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#1 |
Registered User
Join Date: Aug 2009
Location: Woburn, MA
Posts: 127
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Brake Bleeding Woes
I was going to add this post to the sealing bleeder screw post of last week because it hit on exactly what I was experiencing vacuum bleeding my system. I replaced bleeders and wrapped them with Teflon tape which fixed the leaking. I understand that taped threads are scorned in pneumatic and hydraulic applications but in this case, carefully applied, the tape is outside the system.
I finally was able to bleed the system or it appeared bubble free. I went around the truck three times and re-bled to be sure. Before that I bench bled the master cylinder a second time after installing a remote reservoir kit. Up until now I had not touched the brake pedal because the Caddy Seville rear calipers had to be off the rotors and positioned so the bleeders were pointing up. So with rear calipers installed I pressed on brake and it was totally soft. Not even a remote resistance or wheeze of hydraulic fluid movement. What I am asking is what is my next action. Where the system is appears so dead, should I start with another bench bleed or use the pedal and do a two man conventional bleed? I am thinking maybe the vacuum bleed moves the fluid so slowly it doesn't capture bubbles trapped in high points. What thoughts can you add to my failure? |
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#2 |
Registered User
Join Date: Mar 2012
Location: Lakes Region NH
Posts: 3,183
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Re: Brake Bleeding Woes
How many times have you pressed the brake pedal? If there is clearance between pads and rotors then you will not feel resistance at the pedal. The solution is to press the pedal several times until said clearance is removed and the pedal feel returns.
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#3 |
Registered User
Join Date: Apr 2010
Location: Oregon
Posts: 1,184
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Re: Brake Bleeding Woes
Since you have a remote reservoir I would guess your master cylinder is under the truck. If it is and you have front and rear disc brakes, you need a 2lb residual valve.
There's a drawing part way down this page of a 4 wheel disc plumbing diagram: http://mbmbrakes.com/typical-brake-s...onfigurations/ |
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#4 |
Registered User
Join Date: Aug 2009
Location: Woburn, MA
Posts: 127
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Re: Brake Bleeding Woes
I do have 2# residual valves on front and rear. I will pump some more. I pumped a few times but maybe gave up frustrated too soon.
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#5 |
Registered User
Join Date: Nov 2010
Location: calgary alberta
Posts: 8,026
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Re: Brake Bleeding Woes
do you have disc/disc or disc/drum? if drum rear have you adjusted the brakes first, with the park brake adjusted fully off, then adjusted the park brake properly? adjusting the brake star wheel sets the shoes against the drums on the bottom end but the park brake adjusts the shoes at the wheel cylinder end. if no park brake in place then the wheel cylinders get pulled all the way back in when the brakes are released and require more fluid to be displaced upon brake pedal application so you end up with a low pedal or a pedal that needs to be quickly pumped to get any pedal height.
have you checked to ensure the pedal and master push rods have the correct amount of free play but not too much? do you have the correct free play at the master cyl push rod from the booster? not enough play here will not allow fluid to get out to the system because the piston in the bore has not been allowed to come back far enough to expose the hole from the reservoir to the bore of the cylinder. this would require the master cyl be removed from the booster (but not the system) and a depth check of the master input bore compared to what push rod length is sticking out of the booster. a vernier caliper works good here. another way to check this is to take the cap off the master and look for a disturbance in the fluid when you initially push on the brake pedal. this is fluid pushed back into the master res upon initial pedal travel because, at rest, the piston in the bore of the master actually travels back far enough to expose the "fill" hole in the bore so fluid can return to the res as it heats up and expands or cools off and contracts in the system. then when the pedal is pushed a small amount of fluid is pushed back into the res until the pistin travels past the fill hole in the bore of the master. check any linkage wear points that may skew the actual push rod travel at the master cyl? do you have the same ratio of pedal travel as the stock set up? if disc/disc, check to see if the pads are out against the rotors on all 4 corners after you have pumped the pedal a few times( and checked to ensure you have fluid in the reservoir between the pumps. if you pump a few times and don't check the res then check and find it is empty, you may be starting over from scratch in the bleeding department). if the calipers are off then you can use a block of wood between the calipers, where the rotor would fit, so the pistons don't get pushed out of the caliper bores. does your master cylinder have res valves as well? they will be visible where your lines connect to the master. they are usually installed in master cylinders intended for a drum brake application in order to keep a small bit of pressure in the system so the brake cylinder cups stay sealed against the bores. keep us posted |
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#6 |
Registered User
Join Date: Nov 2010
Location: calgary alberta
Posts: 8,026
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Re: Brake Bleeding Woes
the reason I ask if you have the same ratio as stock is to ensure you have a full stroke of the master when you have a full stroke of the brake pedal. maybe your pedal travel to the floor is not resulting in a full stroke of the master cylinder?
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#7 |
Registered User
Join Date: Mar 2012
Location: Lakes Region NH
Posts: 3,183
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Re: Brake Bleeding Woes
The Caddy Seville rear calipers I'm thinking of have park brake linkage built into the calipers. Is this the style caliper you have? Do you have the "arm" attached to the actuator bolt on the back of the caliper?
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#8 |
Registered User
Join Date: Aug 2009
Location: Woburn, MA
Posts: 127
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Re: Brake Bleeding Woes
Thank all of you for your quick responses. For the time being I feel 1project 2many hit it on the nose. When I went back out to garage the discs were still rattling around on their pins and sure enough after pumping quite a bit I have a pedal.
I re-adjusted the length of the actuator rod and the alignment to the pedal and things are looking a lot better. Yes, those pictured are my rear calipers. Thanks again and thank you dsraven for the tutorial. Good basic information that if you don't understand it will have you spinning your wheels. |
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#9 |
Registered User
Join Date: Nov 2010
Location: calgary alberta
Posts: 8,026
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Re: Brake Bleeding Woes
if you have that style of caliper you may need to fine tune the park brake mechanism when you assemble it. there is a tutorial on google. basically the park brake should be snug on the rotor with the park brake "off" but still allow the rotor to turn and if not the piston can be turned to achieve that lever position before the system gets fitted all back together again. there is a detent in the brake pad that has to line up with the piston as well.
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#10 | |
Registered User
Join Date: Nov 2016
Location: Beaumont, Alberta
Posts: 468
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Re: Brake Bleeding Woes
Quote:
Check out this video at the 2 minute mark. You shouldn't have to bleed them off the truck. https://www.youtube.com/watch?v=q4_17Gg7tdg |
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#11 | |
Registered User
Join Date: Nov 2016
Location: Beaumont, Alberta
Posts: 468
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Re: Brake Bleeding Woes
Quote:
https://www.youtube.com/watch?v=opjdu8DdVeA Now I'm just dealing with leaks which I hope to resolve tonight so I can bleed the brakes on the weekend. |
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#12 |
Registered User
Join Date: May 2010
Location: Lawrenceville, Ga
Posts: 2,644
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Re: Brake Bleeding Woes
"should I start with another bench bleed or use the pedal and do a two man conventional bleed? I am thinking maybe the vacuum bleed moves the fluid so slowly it doesn't capture bubbles trapped in high points."
1P2M, what is your opinion on this? I also bleed my brakes with a hand vacuum pump but after I'm done I will usually get my wife out to pump the brakes and finish bleeding one more time. |
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#13 |
Registered User
Join Date: Nov 2010
Location: calgary alberta
Posts: 8,026
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Re: Brake Bleeding Woes
guys, ,make sure youre getting a full stroke on the master cyl so you can move fluid quickly and also so you actually have a full stroke like the master cyl was built to give you. might save your skin some day.
there is also the pressure bleeder theory. pressure up the reservoir and then open the bleeder screws-furthest away first. might take some engineering but, hey, look at all the other stuff we get done on this site. pump up spray bottle full of brake fluid with home made adapters to seal off the master cap? back in the day I had a pressure bleeder that was basically just a ball full of fluid and it went down a hose to a flat metal thing that strapped on the top of the master cyl to form a seal with a piece of rubber in between. check the link for a home made job. would have to fab a cap of some sort. |
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#14 |
Registered User
Join Date: Nov 2010
Location: calgary alberta
Posts: 8,026
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Re: Brake Bleeding Woes
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#15 |
Registered User
Join Date: Nov 2010
Location: calgary alberta
Posts: 8,026
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Re: Brake Bleeding Woes
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#16 | |
Registered User
Join Date: Mar 2012
Location: Lakes Region NH
Posts: 3,183
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Re: Brake Bleeding Woes
Quote:
An old fashioned manual bleed seems to be the best way to get the job done when a pressure bleeder isn't available. Saving time by using vacuum as the first part of a two step process seems to be a reasonable compromise. Sometimes I use a 1 man bleed process. It can be tough to get someone else to describe what's happening with the pedal when you're having trouble getting one. I pump up the brakes 4-5 times, prop a hood support rod between the seat or dash and brake pedal, then hop out and crack a bleeder. I can see if air is coming out, if fluid is restricted, or if there's some unexpected problem. I can also feel the brake pedal to see if it gets better as air is removed. I think it makes it easier to catch a problem. |
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#17 |
Registered User
Join Date: Jun 2006
Location: Idaho
Posts: 8,800
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Re: Brake Bleeding Woes
Pumped a few times? The original Orrie, my grandfather, rule of thumb was minimum 100 pumps with full return to work the air to the ends of the lines. I used auto bleeders and once I got one caliper right side up and a bend fixed that was causing an air pocket it went ok. the caliper bleeders need to be on the top to get the air out. On my 74 truck the calipers will fit on either side, I had two of the same with one mounted with the bleeder on the bottom. Also need to make sure you have a small space between the vacuum rod and MC so it fully releases.
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1959 Chevy Short Fleetside w/ 74 4WD drive train (current project) OrrieG Build Thread 1964 Chevelle Malibu w/ 355-350TH (daily driver) Helpful AD and TF Manual Site Old Car Manual Project |
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#18 |
Registered User
Join Date: Aug 2009
Location: Woburn, MA
Posts: 127
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Re: Brake Bleeding Woes
Reading all the replies and with my own experience, I feel the manual two person bleed is the best. With all due respect to Orrie 1& 2,, repeated pumping with no flow in the system will only collapse the bubbles momentarily and remain roughly as before. With vacuum and gravity bleeding the movement of fluid is so slow, bubbles can hang in high spots without being carried down stream. Pressure bleeding seems more effective if you provide a large enough reservoir to give a more continuos flow campaign.
Another though regarding pumping many times which may help the process which I saw using the vacuum bleeder. Repeated vacuum pumping caused the bubbles to break up and resize down to a froth like cloudy appearance. When the flluid stood for a while the air released from the surface and the fluid began to clear. I wonder if this phenomenon is what 100 pumps creates. If so, a hat tip to Orrie sr. Is there a chemical engineer / physicist in the house? |
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#19 | |
Registered User
Join Date: Mar 2012
Location: Lakes Region NH
Posts: 3,183
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Re: Brake Bleeding Woes
Quote:
But I have run into cases where air does seem to stick in calipers during a gravity bleed. Sometimes after gravity bleeding the pedal doesn't seem right, and cracking the bleeder while a helper presses the pedal will almost instantly push a few bubbles out. |
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#20 |
Registered User
Join Date: Oct 2017
Location: North Carolina, USA
Posts: 7
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Re: Brake Bleeding Woes
We bleed the hydraulic steering systems on boats by running clear tubing from the bleed screws on the steering ram to a reservoir attached to the steering pump and turning the wheel to push fluid through the lines until all the bubbles are gone, then closing the bleed screws. Seems like this would this work for brakes, with tubing from one cylinder / caliper at the time returning fluid to the mc reservoir as you pump the pedal, starting with the most distant cylinder/caliper.
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#21 |
Registered User
Join Date: Nov 2010
Location: calgary alberta
Posts: 8,026
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Re: Brake Bleeding Woes
brdog, that is the same basic principle as the one man bleeder mentioned earlier here. the difference is that the one man bleeder uses a seperate container because it can be placed close to the bleed screw.
brake fluid is like paint remover so being close to the source is a good thing plus the length of hose from the bleed screw to the master cylinder could cause other issues like low spots that can trap air or the weight of the hose pulling the hose off the screw. if you are not familiar with a one man bleeder, it is a small container which gets partially filled with fresh brake fluid. enough to cover a hose that is set down into the bottom of the container. the other end of the hose is connected to the bleeder screw and the bleeder screw is opened. the theory is that gravity will usually want to push fluid out the bleeder screw so there is less concern about air getting in from the screw being left open. when the "one man" steps on the brake pedal fluid/air in the system is forced out the bleeder and down the hose. this is when the second man would normally close the bleeder screw so when the pedal is released no air can get back into the system and also so the master cylinder can refill from the reservoir when the pedal is returned to normal height. with a one man bleeder the screw is left open and any air that would normally be allowed to be sucked back up the hose from that bottle will now be full of brake fluid because the end of the hose is sitting in fluid. it may take a few strokes of the pedal to get rid of the air initially in the hose but this system works well. one thing I learned right away is to not open the bleed screws too far because air can get past the threads of the bleeder screw and mess up the whole theory of operation. however, I use it all the time. when replacing calipers/wheel cylinders or on a fresh system it would be a good idea to take some time and fill the master then open the bleeder screws and allow gravity to assist you in filling the system, just to cut down on the number of pedal applications it takes to fill the system initially. on systems with the pedal below the floor a pressure bleeder would be the best idea if one is available and could be fit into the space under the cab. this is because there is not enough difference in height between the master and the wheel cylinders or calipers. |
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#22 | |
Registered User
Join Date: Oct 2017
Location: North Carolina, USA
Posts: 7
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Re: Brake Bleeding Woes
Quote:
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#23 |
Account Suspended
Join Date: Aug 2016
Location: Florida, USA
Posts: 290
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Re: Brake Bleeding Woes
I have had the most troublesome bleeding issues completely solved with speed bleeders.
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#24 | |
Registered User
Join Date: Jan 2013
Location: League City, TX
Posts: 83
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Re: Brake Bleeding Woes
Quote:
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#25 |
Registered User
Join Date: Oct 2017
Location: North Carolina, USA
Posts: 7
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Re: Brake Bleeding Woes
Years ago I owned a series of early 60's - mid 70's Corvettes and leaking calipers was a very common problem due to galvanic corrosion between the aluminum pistons and the iron calipers. The cylinder walls would get pitted and fluid would leak around the seals. The best cure was stainless steel sleeved calipers.
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