Brake Bleeding Problem

[wiseanhyzer]

Help please!

I was lucky enough to snag one of Rhodie's rear caliper relocation kits. It's a fantastic piece of work. I also got speed bleeder valves from Brent at newbonneville.com. IMO they work great. I switched the bleeder on the front caliper in situ, cracked it open, pumped a couple of times, and now firm, bled front brakes.

In the process of fitting the rear to it's new home on top of the disc, it was necessary to disconnect the whole rear setup and fit a new brake line supplied with the kit.
Fast forward to I've got the rear end put back together, the new brake line routed and attached properly and the caliper in it's new place. Speed bleeder valve on the rear and away I go bleeding. A lot of air got into the system while I had it disconnected. Finally, fluid, fewer bubbles, no bubbles. With every pump of the rear lever, new, clean fluid comes out the bleed valve.

But... I've got no pressure on the rear brake. I've spread the pads to compress the pistons, bleed. Bled with the caliper on the top of the disc, and with it on the floor beside the bike. Same result. Bled with the original bleed valve. Cracked the banjo bolts on both ends, but no air, just a little fluid will seep out. Left it over night (twice) with the lever fully compressed. Tapped the line with a screwdriver to loosen any trapped air.

The pistons push the pads against the disc and release when I pump it. So it has some pressure. But, the bike will role with the brake fully engaged and the lever feels waaaaaay too soft. There is no stopping at the rear brake what-so-ever. So I still have air in the system somewhere.

The brake worked fine last week, the bike has barely 3K miles on it. I don't think any of the components are bad. The hose is new, new copper washers fitted. All bolts are tight. I've checked a dozen times for leaks anywhere along the line, MC, caliper.

Can anyone think of something I haven't tried? (I picked up a MityVac from the auto parts place on loaner today, but it didn't have the fluid catch bottle with it. So I haven't tried that yet.) Any suggestions from the brake experts out there? Help please. I need a trick to get the air out. Or a miracle would be fine at this point.

Thanks in advance.

 

[Rhodie]

Note with this kit we are obviously adapting an underslung Scrambler calliper
which has the bleed valve positioned accordingly.
The America/Speedmaster has the bleed valve in a different position [top] where ours ideally would be.
To keep costs down the bracket was designed to take what we already have,
rather than go out and purchase the America/Speedmaster version to add to the price of the kit.

You may find it easier to detach the calliper and bleed it off the disc,
as the bleed nipple needs to be the highest most point.
Put a wedge in to keep the pads apart and then ease back on the disc when fully bled.

It's a bit of a knack that takes a few goes to master.

I've PM'd you if you need any further help.

 

[wiseanhyzer]

Thanks Rhodie.

The kit went on without any trouble. It's great!
I think it has to do with the Nissin MC and caliper or my technique. There seems to be some air trapped in there somewhere and I haven't got enough pressure built to bleed effectively. I've read that these nissin parts are a pain to bleed, especially for someone who hasn't done it before.

I'll try the vacuum pump today after I can make some sort of catch can that will seal. When I finally get it bled I'm sure it will seem simple.

 

[Threewheelbonni]

Tried it the old fashioned way? Jam jar of fluid connected to the bleed nipple by fish tank type hose. Open-press-close-release until the reservoir is half empty then top up and repeat. Reason I suggest this is that some callipers have internal cavities that need to be cleared out by flow in a certain direction. I've known jam jars, pipe and patience work where factory EOL vacuum fill machines failed.

Got a syringe? Fill the brake hose and calliper with fluid then connect it. The big slug of air with fluid either side of it can have different effects to filling a calliper from dry. That's a long shot, I've only known it work once and that was on a truck. Vacu-fill on that one only worked with the ABS modulator removed and lifted about 6-inches, so seems unlikely on a bike, but worth a try if you've got one.

I assume the fluid is new DOT 4 or 4/5 and was unoppened when you started? Air bubbles and steam are hard to tell appart judging only by the bubbles coming out, although bad fluid will tend to work for a while then go spongy.

Andy

 

[wiseanhyzer]

I've got brakes!

Thank you Rhodie!

Took the caliper off again this morning before work. Hung it from the frame above the disc with the bleed valve at the highest point. Tried bleeding again at lunch, built pressure immediately. Viola! Like new. Thanks for your help Rhodie and Threewheelbonni.