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#1 |
Registered User
Join Date: Feb 2006
Location: Republic of California
Posts: 345
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Truck's got Power Brake issues (disc/drum)
Her brakes don't feel right. When I apply them they work okay, but as the pedal travels, it sinks down midway and I have to apply more pressure to continue stopping.
I bled the the brakes. That didn't help at all. I'm thinking I've got a vacuum leak somewhere. Can I hook up a vacuum pump and gauge to the booster to test it? How much vacuum should I pull to test it? How long should it hold? How much vacuum should I see coming from the manifold? And how do i check that? Disconnect the booster, or T' into the line? Thanks,
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'67 C10 Short Stepside 5.0TPI/700R4 |
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#2 |
67-72 Addict!
Join Date: Feb 2002
Location: The TAX State!
Posts: 7,857
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Re: Truck's got Power Brake issues (disc/drum)
Did you swap out the proportioning valve?
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Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads |
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#3 |
Registered User
Join Date: Feb 2006
Location: Republic of California
Posts: 345
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Re: Truck's got Power Brake issues (disc/drum)
I didn't do anything other that bleed it. Whether it has a proportioning valve that is correct for disc/drum, I don't know.
I bought it the way it is. It's had the funny brake feel since Day 1. The rear was locking up before the fronts too. I haven't noticed it doing that since I bled the brakes, but I haven't driven it very much either.
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'67 C10 Short Stepside 5.0TPI/700R4 |
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#4 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: Truck's got Power Brake issues (disc/drum)
It could be a couple things, if you have disk brakes the master cylinder should have two different sized reserviors the one towards the front should be bigger. If you had a drum/drum reservior then they would be equal in size. Yes, power disk brakes need to have a proportioning valve to work properly. Are you losing any fluid, or do the brakes just feel mushy? When I did my power disk brake swap on my 67 pushing the pedal down more than an inch or so would put some instant tension on the 3 point seatbelts
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#5 |
Registered User
Join Date: Feb 2006
Location: Republic of California
Posts: 345
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Re: Truck's got Power Brake issues (disc/drum)
The MC reservoirs appear to be equal in size. The lines coming out are not the same size.
There is some fluid leaking out over the top of the front reservoir. If I need a new MC, what exactly do I need? Does this look like the stock 4-drum distribution block?
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'67 C10 Short Stepside 5.0TPI/700R4 |
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#6 |
Registered User
Join Date: Jan 2006
Location: sidney , illinois
Posts: 312
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Re: Truck's got Power Brake issues (disc/drum)
my 93 gmc had the same symptoms. soft pedal , but still stopped. did every thing you did and finally fixed it by replacing the rear wheel cylinders.
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hey.....smell my finger 64 nova wagon , 63 nova convertible |
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#7 |
Registered User
Join Date: May 2005
Location: Missoula, MT
Posts: 273
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Re: Truck's got Power Brake issues (disc/drum)
My 72 GMC has that same MC, and appears to be the same Distribution block, but mine is non assist, and I have front disk and rear drum. Your problem isnt vacuum related, if it were, the pedal wouldnt be soft but hard. Did you bleed the MC as well. You can attempt to pin point the problem by disconnecting and isolating compontents. First try bleeding the MC by one at a time just cracking the lines going to the MC, if that doesnt work, get a MC plug, and disconnect one line and then plug the MC and try it, if it still is soft, that area weither it be the front or rear isnt the problem, do the same for the next line, if soft then its not just the the next system, go through and test it down the system. if it still doesnt work, then most likely the MC is bad. I work at les schwab and see this come in alot. Sometimes there is just an air bubble stuck in the system way up there that just wont get out, if you have access to a gravity bleeder, hook it up, if not have a local shop that has one bleed the system for you. The way it works is it attaches to the MC and applies air pressure to it, you open up the bleeders and it forces the fluid out while at the same time keeps the MC full so it constantly feeds fluid. Hope this helped ya at all.
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#8 |
Registered User
Join Date: Aug 2004
Location: san marcos,tx
Posts: 266
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Re: Truck's got Power Brake issues (disc/drum)
just sounds like a bad mc to me.
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72 GMC sierra 3/4 ton 402 bb ![]() 68 GMC 3/4 ton ![]() 2010 camaro rs: daily driver |
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#9 |
Senior Member
![]() Join Date: Sep 2005
Location: Lewisville, Nc
Posts: 10,234
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Re: Truck's got Power Brake issues (disc/drum)
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David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube |
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#10 |
Registered User
Join Date: Feb 2006
Location: Republic of California
Posts: 345
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Re: Truck's got Power Brake issues (disc/drum)
I'll be working on it this weekend. If it turns out to be the MC, what should I get as a replacement?
I don't think Disc/Drum was an option in 67.
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'67 C10 Short Stepside 5.0TPI/700R4 |
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#11 | |
Account Suspended
Join Date: Jan 2006
Location: Visalia, California
Posts: 286
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Re: Truck's got Power Brake issues (disc/drum)
Quote:
same here, except primary locks before every else does.... makes right turns quick!!! lol. right now, its just an eyesore in the drive way... i dont drive it....EVER!! |
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