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Thread: ABS Bleeding.

  1. #1
    IN 2 Deep's Avatar
    Hoonigan

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    ABS Bleeding.

    Right then, As some of you may know I've been busy rebuilding my A4 from the ground up, after stripping the entire brake system down I had no option but to drain the entire hydraulic circuit. Now I've finally got it all back together and tried to bleed the system I'm led to believe there is air in my ABS module which is confirmed by my mushy middle pedal. I know there is a function that can be put to good use with a Vagcom cable so the ABS can bleed itself with a bit of help from me. I know there are some guru's within this forum when it comes to using Vagcom so how do I go about doing this? I've never really used vag com for much so any tips will be appreciated. There is a very brief explanation on the Ross tech site but surely there is more to this I've googled a bit and found some info but is the A4Q any different, any thoughts?
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  3. #2
    CraigG's Avatar
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    have you pressure bled it?

    You shouldnt need to bleed the ABS pump itself unless its new.
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    Sure have, pressure bled them numerous times now, the ABS unit has been drained recently and now I'm struggling to bleed the system. Defo air still in the circuit somewhere. I believe you can connect to the ABS unit with Vagcom and there is someway to run a bleed cycle?
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    Quote Originally Posted by evilscotsman View Post
    I had already seen this and it cant be that simple surely! I was hoping someone on here might have actually done the procedure before and could give me a little more advice. Not to worry I will just have to see what happens! Thanks anyway.
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  7. #6
    "Stick a V8 in it!"

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    I suspect theres more to it than that. All that will do is run the pump.

    We had real trouble bleeding the brakes on craigs s4 after changing the calipers. After some investigation i uncovered a section of the workshop manual that discusses how to "prime" the rear calipers.

    From what i could gather, the handbrake mechanism can trap air inside it due to the shape of the parts. The manual basically tells you to hold the caliper a certain way, before filling it with fluid, to ensure this doesnt happen.

    Clearly on craigs car we hadnt done this, but eventually got it to work by driving the vehicle for a bit (which has presumably shifted the bubbles) then bleeding about 200ml of fluid thru each caliper.

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    if you have air in the abs pump, you will need to run the pump to bleed it I think.

    I would try this, rig up the return tube to go back into the reservoir, as you are bleeding for air in all new fluid, and when ready, run the abs pump test, then crack the nipple that is to be bled back to the reservoir and leave running, tap the abs pump body and the caliper you are bleeding with a deadblow or rubber mallet to dislodge any air to the top, and with pressure on, pump running and air freed it should bleed no problem. Since the fluid will be circulating continuously now with a nipple open, you can rely on the abs test which triggers each caliper repeatedly as well as running the pump, and the tapping with the mallet, to bleed it clear of air.

    You just need steady fluid flow through the system and the air has to eventually pop up and get out. The abs pump will draw from the master cyl reservoir and push to the calipers when running, so the fluid will go round and round, leaving any air you dislodge with the rubber hammer, in the top of the reservoir and it wont go round again with the fluid, just run and tap till no more bubbles appear, no need to press the pedal either, vag will be doing it constantly on and off.
    Last edited by evilscotsman; 24th September 2010 at 14:47.
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    Quote Originally Posted by aragorn View Post
    I suspect theres more to it than that. All that will do is run the pump.

    We had real trouble bleeding the brakes on craigs s4 after changing the calipers. After some investigation i uncovered a section of the workshop manual that discusses how to "prime" the rear calipers.

    From what i could gather, the handbrake mechanism can trap air inside it due to the shape of the parts. The manual basically tells you to hold the caliper a certain way, before filling it with fluid, to ensure this doesnt happen.

    Clearly on craigs car we hadnt done this, but eventually got it to work by driving the vehicle for a bit (which has presumably shifted the bubbles) then bleeding about 200ml of fluid thru each caliper.
    I also suspect there is more to it, I will have a go at it tomorrow and see what happens! Interesting what you said about the rear calipers though, I bled mine bolted to the car as you do, may be this is causing the problem, I will search through the manual in a bit see what I can find. I don't really want to drive it until I get rid of the mush and its all I need to sort out before hitting the road!



    Quote Originally Posted by evilscotsman View Post
    if you have air in the abs pump, you will need to run the pump to bleed it I think.

    I would try this, rig up the return tube to go back into the reservoir, as you are bleeding for air in all new fluid, and when ready, run the abs pump test, then crack the nipple that is to be bled back to the reservoir and leave running, tap the abs pump body and the caliper you are bleeding with a deadblow or rubber mallet to dislodge any air to the top, and with pressure on, pump running and air freed it should bleed no problem. Since the fluid will be circulating continuously now with a nipple open, you can rely on the abs test which triggers each caliper repeatedly as well as running the pump, and the tapping with the mallet, to bleed it clear of air.

    You just need steady fluid flow through the system and the air has to eventually pop up and get out. The abs pump will draw from the master cyl reservoir and push to the calipers when running, so the fluid will go round and round, leaving any air you dislodge with the rubber hammer, in the top of the reservoir and it wont go round again with the fluid, just run and tap till no more bubbles appear, no need to press the pedal either, vag will be doing it constantly on and off.
    Not a bad idea that, I might see what I can rig up.
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  10. #9
    beachbuggy's Avatar
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    Hi I've bleed a few cars using the ABS bleed function on VAGcom and can assure you it is as easy as it looks! Once you're into the right menu, it gives you instructions which you simply follow. It is best doing it with 2 people as one has to press the enter key on the laptop while the other opens/closes the relevant bleed nipple, you can do it yourself but it's slow going. The process takes about 15minutes per cycle and I would recomend you do the bleed at least 3 times to ensure all the air is out the system. It's best to ensure all the air is out of the brake lines, clutch and master cylinder first.

    You'll need an easibleed as well with plenty of fluid in it.

    You only need to bleed the front calipers when doing the abs, so get the car jacked up and on stands as you'll need both wheels off.

    Give yourself an hour and you should crack it.

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    Good man, thank you kindly, I will give it a go in the morning.
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  12. #11
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    thats what i said!!! lol
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  13. #12
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    Quote Originally Posted by evilscotsman View Post
    thats what i said!!! lol
    Yeah but you weren't sure!
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  14. #13
    evilscotsman's Avatar
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    ive used vagcom to bleed the brakes using the abs test, but I have never drained the abs pump or got air in it....thats what I meant lol. I replaced old fluid with new till it ran clear, just didnt empty it first or lose fluid etc as I was just changing it for new. Bled a golf after caliper replacement the same way too but that was a doddle cos I line-locked the flexi pipe using a brake hose clamp before removing the caliper.

    Thats why I said I think you will have to run the pump if the pump itself has air in it...
    Last edited by evilscotsman; 25th September 2010 at 20:08.
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  15. #14
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    Hoonigan

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    Ah OK now I'm with you.

    I can't get my VAGcom to connect to the car! Still can't bleed these buggers and take it for a spin.
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