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#1 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,631
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Some of you may recall my other thread from a few days ago: http://67-72chevytrucks.com/vboard/s...d.php?t=527289
Still have a soft pedal and getting air in the rear lines, but now have more info. The MC seems good -- with the rear line disconnected, the pedal is nice & firm. Hook up the rear line and the pedal goes soft about 1/2 way to the floor. This tells me the problem is in the rear brake lines, which I did nothing with when installing the new rear brake shoes. Trapped air? I have literally pumped several 12-ounce cans of fluid (several hundred brake-pedal strokes) through the rear bleeders with no change -- still get lots of air bubbles coming out with the fluid. I have tried teflon tape on the bleeder threads to help insure no air is drawn in past the threads. And I got a bleeder hose with a one-way check valve so I can pump the pedal continuously without opening & closing the bleeder valves. Still no joy. I'm about ready to take it to a shop and have it power-bled, but I just hate to. This is a simple system and I should be able to bleed it. Anyone got any new ideas?
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#2 |
Registered User
Join Date: Jun 2010
Location: Upland Ca
Posts: 4,143
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Re: Brake bleeding trouble... still
Your getting air into the system from some where. Power bleeding will not solve this unless the tech can I'd the issue and fix it, which maybe your best bet at this time.
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1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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#3 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,631
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Re: Brake bleeding trouble... still
Yes, definitely getting air in. Seems like pedal pressure would drive fluid out wherever the air leak is, but I can't find any sign of a fluid leak....
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#4 |
Registered User
Join Date: Jul 2011
Location: Des Moines, Iowa
Posts: 3,016
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Re: Brake bleeding trouble... still
I'd start over.
Bench bleed the MC, install. Use a clear tube connected to bleeder valve. - Starting with the furthest line away from MC -- Pump pedal 5 or so times. Pressing the pedal as far down it'll go each time. --- Hold the pedal all the way down ---- Release the bleeder valve just a little. ----- Do not allow pedal to bottom out while valve is opened. ------ Stop short of that, then repeat until air bubbles are gone. ------- Ensure lines/valves are tightened good. -------- Repeat process, next furthest away. Do all 4 Blowing out the lines, you introduced a lot of air to begin with. If you still can't get rid of the air, you have a leak somewhere letting air in.
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project: "my happy mess" Last edited by litew8; 06-04-2012 at 09:58 PM. |
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#5 |
Active Member
![]() Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: Brake bleeding trouble... still
There are some connections that you can look at. Work yourself backwards along the brake line until you see a connection. If they check good, check the connections at the rear rubber brake hose on top of the rear axle. If the hose hasn't been replaced, it needs to be.
Another possiblity is to find some way to block the lines with plugs starting at each rear wheel to see which side firms up the pedal. |
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#6 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,631
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Re: Brake bleeding trouble... still
Thanks for the replies so far, guys.
litew8: I did all of those things, and then I did them all again -- some more than others. Got a few bubbles out of the MC the second time around, so I bled the snot out of it. It's good now, for sure. Only thing you wrote that I couldn't do was 'repeat until air bubbles are gone'. ![]() 68gmsee, I didn't replace the rear hose yet simply because I'm already over budget and it's a spendy little devil. I may bite the bullet and do it anyway. Those connections have not been touched, probably since the truck was built, and there's no sign of leaks. Your idea of isolating the problem gave me another thought. Since I have a hard pedal with the rear line off of the MC, I'm going to try disconnecting the rear line from the prop. valve to make sure it's good. Maybe I can find other connections to cap off and pinpoint the problem. I haven't given up yet -- I'm determined to fix this bugger without taking it to a shop.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#7 |
Registered User
Join Date: Aug 2010
Location: covington ga
Posts: 180
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Re: Brake bleeding trouble... still
ok if you have shoes in the rear make sure they are adjusted out far enough.if they are not you will have to push more fluid to the rear to get a feedback at the pedal hence the pedal going further down..the rear shoes should be adjusted out until you can barely feel friction if the wheels are mounted if they are not and you have new drums then adjust them until you can barely slide the drum on. hope this helps.over the years this has been the solution many times in my shop with customers doing their own brakes.
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#8 |
Active Member
![]() Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: Brake bleeding trouble... still
The reason I recommend replacing all the rubber brake hoses is that some of us have had problems with the isides collapsing and swelling -in some cases preventing fluid from passing through. The problem is that you cannot see the failure from the outside.
Auto Zone front are about $19 and rear is about $13. |
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#9 | |
Registered User
Join Date: Aug 2010
Location: covington ga
Posts: 180
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Re: Brake bleeding trouble... still
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#10 | |||
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,631
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Re: Brake bleeding trouble... still
Quote:
Quote:
Quote:
edit: checked online hose prices again
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay Last edited by Stocker; 06-04-2012 at 11:48 PM. |
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#11 |
Registered User
Join Date: Jul 2011
Location: Des Moines, Iowa
Posts: 3,016
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Re: Brake bleeding trouble... still
Replace the MC, go from there. If it persists, you have air entering the system from somewhere.
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project: "my happy mess" |
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#12 | ||
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,631
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Re: Brake bleeding trouble... still
Quote:
![]() Quote:
edit: I found a pic that's a bit hard to see but it looks like the same setup I have.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay Last edited by Stocker; 06-05-2012 at 12:02 AM. |
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#13 | |
Registered User
Join Date: Aug 2010
Location: covington ga
Posts: 180
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Re: Brake bleeding trouble... still
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#14 |
Registered User
Join Date: Aug 2010
Location: covington ga
Posts: 180
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Re: Brake bleeding trouble... still
just re read the first post something else that will cause air in the rear lines but not show a leak is a poor seal on the resovoir on the rear mc piston.their is no pressure there so it wont show/leak when you apply pressure but it can suck in air under vacuum again hope this helps
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#15 |
Registered User
Join Date: Aug 2008
Location: Red Deer ab canada
Posts: 1,250
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Re: Brake bleeding trouble... still
I'd take the tape off the bleeders to start; they bottom out to seal. You need to keep the pin in the end of the prop valve from moving while bleeding; it may want to push out. If you have a vaccum pump they work great to suck fluid to the rear to start the process; I think you have air in the line to the back and its jerking you around going from side to side as you bleed. This has got me twice! I used a cheapy hand pump to draw fluid first to the passenger rear, then drivers (make sure system is sealed at the 3 other brakes). Once the line is free of air, and you're sure the prop valve stays centered, they'll bleed out quick.
My Blazer didn't have enough brake to stop the rear wheels in drive at idle on jack stands! Seems like I used 35 gallons of fluid and still had air in back; it took a while with the hand pump but I eventually got some BIG bubbles that must've been moving back and forth. I went through the SAME thing on a customers '68 GMC too.
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1972 factory 2 Wheel Drive Blazer-Sold 1972 K10 4X4-Sold 1971 Chevrolet Cheyenne/10-Sold 1970 Chevrolet C/10-Sold 1968 GMC 4X4-Project 1968 Chevrolet C/10 Pro Street 1970 GMC 3/4 Ton-Parts 1997 2WD 2DR Yukon-Sweet http://67-72chevytrucks.com/vboard/s...d.php?t=335664 |
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#16 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,631
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Re: Brake bleeding trouble... still
Thanks, Tony. The tape was suggested to help prevent air from entering past the threads during bleeding. So far the pin seems to be in place -- it may have moved but I pushed hard on the pedal several times which should center the prop valve. I hooked up the wire tonight and the light is out. Unfortunately I don't have a vacuum pump, maybe I can borrow one or I'd have to buy one.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#17 |
Registered User
Join Date: Apr 2002
Location: New Carlisle, Ohio,USA
Posts: 1,404
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Try bleeding the "T" where the rear lines split to go to either side. Found lots of air there when I did mine. Just my $ .02
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![]() ![]() ![]() LIFE AIN'T EASY WHEN YER FAT AND GREASY! GMC= Got More Class! ![]() ![]() |
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#18 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,235
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Re: Brake bleeding trouble... still
Stocker you might be money and time ahead to take it to a shop who has a pressure bleeder.
Quick and easy. Or you may be able to rent one from your local parts store. Outrageous prices on those hoses in your area too.
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Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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#19 | |
Registered User
Join Date: Oct 2018
Location: Minneapolis, MN
Posts: 35
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Re: Brake bleeding trouble... still
Quote:
Thanks for your comment on bleeding brakes. It helped me. What I was observing after replacing the rear braking system: - Pedal would go to the floor, and brake light would turn on. - Pumping the brake a few times gave me working brakes, and the light would turn off (I'm assuming the piston inside that sensor would recenter once I got pressure on each side.) What I was doing: - Bleeding the brake system like crazy. Mostly in the back, but also at the master cylinder and the front calipers too. - I was observing foamy air bubbles in the back. It seemed worse on the passenger side. What I did: I almost gave up, and drove it to a shop in town that I think is decent, but I tried your recommendation of using a vacuum pump to bleed the system. I bled out a full cup of fluid from both rear cylinders at the bleeding nipples, and I had good brakes. What a relief. I'm never going to bleed brakes again without using one of these vacuum pumps. I also really like that I don't have to get a second person involved to do this. Thanks again, JP |
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#20 |
Registered User
Join Date: Feb 2012
Location: So. Cali.
Posts: 2,644
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Vacuum bleeders are simple and easy to use .
So are pressure bleeders, I vastly prefer my Motion Pro pressure bleeder ~ it's also a one man job tool .
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-Nate Geezer '49 3100 235 W/ Muncie SM420 SOLD '69 C/10 shortbed sidemount survivor 250 L6 W/ 350TH ![]() |
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#21 |
Senior Member
Join Date: Jul 2010
Location: South Dakota
Posts: 4,093
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Re: Brake bleeding trouble... still
Saving
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1969 Chevy c20(Miss Hackjob) |
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#22 |
Registered User
Join Date: Jun 2011
Location: Richmond,Va
Posts: 2,934
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Re: Brake bleeding trouble... still
Attempt Gravity Bleeding first (after removing that tape). Go to the plumbing section at Home Depot or Lowes and get the smallest diameter 12" section of clear tubing that will fit over the bleeder. Slip it on and let it drain without letting the MC go dry. If its a bad MC you can get the air out and it will still have a soft pedal. Start at the LR corner of the truck because it is actually furthest from the MC. If or when you get the bubbles out of the LR move to the RR, you should only have to drain that one for a minute to clear from the "T" out. If you can't get the bubbles out you are taking in air along the line to the rear. I doubt this is the case because if you take in air you will let out fluid and a wet spot would indicate your leak. If you still have a soft pedal put an MC on it. RockAuto.com has both the hose and MC you are looking for for less than $20.00 each. My money is on a bad MC.
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Nick Carter 1967 C10 Short bed Fleetside Project Cheap Thrills! 2WD C10 Modern/Performance Alignments Easiest Alignment Ever! |
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#23 |
Registered User
Join Date: Jun 2010
Location: San Diego Co.
Posts: 1,162
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Re: Brake bleeding trouble... still
Subscribed.
Just be advised that should you decide to replace that rear hose, depending on what you have, the replacement hose is likely to be at least 3 " longer than original. My original measures 14.5" overall length ('72 C-10, SWB Coils). The replacement that I ordered (Wagner) was 20.5" long! I'm sending it back for the Centric hose which, at 17.5" is the closest I could find among any of RockAuto's vendors, or local autoparts stores. |
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#24 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,631
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Re: Brake bleeding trouble... still
Spent hours yesterday gravity bleeding (drip, drip, drip) and didn't notice any bubbles coming out but it's such a slooooww process.... and afterwards, the pedal was still soft. Bled again by pumping the pedal and cracking the bleeders and still got lots of air.
This morning I installed the 2nd new MC (bench bled very thoroughly), still getting lots of air from the rear bleeders after pouring a few more cans of fluid through the system. Crawled underneath with a flashlight looking for any sign of leaks or damage -- nothing. Remember I never touched the rear lines beyond the prop. valve, and I replaced the rear shoes but not the wheel cylinders. I have made no progress at all so I'm headed out now to talk with a shop or two. Just have to get the truck there with no rear brakes, and I mean none at all. With the pedal held down firmly, I can rotate both rear drums easily by hand. At least the parking brake works....
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#25 | |
Registered User
Join Date: Oct 2006
Location: Dundee, Oregon
Posts: 311
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Re: Brake bleeding trouble... still
Quote:
Sucks pulling 3/4 drums back off, but maybe a picture of each side would show something that got missed? |
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