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1971 Chevy brake problems
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kwikdeals
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Oct 6, 2012, 12:37 PM
Post #1 of 8
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1971 Chevy brake problems
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1971 Chevy truck, C10, 350 engine, Front brake not holding.
I was reading through the threads and to test the vacumm booster, it was stated to shut the engine off, pump the brakes 2 or 3 times, then hold em and start the engine. If the pedal dropped on down the booster was working...Tried that and the booster is working. Here's the problem. The front brakes still want hold, even on slick concrete. I've changed the booster, the master cylinder, tried new pads. The rotors look great, no dips or cracks. The calipers seem to be working. I took off the inside brake pad, inserted a block of wood between the piston and the brake rotor, the piston was pushed out tight against the wood block when brake was applied. Any other suggestions??? Thanks...
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Tom Greenleaf
Ultimate Carjunky
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Oct 6, 2012, 1:52 PM
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Re: 1971 Chevy brake problems
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Nothing new but a bit confused at what you are experiencing. If back drum brakes are way out of adjustment you could have a lot of pedal travel taking up pressure to get those to apply and balance out the braking. Proportioning valve may be frustrated because of rears. They all count. Dual (meaning front and rears are separate since MY 1967) still don't give you 1/2 if 1/2 has failed.
If new pads on old but good looking rotors they wont grab well friction wise for some time and isn't the way to do brakes. Even all new stuff the first few stops isn't so great not just my opinion - they aren't till at least a few stops then should get better from there.
If you have excessive brake pedal travel that will build up with quick successive pumps the rear may be causing issues or air. Master cylinder if not bench bled well first can be VERY tough to get all air out once installed on some. Not sure but some GMs + others had positioned that on quite an angle but don't recall trucks so much that way.
Think rear for now is my guess,
T
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re-tired
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Oct 6, 2012, 2:32 PM
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Re: 1971 Chevy brake problems
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Some of the most common faults with brakes .... The rear shoes are not adjusted properly as Tom mentioned. The rear drums are cupped (need to be turned).The calipers are switched LH to RH putting the bleeder lower than inlet , making it impossable to bleed air . One of the rubber hoses (3) one at each caliper one at rear axle is defective ,uisally soft and swelling.
LIFE'S SHORT GO FISH
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kwikdeals
New User
Oct 8, 2012, 3:18 PM
Post #4 of 8
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Re: 1971 Chevy brake problems
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The back brakes seem to do the most stopping. The front brakes want even slide on slick concrete, barely lock up in gravel. Just seems they are not getting enough pressure. The piston seems to be sliding out when I tested it by removing the pad on the piston side and let the piston push up against an inserted block of wood against the rotor as the brakes were applied. When trying to stop, it does stop straight, no pulls to the left or right, just takes a while to stop. Can the proportioning valve be messed up? Is there a way to check it? If I pull the brake line loose from the rotor and fluid squirts through when pressing the brake, will that tell me the valve is OK? Thanks again...RM
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re-tired
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Oct 8, 2012, 4:41 PM
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Re: 1971 Chevy brake problems
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As stated . Problems with the rear brake are common and WILL affect the front brakes .. Did you check the items mentioned? ITs a process of elemination.. you can keep quessing or start checking and eleminating things
LIFE'S SHORT GO FISH
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Oct 8, 2012, 4:43 PM
Post #6 of 8
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Re: 1971 Chevy brake problems
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What is with this wood block test and trying to make it skid thing? By nature and especially trucks as the cargo weight could be very low to maxed out and I don't know of any variable compensation for that. Just proportioned to a fair average of what it would likely be exposed to. Meaning the backs would be more likely to lock up if brakes slammed or very hard stops without a full load in back. Disc brakes by nature don't just lock up and skid as easily as drum brakes can.
With everything put together and rears adjusted properly how much pedal travel do you have now? Air in system and adjustment of rears matters a lot.
Pretty sure most proportioning valves for ordinary pick-up trucks applied more pressure to rears first as you would on a bicycle so you don't go flying over the handle bars like effect.
Since you keep taking off calipers it seems take a look at the pads. Are they showing that they are both in full contact with the rotor?
If you believe this is free of air and there isn't a ballooning flex hose in the mix then this is most likely rear brakes messed up. Parking brake cable may not be allowing proper retraction of rears too with sticky or frozen cables.
Pretty sure that the proportioning valve is also a "combination" valve such that a great imbalance would get you a red "BRAKE" light same bulb as if parking brake is on. Does that even light up or staying on?
Other: New pads or shoes do not have their full friction for some time and use. They need some heat and some initial wear to get to their best. I recall these vehicles new and many had a paper band around sun visor stating that you should avoid sudden stops or hard use for about the first 200 miles. You can wreck new friction material easily if testing them too hard right away and glaze right up meaning shiny and poor friction,
T
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kwikdeals
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Oct 8, 2012, 5:10 PM
Post #7 of 8
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Re: 1971 Chevy brake problems
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Sorry to be confusing about the wood block. I'm trying to get her back running again. I wanted to check the calipers and make sure they weren't stuck/frozen so I removed the pad that fits against the caliper piston, put the caliper back on and inserted a small block of wood between the caliper piston and the rotor, then applied the brakes to see if the piston was coming out as is should, when pressure was applied. Yes, they both came out under pressure. I squeezed the piston back in and put the pads back in place. Just seems there is not enough pressure being applied to the front. When rolling about 5 or 10 mph, it should stop or throw you forward in the seat. I'll check the rear and a few other things. Just didn't want to start buying hoses, calipers, rotors, etc. without knowing the problem... Maybe the new booster is not working as it should??? Thanks again...RM
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