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scooter-d
Novice
Nov 24, 2007, 1:34 PM
Post #1 of 11
(4106 views)
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to no avail have i been able to fix this thing. mostly in cold weather when you touch the brakes the pedal will draw away from your foot. not enough to lock up the brakes but enough to turn off the brake switch. if you push the pedal about half an inch it will stay and not come back to top of travel. so far i have bled the brakes, made sure rears are in adjustment, replaced power booster(which in warmer weather made it a little better), replaced master cyl. and replaced vac. valve at booster. still wont let the pedal travel normal.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 24, 2007, 5:20 PM
Post #2 of 11
(4100 views)
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Did this happen with both old and new master cylinder?
T
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scooter-d
Novice
Nov 26, 2007, 3:56 PM
Post #3 of 11
(4095 views)
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yes. the truck has 95000 miles on it. all the pads look to be in really good condition. lots of pad remaining. lots of pedal travel also. or more than what i think it should have. one way to put it is that when the pedal does come back up there is no force to it . on the other vehicles in the driveway when you let off of the brake the pedal has tention on your foot when it returns. this has nothing. its a 2 footer, one to push one to pull the pedal back up. im about ready to give up.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 26, 2007, 4:45 PM
Post #4 of 11
(4093 views)
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I'm at a loss with this one. I thought the master cylinder had the spring force to return pedal to top of travel but the booster would have some too. Vehicles without power brakes at all didn't have a problem?? I haven't needed to replace a vacuum brake booster since the Nixon administration so I don't know about those too much anymore.
My guess is the master cylinder's return spring, new or not is the issue as when I've bench bled them they fight back pretty hard. It would be a pest to take it off again and bench bleed it to just feel that force again with that one??
T
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scooter-d
Novice
Nov 26, 2007, 6:23 PM
Post #5 of 11
(4089 views)
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that is the weird part. when i took off the old one i pushed it against the mounting bolt on the booster and it would move easily so i figured for sure that was it. even the new one i could push with my finger. even without fluid in it there should have been more there. it semed really weak ( new one). what would be the chance? maybe i should go try another new and see how weak it is first. 20 years ago i could take the boxes of parts and throw them under the vehicle and it would fix it. now nothing works. if you can think of anything else let me know if not thanks for this much.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 26, 2007, 11:42 PM
Post #6 of 11
(4086 views)
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YOU COULD PUSH IN THE MASTER CYLINDER'S BORE WITH YOUR FINGER?!! Some finger or that isn't like any I've dealt with.
I have had whole lines of parts be bad before. Sounds like this might be just like that. Ask where you bought it to check it out (they are not necessasarily mechanics) with another brand if possible,
T
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scooter-d
Novice
Nov 27, 2007, 6:46 PM
Post #7 of 11
(4081 views)
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ok one more. i took back the core and checked another one and it was soft also. so i stopped by the local murrys auto and the fella behind the counter didnt want to pull a master cyl. to check. but another customer overheard me and told me it is the power booster. he works for ford prototype and said that in the past they had a large problem with the same type of things. is there any way to chek the booster for fault? i guess i can take it to work for that. i work for roush so i should be able to find out something. i just havent got the right person. sounds like a weekend job to me. why cant things go wrong in warm weather?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Nov 28, 2007, 4:07 AM
Post #8 of 11
(4080 views)
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The booster would also be sprung for a "home" position or pedal back up. I'm learning here too! I would have thought the master cylinder was strong enough or the primary force but perhaps not. Over all the years I just haven't had many boosters be bad for any reason - just chance,
T
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scooter-d
Novice
Dec 13, 2007, 4:25 PM
Post #9 of 11
(4055 views)
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hello once again. well now i have tried unbolting the master cyl. from the booster and starting the truck and the vac pulls the pedal just the same as before. so i took the booster back for exchange, replaced with a new one and the same thing is happening. im ready to give up now!is there some place i can get a vac. diagram for this to see if something is missing. maybe too much vac. the hose comes off the top of the plenum with several other hoses. i dont see any description in any manuals i have here.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 13, 2007, 5:53 PM
Post #10 of 11
(4053 views)
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Booster has only one vac hose involved with it - I believe that's a law. That little elbow is a check valve and when they fail they usually don't hold a vacuum like going up hill or if engine quits you get another shot before no power assist. It's not getting too much vacuum as under extremes it would have to hold at least 25Hg and the max at sea level possible is about 30Hg with a vacuum pump.
When this was apart did the brake pedal move freely? I suppose it could be the pushrod and pivot to it screwing up the show.
The brakes should work and behave as normal without vacuum at all except you need both feet and a pry bar to push hard enough without assist. Ok - I'm an old f@rt but this engineering only changed with some cars using the power steering pump for the power assist. Lots of cars back when didn't have PB at all and the lever action of your pedal was stronger but took more travel - you could add PB to those with no big deal. You shouldn't need a diagram as this is just plain hardware except for the exact layout of what's happening inside the master cylinder and I don't know anyone who bothers to rebuild their own anymore.
Perhaps try taking the pedal off at the brake light switch and see if you can get the pedal alone to swing freely??
T
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scooter-d
Novice
Dec 13, 2007, 6:26 PM
Post #11 of 11
(4050 views)
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yes the pedal is free. and the check valve is new and i replaced it before the last booster. i havent checked the vacuum yet but the engine doesnt have that much vac does it. isnt 30 in. perfect vacuum? anywho, tomorrows another day.
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