109" Master Cylinder bleeding

Am I also correct in that as my 109" has two wheel cylinders on the front, the one with the bleed nipple is on the bottom...? Strange design if you ask me.

Correct, strange concept and makes it particularly tricky to bleed but is possible with perseverance and the right tools.

There is a way to link them up so the flexi goes to the bottom cylinder first and then to the top. Requires some more copper brake lines but a consideration.

Springs need to on correctly too , i rotated my backplate to allow easier installation new pipes and better access for bleeding , but never had a problem bleeding when set up normal.

bill.hiscock said:

Am I also correct in that as my 109" has two wheel cylinders on the front, the one with the bleed nipple is on the bottom...? Strange design if you ask me.

Click to expand...

Yep. I have the eleven inch drums in the front with twin slaves. If that’s the issue you can crack the top pipe if someone is pumping once normal bleeding is complete. Gently does it though or you get covered in it.

You don't need to rotate backplates or anything like that.

The mistake people make is to adjust the brakes UP. DON'T do this.

The thing to do is to FULLY back them off. Even better, use a strap to hold the shoes fully back.

The problem is that you get air bubbles in the slave cylinders. Backing the brakes off allows the pistons in the slave cylinders to expel any fluid and/or air from the slave cylinders back into the pipes.

When you do this, you'll see the air bubbles leave the system after a couple of pumps of the pedal. Then, obviously put the drums back on,and adjust up.

Thanks for this, everyone. I've done the same, installed the master cyl dry and am getting absolutely nowhere with bleeding and two mobile brake 'specialists' have said they don't even want to look at it. Can I not fill the master with fluid in situ as the outlet is already the high point? Doing exactly that but on a bench seems a fruitless exercise. . .

Have you tried clamping the 3 flexi hoses and there should be a firm pedal, then remove one clamp at a time and bleed until you get the air out and pedal goes firm

Yes, put about a cupful of fluid with all three clamped, trying to bleed the master - still zero pedal.

Dry master on first press of pedal piston sticks at the end of travel. I had same issue long time ago. Used air line pressed in fluid exit port to blow piston back, just a quick puff. Since then have made sure they are wet before installation.

Exactly what the problem was. Thanks Tottot.
only cost me about 12 hours and $314 in towing and troubleshooting by Kym Urmersbach here in South Australia to work that out. Kym spotted the stuck piston in a few minutes, disassembled and relubricated the lot for reassembly and bleeding, all in about 3 hours whilst I watched, drank the Assam Bold tea and half of the fruit cake I'd brought.
Piston is still a bit slow to return but Kym believes it will bed in to give what was originally a perhaps surprisingly solid brake.

Thanks to everyone for your interest and I hope this helps others.
PS one ray of sunshine is that my early 2A had the older, better CV type master cylinder as the later 2A with the big bolt at the back is even more of a dog to work with. That one is best assembled submerged in a bucket of brake fluid prior to fitting up.
Viva!

Good to know you are sorted. I recon spare cylinders can spend much time in storage and what ever is used as a protective coat goes sticky. Cheers.