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#1 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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What's making my front brakes lock up and stay locked up?
Driving down a curvy mountain road the other day and applied the brakes to slow around a corner and my front brakes wouldn't release. I pulled over and tried going back and fourth hitting the brakes and they finally let go. This is on my 72 GMC K1500. I have power disc brakes on the front and just replaced the calipers a couple years ago. I looked for anything lodged in them but found nothing. This has since happened a couple more times. Any idea what would cause this?
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#2 |
Registered User
Join Date: Aug 2007
Location: Redwood City, CA
Posts: 1,177
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Re: What's making my front brakes lock up and stay locked up?
I would start with a good visual check of all your brake components:
1. Is the fluid clean and at the correct level in the master cylinder? 2. Do you see any leaks/wet spots around the master cylinder, proportioning valve etc. 3. Follow all the lines from there down to the front calipers, any leaks? 4. What is the state of the rubber flex lines between caliper and hard lines? are they old and cracking or are they newer and replaced when you did front caliper replacement? are they binding up anywhere? 5. Break a bleeder screw loose on one of the front calipers, does fluid come out? maybe have a friend pump the brakes when you break a bleeder screw loose to see if you get fluid. Eliminating some of the above should help you know where to concentrate the troubleshooting efforts. Hope this is helpful, let us know your progress as others will chime in to help out.
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66 GMC Suburban Custom 66 Chevy K10 Suburban |
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#3 |
Roadtrip!
![]() Join Date: Feb 2003
Location: Grand Rapids MN
Posts: 13,726
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Re: What's making my front brakes lock up and stay locked up?
I would start with the rubber hoses. They can collapse inside and hold pressure if they get bad...
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67 gmc custom lwb dakota truck. Sold...And bought back 69 swb 4x4 project (in progress) 70 c-10 lwb texas truck 70 4x4/BB/bkts/posi/tach(retired) 70 swb (wifes) 70 jimmy camper 71 K-5 factory 2wd 71 cheyenne 4x4/tach/posi/ plow rig 71 Cheyenne20 BB, buckets, tach, tilt, 4 speed 72 jimmy CST wyoming rig 72 jimmy Colorado rig 72 lifted texas 4x4 3/4 ton burb 65 fury conv. 383/auto 65 chrysler 300 "L" 413 auto |
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#4 | |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Quote:
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#5 |
Registered User
Join Date: Apr 2015
Location: East Tn (In the heart of the Smoky Mtns)
Posts: 1,868
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Re: What's making my front brakes lock up and stay locked up?
Hoses and cylinders
both are cheap and easy to replace. |
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#6 |
Senior Member
![]() Join Date: Jun 2002
Location: Murray, Kentucky
Posts: 3,479
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Re: What's making my front brakes lock up and stay locked up?
I also vote hoses, been there done that...
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Roger '68 Short step - https://67-72chevytrucks.com/vboard/...d.php?t=849675 '69 ('70?) 2wd Blazer '70 GMC Jimmy 2wd '73 Firebird - https://67-72chevytrucks.com/vboard/...d.php?t=853203 |
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#7 |
Registered User
Join Date: Mar 2016
Location: Portsmouth, NH
Posts: 45
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Re: What's making my front brakes lock up and stay locked up?
I have had hoses that look good on the outside do it also, the inside lining separates and it acts like a check valve.
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1971 C10 long bed, fleet side. 200R4 Auto, leaf spring rear. power steering. |
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#8 |
Registered User
Join Date: Mar 2017
Location: Aptos, CA
Posts: 5
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Re: What's making my front brakes lock up and stay locked up?
Sticking pistons? Maybe the calipers need rebuilding.
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#9 |
Registered User
Join Date: Jul 2012
Location: Marshall, NC....heart of the Appalachians.....aka, Gods country!!
Posts: 537
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Re: What's making my front brakes lock up and stay locked up?
Here's a quick and dirty way to tell if its the hoses or calipers. With the brakes stuck, open the bleeder valve on the caliper....if it releases / frees up, then its the hose. If it doesn't, then its the caliper.
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#10 |
Registered User
Join Date: Jul 2011
Location: strausstown pa
Posts: 3,394
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Re: What's making my front brakes lock up and stay locked up?
I've had the hoses lock up the brakes like a one way valve.
And I've had a sticky piston in a master cly do it too. This can get tricky during bleeding.
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81 camaro 355 4/spd 342 posi my first love ![]() 67 swb step 454/4spd ott 373 posi 4/7 drop. 2000 s10 zr2 little blue truck that never gets stuck. '74 heald super bronc vt8. tecumseh powered moon rover. |
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#11 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,104
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Re: What's making my front brakes lock up and stay locked up?
Were both brakes stuck? What were the symptoms? The odds of both hoses or calipers being bad are pretty high. Even if it was a bad hose on one side and a bad caliper on the other side. I would look at the master cylinder first. Or a pinched line between the master cylinder and the Tee on the front cross member would be easier to rule out. It is also possible that you have a drum brake master cylinder and it has a 10 lb residual valve that is trapping fluid and as the fluid gets hotter it expands and forces the caliper to apply the brakes. Once the fluid cools the pressure fades. This kind of problem only occurs when you are really working the brakes. Hope this helps.
Good luck.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#12 |
Senior Member
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Location: Harrison, Arkansas
Posts: 9,815
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Re: What's making my front brakes lock up and stay locked up?
Hoses.
Been there and done that. Several times.
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other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless. |
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#13 |
The Older Generation
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Location: Montezuma, Iowa
Posts: 25,481
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Re: What's making my front brakes lock up and stay locked up?
-
I just had that happen on my '72 Dually. Mine was only the right front but I replaced both hoses anyway. Hoses looked good, but I haven't had any problems since..... LockDoc
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Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - |
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#14 |
Special Order
![]() ![]() Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,859
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Re: What's making my front brakes lock up and stay locked up?
One hose can start collapsing before the other but you don't notice till the other does. Lots of originals still on these trucks that look great. It's not unusually for both to have the issue after 45 years.
Opening the bleeder(s) test will tell the tale.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
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#15 | |
Registered User
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Location: WEST PALM FLORIDA
Posts: 1,174
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Re: What's making my front brakes lock up and stay locked up?
Quote:
If you replaced the master and its too close to the booster it will do this same thing , usealy when hot , if you have rear drums , drums are kind of self actuating , and your hose from the dif to the crosmember is bad this could very well happen , they will lock or just not work at all . I assume the front brakes are newer , so those hoses are newer .
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68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#16 |
Registered User
Join Date: Mar 2009
Location: WARRENSBURG,MISSOURI,64093
Posts: 1,518
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Sounds like collapsed hoses to me too.
Ben ![]()
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"Persistence is the twin sister of Excellence.one is a matter of quality,the other, a matter of time" ![]() “Serious Black” my 1971 Short Bed Fleetside Sold to an outstanding man in Lees Summit,Mo. “Gone, but by no means,Forgotten” |
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#17 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: What's making my front brakes lock up and stay locked up?
Thanks all! I'm going to replace the hoses, shoes and calipers. No sense messing around! Found rebuilt calipers at NAPA for $25 each, probably cost $150 to do everything so I may as well get it right the first time. Master cylinder is new as is the booster so hopefully I won't have to mess with those!
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#18 |
Registered User
Join Date: Jul 2007
Location: Fall River California
Posts: 2,026
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Re: What's making my front brakes lock up and stay locked up?
Turned out the caliper was seized up. The piston was absolutely stuck. I took the old hose off and it still wouldn't move. I flushed all the old fluid out of the system to make sure no crap was in there. I went ahead and replaced the callipers, pads and hoses. Need to bleed them again as they're a little spongy but my helper (wife) had to leave. Hopefuly I can get the proportion valve centered, the light is still on.
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#19 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,623
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Re: What's making my front brakes lock up and stay locked up?
To center that prop. valve try stomping on the brakes really hard. Often does the trick.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#20 |
Senior Member
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Location: Harrison, Arkansas
Posts: 9,815
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Re: What's making my front brakes lock up and stay locked up?
I'm sure you will get the brakes working properly. But to clarify, is the wife coming back?
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other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless. |
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#21 |
Registered User
Join Date: Jun 2015
Location: Melbourne, Australia
Posts: 231
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Re: What's making my front brakes lock up and stay locked up?
This is unlikely.
But I had the same issue and it ended up being a split pin behind the booster rotating and jamming against the firewall. I put in a smaller pin, folded it over good and no more problems.
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John 69 c20, 396, th400, dana60, ps, ac |
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#22 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: What's making my front brakes lock up and stay locked up?
I dunno, he says "front brakes", as in both, which can't be the hose (unless both magically did the same thing at the same time, highly unlikely).
If it's both, it's gotta be in the master, doesn't it?
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#23 |
Registered User
Join Date: Jun 2015
Location: Melbourne, Australia
Posts: 231
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Re: What's making my front brakes lock up and stay locked up?
Yeah I agree davepl.
But I would have said it was my front brakes as well ( they were smoking). I figured though unlikely it was the easiest to check.
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John 69 c20, 396, th400, dana60, ps, ac |
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#24 |
67-72 parts collector,…
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Re: What's making my front brakes lock up and stay locked up?
x2
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Keith Convert to disc brakes. http://67-72chevytrucks.com/vboard/s...d.php?t=444823 |
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#25 |
Senior Member
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Location: Harrison, Arkansas
Posts: 9,815
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Re: What's making my front brakes lock up and stay locked up?
The son in law had a caliper lockup on his Blazer a while back. He changed the hose and fixed it.
I says "why didn't you change both hoses", he says "nothing was wrong with the other one". The next week the other hose went bad.
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other Larry Build thread, Arkansas K10 https://67-72chevytrucks.com/vboard/...=755797&page=5 The ability to speak several languages is an asset, but the ability to keep your mouth shut in any language is priceless. |
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