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Old 01-22-2012, 04:59 PM   #1
Stingray_1976
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Default hissing sound when push brake pedal?

I have to admit that I don't know much about the brake boost system in my '76 L-48 (or any other system, for that matter). Today I backed the Vette out of the garage after it had been sitting for about 3 weeks. When I pressed the brake pedal it felt like I had no power assist at all, and I heard a weak hissing sound coming from the firewall area.The brakes still stopped the car, but required significantly more pressure on the pedal than normal.

I was just moving the car out of the garage to allow access to my workbench, but decided I should very carefully go up and down the street once to see if the condition persisted or went away. I always got the same result, and also noticed that engine RPM decreased by 200-400 when I pressed the brake pedal. I tested this by putting the car in park, then pressing the brake pedal.

Since I was moving the Stingray to allow access to work on another, more important project (my son's pinewood derby car), I haven't had time to troubleshoot the Vette at all. However, I'm guessing that there is a vacuum line running from the engine to the brake booster and that is likely leaking.

Does that sound plausible, or is there a more likely explanation?
I just had new calipers installed all the way around about 3 months and 300 miles ago... can't think of why that would cause this though.

Thanks in advance.
Jeff
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Old 01-22-2012, 05:26 PM   #2
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Sounds like the booster needs to be replaced.

Lots of posts here about how to replace. Patience and perseverance are required as well as extensions for tools.

Dan
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Old 01-22-2012, 05:39 PM   #3
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Thanks for the reply.
After posting I googled my problem and found a variety of posts across the internet where others had similar problems and the commons solution is replacing the brake power booster.
I'm thinking I'll replace the master cylinder also, since it would be the only major "old" part left, and likely subject to failure soon since it would be the weakest link.
Ecklers, zip and VBandP have boosters, but they are more than twice what I can get this one for at the local AutoZone:
http://www.autozone.com/autozone/par...723205_0_8550_
Anyone have thoughts on why this reman is so much cheaper?
Should the Cardone be avoided?
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Old 01-22-2012, 06:28 PM   #4
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I have had good luck w/ Cardone but I haven't bought a brake booster, several other parts still running strong!
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Old 01-22-2012, 08:00 PM   #5
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My 76 was doing the same thing, lots of whoosing and hissing noice under the dash with rpm changing when I stepped on the pedal. Anyways, I bought the cardone assembly that was the booster and master cylinder as one package. Alot better to install and only $30 more. The hardest part of the swap for me was the pin that holds the pedal to the booster arm. Not alot of room under the dash. it did solve the problem though.
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Old 01-22-2012, 08:27 PM   #6
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DON'T GET IT FROM AUTOZONE!!! i did and it didn't work well. they will pull a booster from any vehicle and say it fits yours but it might not. $200 is worth it to get the right one. the problem i STILL have is that when i installed it and hooked it to the brake pedal it pulled the pedal closer to it and away from the sensor that tells if your brakes are on or off, so i had to fix that with 4 pennies and duct tape as a spacer
i thought the hardest part was the bolt in the upper left corner. just really hard to get to. i got more at... corvette central i think, can't find the receipt, and it was just over $200 after s&h

Last edited by 75vetteman; 01-22-2012 at 08:32 PM. Reason: ,,,,,, button don't work!,,,,
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Old 01-22-2012, 08:34 PM   #7
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INSTRUCTIONS:

Step 1 : Remove drivers side seat.






....

Dan
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Old 01-22-2012, 08:58 PM   #8
Stingray_1976
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Quote:
Originally Posted by 75vetteman View Post
DON'T GET IT FROM AUTOZONE!!! i did and it didn't work well. they will pull a booster from any vehicle and say it fits yours but it might not. $200 is worth it to get the right one. the problem i STILL have is that when i installed it and hooked it to the brake pedal it pulled the pedal closer to it and away from the sensor that tells if your brakes are on or off, so i had to fix that with 4 pennies and duct tape as a spacer
i thought the hardest part was the bolt in the upper left corner. just really hard to get to. i got more at... corvette central i think, can't find the receipt, and it was just over $200 after s&h
Interesting. I'll have to weigh the risk on this. AutoZone has a deal where they give you $20 off for each $100 you spend and have shipped to your home. That makes this $112 booster + master cylinder kit $92. I'm leaning towards taking the risk that it could be a mismatch, since I can take it back to the store around the corner if it isn't right. This is my sunny weekend car... and it hasn't been sunny on a weekend around here in a few weeks... so I'm not in a huge hurry. I guess I'm leaning towards taking the risk with AZ, but who knows how my feelings may change before I order. Thanks for the feedback, though. Far better to be informed before making a choice.
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Old 01-22-2012, 09:01 PM   #9
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Quote:
Originally Posted by dannyman View Post
INSTRUCTIONS:

Step 1 : Remove drivers side seat.

....

Dan
Got it.
I shimmied around under the dash to loosen my steering column mount to slide it aft so I could change the rag joint a few months ago. Can definitely see how the lack of space down there would be an issue. At 6'4" tall and with long arms, working under there should be easier without the seat in the way.
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Old 01-22-2012, 09:02 PM   #10
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Quote:
Originally Posted by scrappy76 View Post
My 76 was doing the same thing, lots of whoosing and hissing noice under the dash with rpm changing when I stepped on the pedal. Anyways, I bought the cardone assembly that was the booster and master cylinder as one package. Alot better to install and only $30 more. The hardest part of the swap for me was the pin that holds the pedal to the booster arm. Not alot of room under the dash. it did solve the problem though.
Great feedback. Thanks! Wish me luck.
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Old 01-22-2012, 09:07 PM   #11
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I was surprised when I got in the car to pull it back in the garage this evening. The brake pedal was a bit squishy... not rock hard like before. Still some softer hissing when depressed, but not as loud as before. I didn't push my luck and just idled it the 15 feet back to it's home in the garage.
Looks like maybe the booster hasn't completely given up yet. However, I won't be taking any chances. As soon as I sort out which place I want to order from I'll get the new booster and MC to install before I drive it again.

Thanks again for the comments. Any further tips or hints are appreciated.
Jeff
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Old 01-23-2012, 08:05 AM   #12
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Default Not an easy job!

Quote:
Originally Posted by Stingray_1976 View Post
I was surprised when I got in the car to pull it back in the garage this evening. The brake pedal was a bit squishy... not rock hard like before. Still some softer hissing when depressed, but not as loud as before. I didn't push my luck and just idled it the 15 feet back to it's home in the garage.
Looks like maybe the booster hasn't completely given up yet. However, I won't be taking any chances. As soon as I sort out which place I want to order from I'll get the new booster and MC to install before I drive it again.

Thanks again for the comments. Any further tips or hints are appreciated.
Jeff
Jeff,

I had the same symptoms as you just before Christmas, so I pulled my booster out. It's a 1974 manual, and I just couldn't get a socket onto the top left bolt. There is a safety starter interlock switch that's in the way. I ended up removing:-

the driver's seat,
the steering column,
the pressed metal plate that holds the column,
the cast iron plate that holds the above,
the stop light switch bracket, and loosened the IP to get at a couple of bolts on the cast iron bracket.

I used a long 9/16" socket with a 1/4" drive, a uni joint on the socket and a long extension arm. As I'm fitting a Hydroboost, I also removed the pedal assembly and welded 3/8" UNC nuts on the inside of the front part of the pedal assembly. On Australia Day this Thursday, I'll be putting as many parts back as I can.

I have a hydraulic fitter coming on Friday and he can make up hoses on site to connect my GM "metric" pump to the HB, the Borgeson box and the remote reservoir I've built. I'll use 3/8" UNC bolts from the front of the firewall to attach it to the pedal assembly. I don't ever want to get up under the dashboard again!!!

Good luck with your project.

Regards from Down Under.

aussiejohn
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Old 01-23-2012, 10:49 AM   #13
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Quote:
Originally Posted by aussiejohn View Post
Jeff,

I had the same symptoms as you just before Christmas, so I pulled my booster out. It's a 1974 manual, and I just couldn't get a socket onto the top left bolt. There is a safety starter interlock switch that's in the way. I ended up removing:-

the driver's seat,
the steering column,
the pressed metal plate that holds the column,
the cast iron plate that holds the above,
the stop light switch bracket, and loosened the IP to get at a couple of bolts on the cast iron bracket.

I used a long 9/16" socket with a 1/4" drive, a uni joint on the socket and a long extension arm. As I'm fitting a Hydroboost, I also removed the pedal assembly and welded 3/8" UNC nuts on the inside of the front part of the pedal assembly. On Australia Day this Thursday, I'll be putting as many parts back as I can.

I have a hydraulic fitter coming on Friday and he can make up hoses on site to connect my GM "metric" pump to the HB, the Borgeson box and the remote reservoir I've built. I'll use 3/8" UNC bolts from the front of the firewall to attach it to the pedal assembly. I don't ever want to get up under the dashboard again!!!

Good luck with your project.

Regards from Down Under.

aussiejohn
Geez!
Ok, I'm officially worried about how long this job is going to take.
I hope yours goes smoothly from this point forward, John.
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Old 01-23-2012, 12:09 PM   #14
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You can take it to a repair shop to have that work done...but it is labor intensive and expensive. Also, with all that "stuff" in the way under the dash, you don't know how much collateral damage you will get as a result. If you can do it yourself (or have some help with you), you have a better chance of success, because of the extra care you will take to prevent other damage.

Personally, for the little difference in cost, I would opt for the better grade of booster than to buy at the "Zone". Also, you might want to put a coat or two of Dupli-color "clear" engine enamel on the unpainted booster surface (if that's what is available) to keep it looking good. Let dry for at least 2-3 days for good cure, before you try to install it. Otherwise, if you paint, it will get all scratched up from installation. {enamel takes about 7 days to completely cure}
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Old 01-23-2012, 12:55 PM   #15
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BOOSTER DEWEY 503-238-8882 time and $ well spent!!!!!!!!
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Old 01-23-2012, 01:05 PM   #16
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Quote:
Originally Posted by Stingray_1976 View Post
Geez!
Ok, I'm officially worried about how long this job is going to take.
I hope yours goes smoothly from this point forward, John.
I myself am only 5'-4" tall, so it was easier to just go in under the dash upside down. I do not take stuff apart till I atleast try to do the job first. I did not take anything apart or out. The top left mounting bolt is up there and tight. I used a wrench on that and just turned it about a half a turn at a time. I did the job in about 3 hours. Like I wrote before, the hardest part for me was putting in the pin to join the pedal and booster shaft. I could not see when the two were lined up. I took a small screwdriver and stuck it thru both holes and rolled it till the hole felt lined up. it took three times doing this and the pin dropped it. then using long needle nose I was able to put the cotter pin in and bend it. Everthing else fell into place.did not have to remove a thing to do this, of course except for the old booster, lol.

With a discount at Advance, I only paid 130 for the booster/master cylinder combo. They are made by cardone. I have yet to have anything fail that was done by cordone.

Last edited by scrappy76; 01-23-2012 at 01:08 PM. Reason: Add
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Old 01-23-2012, 01:08 PM   #17
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Quote:
Originally Posted by scrappy76 View Post
I myself am only 5'-4" tall, so it was easier to just go in under the dash upside down. I do not take stuff apart till I atleast try to do the job first. I did not take anything apart or out. The top left mounting bolt is up there and tight. I used a wrench on that and just turned it about a half a turn at a time. I did the job in about 3 hours. Like I wrote before, the hardest part for me was putting in the pin to join the pedal and booster shaft. I could not see when the two were lined up. I took a small screwdriver and stuck it thru both holes and rolled it till the hole felt lined up. it took three times doing this and the pin dropped it. then using long needle nose I was able to put the cotter pin in and bend it. Everthing else fell into place.did not have to remove a thing to do this, of course except for the old booster, lol.
Sounds like we have a similar approach. Hopefully I'll be in the 3 hours or less range as well.
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Old 02-01-2012, 01:13 PM   #18
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Hey gang. I went with the Cardone from Advance and it has finally arrived. I've never ordered a MC and booster before, and can't tell if it arrived with silver paint, or if it was just media blasted... and I'm looking at bare metal. Regardless, i'm thinking that I should shoot some paint on it before I install. Thoughts on what type of paint to use, or any hints on not screwing up that part of the job?
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Old 02-05-2012, 11:53 AM   #19
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Well. It is definitely bare metal.
I bought a can of Rostoleum black engine enamel and started spraying. Not good. It is getting little spots of poor adhesion everywhere (is that "fish eye"?). First time I've tried spraying something like this, so I didn't know what to expect. I probably just failed to prepare the surface properly.
Looks like I'll have to sand/mineral spirits this off and start with primer, then black.

On another note, the currently installed (as in, not the new one that I'm painting) brake booster has worked flawlessly the past 10 times I've driven the car. I wiggled the vacuum hose connections where it connects to the booster check valve and the vacuum source and it has worked fine ever since. Looks like it may have been a vacuum leak.
Regardless. I've got the new MC and booster and will swap them in as soon as I get the paint sorted out. As it is now, the old one's are who knows how old, and I've got new lines and calipers... so I figure the MC and booster are the oldest/weakest links in the system. Will be good to get them updated before they fail again.
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Old 02-05-2012, 05:09 PM   #20
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Before you replace the master cylinder and booster, make sure the fitting that connects the vacuum hose to the booster has not ruptured.
The fitting is a 90 degree piece and can open up causing this problem as well.
Hope this helps
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