My '64 Cadillac DeVille had been sitting for awhile while I was travelling this summer and when I came home it had some issues starting. After replacing the plugs and the ignition coil, it was running better than it had in a long time but the brakes were sticking. I noticed the brake pedal was traveling a little farther than usual when slowing down. Soon after I noticed a hissing noise coming from around the brake pedal. Then I lost the brakes pretty much completely. I couldn't find any leaks from the brake lines or the master cylinder when I took a look around. Is my master cylinder the culprit, or does anybody have any ideas on what to do next? Is it possible I cracked the brake line removing the plugs?

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Comment by Tony and Ginny 429 on August 8, 2018 at 2:38pm

I erased my second note ( two copies ) here  by accident that you can still find on the - dashboard 



Comment by Tony and Ginny 429 on August 8, 2018 at 2:17pm
If your peddle goes to the floor and no brake fluid staining on the inside of the tires --its time for a new master cylinder
Those are the signs you look for when the MC fails

The MC failure is most likely effecting the brake power booster so the reason for the vacuum air sounds you here

Comment by Jeroen Welgemoed on August 8, 2018 at 1:21pm

Small differences in rpm when brakes are aplied is a normal thing. Because you are switching from underpressure to overpressure in the booster.. Or the other way around.

Good luck. 

Comment by Chris Codd on August 8, 2018 at 9:50am

Thank you guys for the replies. I haven't done much more than a quick look around the car as it was late last night when it occurred. I did glance under the dash and look at the neutral safety switch but I didn't see any loose hoses. The hissing noise occurs when the brake is pressed and seems like it's coming from where the brake pedal goes through the firewall. I'll fiddle with the neutral safety switch and see if it makes any changes.  

The brakes were completely redone about ten years ago, so it's probably about time to go through them again. I haven't seen any fluid leaking yet. 

I have not checked the fluid reservoir level or wheel cylinders, but I will go check on them. I forgot to mention, the RPMs go up when the brake pedal is pressed. 

Comment by Russ Austin on August 8, 2018 at 9:31am

Look under the dash by the steering column  for the Neutral Safety Switch. There are 2 vacuum lines. The switch may be leaking vacuum.  Disconnect the vacuum line coming from the vacuum check valve (white plastic T) and plug the end. See if the hissing sound stops.  

If the hissing does not stop, then it sounds like a brake booster leak.  You can get a new booster/master cylinder here;  Just google the info.  Brake booster/master cylinder combo CARDONE 50-1301

How old are the brake hoses? They will let in air if they are old and cracked.  There are 4.

If you cracked a brake line, there will be fluid coming out. I don't think you did that.

Comment by Jeroen Welgemoed on August 8, 2018 at 9:19am

Hi christopher. 

Did you check the reservoir fluid level? And did you check your wheel cylinders? Air could be coming into the brake system. Air can be compressed unlike fluids. So your pedal can get a bit sticky or spongy. Is your engine running at a higher rpm than usual? That could be a vacuum leak from the brake booster could also result in starting trouble. If you cant get pressure to build up in the system my guess would be a wasted main cylinder.

Good luck. 


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