Front Brake Question

[TSConver]

So yesterday went to get on the bike and the front brake lever went to the grip.  A few pumps and it would build pressure and it held pressure but as soon as I released it and it sat for a minute it would go to the grip again.

 

Today I pulled the brake pads and pushed the pistons out quite a bit and cleaned and scrubbed everything well with a nylon brush and brae cleaner.  Lubed up the pistons with Permatex purple brake lube and then worked the pistons in and out a few times.  Reassembled and did a fluid flush for good measure since I was already working on them.  It was a little yellow but was less than a year old.  Also there was absolutely no air in it when I flushed and bled them.  I have speed bleeders and use the iv bag to catch it so air bubbles are pretty easily seen.

 

Now they function as expected again.  Can only pull about 50% to the grip and at that point full pressure is built up.

 

There was a lot of crud on the piston calipers.  I am guessing it was causing the pistons to bind and retract more than they should after applying pressure resulting in a spongy initial brake lever?

 

Any other thoughts?  Maybe this will help someone else in the future.

 

 

[CraigTBrooks]

Hey, I was having some problems with my front brake lever coming in to far, when I replaced my pads ( that were still well within specs) and cleaned everything up they are very good and predicable again. 

[dirtrider]

1 hour ago, TSConver said:

So yesterday went to get on the bike and the front brake lever went to the grip.  A few pumps and it would build pressure and it held pressure but as soon as I released it and it sat for a minute it would go to the grip again.

 

Today I pulled the brake pads and pushed the pistons out quite a bit and cleaned and scrubbed everything well with a nylon brush and brae cleaner.  Lubed up the pistons with Permatex purple brake lube and then worked the pistons in and out a few times.  Reassembled and did a fluid flush for good measure since I was already working on them.  It was a little yellow but was less than a year old.  Also there was absolutely no air in it when I flushed and bled them.  I have speed bleeders and use the iv bag to catch it so air bubbles are pretty easily seen.

 

Now they function as expected again.  Can only pull about 50% to the grip and at that point full pressure is built up.

 

There was a lot of crud on the piston calipers.  I am guessing it was causing the pistons to bind and retract more than they should after applying pressure resulting in a spongy initial brake lever?

 

Any other thoughts?  Maybe this will help someone else in the future.

 

 

Afternoon  TSConver

 

Typically the problem (happening the way that you initially explained it) is caused by air entering the brake system.

 

If you are 100% sure that there was no air in the brake system then the next probable explanation is for some reason the master cylinder fluid port in the bottom of the master cylinder reservoir was plugged (with some crud) or possibly closed off by the master cylinder piston not fully retracting therefore allowing the cooling brake system fluid to suck the caliper pistons back into their bores a bit.

 

It's not impossible but fairly unlikely that excess crud on the caliper pistons would cause a loss of brake lever pressure, that usually causes brake drag as the pistons don't retrack slightly at brake release due to the piston seal design. 

 

The other slight possibility is that the master cylinder piston seal has shrunk slightly, or possibly lost it's shape so it doesn't properly seal to the bore until the lever is pulled a few times to force it to seal.   I haven't seen this on the wethead but have on older BMW motorcycles. The typical test for this is to allow the motorcycle to sit overnight, or a couple of days,  then s-l-o-w-l-y pull the hand lever to see if it will make pressure or if the fluid will just slowly bypass the piston seal. If the lever travels a lot farther, or all the way to the grip at a first slow apply but gives you a decent feel if the first pull is very fast & very firm then suspect piston fluid bypass. 

 

If your problem doesn't return then it is possible the caliper cleaning did the trick but I am somewhat doubtful. 

[TSConver]

Thanks for the thoughts. But it is definitely not bypassing. Only thing I did was clean the pistons and add lubricant. This immediately fixed the issue. Then I bled them since I had the supplies. No air was trapped. 

 

I will monitor and report back if it comes back. But right now they are rock solid. And after sitting they remain solid on the initial squeeze prior to cleaning they would be mushy almost immediately after releasing the built up pressure.

[realshelby]

Remember what DR said. While cleaning the pistons seems to have fixed it there is another thing that happens that directly effects the master cylinder. The act of removing the pistons, replacing the fluid with new and actively moving the master cylinder piston back and forth many times to complete the flush/bleed process can also cause the m/c piston and seal to work properly. From dislodging a piece of debris to simply working the seal and cleaning it can make it seal properly. May stay that way. Or may not so keep that in mind. 

[TSConver]

29 minutes ago, realshelby said:

Remember what DR said. While cleaning the pistons seems to have fixed it there is another thing that happens that directly effects the master cylinder. The act of removing the pistons, replacing the fluid with new and actively moving the master cylinder piston back and forth many times to complete the flush/bleed process can also cause the m/c piston and seal to work properly. From dislodging a piece of debris to simply working the seal and cleaning it can make it seal properly. May stay that way. Or may not so keep that in mind. 

 

This is true but I worked the lever a lot trying to get it to work right before I took it apart. 

 

I will update this thread if it comes back or if it continues to function correctly.

[dirtrider]

7 minutes ago, TSConver said:

 

This is true but I worked the lever a lot trying to get it to work right before I took it apart. 

 

I will update this thread if it comes back or if it continues to function correctly.

Morning  TSConver

 

Did you get it working OK after working the lever a lot but before the cleaning? 

 

If so then that lever working can move any trapped air that was in the master cylinder, or trapped in the upper part of the brake hydraulics, back up into the master cylinder reservoir (basically bench bleeding)  so that could have rid the upper system of any air prior to you bleeding it. (just a thought)

[TSConver]

28 minutes ago, dirtrider said:

Morning  TSConver

 

Did you get it working OK after working the lever a lot but before the cleaning? 

 

If so then that lever working can move any trapped air that was in the master cylinder, or trapped in the upper part of the brake hydraulics, back up into the master cylinder reservoir (basically bench bleeding)  so that could have rid the upper system of any air prior to you bleeding it. (just a thought)

 

No sir. It would pump up in about 3 squeezes and build and hold pressure. As soon as I released it it would need to be pumped up again.

 

Just checked again this morning and it has pressure by 1/3 to 1/2 squeeze. Cannot pull it.to the grip. Pressure is firm at 1/2 and I can maybe pull it a little past that but it has really good pressure and hold for as long as I hold the lever.

 

[TSConver]

Update, brake still firm on initial squeeze.  No bleed down when sitting, been over a week or so since I cleaned and lubed them.