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Brake Caliper Rebuild

[ This is a work in process. Maybe someone can supply some photo's. Otherwise, you'll have to wait until I put another 100,000 km's on mine.]

I just did this job and it's really a piece of cake and still pretty fresh in my feeble mind.

Special tools:

Dental pick set. Go to the drugstore and look for the little dental pick kits on a blister pack. Some of the kits have a small wire shaped one and a larger one. The small wire shaped one, which is sharp pointed, is perfect for hooking the seals and pulling them out without risk of scratching up the cylinder. The large one is good for cleaning the grooves that the seals go in.

Disposable items:

Brake cleaner spray - a couple of cans.
Large bottle of DOT4 brake fluid [do not substitute 3 or 5]
Disk brake grease for the slider pins.
New washers for the banjo bolts (4 each)

Step by step:

1. Dismount the calipers - 2 bolts each.

2. Remove the pads, and the spring clip, and retainer clips from the calipers.

3. Put a bucket under each caliper to catch the brake fluid mess. Carefully squeeze the front brake lever, forcing the pistons out. They'll all probably come out far enough so that you can extract them with your fingers. Don't use any tools on them. You should probably keep the pistons matched with the calipers they came from. Don't lose the nylon inserts from the pistons.

4. Take the bolt out of the banjo fitting to remove the brake lines from the calipers. (It may be easier to remove the bolt if you loosely remount the caliper to the bike so it hold the calipers for you.) Save at least one of the washers from the banjo bolts so you can take it down to the auto parts store to match up with a new set of 4 (2 for each caliper). Pull the piston side of the calipers off of the mount side. It'll make kind of a schmuck sound as thay come apart. Remove the breather.

5. Hook the seals with your small dental pick and extract them.

6. Take everything outside and spray the crap out of all the dirty parts with brake cleaner - old tooth brushes come in handy for getting stuff clean.

7. I used the dishwasher at this point to clean things, but it was a waste of time. It didn't accomplish enough to be worth the effort. If you want to, soak everything in hot water with detergent, then brush again and rinse good. Then make sure you shake all the water out real good. You can probably skip this step altogether if you do a good job in step 6.

8. Use the larger dental pick to clean the seal grooves in the cylinders. This is critical. If your pistons are not retracting when you let off on the lever, this is probably what's causing the problem. The seal is square and twists in its grove (the groove is deeper toward the face of the piston) when brake pressure is applied. When pressure is released, the seal goes back to its normal set, retracting the piston very slightly. If the groove has corrosion in it, the seal won't be able to do its job properly.

9. When you're convinced the grooves are clean, you're ready to spray out the cylinders again with brake cleaner and shake 'em dry.

10. Lubricate the seals with brake fluid one at a time and install them into the grooves, main seals first, then the lighter weight dust seals.

11. Lubricate the pistons real good with brake fluid and slide them in, one at a time. If you just work them back and forth a little, they'll pop right back into the cylinders.

12. The slider pins have rubber boots to protect them, keep the water out and the grease in. One of the boots goes all the way thru the caliper and is retained by a mushroom head on the end of the boot. If you lube the head of this boot with brake fluid and then get it started into the caliper, the slider pin will push it on thru. (This is real similar to another act we're all familiar with, so it shouldn't be too difficult to figure out.) Grease the pins real well with the disk brake grease and mount the piston side onto the mounting bracket.
[Editor's note: that's my '75 Wing caliper in the photo, not a Concours. The point of the photo was to show you the grease tube. Note also from the label that it works on French brakes. Don't use ordinary grease as it will just melt away under the heat from the brakes; this stuff won't]

13. Reinstall the retainer and spring clips, and your breathers and the calipers should look like new. Don't forget the nylon inserts in each of the pistons. Add new pads, or reinstall the old ones if they're good, and you're ready to remount the calipers on the bike.

14. Remount the calipers, reattach the brake lines with new washers, being sure to align the brake line in its retainer on the caliper.

15. Flush and bleed the brakes and you should be good to go.


Followup by Darren Fuerst
I'd just add a few points:

1) You can usually reuse the crush washers once or twice (if you're real cheap).
2) A vacuum brake bleeder is the cat's pajamas for bleeding the lines (but not necessary -- just faster and easier).
3) You can usually pump the pistons out of the calipers using the hydraulics, but it's slow and messy.  Shop manuals always advise using compressed air.  They usually show a blow-gun being used, so people tend to think that you need an air compressor to do this. Not so. Any source of compressed air, including a simple tire pump, will do, as it doesn't (usually) take a lot of force to get the pistons out.  Use the fitting for inflating air mattresses (comes with every tire pump I've ever bought).  Remove caliper, put a rag over the piston, shove the business end of the pump into the hyraulic fitting and hold tightly, and pump away. The piston will pop right out, no fuss, no muss.
4) Personally, I wouldn't use anything but brake cleaner (or clean brake fluid) on any part of the brake system (no water, no other solvents).
5) Implied, but it should be explicitly stated: be absolutely sure that you've got a firm lever and functioning brakes before
riding the bike.  Some professional mechanics even overlook this, judging by the horror stories croppping up on the list over the years.

Rebuilding the calipers is actually pretty easy.  Some folks get nervous working on brakes, but hydraulic brakes are really fairly simple to understand and to service.


Hopefully I haven't forgotten anything. If I have, I'm certain it will be obvious what you need to do.
Bob Ward - Motorcyclist
COG #2936 - Bonney Lake, WA
Blatantly pinched from the COG Listserv #4436 , April 9, 2003

Article By: Bob Ward

April 2003

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