Caliper Rebuild Question

Hey All,

I've been working on rebuilding my MC and Caliper on the 82' Xj650. I'm stuck at putting the piston back in with the seal. I recently had the caliper blasted and powder coated. The guys did a crap job sealing the MC but they did a good job sealing the Caliper. The piston drops in the Caliper easily without the square o-ring seal. However, when I insert the seal I can't get the piston past it for the life of me.

I purchased rebuild kit from Chacal. Any tips/tricks in getting it past the seal? Should I have to force it down? I thought it should slide relatively easily in the bore with the seal.

I can attach pics if needed.

Thanks,

 

Lubricate it with brake fluid. Get it started square, and slowly press it in with a large C clamp.

 

Was looking for the OK to use c-clamp -- trying now. Thanks k-moe.

 

Okay -- it's in. That was not easy.

:0)

 

@MattiThundrrr

 

I see what you did here -- I deserve it. Damn it.

I am laughing at myself at the workbench though. Touche.

 

With enough lube, you can slip anything into anything!

 

Okay k-moe, I'm back with more problems. I put everything back on the bike tonight and I can't build pressure in my brake system. I have a feeling that the problem is in the caliper/piston. I am getting pressure from my master cylinder. I held my finger over the outlet and got very good "pop" sound when I let go. I took all the lines apart and I'm getting a bit of fluid dripping from every section. I'm using a vacuum pump to suck the fluid down from the MC through the bleeder. I'll pick up some syringes tomorrow to try to push it back up but I am concerned. Should I try anything else before taking the caliper apart?

Thoughts?

 

Get a drip pan.
Set it under the caliper.
Open the bleeder.
Tie the brake lever to the bar.
Make sure that the master cylinder is full and the cover is loose.
Go to bed.
Wake up.
Close the bleeder.
Top off the master cylinder.
Use a vibratory sander (no sanding pad), or similar device to shake the remaining air bubbles out, by slowly running it from the bottom of the caliper, up along the brake line, all the way to the master cylinder.
Untie the brake lever and put the cover back on the master cylinder.

 

Alright. Two failed projects today so my morale is a bit low. I did what you said K-Moe and definitely had a "full" system. I pumped and pumped and no pressure. Next, I stole some syringes from work and did the backwards fill method. I went through 2 syringes (120cc) to ensure that there were NO air bubbles. I pumped and no pressure.

I decided to check MC once again. Disconnected the brake line to see if it was building pressure. When I put my thumb over the outlet and squeeze the lever, I get a good jolt of pressure and fluid but when I release the lever, I feel suction against my thumb. I didn't see any air bubbles from my tiny "return" hole (not sure the name but it's tiny). I'm going to take the MC apart in a second and clean it out again but I want to make sure that I'm on the right track. I shouldn't feel that suction when releasing the lever correct?

I have to admit that the MC was recently powder coated and the guys did a crap job sealing the holes -- I had to wrap some 600 grit paper around a dowel and clean some crud out from the cylinder. I cleaned it 3 or 4 times and took it apart twice so far. Here goes the 3rd time.

 

Here's a video of the MC building pressure -- this is a successful test correct?

 

I'd say so.

The trouble has to lie elsewhere.
Are the brake lines new?

 

Replaced with SS lines within past 4-5 years.

 

Okay -- I hooked everything back up.

Here is the link to my MC fluid as I fill the system from caliper with syringe.

Here is the link to my Caliper piston after pumping the lever for 5 minutes.

Shouldn't the piston be inching out slowly as pressure builds? Sorry for n00b questions but i'm a n00b.

 

videos are set to private

 

Fixed -- thanks for the heads up .

 

You still have air in the line or in the caliper body somewhere.
Does the brake lever offer resistance? If the caliper is pressing against something (like the rotor) it should feel firm after squeezing a short distance.
Sorry to be basic, but are you closing the bleeder screw after each pump? If you don't, it just sucks air back in when the lever is released.

1. Open bleeder screw. It may be helpful to attach tubing to it to keep things cleaner, with the other end in a collection container. Not necessary if not available, but helpful. Clear tubing allows you to see the bubbles/fluid flow through.
2. SLOWLY squeeze brake lever.
3. While brake lever is still squeezed, close bleeder screw.
4. SLOWLY release brake lever.
5. Repeat.

Make sure the reservoir remains filled as fluid moves through.
Continue repeating until no more bubbles are seen coming out of the bleeder screw. Then repeat some more until the brake lever feels firm. (You will need something to stop the caliper piston from closing too much and coming out of the caliper cylinder; like a block of wood or the brake rotor if caliper is installed.​

 

I took the Caliper apart and found a small scratch. Would this impact the integrity of the system? It's brand new so I'm not sure how it got there. Maybe during install.

 

I really hope this works -- going to reassemble once someone signs off on this piston. I was just squeezing and squeezing without adjusting the bleeder. Duh. Dufus x 3. This is very basic but I'm very basic so THANK YOU!

 

If you're referring to the small pair of scratches about 3/8" down from the edge, I would not think they would be enough to prevent pressure build up. Even then, the scratch would have to be right on the seal ring and extend to both sides and only when the piston was extended to that point. I think you're good.

If you're referring to the bigger set of scratches on the corner edge; absolutely no problem, not a seal area.

Don't worry about it. We all have been there and learned once. Didn't know your experince level but didn't want to make assumptions.

 

Ok so I tried this method and was pumping and releasing for a good 5 minutes. There still seems to be air in the system. The system worked completely well before MC rebuild and Caliper rebuild which is why I don't think it's the lines. Any other methods of checking?

 

Did you see fluid exiting the bleeder screw? If caliper is not installed, is the bleeder screw pointed up? If there is air in the caliper body, the air will float up. This is where the bleeder screw needs to be positioned. It will take more than 5 minutes if there is a lot of air.


Try this; slight revision to process.

1. While bleeder valve is closed, squeeze brake lever several times
2. Hold brake lever closed.
3. While still holding brake lever, open bleeder valve. Fluid / air should exit. You may feel the brake lever give a little. Don't let go, keep it squeezed.
4. Close bleeder valve. Release lever.
5. Repeat.

Not very much fluid moves through at a time, so it may take several repetitions.
Take your time, you'll get this.

 

Okay -- I got it. I still pull air through with my pump but pressure is there and brakes seem to work. Tire spins about 2 rotations on it's own without weight until slowly stopping. Lever squeeze is a bit looser than I remember but again, it stops on a dime. Thanks for the patience Dadoseven -- I'm embarrassed to admit it but the problem was my pads were installed incorrectly and they were so far away from the piston that it never created a firm system. Below is the video of vacuum line -- I'm still getting these symptoms. Anything to worry about? Also, my little sister says hi.

 

The tiny bubbles are from air being sucked past the bleeder threads. You'll always see those whenever you crack the bleeder open under vacuum. I didn't see any big bubbles, so you're good.

 

Hopefully the last update. I know it's a bit off topic from "caliper rebuilding" but when I apply the front brake with the slightest force (enough to decompress front shocks) there is a "Pop" sound from the caliper. My only thought is that the caliper may not be mounted tightly enough and it's being dragged during hard braking. I'm apparently not too great with a torque wrench but i'll check specs tonight. Any other ideas as to what could cause this "pop"?

I've read that it may be related to the front suspension but this definitely feels like a caliper problem.

 

I was really surprised at how gummed up my return hole was in my master cylinder - had to take a fine piece of wire (thanks Chacal) and ream out the hole to remove the crud built up there.
For other locations I used q-tips, forceps & denatured alcohol to clean all of the crap out of every orifice in the MC.
Also check to see if the seal on the piston is not reversed or folding over - why they don't ship it installed correctly with the rebuild kits I have no idea, I ordered 2 rebuild kits just in case I busted the seal off of the MC piston trying to put it on...

 

Because it's a kit, not an assembled.

 

Totally understand about it being a kit but darn is that stupid seal a bear to install.

 

Did you remember to install the shim plate between the caliper and the fork tube?

 

I believe I have every part for my rebuild in the picture below -- thanks to you Chacal. If #18 is what you're referring to as "shim plate", the washer is installed. I didn't hear the popping last night while riding. Perhaps it's just the new disc and pad breaking in?

 

#18 is the actual caliper. The shim plate is shown in this diagram as part #10, but it's woefully out of position. It actually goes in-between the caliper and the fork tube.

HCP18486 Aftermarket brake pad ANTI-RATTLE CLIP, dual-armed clip that fits in-between the caliper and the fork tube, used on all XJ650 Maxim and Midnight Maxim models, 1979-81 XS1100 Special and 1980 XS1100LG Midnight Special front calipers; and all XJ1100 and 1981 XS1100LH Midnight Special rear caliper. This clip aligns the mounting of the caliper body to the fork tube extension, as well as providing brake pad alignment. NOTE: due to variations in thickness of original shims, you may have to remove the paper coating from this replacement shim and/or file the brake pad backing plate "ears" that fit into the recess of this ship to prevent pad binding in the shim.