1981 single piston rear brake caliper - help!

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chrisbags

chrisbags

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Greetings fellow wingnuts -

I've been prepping my 81 for spring as many of us have been i'm sure, I went to replace my brakepads and change out my brake fluid all around (bike is new to me and want to make sure the brakes are in good order) - and it turns out my 81 has a single piston rear caliper.

Does anyone know how to properly disassemble/assemble? I got it dissasembled when I pulled the rear wheel for a new tire, it's all put back together to spec except for the brakes. I am concerned that I may not have put the caliper back together correctly since all the how to's for rear brakes (they're awesome on this site btw) talk about dual piston setups.

If anyone can point me at any info I would be most appreciative, I know it's properly fit together, but I am concerned because the pads seemed to just drop in and I can't see how the piston will be able to function - so I'm looking for some info.

In the meantime I'm looking for a dual piston caliper for the rear, but I've blown my parts budget for the moment, so it'll have to wait a little while, longer than I am hoping for it to take to get us some riding weather here in Delaware.

Thanks, and ride safe!
 
Hi Chris, Check out exploded parts views and hopefully that will make re assembly easier for you. Have you rebuilt the caliper with new seals? If you want to go dual piston caliper you need to make sure the master cylinder is suited ( volume and stroke), for my money if you can lock up the wheel then you have enough brakes. Vented rotors have a greater effect in braking performance as it is directly related to heat dissipation.
 
Changing to dual caliper also means changing the bracket and spacers on the axle between the wheel and the nut. I have an '82 with dual rear, but was using my '81 single caliper for a quite some time until I got around to rebuilding the '82 calipers. I had to transfer everything from the '81 frame to the '82 frame since the '80-'81 wheel is slightly different than the '82 or '83 wheels.
 
As far as the pads dropping in, that is normal. With the caliper off, you should be able to set the pads in place on the retaining frame and just drop the caliper over the pads and bolt it up.

Do you still have the retaining spring on top of the pads? (Looks like a metal H - part #13 in the picture) Kinda need that to hold the pads in place.

80-82 GL1100 OEM Parts Manual Page 094

80-82 GL1100 OEM Parts Manual Page 094

 
Thanks gents!

Gerry - yes the spring is in the caliper, once I drop the pads in do I need to do anything special to engage the spring? It went back together the way you described I'm just asking since I'm not keen on the idea of messin up my brakes.

Thanks!
 
No engagement needed on the spring. When you installed the caliper, you had to lightly press it down to get the bolts started - that's the spring pressing against the pads.

Every time you press the brake pedal, the piston is pushed out slightly, and when released, the rubber seal inside the caliper pulls the piston in a tiny bit. You'll need to operate the pedal several times after you've installed the caliper to get the piston where it needs to be. Be sure to keep the brake fluid reservoir filled to the proper level. If you disconnected the hose from the caliper, you will need to bleed the system

As Ansimp stated, a dual-piston caliper will require a matching master cylinder, and as Mcgovern stated, all the mounting hardware will be different as well. Your single-piston will be fine.
 
Thanks again boys.

Not to be a total pain, but let me just ask since you guys are so knowledgeable -

I put the brake back together thusly:

Attached the cover to the rear of the caliper with two screws

Put the bolt through the tie rod and finger tightened

Lifted the caliper bracket over and onto the rotor

Dropped in the fresh pads on either side of the rotor

Placed the caliper body over the pads and bracket and pressed down to align the bolt holes

Installed bolts to spec.

The top retaining pin was in place on top of the caliper, as was the spring inside the top of the caliper so I didn't mess with em except to press down to bolt it up.

I should note that I didn't replace the seals as they seemed ok - no dry rot etc. but I'll do that as my next project sounds like the right thing to do. Question though is this - I opened the bleeder screw so I could retract the piston so the new pads would fit and so the brake fluid in the caliper wouldn't stay in the caliper with the new pads. Once I bleed the brakes out what else do I need to do to 'seat' the pads or anything else to keep them in proper distance from the rotor when disengaged, and are there any telltales that something isn't kosher? The brake was functioning properly so I have no reason to believe there's anything wrong.

Thanks again guys, I really appreciate the help.
 
If you have bled the system and all your seals are working then you are good to go. Always make a few applications before you ride and I also recommend using the brakes as soon as you set off so that system is primed and any crud on the discs is wiped off before you really need them. Most per ride checks recommend observing the condition of the brakes, looking for leaks, tire pressure,oil and loose bolts as a minimum ( also chain and sprockets if you are not shaft drive. The caliper will center and return when pedal or lever is released.
 
Should you fit dual piston calipers you might also consider changing the brake master cylinder. The fluid transfer rates differ quite substantially and will seriously affect the feel of its action.

Just a thought - hope it helps.
 
Let us know if you have any trouble bleeding and ending up with a spongy pedal. There is a distinct trick to bleeding these calipers and getting all air out!
 
I might be splitting hairs here, but I don't see where you mentioned the cotter pin for the brake stopper arm. If the OEM nut and bolt are still in place, that bolt should require a cotter pin to retain it.
 
Thanks again guys,

Brian - there was a replacement, not the original in place, not surprised as it's 32 years old - but there wasn't a cotter pin on the brake stopper.

Gerry - what's the secret sauce on bleeding the brakes? I haven't done the bleed yet, that's coming this weekend along with the rear drive gear oil refill. I'm still a week or so from putting it on the road, so it's up on my jack stand and hasn't moved yet. i'd rather bleed it right the first time!

Thanks!
 
Bleeding:

The shape of the caliper traps air at the top because the bleeder screw sits below the highest point on the caliper.

Unbolt the caliper from the bracket and remove it.

Push the piston all the way in and clamp it so that it cannot come out. (I have a pair of large jaw channel locks that fit over the caliper at the piston that work well enough.) You can also stick a block of wood in there. All you are trying to do is hold the piston all the way in.

Make sure the bleeder screw is facing up and go ahead and bleed. (Absolutely do NOT let the rear reservoir go below half full while bleeding!)

After there is no air bubbles and you have a good stream of fluid, install caliper and push pedal until the piston contacts the pads.

Top off the reservoir, close cover and now press the pedal several times to tighten up the brakes.
 
I had lots of trouble bleeding the linked brakes on mine.
It was weird too, I thought my rear master rebuild was leaking past.
The pedal would fade down just like a leaking piston.
After vacuum bleeding the front the pedal is solid and no more problem.
Harbor Freight has a kit pretty cheap and well worth it.
 
joedrum":b49vj53q said:
you can useally take bolt out of bommton caliper mount to forks and tilt it to where its still on rotor and the bleeder is strait up and down ....
Click to expand...
Great idea Joe, air must rise. As I have stated before I am a great fan of gravity when bleeding brakes. Pump up the master cylinder to get some fluid through ( I normally remove the bleed nipple and use my finger over the port to work as a one way valve) leave the bleed screw a little loose ( make sure you have checked to make sure it is not clogged) and just let gravity flow the fluid through the system. Make sure that the brake fluid reservoir does not empty completely. This process normally doesn't take more than 5 minutes. Once you are happy with the brakes and have used the quite a few times you can do a final pressure bleed. Pump the maters cylinder a few times and hold pressure applied to system, crack bleed nipple and release a small amount of fluid and possibly a tiny amount of air.
 

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