Caliper issue on 1981 650 Maxim

Hi guys / gals,

I changed the fluid for the front brakes, bled the lines and everything. With the bike on the center stand and lifted off the front tire, it is difficult to spin the front tire. In other words, they're on when not suppose to be.

I checked the handle and the proper play is there. So, I took the caliper off and the piston didn't seemed to be seased. I was able to push it back in with a "C" clamp rather easily.

I did notice that before I took the caliper off the bike, it was on solid. Shouldn't it be free to move so that it centers itself on the disc?

Unfortunately, the bike is at our shop, and I'm home... so I can't check if one pad as worn faster then the other.

Any help, insite, is greatly appreciated.

THanks,

Dan

 

Dan:

The Caliper is supposed to Float.
There's two "Piston-like" -- Travel Rods that extend into two Cylinders.

When the brake is put-on ... the Caliper is supposed to Pinch the Rotor with BOTH Pads as the Caliper moves to allow it.

If the Travel Rods are stuck in old grease ... that doesn't happen and only the Pad being pushed by the Caliper Piston makes good contact.

Look at this thread:

http://xjbikes.com/Forums/viewtopic/t=5007.html

 

Hey Rick, thanks for the link, but my caliper looks nothing like that one. It mounts to the left fork with one long bolt that goes through the caliper. On this bolt is a bushing as long as the caliper.

I really should be writing these posts when I'm near the bike so that I can describe this better.

So we're certain the caliper moves on all models?

 

I have a 81 xj 650 and yes.....the caliper floats. mine has alittle play from side to side.

 

That's what I thought. Looks like the PO had tightened it so much that there was no play at all.

 

Oh ...
The OLD-old one.

Best thing to do is take-out the center sleeve and clean-up the sleeve and where it fits in the caliper.

Then, do the real restore on the caliper ... where the Brake Pad "Ears" fit.
Super Clean
Scrape
Sand or Dremel the "Ear Channels" as nice as can be.
Dress the "Ears" on the Pad with a Dremel and fine sanding tool. Make them want to slide.

Chuck the Pin in a drill and put an especially fine, new, surface on it.
400, 600, 800, 1000 and finish it off with 1200 Wet with WD-40.

The finishing touch is to roll 400, 600, and 800 inside the hole in the Pads that the Pin passes through.

Then, when you pull the Lever and put the hydraulic pressure to the Caliper Piston ... everything that's supposed to move, down there ... ain't got NO reason not too.

 

Thanks for the info rick. I'll do all of that. I new it was strange for a caliper not to move.

Thanks again.

Dan

 

On the 650 the caliper doesn't slide, it pivots around that mounting bolt to center itself on the disk. Look at the diagram:



When the caliper squeezes the pads (6) against the disc the disc pushes the pads up against (part 14) which actually rides in the ear on the LH fork. This transmits the braking force directly to the fork without the caliper carrying the load.

The caliper pivots around the sleeve (9) to stay centered on the disc. The bolt (11) should be tight - NOT LOOSE. The sleeve prevents the tight bolt from locking the caliper.

When I got my 650 Maxim the washer (7) was missing. This causes the caliper to ride too high and binds the pads against part 14 and locks everything up.

When you say the PO has it on too tight - is that because you are missing the same washer?

 

Another option - and one I've seen - that can cause this is improper mounting of the front wheel.

Proper procedure is to tighten the axle nut FIRST, then the pinch bolt SECOND while making sure the brake disc is centered in the caliper.

If someone was putting it back together and tightened the pinch bolt, then the axle nut - what happens is the disc doesn't ride properly in the caliper, and can even be rubbing up against the caliper housing itself! This causes a constant drag, and poorly performing brakes.

 

Bingo! Thanks MiCarl. I'm missing the plate washer. Here's the diagram from my service manual. It's labeled as # 6 on mine, but we're talking about the same thing.



Does anyone have the exact dimensions of this plate washer so I can replace it?

 

On further inspection, I have one plate washer, and the PO used a much larger one for the top, as you can see in my picture. Are both plate washers suppose to be exactly the same size?

 

That doesn't look quite right - I'll check on mine at home at lunch and will report back

 

Altus,

That would be great. Thanks man.

Also, what can I use to clean the caliper out now that I have the piston out of the housing? There's some dried up gunk on the inside, etc. Carb cleaner? brake cleaner???

 

Brake cleaner - always always always with brake parts.

 

Well, I just got some fender washers from the hardware store and stacked them until the pads didn't bind.

The top washer is close to an inch in diameter if I recall correctly. There is a dust seal (o-ring #7 in your diagram) on the top of the caliper that rides on it. I suspect you have the correct washer there. I'd clean the crap off and make sure the o-ring is intact.

 

Okay - sorry for the delay - have checked, and mine DOES look exactly like your picture above - so that sure does look like the correct plate washers you have there.

Although I haven't pulled my caliper off in a while, I can't say as I remember that O-ring being there...

 

I love O-rings.

If you go to the Hardware Store and buy some big, fat, neoprene O-rings ... you can fit them in the channels of the Shift Lever Rubber.

Then, shoot-on some Armoral.

When the Armoral dries ... you'll have some synthetic protection against leaving that ugly stain, the Rubber Part does, to your nice Cowboy Boots.

 

Before you assemble the caliper make sure the piston is in good shape. On previous bikes I have seen the chrome surface lift and flake off. When cleaning things like caliper pistons and sleeves etc. I tend to use a buffer wheel on the drill press with jeweler's wax. When the surface is done properly it is very smooth, the only trick is to pollish until no wax remains in the little imperfections.

 

having a hard time getting the piston out, seized up big time....any tricks ??

 

If the Piston won't budge from the Hydraulic Pressure supplied by the Bike's Master Cylinder you:

Try pushing it out with a line hooked-up to a high-pressure grease gun ... or,

Bring the Caliper and the Banjo Bolt to an Automotive Brake Specialty Shop.

(Have a pretty girl bring it in and they'll "Stop-the-Music" and fight over who gets to do it.)

Or, ... My favorite.

On the way to the Brake Shop ... stop-off at Duncan Donuts and get a few Medium Blacks with all the fixings on-the-side.
Hit the Brake Shop with the rack of Coffee's and stuff in one hand ... and your Brake Caliper in the other.

Tell the busiest, dirtiest, sweatiest guy, wrestling with the most thankless brake job that God sent you with Coffee for him and his pals. Black with all the fixings on-the-side. Just for you! By the way ... while you're enjoying the Coffee ... God also wants you to hook-up this little Caliper to His bike and get the Caliper Piston out! He sent me to see the right guy; right???

Who's next; please?

Alternator Brushes ... Yes, we have them!