Front brakes are mushy, what should I try?

[chuck c]

mcgovern61 » Sat Jul 23, 2016 9:30 pm[/url]":x80bbu62]
Chuck, is it still the right side caliper that is mushy? I wonder if the the seal on the piston on that side might be letting air in?
At the master, try this. take the cap off the reservoir and slowly pull the handle in and out. Be sure you see fluid moving up and down in the master as you pump the handle.

If air is getting in around that seal shouldn't fluid be leaking out?
The right side has always been the one that seems to give me the most trouble. I'm about to tear it down and look inside.

 

[mcgovern61]

I would think so, but remember the bleeder screw wasn't leaking fluid either, but it sure was pulling air.

 

[OldWrench]

Seals can have air leak past them and not leak fluid, but it is rare. Generally when that happens it isn't actually the seal but the surface it is on, this is especially true with the old master cylinders.

 

[Terry]

One other tip I used successfully on my rebuild was to coat bleeder threads with grease.
This prevents air being sucked back in here.
After bleeding just wipe it off.

 

[mcgovern61]

Thinking about it again. That right caliper seems to be an issue, but I am stuck as to why. We know that when you clamp off the hoses the MC works correctly and is tight. Let off the left side and you have found that it is still tight? Let off the right clamp and it goes mushy again.

Try this. You will need to get more brake fluid first. Take the right side off again and push the piston back in like we did and clamp it back in. See if you can get the left side to work tight. If it does, move to the right side, set up the bleeder bottle, pull the handle and open the bleeder screw to be sure the handle drops right down tight to the handlebars (and pushes fluid out real easy). Close the bleeder screw before letting the handle up. Add fluid as needed.

I would do this at least 3 times to be sure there is no air slug caught anywhere on that side. If the right side tightens up, loosen the c-clamp a little and pull the handle to move the piston a little bit until it is tight to the clamp again. Still tight? Keep going with the same procedure until the handle goes mushy. At that point, take the clamp off and look at the piston. Check for pitting.

Also, be sure all of the banjo bolts are tight at the crossover and the calipers. These are pretty simple systems and somehow, air is getting back in on that side.

 

[chuck c]

I must have tried 20 times on the right side. Put half a bottle of new fluid through it. It will not get firm. I'm taking it apart.

 

[joedrum]

wonder whats up here opcorn:

 

[OldWrench]

You might consider a new master cylinder. I replaced mine several years ago and it did make a big difference. I know money can be tight, but brakes are too critical to not have working perfectly, or as close to as possible.

 

[chuck c]

It's been too darned hot here to work in the garage but it finally got tolerable thursday. I took the caliper apart and found nothing wrong. Put it back together and tried it again, same result as before. Yesterday I got in touch with a mobile mechanic and he's out of town. Can't come until the 19th. In the meantime I'll do paint and electrical work.

He mentioned running into the same problem before including the right side being the problem until he realized it had linked brakes and the line connecting the front and rear had air in it. My symptoms are identical except that the linked system didn't come out until 83. For a moment I thought we'd found the problem and there was a hose I had somehow completely missed in spite of having the whole system apart :roll: .

 

[joedrum]

good deal....been really hot here as well

 

[slabghost]

chuck c » Sun Aug 07, 2016 8:07 am[/url]":1vixsa2d]
It's been too darned hot here to work in the garage but it finally got tolerable thursday. I took the caliper apart and found nothing wrong. Put it back together and tried it again, same result as before. Yesterday I got in touch with a mobile mechanic and he's out of town. Can't come until the 19th. In the meantime I'll do paint and electrical work.

He mentioned running into the same problem before including the right side being the problem until he realized it had linked brakes and the line connecting the front and rear had air in it. My symptoms are identical except that the linked system didn't come out until 83. For a moment I thought we'd found the problem and there was a hose I had somehow completely missed in spite of having the whole system apart :roll: .

When you are trying to bleed is it on the side stand or center stand? side stand might be okay for left caliper but not right side.

 

[chuck c]

I would think the opposite would be true. No matter, I've done it in several positions including completely off the bike with the bleeder pointing up.

 

[joedrum]

hmmm i wonder whats going on here ...

 

[Ansimp]

+1 :head bang:

 

[OldWrench]

Lets assume you have all the air out, the brake lines are good, and there are no leaks. To my way of thinking the only thing it can be is the master cylinder bypassing the seal. Remember the bore in the master cylinder needs to be perfectly smooth for it to work properly.

 

[chuck c]

OldWrench » Tue Aug 09, 2016 12:19 am[/url]":21t594ed]
Lets assume you have all the air out, the brake lines are good, and there are no leaks. To my way of thinking the only thing it can be is the master cylinder bypassing the seal. Remember the bore in the master cylinder needs to be perfectly smooth for it to work properly.

I clamped the line from the ms and I couldn't budge the lever. It's absolutely rock solid. The ms appears to be perfect.

 

[Ansimp]

Try clamping the line near the calliper and see if it is still mushy. If it is mushy remove the line from the calliper and try bleeding the line while holding it above the master cylinder in a clear bottle of brake fluid so that you can see air bubbles and then you only suck back brake fluid into the line.

 

[dan filipi]

Have you tried strapping the brake lever over night?

 

[dan filipi]

Following this thread I'm starting to think maybe the mushy feel is there simply because you're feeling the mechanical action of the calipers and the pads pressing on the disk?

I'm not sure about other bikes but my front brake has never pressed with a solid stop firmness, always what could be described as a mushy feeling though minor but the brake works good.
Have you tried it riding? It may work great as is.

 

[mcgovern61]

His brakes go mushy for sure! We tested and bled a lot. Plus, he got a chance to ride my bike and feel the difference.