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Bleeding Front Drum Brakes, What Am I Missing?


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#1 Avtovaz

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Posted 16 June 2018 - 04:43 PM

Trying to bleed the brakes on the mini van, so its duel circuit, drums all round. Used the pumping pedal technique, and also easy bleed, and still not right. I worked out that the air is in the front brakes as i clamped the front flexis, and i got a pedal.

 

I can see that one cylinder is linked to the other via a link pipe, and im guessing the air is in the first of the cylinders. So how do you get it out? there is no bleed nipple on that side.

 

 

Ive had a look threw google and no one mentions about this really.

 

thanks



#2 absx2

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Posted 16 June 2018 - 05:09 PM

Firstly make sure you have adjusted the brake shoes to give the correct running clearance.

The flexi hose goes into the first slave cylinder then a link pipe connects to the second cylinder which has the bleed nipple so there is no way air can get trapped in the first cylinder.

How long has the car been stood without a working brake system as it might be an issue with the master cylinder or more likely the brake limiter valve on the bulkhead being seized in rear only position.

Also the front flexi hose could be partially collapsed.

If you get an assistant to stab the brake pedal down hard and fast with the bleed nipple fully undone you should get a good blast of fluid, mind your eyes and paint work etc.

Try that on all four corners and go from there.

If you use an easy bleed and dont get a steady flow from the bleed nipples the it could be the master not allowing fluid to displace on the pedal up stoke or the bulkhead valve is stuck. You can bypass the valve to check if its causing the problem, the fittings are metric on the valve.



#3 Avtovaz

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Posted 16 June 2018 - 05:15 PM

thanks for the reply, its a brand new master cylinder, new wheel cylinders, lots of new pipes. Defo pumping fluid into the front cylinders when pressing the pedal, all flexis are ok too.

 

Dont think the air is in the master of the valve as when i crimped the front pipes the pedal becomes hard but i could be wrong? Not tried stabbing the pedal, may do that tomorrow or next weekend !



#4 cal844

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Posted 16 June 2018 - 06:30 PM

thanks for the reply, its a brand new master cylinder, new wheel cylinders, lots of new pipes. Defo pumping fluid into the front cylinders when pressing the pedal, all flexis are ok too.

Dont think the air is in the master of the valve as when i crimped the front pipes the pedal becomes hard but i could be wrong? Not tried stabbing the pedal, may do that tomorrow or next weekend !


You say you crimped the front flexis and the pedal goes hard, I'd now suggest you loosen the unions across the valve on the bulkhead, until you get fluid in and out of the valve and chase from there to the wheels

#5 unburntfuelinthemorning

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Posted 16 June 2018 - 06:38 PM

Are you sure it's air in the system and not incorrect brake adjustment?



#6 Avtovaz

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Posted 16 June 2018 - 08:09 PM

 

thanks for the reply, its a brand new master cylinder, new wheel cylinders, lots of new pipes. Defo pumping fluid into the front cylinders when pressing the pedal, all flexis are ok too.

Dont think the air is in the master of the valve as when i crimped the front pipes the pedal becomes hard but i could be wrong? Not tried stabbing the pedal, may do that tomorrow or next weekend !


You say you crimped the front flexis and the pedal goes hard, I'd now suggest you loosen the unions across the valve on the bulkhead, until you get fluid in and out of the valve and chase from there to the wheels

 

 

yep did that all ok fluid wise



#7 Avtovaz

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Posted 16 June 2018 - 08:11 PM

Are you sure it's air in the system and not incorrect brake adjustment?

 

 

no, not sure, i fitted the new cylinders and shoes maybe 2 years ago, ill jack it up and check the adjustment, but the pedal is nearly to the floor... could well be that.

 

When ive bled it, no air has come out of the system after the initial bit. Ive gone threw over 1/2 ltr of fluid today... Maybe its just adjustment...



#8 timmy850

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Posted 20 June 2018 - 03:46 AM

Turn both the adjusters tighter in the direction the wheels spin forwards. You need them to be skimming the drums and still be able to rotate the wheels with your hands.

Once they’re adjusted and you get a pedal you may need to readjust them one the shoes centre inside the drum

#9 Rorf

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Posted 20 June 2018 - 05:34 AM

Turn all the adjusters until the drums lock, then bleed the system ensuring the MC reservoir stays brimmed at all times. Once brakes are hard then loosen the adjusters slightly.

 

What dual system do you have, diagonal or back/front split?



#10 Bat

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Posted 20 June 2018 - 07:55 AM

Hi,

If you clamp the front flexys and the pedal goes hard the problem must surely be in the front drums as you have isolated them and the pedal has improved. Check everything from the flexy down, shoes, cylinders, link pipes, adjusters, springs and drums.

Cheers  :proud:



#11 Boycie

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Posted 20 June 2018 - 08:37 AM

I'd also add that it's important to have the shoes the right way round... that means a leading shoe at the front of the drum and the other shoe 'flipped the other way round' to act as a trailing shoe.  It makes a big difference.

 

Here's how both rears should be arranged-

 

29043152118_45c1776916_c.jpg20180613_193035 by David James, on Flickr

 

42915546781_a324707349_c.jpg20180612_113222 by David James, on Flickr

 



#12 kws

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Posted 20 June 2018 - 09:11 AM

i just had a similar issue with my MK4 with FR/RR split drums.

 

I had to bleed them in the correct pattern, using the "pedal fast down, hold 3 seconds, slow release, wait 15 seconds, repeat" method. The biggest difference for my car though was correctly adjusting the drums.

 

This video was a great help, https://youtu.be/M02bqqNOlkY and by adjusting the drums front and rear so that there was a resistance to turning by hand means i now have a nice firm pedal and brakes that actually work.



#13 Steve220

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Posted 20 June 2018 - 11:06 AM

Make sure the handbrake is off. Not sure why, but this made night and day difference when bleeding mine. I also just used the standsrd pedal pump method and have a strong biting point now!

#14 Avtovaz

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Posted 23 June 2018 - 05:13 PM

thanks again for the replies, adjusted the front brakes today, and the pedal is rock solid! thanks... Tired it up the driveway, and the pedal dosnt do much, i think they just want bedding in.






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