Front Master Cylinder Leaking

[Vmass]

I rebuilt the front brakes recently. I thought I did a good job, apparently not.

I noticed pressure loss and did a little checking. I thought I found the leak source when I rubbed my finger under the left front caliper and found some fluid. I ordered another rebuild kit in anticipation of rebuilding it over this weekend, along with replacing the tach seals.

I thought I would get a jump on the tach seal and pull the housing. I decided to check the front brake lever and it was very spongy.

Then I noticed a leak around the master cylinder. I drained the system and dismantled the reservoir.

It looks like it was leaking through the bolt holes that hold the MC/brake lever to the bars. Which if I am reading it right, means that fluid is getting into the chamber that is only meant for air? There was definately residual fluid in the second chamber.

Any ideas?

[spyug]

It looks like it was leaking through the bolt holes that hold the MC/brake lever to the bars.

This part really confuses me. How is that possible? The fluid chamber is sealed to the screws at least the screws don't penetrate it.

Apart from that I would think that leakage could occur if the piston and seals weren't installed correctly or the sight glass was cracked or came lose.

Can you provide a pic to show?

Cheers,
Spyug

[Vmass]

This part really confuses me. How is that possible? The fluid chamber is sealed to the screws at least the screws don't penetrate it.

Apart from that I would think that leakage could occur if the piston and seals weren't installed correctly or the sight glass was cracked or came lose.

Can you provide a pic to show?

Cheers,
Spyug

You are thinking of a different MC. This is the rectangular type with the plastic see through reservoir, no sight glass.

Once the reservoir is removed, there are two chambers. One for fluid and the other for air. The bolts to hold the MC to the bars go straight through to the air chamber, where I believe the fluid was coming from.

I am not sure if my terminology is correct and I do not have access to pictures at this time.

[hampshirehog]

The only way the MC can leak is if the O ring on the bottom of the reservoir (part no 59686-49000) is knackered or you have a rough edge on the bottom of the reservoir. When you re-assembled the MC did you twist the reservoir to line it up and was the o ring dry? If so it can tear / buckle etc.

However, have you checked the piston bore? MC leaks can be deceptive.

For your caliper leak have a real close look at your pistons (use a magnifying glass). I had one with the tiniest pock mark on it - I probably wouldn't even be able to see it with my eyes now - and that was enough to fail. Or again, you may have twisted a seal if you put it back together dry.

[Vmass]

The only way the MC can leak is if the O ring on the bottom of the reservoir (part no 59686-49000) is knackered or you have a rough edge on the bottom of the reservoir. When you re-assembled the MC did you twist the reservoir to line it up and was the o ring dry? If so it can tear / buckle etc.

However, have you checked the piston bore? MC leaks can be deceptive.

For your caliper leak have a real close look at your pistons (use a magnifying glass). I had one with the tiniest pock mark on it - I probably wouldn't even be able to see it with my eyes now - and that was enough to fail. Or again, you may have twisted a seal if you put it back together dry.

I have a new rebuild kits on the way, for both the MC and caliper.

I recall having a heck of a time with the MC, just don't recall exactly what the issues were.

I am thinking that I could have damage something or intalled something incorrectly, within the master cylinder assembly.

If I did, is it possible for the fluid to get it the reservoir that is not sealed...because that is what it looked like.

[Vmass]

Justa follow up describing the leak in more detail as well as asking the question again:

It appeared to me as if the fluid had come up through the air passage hole in the unsealed reservoir, located under the cup. The fluid then came out of the bolt holes that hold the MC to the bars.

Has anyone seen this happen before? The brakes actually were performing quite well. A little spongy by todays standards, but adequate.

[Vmass]

Does anyone recognize this problem I listed above?

[Vmass]

Well, I rebuilt the caliper again and it seems fine know. I am not 100% certain, but I believe the piston cup set was not seated properly, allowing fluid to get on the wrong side of the piston and get pushed up in to the dry reservoir.

Got it?