Front Caliper Rebuild

Dan Kyle · Aug 7, 2020

swooshdave said:
Ok, does this look right? I just see fluid coming out, not really any bubbles. And it's not having any effect on the lever yet. Will try some more.

The lever feel is not going to change, as there is still air in the lines.
The idea is to get the air out of the master cylinder.
Once you are getting mostly fluid, bleed it at the caliper.
While there is air in the master cylinder it does not move fluid to the lines and caliper.
Now it will.

swooshdave · Aug 7, 2020

Dan Kyle said:
The lever feel is not going to change, as there is still air in the lines.
The idea is to get the air out of the master cylinder.
Once you are getting mostly fluid, bleed it at the caliper.
While there is air in the master cylinder it does not move fluid to the lines and caliper.
Now it will.

There shouldn't be much air in the line as I pushed the fluid up to the MC. At least in theory.

I am really getting tired of the smell of brake fluid...

gortnipper · Aug 7, 2020

You'll make it man.

Try it on a CNW hydraulic clutch with no slave bleeder.

And then realize after a day of it, that the shorty cammed lever you put on off the old Duc is adjusted all the way backed out.

swooshdave · Aug 8, 2020

Unbolted the caliper and put it higher than MC. Clamped back lever overnight. Went from floppy lever to brake. May need to still bleed a little more but maybe air came out MC.

swooshdave · Aug 8, 2020

Brake got softer when I put the caliper back on. But not as bad as before. Need to get it off the lift and on the ground so I can turn the bars and clamp in the lever down.

swooshdave · Aug 10, 2020

cliffa · Aug 10, 2020

Dave, from what I can see in the video, you didn't lube the seals before inserting the inner piston, hence the force required. I'm not criticizing just making a point for potential newbie DIY folks. Lube is essential on any brake component (for car or bike) to stop seals being damaged or rolling over on reassembly. It also aids free movement of components when bleeding and initial use. Brake fluid or red brake grease makes assembly easy-peasy as well. This guy John Twist (world famous MG guru) swears by Sil-Glyde from somewhere called NAPA (you probably know it).

Cheers,

cliffa.

swooshdave · Aug 10, 2020

cliffa said:
Dave, from what I can see in the video, you didn't lube the seals before inserting the inner piston, hence the force required. I'm not criticizing just making a point for potential newbie DIY folks. Lube is essential on any brake component (for car or bike) to stop seals being damaged or rolling over on reassembly. It also aids free movement of components when bleeding and initial use. Brake fluid or red brake grease makes assembly easy-peasy as well. This guy John Twist (world famous MG guru) swears by Sil-Glyde from somewhere called NAPA (you probably know it).

Cheers,

cliffa.

You may have missed it but I did lube the seal, but probably not enough. The outer seal did get more fluid and it was a little easier.

Here's a shortcut to where I lube it.

elefantrider · Aug 10, 2020

Brake fluid is a good lube , lightweight and doesn't contaminate rubber.
When assembling the pistons in mine, I used Permatex synthetic green brake lube and I just saw they are not recommending it for rubber anymore due to swelling.
So it will be cleaned out of there at the first opportunity.
Most "caliper" lube is very thick, and designed for car caliper pins only.
I have not found one which is brake piston-specific.

cliffa · Aug 10, 2020

swooshdave said:
You may have missed it but I did lube the seal, but probably not enough. The outer seal did get more fluid and it was a little easier.

Here's a shortcut to where I lube it.

Like I say Dave, I wasn't trying to criticize, just trying to make it easier for folks who may become the caretakers of ours and other relics

swooshdave · Aug 10, 2020

cliffa said:
Like I say Dave, I wasn't trying to criticize, just trying to make it easier for folks who may become the caretakers of ours and other relics

No offense taken. I did get fluid on the inner seal but it still fought me. In hindsight I should have lubed it before putting it in. I edited out a whole lot of me fighting to get the seal in. I mostly edited it out because y'all didn't need to learn to more profanity.

bill · Aug 10, 2020

NAPA is
No
Auto
Parts
Available.

cliffa said:
This guy John Twist (world famous MG guru) swears by Sil-Glyde from somewhere called NAPA (you probably know it).

Cheers,

cliffa.

swooshdave · Aug 10, 2020

I’ve had relatively ok success at NAPA as they have a distribution center here.

maylar · Aug 11, 2020

My local NAPA is my go-to for auto parts. If they don't have something they can get it usually in a day. There's also a Tru Value hardware store in the same building (owned by the same guy). I like doing business with local shops instead of the big box stores.

As for Sil Glyde, I use that all the time. It doubles as rubber lube and electrical dielectric grease. Lube your iso rubbers and gaters, spark plug boots, bullet connectors, bulb sockets etc. Good stuff.

olympus · Aug 11, 2020

It may be the case that there is no trapped air bubbles and what your seeing is the new seals acting like a spring and pulling the pistons away from the disc... this is what happens in normal operation but on a very small scale.
Try putting a cable tie (zip tie) around the handlebar & brake lever and leave the system under pressure for 24 hours.
I had the same with my new CP calliper, and despite there being no air, forward /reverse bleeding, pressure bleeding and holding the calliper above master cylinder height, when you pulled in the brake lever it near came in and touched the handlebars..
I think that the seals gave a little whilst under pressure and reduced the piston pull back

swooshdave · Aug 11, 2020

olympus said:
It may be the case that there is no trapped air bubbles and what your seeing is the new seals acting like a spring and pulling the pistons away from the disc... this is what happens in normal operation but on a very small scale.
Try putting a cable tie (zip tie) around the handlebar & brake lever and leave the system under pressure for 24 hours.
I had the same with my new CP calliper, and despite there being no air, forward /reverse bleeding, pressure bleeding and holding the calliper above master cylinder height, when you pulled in the brake lever it near came in and touched the handlebars..
I think that the seals gave a little whilst under pressure and reduced the piston pull back

It’s been clamped back for a couple days. When I take it off and check it and it’s really good now. Cannot pull the lever back to the grip. Need another test ride.

Front Caliper Rebuild

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