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Getting the Air Out

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cal.bar View Drop Down
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    Posted: 20 May 2019 at 4:38pm
OK - just finished rebuilding my front axle and am trying to bleed the brakes. (trying being the operative word).

When I started, I knew I had air in the lines as it took a few pumps to get the brake pedal firm.

So... with my (very disinterested) teen-aged son at the pedal, I opened the right rear bleeder with a hose running to a bottle with brake fluid in it, then had him push the brake all the way down and hold it there until I closed the bleeder valve.  Did that 3x  until no bubbles in the bottle, and repeated with each line refilling the master cylinder after each wheel. Result?  WORSE than before. Almost no pressure in the lines and the pedal was completely spoungy and goes to the floor w/o much effort.

Did I need to have him pump it up each time after closing the valves?  What am I missing?

No leaks that I can detect and the MC is less than a year old.  Had perfect brake pressure before I tore it all apart before the axle rebuild.


Edited by cal.bar - 20 May 2019 at 5:47pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2019 at 5:25pm
Got a leak?
Are the pads adjusted?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 47 deuce alpha Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2019 at 5:39pm
You may not have maintained the level in the master cylinder at a high enough level and pumped more air into the brake system. Even if you are getting fluid without bubbles in the catch bottle you could still have air in the line. Before I did anything else I would start over and bleed the brakes again with close attention to the fluid level. 3 pumps of the brake may not be enough to clear out the longest brake line(right rear).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cal.bar Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2019 at 5:47pm
OH, true.  More pumping. Brand new pads that are well adjusted, so OK on that front.  I will start again and pump the hell out of it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 47 deuce alpha Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2019 at 5:49pm
[QUOTE=47 deuce alpha] You may not have maintained the level in the master cylinder at a high enough level and pumped more air into the brake system.
It can be difficult to keep the master cylinder full while you bleed the brakes. If you have an old master cylinder cap you can drill and tap it to use for bleeding. just attach a piece of clear tubing and a funnel and you can watch the level as you pump and bleed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cal.bar Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2019 at 4:19pm
wow- I don't have an old MC cap sitting around, but that's damned clever.  But I'm pretty sure I didn't let the fluid level in the MC fall too low.  As I said, I refilled the MC after ever brake line I bled.  I never saw it below the 2/3 mark.  Still not sure how I failed so badly.  Actually WORSE when  I finished bleeding than before.   I'll try again.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 67charger Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2019 at 6:01pm
If you pump the breaks too hard you could have damaged the rubber plunger on the piston. If you do that it will not build pressure because there is no seal.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jasonbass Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2019 at 8:09am
i always pump brakes 3 times then hold it down onto the floor before cracking the valve. or you can get a "one man" brake bleeder tool at your local auto parts store. its a hand pump that works fairly well 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rus Curtis Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2019 at 9:24am
Originally posted by cal.bar cal.bar wrote:

Did I need to have him pump it up each time after closing the valves?  What am I missing?
No leaks that I can detect and the MC is less than a year old.  Had perfect brake pressure before I tore it all apart before the axle rebuild.
 

Definitely pump several times to build up pressure - doesn't need to duplicate a "panic stop" but needs to be firm.  One push won't build enough pressure to force all the air out.  Peddle doesn't move until you secure the screw, so positive communication really helps. "Pump it up."  Thump, thump, thump.  "Okay, ready."  Open the bleed screw, watch the stream and close before the stream stops (see below).  "Pump it up."  etc, etc.  Working with someone that doesn't do this on a regular basis may need some gentle coaching.

 

I personally had shifted to closing the screw before the flow stops (to keep a bubble from back flowing).  The order is furthest to closest. That back rear has a long run and it may be possible to cavitate in the master cylinder so my preference is to keep the m/c topped off ( the assistant can help watch this through the inspection hole). Right rear, left rear then right front, left front. I also keep bleeding until the fluid runs clear - even after the bubble.

 

That was then.  I was taught how to pressure bleed and won't do it any other way now.

 They have a red aluminum threaded cap that matches the threads for the m/c.  I had to add a rubber gasket to ensure a seal. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveBonny Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2019 at 12:42pm
I second the Motive Products Power Bleeder.   Takes all the pain and suffering out of it.  I have an old filler cap from a failed master cyclinder I use with teh power bleeder.

I also found that this tool is pretty handy for filling your transmission / transfer case oil.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2019 at 1:32pm
  If you use one of those to fill your transmission/transfer case, it should be labeled and used only for that from then on. NEVER risk getting even a drop of oil of any kind into your brake fluid. It only takes a very little bit of oil to destroy all of the rubber parts in an entire brake system!  BW
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cal.bar Quote  Post ReplyReply Direct Link To This Post Posted: 22 May 2019 at 2:05pm
Originally posted by Bruce W Bruce W wrote:

  If you use one of those to fill your transmission/transfer case, it should be labeled and used only for that from then on. NEVER risk getting even a drop of oil of any kind into your brake fluid. It only takes a very little bit of oil to destroy all of the rubber parts in an entire brake system!  BW


WOW - I didn't know that. (not in the manuals)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RSR_MK Quote  Post ReplyReply Direct Link To This Post Posted: 23 May 2019 at 8:38am
I agree with Bruce one this one. Cost me around 1,200$$ last year to replace the brake system on a New Holland tractor. Brakes are in the final drive which run in hydraulic  fluid so the breaks also use hydraulic fluid. Brake fluid was added to the system to top it off and dissolved the seals in the master cylinder as well as the cylinders in the final drive. 

Brake fluid and oil are not enter changeable. 

Mike


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rus Curtis Quote  Post ReplyReply Direct Link To This Post Posted: 23 May 2019 at 9:13am
Don't mix!  Very good advice!
 
For me, I'm looking at using a screw-on pump to fill gear oil.  That way, I can use the original container and dispense under control.
 
Found one at Walmart.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cal.bar Quote  Post ReplyReply Direct Link To This Post Posted: 23 May 2019 at 12:05pm
Originally posted by Rus Curtis Rus Curtis wrote:


Don't mix!  Very good advice!
 
For me, I'm looking at using a screw-on pump to fill gear oil.  That way, I can use the original container and dispense under control.
 
Found one at Walmart.


Yep. Tried that. You are going to have two problems with that set up. One, the hoses are too short to get into the fill holes if you want/need to keep the container of fluid HIGHER than the fill holes to use gravity to assist.

Two, the pump on them is usually too weak to really get much done. You pump and pump and really get no where. I have had MUCH better luck with hand pumps like this: https://www.harborfreight.com/multi-use-transfer-pump-63144.html
the hoses are longer allowing you to keep the container above the fill holes and it does pump a larger volume with each pump. BUT, buy two (or 3) as they are also cheap and made in China and are prone to breaking.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Red Willy Quote  Post ReplyReply Direct Link To This Post Posted: 23 May 2019 at 1:19pm
Keep in mind, if you pump the pedal to fast you will aerate the fluid. Slow steady pumps until you feel a pressure build up. I have had good luck with gravity bleeding. Open the the bleeder screw and leave it open until you have a solid flow of brake fluid. Topping off as necessary. Do this with all four cylinders. If that doesn’t get all the air out follow up with the pump and bleed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cal.bar Quote  Post ReplyReply Direct Link To This Post Posted: 23 May 2019 at 5:01pm
Originally posted by Red Willy Red Willy wrote:

Keep in mind, if you pump the pedal to fast you will aerate the fluid. Slow steady pumps until you feel a pressure build up. I have had good luck with gravity bleeding. Open the the bleeder screw and leave it open until you have a solid flow of brake fluid. Topping off as necessary. Do this with all four cylinders. If that doesn’t get all the air out follow up with the pump and bleed.


How does gravity bleeding work??? If I open the bleeder valve, the fluid barely trickles out or doesn't come out at all. If I were to pump the brake with the bleeder open, each time I lifted the brake air would be sucked back into the bleeder.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ol' Unreliable Quote  Post ReplyReply Direct Link To This Post Posted: 23 May 2019 at 9:08pm
Have you ever seen the "one-man" bleeder screws with the little check valve in them?  You can crack open the bleeder screw and just pump the brake pedal until the fluid is clean or bubbles are gone, whichever.  The check valve keeps air from getting in when you let off the pedal.  You still need to keep an eye on the MC level.  When you're done you just tighten the bleeder screw and go...and stop.  That's if you can find the screws, that is.  I have no idea where or if they're still available.
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