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#1 |
Active Member
Join Date: Mar 2004
Location: Virginia
Posts: 169
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Ok, I'm stumped and need help with my 72 K20.
When driving on the highway, it will start to studder (can't find any coincidence as to what causes it, it isn't due to pressing the brakes), while it is doing this, if you hit the brakes, the whole truck shudders like crazy, and it feels like there's no vacuum in the brakes. Then after 40 seconds or so it goes away. So, I just put new rotors, calipers, pads, stainless steel brake lines and hoses, and a new proportioning valve from GMC Pauls. None of that worked. The rear is a brand new 14bFF, with all new brakes (still drums) back there too. Before I did all the work to the front, if it was acting up and I stopped, the rear hubs were really hot, but is that just normal? Would a problem with the rear brakes cause the truck to shudder so violently? Any ideas? I'm going on a camping trip in two weeks and have a 5 hour drive, I need to solve this.
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71 Blazer CST 72 K20 Capt USAF |
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#2 |
Senior Member
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Location: Lewisville, Nc
Posts: 10,234
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Re: I'm stumped...Yet another brake problem
sound like the Rear brakes are adjusted 2 tight and heatting up but this shouldn't cause any shudders. sounds like the vac booster is either bad or not getting enough vacumm
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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 Last edited by truckdude239; 08-24-2006 at 09:26 PM. |
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#3 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: I'm stumped...Yet another brake problem
Did you install new wheel bearings when you installed the rotors? If you jack up the truck can you make the front wheel wobble? My other guess would be worn ball joints or tie rods. That should at least give you something to look at anyways.
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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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#4 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: I'm stumped...Yet another brake problem
Been drinkin tonight bud? ![]() *just messin with ya ![]()
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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 |
sufficiently talented fool
![]() Join Date: Jun 2006
Location: Forest Hill, MD
Posts: 2,231
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Re: I'm stumped...Yet another brake problem
The rear hub may be warm, but really shouldn't be hot. Check the rear drums for discoloration ( blue ) or hot spots/ cracks. The rear brakes could cause the shaking, but it could also be loose front end parts.
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#6 |
Active Member
Join Date: Mar 2004
Location: Virginia
Posts: 169
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Re: I'm stumped...Yet another brake problem
The front end is tight, and the bearings are in great shape. The weird part is that it just comes and goes. Could the master cylinder be causing it? there's only so much left to replace. I don't understand how when it happens and I press the break, there's no vacuum and the shuddering gets so violent, the truck feels like it is going to break apart!
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71 Blazer CST 72 K20 Capt USAF |
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#7 |
sufficiently talented fool
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Location: Forest Hill, MD
Posts: 2,231
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Re: I'm stumped...Yet another brake problem
Is it possible the brake pedal is sticking?
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#8 |
Registered User
Join Date: May 2005
Location: Spring Branch Texas
Posts: 177
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Re: I'm stumped...Yet another brake problem
That sounds like badly warped rotors but shouldn't be if new... check them with a dial indicator because something ain't running true or pressure ain't releasing from the brakes. I had a similar problem on a 92 suburban caused by the brake hoses. the inner part had torn and made a flap that would allow pressure to be applied but wouldn't release... That was a PITA to figure out... Just because somethings new don't mean it can't be defective... Quality control ain't what it use to be....
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If you can't drive it park it! If you can't park it milk it! Last edited by Geezer; 08-23-2006 at 10:46 PM. |
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#9 |
Registered User
Join Date: Jun 2002
Location: central pa
Posts: 1,525
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Re: I'm stumped...Yet another brake problem
A couple of questions. Is it a shake in the truck or a stutter like engine missing?
A shake could be a universal joint or tires out of balance. Check the joints and rotate the tires and see if it changes anything. Out of balance tires will be speed related meaning at say 40-48mph it does it and again at 60-65mph leave off speed and it will stop or lessen the shake. Universal will shake badly in a coast condition and clung when you step on gas or brake. Engine stutter could be alot. Do you have a vacuum gage to see if you really have a vacuum lost.
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72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne |
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#10 |
Registered User
Join Date: Sep 2005
Location: 9000' Mountain Man
Posts: 326
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Re: I'm stumped...Yet another brake problem
I'd replace the rear brake return springs and the self adjuster springs. If they get overheated, they will self adjust up too tight and cause overheating. I know, been there done that on a new 1969 c20 in 1969 pulling my 1945 Jeep around in the mountains.
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#11 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: I'm stumped...Yet another brake problem
i'd check the emergancy brake cables to make sure they're completely releasing all the way and also try bleeding the brakes when they're hot right after use
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#12 |
Never enough time!!
Join Date: Mar 2004
Location: sw Wisconsin
Posts: 602
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Re: I'm stumped...Yet another brake problem
Is this a 4 wheel drive? I had one that had a terrible shake that only happened once in a while and got worse when you tried to brake, it turned out to be broken rivets that held the front spring perches to the frame behind the front bumper, it doesn't explain your loss of vaccuum, but is just something else to look for. Good luck, let us know what you find!
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#13 |
Active Member
Join Date: Mar 2004
Location: Virginia
Posts: 169
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Re: I'm stumped...Yet another brake problem
Could it simply be the rear wheel cylinders? The engine is fine, it just has to work hard to keep the truck moving when it happens. But would any of these possible causes just happen without being related to hitting the brakes?
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71 Blazer CST 72 K20 Capt USAF |
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#14 |
Active Member
Join Date: Mar 2004
Location: Virginia
Posts: 169
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Re: I'm stumped...Yet another brake problem
Would any brake parts that are located at the wheels cause the feeling of no vacuum, or does that mean it must be a problem with the master cylinder or booster under the hood??
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#15 |
Registered User
Join Date: Apr 2002
Location: New Carlisle, Ohio,USA
Posts: 1,404
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Have you checked the brake pedal freeplay? What about the length of the rod between MC and booster? (assuming you might have replaced or repaired anything?) Not enough pedal freeplay, will cause plunger to booster to stay engaged causing booster to not reset allowing vacuum to be low or none. Rod between booster and MC could be adjusted to the point to where MC will sometimes not release? Just something else to check, before ya start laying out the bucks for a new setup.
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#16 |
I am a Referee of life.
Join Date: Jun 2000
Location: Greensboro N.C.
Posts: 13,993
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Re: I'm stumped...Yet another brake problem
I had a Ford(Fouled-up old run-down dodge) that would shimmy ocassionally.It would just start suddenly and heavy braking to almost a halt would stop it.I had it in the shop twice and new tires and wheels.I finally found the problem.The steering box was loose to the frame.Tightened and replaced the missing bolt(1 of 5) and solved the problem.
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The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil" |
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#17 |
Senior Member
![]() Join Date: Sep 2005
Location: Lewisville, Nc
Posts: 10,234
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Re: I'm stumped...Yet another brake problem
the batteries in my key borad died and i didn't look to check the spelling i did think about wraped rotors i have get new rotors before that where wraped
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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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