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Discussion Starter #1
i had the brakes redone when i got the car, 69 ss 396 with front power disc brakes - new rotors, shoes, lines. nothing done to the master cylinder or booster. this was about 1500 miles or so. the brakes seem sort of spongy, especially after you first hit them and then keep your foot on them (the pedal will sometimes go all the way to the floor) or at idle like when pulling into the garage. pumping them seems to help. i've got a 280h comp cam and not sure if i just don't have enough vacuum (would a canister be the solution?) or if it could be something in the cylinder/booster or just need adjustment (never adjusted since new brakes installed). since i paid a mechanic to redo the brakes (i had just got the car, let him go through it and didn't have time to do it myself as i should), i plan to let him look at it. i was just wanted a little more knowledge/possibilities before i took it in. i know it could be a lot of things, but any suggestions? i did replace the vacuum line from the carb to the booster just in case it had a leak.


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Make shure the vaccum hose is made for the job or it will suck shut.

Spongy pedal can be caused by several things.

Air in system. might need to bleed at master, or replace master.
loose wheel bearing, or wrong bearing with too big an ID. (I've seen it, after a hard turn the pedal drops)
Sticking caliper, not sliding, if single piston.
Bent pads, or twisted mounting. have someone press on the pedal while you look at the calipers, they should move a little to the side but not twist or rock.

Low vaccum would cause a hard pedal, not low. So I think your problem is probably in the hydraulic side of it.
David

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David's Homepage
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer
 

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I used to have a similiar problem with the brakes on my daily driver. I would have to put the pedal to the floor and the pedal was soft. I adjusted my rear drums and the pedal came back up and the pedal feel was much better.
 

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In most cases after new brake job, the master goes south!
The way you describe it I would believe that the master cylinder is in need of replacement.
 

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Do like Fred Flintstone; get new shoes first


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"A days pay on the wild side"
67'Chevelle 396/400/4.10
used to have 84' z28 with all the goodies
 

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I agree with the bleed/replace of the master cylinder. I doubt it is a vacuum problem because it happens the first time you touch the brakes. Low vacuum usually shows its symptoms (hard pedal, no braking) after multiple stops when there isn't enough time to re-build vacuum.
 

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Discussion Starter #7
turns out it was the master cylinder. thanks for the replies.
 

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Discussion Starter #9
difference in the feel of the pedal makes me think i've got Viagra in my brake fluid!
 
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