Brake bleeding

[bosco659]

Well I’m puzzled. I did some front end work to the XS and now I seem to have some brake related issues. Problem is when I squeeze the brake lever with moderate pressure, the brake lever almost touches the throttle grip. But if I release it and squeeze it again, the lever stops about 1” away from the throttle. This is odd because I never touched the hydraulics on the front. I tried bleeding the master cylinder and both calipers. I bled them conventionally as we as with vacuum. Same condition persists. Should I try tying the brake lever closed overnight?

In the pics you’ll see this is not an OEM setup. I’m using a Brembo radial master cylinder and twin calipers from a YZF-R6. The left brake line is routed in an odd fashion and I disconnected the distribution block to get rid of the high spot that may entrap air. Still no better. I’m thinking the master cylinder may need a rebuild. I googled the rebuild kit and they sell for $400++!

I think now that messing with the brakes I think I’ll make new lines with a better fitting length.

Looking for ideas or suggestions on what to try next. Obviously a caliper rebuild will be a last resort.

 

[GLJ]

Good chance there is air in the high spot of the brake line on the right side in the pic. Try bleeding it at the banjo fitting on the left.

 

[bosco659]

Good chance there is air in the high spot of the brake line on the right side in the pic. Try bleeding it at the banjo fitting on the left.
View attachment 340609

Thx. I can try that but I unbolted the aluminum manifold block it’s attached to and straightened the line to eliminate the high spot. I bled it again at the bleeder and there wasn’t any air.

 

[5twins]

There might be a big air bubble trapped up at the top, where the line connects to the MC. To get rid of that, you can try a "reverse" bleed, force fluid back into the caliper so it comes out in the MC reservoir. With the better MityVac, this is pretty easy because it has a 2nd spot to attach the hose that pushes pressure in instead of creating a vacuum and pulling the fluid out. Start by doing a bit of regular bleeding so the line attached to the bleed nipple on the caliper fills with fluid. Then switch the hose connection on the MityVac and push that fluid back in. Watch that clear line up at the MC that connects to the reservoir and look for any bubbles. You can also watch the fluid in the reservoir to see if any bubbles float up through it.

 

[bosco659]

There might be a big air bubble trapped up at the top, where the line connects to the MC. To get rid of that, you can try a "reverse" bleed, force fluid back into the caliper so it comes out in the MC reservoir. With the better MityVac, this is pretty easy because it has a 2nd spot to attach the hose that pushes pressure in instead of creating a vacuum and pulling the fluid out. Start by doing a bit of regular bleeding so the line attached to the bleed nipple on the caliper fills with fluid. Then switch the hose connection on the MityVac and push that fluid back in. Watch that clear line up at the MC that connects to the reservoir and look for any bubbles. You can also watch the fluid in the reservoir to see if any bubbles float up through it.

My MityVac has a valve to switch from vacuum to pressure so that’s good. I’m thinking about how to fabricate a “pressure pot” of brake fluid that has enough volume of fluid to push any possible entrapped air up through the reservoir. I suppose I could just use a long vinyl tube. When I do this I’ll have to have someone siphon off the rising fluid in the reservoir. The theory is sound. I just need to think it through to rig it so I don’t have brake fluid spraying everywhere.

 

[bosco659]

Would entrapped air downstream make the master cylinder behave as it is right now?

I had to buy DOT4 brake fluid today. I bought a 345ml bottle thinking I’d never use 1L. I need to go back and get more now. 1L is over $25 now. The world is so expensive now.

 

[gggGary]

Valvoline 3-4 syn brake fluid is pretty reasonable.
Remove calipers make sure all lines junctions etc. are headed up hill to the MC and that the MC banjo is at the low spot of the MC (usually on the side stand bars at left lock is enough) sometimes you need to take the MC off the handlebar. Now force all the caliper pistons in as far as they will go, watch for air bubbles at the reservoir. Pump the pistons back out, maybe repeat. Had to do this on CB900F to get the lever stiff.

pic from before I changed brake lines to SS.

 

[bosco659]

Valvoline 3-4 syn brake fluid is pretty reasonable.
Remove calipers make sure all lines junctions etc. are headed up hill to the MC and that the MC banjo is at the low spot of the MC (usually on the side stand bars at left lock is enough) sometimes you need to take the MC off the handlebar. Now force all the caliper pistons in as far as they will go, watch for air bubbles at the reservoir. Pump the pistons back out, maybe repeat. Had to do this on CB900F to get the lever stiff.
View attachment 340617
pic from before I changed brake lines to SS.

Thx. One of my big challenges is to get everything pointing uphill. With my brake hose fitment it’s tough to get everything pointing the right way. I’ll have a go at it tomorrow and try some of the recommended remedies.

 

[bosco659]

Go figure - I had the brake lever tied up last night (didn’t think it would help - but it was free to try) and this morning I went to the garage to plan my next move. I removed the Velcro strap from the lever, gave it a squeeze and it was rock hard. I had read last night that this was an urban legend so I didn’t expect much, but it helped. Upon inspection of the connections I noticed the two fittings on the distribution block were a bit wet so looks like I need to replace the washers and start all over again.

 

[Jim]

I had read last night that this was an urban legend so I didn’t expect much, but it helped.

I used to believe that too... a silly urban legend. But if you think it through, it makes sense. When you pressurize the brake lines, any air bubbles trapped in there will be compressed down to tiny little bubbles of air... small enough so that they make their way passed any restrictions stopping them and up to the master cylinder where they dissipate in the reservoir when you release the lever. At least that's how I think it's working.

 

[Max Midnight]

Not an urban legend, something I have advocated and has worked for me over many years.

 

[bosco659]

I’m a believer now! Heading out to get more brake fluid and I checked inventory and I have lots of nrew crush washers. I should be “back in business” by the end of the day. Thanks for all the help.

 

[bosco659]

Well that didn’t work out as planned. I installed new copper washers on the leaky fittings and it leaked worse. I then decided to take everything apart and start from scratch. New lines will be ordered that will allow proper routing and eliminate the uphill hump. I think I’ll rebuild the calipers while I’m at it too. This is turning out to be a costly project. Fortunately it can be done at my leisure.

 

[bazz]

Go figure - I had the brake lever tied up last night (didn’t think it would help - but it was free to try) and this morning I went to the garage to plan my next move. I removed the Velcro strap from the lever, gave it a squeeze and it was rock hard. I had read last night that this was an urban legend so I didn’t expect much, but it helped. Upon inspection of the connections I noticed the two fittings on the distribution block were a bit wet so looks like I need to replace the washers and start all over again.

I've done this many times
It really does work well,it's also worth doing even if you're brake has bled properly
If that doesn't work try pulling the air with syringe attached to the bleed hose

 

[bazz]

Well that didn’t work out as planned. I installed new copper washers on the leaky fittings and it leaked worse. I then decided to take everything apart and start from scratch. New lines will be ordered that will allow proper routing and eliminate the uphill hump. I think I’ll rebuild the calipers while I’m at it too. This is turning out to be a costly project. Fortunately it can be done at my leisure.

View attachment 340660View attachment 340661

Try annealing your washers even if brand new because they are stamped out of sheet

 

[bosco659]

Try annealing your washers even if brand new because they are stamped out of sheet

@bazz I did a little experiment this evening. I tried bending a virgin copper washer and another new one that I annealed. What a difference between the two! The annealed one was very easy to bend. This might answer why I have such poor luck with sealing hydraulic fittings. I was always thinking a new washer should seal well out of the box. On the matter of annealing, I find that after the washer is heated up, it’s left with a black surface coating that doesn’t look smooth to the naked eye. I tried a grey 3M scuffing pad but the coatings a bugger to remove. Am I doing something wrong?

The Russell fittings I use sometimes come with a set of crush washers. They supply aluminum washers, not copper. Does aluminum seal better? I’m guessing they’re one time use?

 

[Jim]

They supply aluminum washers, not copper. Does aluminum seal better? I’m guessing they’re one time use?

Aluminum seals about as good as copper and just like copper, it can be annealed. So no, not one time use.

 

[5twins]

I've pretty much always re-used the original copper washers and never had any leak issues. I very rarely replace them, just clean them up, sand them a little to remove any obvious imperfections and "grooves" on the sealing surfaces, then anneal them. I'm pretty sure I just use the little wire wheels in a Dremel to remove that black coating from the annealing process, it works well.

No, I don't think aluminum seals as well as copper, and yes, they're a one time use usually. I remember when BMW switched to the aluminum washers on their R bikes. Of course I tried them, but they didn't work as well as the original copper crush washers, so I've continued to use those. Now, this is on the drain and fill plugs for the motor, tranny, drive shaft, and rear end. Yes, there's lots of them, lol, about 8 I think. And for stubborn leakers, I'd switch to a red Bakelite washer, and that usually did the trick. But I don't think those would work on a brake line., annealed copper ones are your best bet.

Hmmmm, after reading Jim's post, I never knew aluminum could be annealed. Maybe I'll have to try that.

 

[ckahleer]

Is aluminum heated than dipped in cold water, and copper heated and left to slowly cool, or is it the other way around?

 

[Jim]

I never knew aluminum could be annealed.

Aluminum isn't any harder to anneal, it's just different... 'cause it melts before glowing from the heat. Harder to tell when you reach the right temp.
Here's a "back yard" method...
Run a candle under the washer to deposit some soot on it. Now use your propane torch to burn the soot off. Soon as the soot's gone, it's hot enough to anneal itself. Unlike copper (and like steel) you let it air cool without quenching.

I've had to work a piece of aluminum where it took multiple annealing steps.. I'd say it can be annealed indefinitely.