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Old 02-21-2003, 09:45 AM   #1
TC70C10
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Question Brake Diagnosis

On my 81 K5 4x4 I've noticed my brakes acting funny the last couple of days. After I've come to a complete stop at a stop light I noticed the pedal will start moving towards the floor. The brakes also seem softer. Checked pads and shoes last night. They look fine. No leaks at wheel cylinder, brake lines or master cylinder.

My Ford buddy thinks the master cylinder is going out. They're only about 30 bucks, but I don't like to fix it if it ain't broke.

The problem could also be the check valve on the power booster or the other valve coming off the rear of the intake.

Anyone had similar problems??

Thanks
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1995 T10 Blazer 4.3L 4x4 (Son's)
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2005 GMC Sierra Crew Cab Z71 4x4 5.3L
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Old 02-21-2003, 09:54 AM   #2
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Yeah, sound to me like your booster is going bad. Mikes site has a good article on what it will do when its going bad and how to check and replace it. Heres the address http://www.73-87.com/garage/booster.htm

Hope that helps,
Cameron
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Old 02-21-2003, 01:10 PM   #3
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Thanks for the info. I don't think it's the booster, but I'll look for vacuum leaks. Just bought a master cylinder and rear brake shoes. I'd be curious to see if anyone else has had to replace their master cylinder and what it's symptoms are.
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1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch
1995 T10 Blazer 4.3L 4x4 (Son's)
2004 GMC Envoy 4.2L 2WD
2005 GMC Sierra Crew Cab Z71 4x4 5.3L
240 Fun Finder Travel Trailer

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Old 02-21-2003, 02:27 PM   #4
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My vote is master cylinder. I did mine a few years back.

Symptons were exactly like yours. Stop at a light (pulling my trailer no less). Foot would slowly go to the floor until it would go no farther. Then the truck would start to roll. I'd have to do a quick pump on the brakes to keep from rolling too far ahead, or into the guy in front of me.

She still always stopped when I need to, but I replace the cylinder before it got too bad.

Problem solved.

That's my $.02

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Old 02-21-2003, 02:30 PM   #5
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Thanks Zilverado. I'm glad to hear comments like that before I replace a part for no reason.
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1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch
1995 T10 Blazer 4.3L 4x4 (Son's)
2004 GMC Envoy 4.2L 2WD
2005 GMC Sierra Crew Cab Z71 4x4 5.3L
240 Fun Finder Travel Trailer

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Old 02-21-2003, 02:41 PM   #6
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Quote:
Originally posted by TC70C10
Thanks Zilverado. I'm glad to hear comments like that before I replace a part for no reason.
You're Welcome.

And I agree, that's what makes this such a great place to hang out and seek advice.

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Old 02-21-2003, 03:13 PM   #7
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Yes a very good sign that the seals in the master cylinder are leaking internally, go with a good new one I would stay away from rebuilds if your life depends on excellent brakes !
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Old 02-24-2003, 09:38 AM   #8
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I got the new Master Cylinder put on Friday night. Swapped out the rear brakes while I was there. All systems back to normal. Thanks for the inputs

Tim
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1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch
1995 T10 Blazer 4.3L 4x4 (Son's)
2004 GMC Envoy 4.2L 2WD
2005 GMC Sierra Crew Cab Z71 4x4 5.3L
240 Fun Finder Travel Trailer

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Old 02-24-2003, 10:34 AM   #9
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Excellent - glad to hear it worked out for ya. Always feels good to get things working well again - - especially brakes.

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Old 02-25-2003, 10:13 AM   #10
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The brake system is one area that I want the newest or best parts I can find, when you want to use them 100% YOU need them to work 100%
Glad to hear that you went with a new master cylinder.
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53 Chevy Moldy pearl green ZZ-4 4L60E 9" 3:25
55 GMC 1st Black Mll (ZZ4) ZZ6 TKO 600 5 sp 3:73
62 Solidaxle Corvette Roman Red (327
340hp 4spd 3:36) C4 & C5 suspension tube chassis
LS 3 4L70E
65 Corvette Coupe 327 350hp 4spd 4:11
78 Black Silverado SWB (350/350) 5.3 & 4L60E 3:42
2000 S-Type 3.0 (wife cruiser)
2003 GMC SCSB 5.3 4L60E 3:42
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