster. I'd first check the integrity of the check valve. If you step on the brake pedal after the engine is shut down while that whining is occurring and the brake pedal goes firm right away & the whining immediately stops, it might suggest air (vacuum) is escaping and the booster isn't holding vacuum. Are the brakes working OK and you can build a vacuum while bleeding the brakes and the brakes work during driving?

 

I got to look at it again for a bit this evening. The check valve works but I switched it out with the old one just to see if it may be the cause and it did the same thing. Looking at it closer the whistling sound is coming from the vent hole on the master as shown in the diagram below. When I plugged it with my finger the whistle stopped. I also got a couple dribbles bit of brake fluid leaking down the booster housing when I turned the car off where the master connects.



When I started looking it up I came across an article that wrote this "Chronic master cylinder failure due to fluid leaking past secondary seal in the master cylinder bore. A defective master cylinder pushrod seal in the power brake booster allows vacuum to draw fluid past secondary seal of the master cylinder". Not sure if the leaking is caused from a bad booster or if its from a bad seal?

 

I hate cliff hanger threads so an update for anyone who looks at this threads in the future.

I am not sure if the brand new booster failed or the new master failed. I am pretty sure the secondary seals on the master was bad. I returned the booster back to Inline and I called Wilwood and requested to send it back for inspection. They ran tests on it and told me they did not find any leaks but offer for me to replace the master with a 15/16" to go manual. I already went manual and am using a Corvette style CPP 15/16" master with no issues so far. I will install the Wilwood down the road. After changing the master and bleeding the brakes 3 times in a month, I am a bit exhausted doing it again.

Manual brakes feel much better to me personally. I like being able to apply the same pressure to get the same results each time. I have a Wilwood adjustable prop valve which I need to dial in the brakes once I get the car out.