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Front brake

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Hi all,I've been on here a while and always found the answers without having to ask the question, but this time I'm struggling, I'm restoring a mk3 and having trouble with the front brake I've put a seal kit in the master cylinder and caliper and all new pipes but it feels like it's got air in it and I've got to pump it 3or 4 times to get a brake, leave it for 5 seconds and the lever will hit the handlebars.any suggestions.

Thanks in advance 

Gordon 

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Hi Gordon

Let us assume the kit has been fitted ok. The pump 3 or 4 times action will compress any air in the system and give a moderate brake action. Then, leave the lever fully out and fluid plus air flows up and into the reservoir. But, air is still trapped somewhere in the calliper.

Yes it is a fraught task to bleed them. My method is to take the calliper off, put a disc-sized wedge between the pads, and hold it in a fancy flexible arm (laboratory clamp and stand) and rotate it before every few pumps so that the air bubbles find their way out in an upward direction through the calliper. Then I bolt it back on.

Now I have a Lockheed calliper and it is on a long stainless flexible pipe so I am fortunate. But, I think, if you have the original alloy calliper and its metal bundy, then you can undo the bracket that affixes by two studs to the mudguard stay and use the flexible above that to rotate.

I used to have the original calliper on my Mk3 and it took hours to bleed, until I got the Lockheed calliper, found that even worse, and solved it by the 'take it off and rotate' method. Now I get a perfect lever action in a few minutes. It is the case that if you get a 'sort of ok but spongy' lever action then leaving it overnight, with a few strong rubber bands on the lever pulling it on, does seem to help purge small bubbles from the line.

Norm

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Gordon,

You're not alone!  Bleeding my Mark 3 front brake frustrated me for a long time.  Andover Norton have some useful advice that I received when I bought one of their new master cylinders.  This involves leaning the bike to one side, bleeding the system, then leaning to other side and bleeding again.  This was to get the air out of the pockets in the brake caliper.  I'm sure AN would let you have a copy of this procedure if you ask.

Otherwise, Norman's advice is useful and the long flexible brake hose makes this easier.  RGM made me a bespoke hose to go from the brake caliper to the connector on the lower fork yoke, so I now have an easy way to do the bleeding or lift the caliper off.

Phil

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I've a Mk III with standard caliper & AN's replacement 13mm m/c, I originally replaced the stock hoses with Goodrige braided hoses retaining all the Bundy pipes, this was always a complete bastard to bleed& the lever always came to within a 1/2* of the bars. I even has it 'professionally' bled at a bike shop & they could do no better (I never had a problem with the original m/c & the braided hose). I was beginning to think the m/c was at fault until I checked it with a short piece of hose & a tee piece.

I've recently replaced everything between the lever & the lowest piece of bundy pipe with single piece of  Venhill braided cable, much better results have now been achieved as follows:

!) Bike on sidestand & brake line filled from the top using a Gunson Eazibleed.

2)  Whilst bleeding keep tapping the the brake line to help the air bubbles rise, apparently they can stick in the narrower braided hoses.

3)  When a reasonable pull has been achieved, leave the bike for a few days (or longer) on the sidestand, with handlebars turned to the left & a cable tie pulling the lever as far back as possible.. (see photo for result).

Now with just a few strokes, you'll find it nice & hard sir!

You could also check that all the joins are tight, and the bleed screw is tight & the threads are not worn, Ashley at AN told me that the caliper was developed for right hand fitting, hence for us (distinguished) mk III owners the caliper is the 'wrong' way round making bleeding more awkward.

My RGM kit with the AP disc  is scheduled for delivery tomorrow, so a new process to learn (& the last piece of bundy pipe will be replaced with braided hose (when Venhill get their act together!) .

Good luck, 

Mike

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How do people bleed their brakes ? I must admit that I don't trust the valves, nor simply immersing the bleed tube in fluid. I always apply pressure and only then crack the nipple open, closing it before I reach full stroke.

I don't have any trouble bleeding my Mk3 which has a standard caliper, but I have Aeroquip lines replacing the rubber (I kept the rigid pipe as original)...Biggest difference perhaps is that I have the Lockheed CP3125 'variable ratio' master cylinder which means no switch for the brake light...I recall that they are a favourite place for trapping air or even for drawing it in.

 

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