brake caliper rebuild

[Fire-medic]

Boy, it sure sounds like you're already on-top of replacing parts which should restore your brake function, was there any corrosion on the caliper surfaces inside the bore, or did it clean up easily to a smooth surface? I suspect pitting could make the O-rings not seal properly, to retract the pistons.

 

[Stigmata]

No corrosion anywhere. The piston was clean as the day I put it in. Brake fluid looked brand new also. Just ordered a piston & seal kit from Brake Crafters. Once in I'll see if the pistons retract properly and keep you posted.

 

[Stigmata]

I just rebuilt my rear brake caliper with a piston and seal kit. I went to bleed the system and saw brake fluid exit the bleeder screw into the tube about 3 inches. Couldn't get it to drain into the bottle on both screws. Thought it was strange that I didn't have to add fluid to the reservoir. The level never dropped. No bubbles in the line. Tried pumpming the brake and felt no pressure at all. Did I miss something?

 

[Parminio]

First off, get yourself a Mityvac.

https://www.amazon.com/gp/product/B0002SQYUA/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
Secondly, have you looked at your rear Master Cylinder and checked it? That may have been your problem all along, not the caliper.

 

[Stigmata]

The master cylinder is brand new as I had brakes before. What am I looking for? What test can I do to see if its working as it should?

 

[02GF74]

That doesn't sound right.
Stupid question but have you bled hydraulic brakes before?

Firstly close both bleed screws

When you push down on the pedal is there resistance?

Is there free play in the pedal?

Remove cap. (the one on the rear master not on yer head)

Put tube over one of the bleed screws.
Press down on the lever.
Open the bleed screw.
Pedal should drop to bottom.
Close bleed screw.
Release lever.

Repeat this a few tines and there should be brake fluid coming out the tube into a jar. Keeping an eye on the fluid level, topping up as necessary.

Repeat for the second bleed screw, obviously the first one has been tightened.

If rhe pedal does nor firm up and sinka all the way down, then suspect the master cylinder is no good.

 

[Fire-medic]

The Reverse-Bleed is very easy to do for the rear caliper because it's such a short distance from the rear caliper to the master cyl. If you haven't done this, try it. It doesn't matter whether it's a handlebar master cyl for the clutch or the front brake, or the rear caliper; a Reverse-Bleed will make it work, if it's gonna work. If that doesn't work, something's wrong.

https://www.vmaxforum.net/threads/caliper-rebuild.47304/
https://www.vmaxforum.net/threads/brake-bleeder-syringe-to-make.44973/
https://www.vmaxforum.net/threads/clutch-slave-cylinder-replacement.45011/#post-484980

 

[Stigmata]

That doesn't sound right.
Stupid question but have you bled hydraulic brakes before?

Firstly close both bleed screws

When you push down on the pedal is there resistance?

Is there free play in the pedal?

Remove cap. (the one on the rear master not on yer head)

Put tube over one of the bleed screws.
Press down on the lever.
Open the bleed screw.
Pedal should drop to bottom.
Close bleed screw.
Release lever.

Repeat this a few tines and there should be brake fluid coming out the tube into a jar. Keeping an eye on the fluid level, topping up as necessary.

Repeat for the second bleed screw, obviously the first one has been tightened.

If rhe pedal does nor firm up and sinka all the way down, then suspect the master cylinder is no good.

Yes, when I replaced the seals a few months ago. Had pressure and worked fine. Will investigate further

 

[Stigmata]

Went out this morning and tried to bleed brakes again. This time I used a Motion Pro brake bleeder ( a one way valve to make sure air doesn't go back into the system ) and It worked fine. I now have brakes. Couldn't explain what went wrong. It didn't make any sence. I've bled plenty of brakes before with no problem. It's no brain science, just trial and error.

 

[Parminio]

That's why I have grown to love the MityVac so much: it virtually eliminates any personal errors you can make. Well worth the 60 bucks if you ask me.

And trust me, when you bleed the entire brake system on a car you'll thank yourself for getting one.

 

[Stigmata]

That's why I have grown to love the MityVac so much: it virtually eliminates any personal errors you can make. Well worth the 60 bucks if you ask me.

And trust me, when you bleed the entire brake system on a car you'll thank yourself for getting one.

Thanks for the tip. I will invest in one.

 

[Stigmata]

The Reverse-Bleed is very easy to do for the rear caliper because it's such a short distance from the rear caliper to the master cyl. If you haven't done this, try it. It doesn't matter whether it's a handlebar master cyl for the clutch or the front brake, or the rear caliper; a Reverse-Bleed will make it work, if it's gonna work. If that doesn't work, something's wrong.

https://www.vmaxforum.net/threads/caliper-rebuild.47304/
https://www.vmaxforum.net/threads/brake-bleeder-syringe-to-make.44973/
https://www.vmaxforum.net/threads/clutch-slave-cylinder-replacement.45011/#post-484980

Thanks for your advice. I just purchased a mityvac. Next time I will try the reverse bleed.

 

[Fire-medic]

Yes, the Mityvac is a good tool. I have three of 'em, my oldest is probably 40 years old. I actually prefer the reverse-bleed for my motorcycles, I own nothing with ABS for motorcycles. Based upon the simplest of physics, "bubbles rise-to the surface," the use of a large-capacity (60ml or cc) syringe forces the trapped bubbles to the master cylinder, and out of the hydraulic lines and fittings. I find it especially useful for that pesky hydraulic clutch system, to quickly achieve a firm lever, and fully-operational system.

Whatever is easiest for you is the way to go.

 

[Stigmata]

Yes, the Mityvac is a good tool. I have three of 'em, my oldest is probably 40 years old. I actually prefer the reverse-bleed for my motorcycles, I own nothing with ABS for motorcycles. Based upon the simplest of physics, "bubbles rise-to the surface," the use of a large-capacity (60ml or cc) syringe forces the trapped bubbles to the master cylinder, and out of the hydraulic lines and fittings. I find it especially useful for that pesky hydraulic clutch system, to quickly achieve a firm lever, and fully-operational system.

Whatever is easiest for you is the way to go.

Have you tried the hydraulic brake bleeder by Motion Pro? I picked one up on Amazon for $14. Doesn't look like much but works fast. Less then two minutes and I had good brake pedal pressure.

 

[Stigmata]

That doesn't sound right.
Stupid question but have you bled hydraulic brakes before?

Firstly close both bleed screws

When you push down on the pedal is there resistance?

Is there free play in the pedal?

Remove cap. (the one on the rear master not on yer head)

Put tube over one of the bleed screws.
Press down on the lever.
Open the bleed screw.
Pedal should drop to bottom.
Close bleed screw.
Release lever.

Repeat this a few tines and there should be brake fluid coming out the tube into a jar. Keeping an eye on the fluid level, topping up as necessary.

Repeat for the second bleed screw, obviously the first one has been tightened.

If rhe pedal does nor firm up and sinka all the way down, then suspect the master cylinder is no good.

I knew something was wrong when you stated remove cap, not the one on your head. When it came to this step I kept taking my derby off. Poblem solved, I now have brake pressure. Thanks for the tip. You Brits are so smart

 

[Fire-medic]

Have you tried the hydraulic brake bleeder by Motion Pro? I picked one up on Amazon for $14. Doesn't look like much but works fast. Less then two minutes and I had good brake pedal pressure.

Yes, I have a 1-way valve and tube, connect to the bleeder & pump-away, the valve being in brake fluid. I prefer the reverse-bleed syringe, because it actively pushes the bubbles up and out of the tubing/hoses to the master cyl. What works best for you is what you should use. The Motion pro tool sounds like a good choice given your results. I have a number of Motion Pro tools, they're very 'motorcycle-specific,' like Park Tools are 'bicycle-specific.' The Park Tool steering head outer race tool works well on both bicycles & motorcycles.

 

[DreamV4]

del

 

[WC Hart]

Ok gents, not a professional wrench by any means, but have blead brakes before without problem. Here’s my problem now, just put 94 front end including brakes on my 86. Disassembled calipers and replaced seals reassembled and installed. all went great,,,,but now I can't get the brakes to bleed. I get no pressure of any kind but I can see air moving residual fluid in the drain line when handle is squeezed but no fluid, master is new also. My next step is a reverse bleed but I would welcome any ideas.

 

[DreamV4]

Air goes up overnight.
I had problem with 12mm (piston) master cylinder, where 16mm had to be. (VTX1800)
I bought a few 14mm from ebay advertized as 16.
M. cylinders looked identical.

 

[Fire-medic]

Before you install brake hoses on the calipers, put brake fluid into the calipers until they're full, and then install the brake hoses. If your master cyl was empty because the brake hoses were disconnected from the calipers, now put brake fluid into the master cyl. If you use a MityVac you should be able to get brake fluid entering the MityVac very quickly. Keep an eye on the master cyl fluid level, and fill it before it goes empty. If it goes empty, you need to start with a full master cyl, and begin to siphon the brake fluid from the caliper bleeder nipple, again. The empty master cyl introduced air into the brake lines, and you need to work the MityVac until you only have brake fluid and no air in the MityVac line & reservoir.

If you use a reverse-bleed, you do not need to put any brake fluid into the master cyl. It can be empty. Why? Because using the syringe, you are pushing brake fluid into the empty brake lines, and then, into the empty master cyl. In the master cyl, as it fills with brake fluid from you using the syringe (pushing the plunger IN), you will see the bubbles in the filling master cyl become smaller and less frequent, and then, no bubbles. Now you should be able to replace the master cyl cap, after seeing that the brake fluid level is showing between the lines on the sight glass window. If not, add more brake fluid before installing the cap. Then install the master cyl cap. Tighten to being shut the brake caliper bleeder. Now rapidly and repeatedly fan the brake lever: squeeze, release; squeeze, release; repeat. You should feel the lever gets firm, and the point at which its travel stops is further from the handlebar. You bled your brakes.