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Old 08-02-2010, 06:08 PM
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Could a brake booster cause this?

My Dodge 1500 has developed very "spongy" brakes, they seem to hold OK and do not leak off but has way too much pedal travel and the pedal will go all the way to the floor. Pumping them only helps slightly and they will lock the wheels in a hard stop only after the pedal has reached the floor although braking can be felt as soon as the pedal starts to move. Pads/shoes were changed recently so I replaced the master cylinder, bled the entire system and made sure the rear shoes were adjusted properly but this made zero difference. The booster does not leak vacuum and seems to be working properly, no strange noises, etc, unless what I have described might be a symptom that all is not well with it. Could a brake booster cause a problem like this? Any other things I might be overlooking?

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Old 08-02-2010, 06:21 PM
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not the booster. two things come to mind. wrong piston size in the master, (was that size working good before?) or to much rear proportioning. proortioning valves dont realy go bad often but....are the rear brakes adjusted up fairly tight? hmnnn ... anything that flex`s in the system as in caliper mountings wheel cylinder mounts etc...good luck.
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Old 08-02-2010, 06:30 PM
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You are getting air in the system. Probably from the master..
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Old 08-02-2010, 06:35 PM
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oldred, did you do the bench bleed routine with the master cylinder?
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Old 08-02-2010, 06:47 PM
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Definitely sounds like you still have air in the system. I would re-bleed the system. JMO


Cole
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Old 08-02-2010, 07:01 PM
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Yes I did bench bleed the master cylinder and I tried to do a though job (had that problem before! ) I kept pumping and even did the tapping routine on the MC to dislodge any tiny bubbles so I am sure there was no air in it but of course there is the problem of keeping air out when the lines are attached. As for bleeding the brakes I used a vacuum bleeder and made sure I pulled enough fluid through to have filled the line back to the MC plus the Cylinder/caliper being bled, I did this at each wheel. This is what has me so confused, I replaced the master cylinder and checked the wheel cylinders/calipers/brake lines and I am confident there are no leaks and that no air could be left in the system, still it sure seems like air. Well if the booster can not cause this then I guess I was about to make a $100 mistake so I am glad I asked first, I think maybe I will bleed the system again and see what happens.


FWIW, the original MC was fairly clean, full of fluid and showed no signs of leakage from the back where they commonly leak.
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Old 08-02-2010, 10:24 PM
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whow old are the flex lines?? I have seen old ones swell from age when you apply the brakes , you could physically see then grow in diameter when applying the pedal . and also are you sure the pedal is coming all the way back when releasing them .
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Old 08-03-2010, 09:10 AM
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Quote:
Originally Posted by stimpy
whow old are the flex lines?? I have seen old ones swell from age when you apply the brakes , you could physically see then grow in diameter when applying the pedal


Never seen that before and would have never thought of it but it sure makes a lot of sense and could certainly cause the problem, I have not re-bled the brakes yet so when I get out there I will definitely check those lines first thing.
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Old 08-03-2010, 09:16 AM
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IMHO there is nothing like a good old fashioned pressure bleed with the engine running to get all the air out of the system . Just MHO .
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Old 08-03-2010, 10:21 AM
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Quote:
Originally Posted by stimpy
whow old are the flex lines?? I have seen old ones swell from age when you apply the brakes , you could physically see then grow in diameter when applying the pedal


Well I just checked those lines and the one on the driver's side looked slightly swollen before I even applied the brakes, sure enough with the pedal depressed this thing does indeed expand by quite a bit! Never seen or heard of that one until now but apparently this is the problem so I am now off to the parts house for a new hose.

Thanks a bunch
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Old 08-03-2010, 10:33 AM
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Quote:
Originally Posted by oldred
Well I just checked those lines and the one on the driver's side looked slightly swollen before I even applied the brakes, sure enough with the pedal depressed this thing does indeed expand by quite a bit! Never seen or heard of that one until now but apparently this is the problem so I am now off to the parts house for a new hose.

Thanks a bunch
Makes perfect sense to me . Good call , stimpy ! I'd replace both sides while I was at it and maybe even the one on the rear diff . They are all the same age ?
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Old 08-03-2010, 05:11 PM
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Yes it was a good call, a very good call because it solved the problem!

It don't take much expansion on those front calipers to cause a lot of brake pedal travel and this line was swelling to about to about half again it's original diameter allowing the pedal to go all the way to the floor. Sure had me puzzled because I thought I had checked everything and since the line was not leaking I didn't notice anything wrong. Don't know how long it would have taken me to find this problem without that tip, might not have found it until the line ruptured which I am sure it was about to do. Thanks again to everyone and especially to Stimpy, that sure was an odd one but one I will remember.
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Old 08-03-2010, 05:15 PM
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This is something to remember, I never would have thought of that.
Glad you got it fixed.


Cole
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Old 08-04-2010, 03:56 AM
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thank the japanese motorcycles I used to work on , this was a common problem with then in the 70's when they started to use a synthetic rubber , my dad almost had a accident on my Bike one night as he tried to use only the back brakes ( because I couldn't find a new hose for the bike and the front replacement cost $120 ) and almost flipped himself over the bars as the front line was a new stainless braided teflon hose one I had made for it made the fronts very twitchy . like I said you could see the hose grow in size almost a 1/16th of a inch .

on any old vehicle I look at the brakelines first and replacethem if they over 20 years old as cheap insurance , my pickup ( 96 chevy 3500 ) I put staineless braided on it and it stops faster and the pedal is nice and hard not mooshy like they typical GM .
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Old 08-04-2010, 09:10 AM
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Quote:
Originally Posted by stimpy
thank the japanese motorcycles I used to work on , this was a common problem with then in the 70's when they started to use a synthetic rubber , my dad almost had a accident on my Bike one night as he tried to use only the back brakes ( because I couldn't find a new hose for the bike and the front replacement cost $120 ) and almost flipped himself over the bars as the front line was a new stainless braided teflon hose one I had made for it made the fronts very twitchy . like I said you could see the hose grow in size almost a 1/16th of a inch .

on any old vehicle I look at the brakelines first and replacethem if they over 20 years old as cheap insurance , my pickup ( 96 chevy 3500 ) I put staineless braided on it and it stops faster and the pedal is nice and hard not mooshy like they typical GM .
Makes me think that I ought to replace the rear flex line on my T-bucket . Everything else is steel or stainless flex . Wish everybody could read this post . Great tip stimpy .
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