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the same but different?

  • Thread starter Thread starter rusty boltz
  • Start date Start date
R

rusty boltz

Guest
Swapped the brakes out on my 79 gs1000. I used rotors and calipers from an 81. The calipers are a different design than the old ones and the master cylinder looks different as well. The only difference I see is the reservoir is round on my 79 and the parts bike has a flat reservoir. The master worked fine before I changed the calipers. Now it seems it wont build pressure and if it does it is at the last 3/4" to 1/5" of travel of the lever. I've bled a half pint of fluid through it already and it gravity bleeds easy. I'm wondering if I need to use a newer master. Are they even different? Or is it always a PITA to bleed these brakes? Oh, and I put new seals in the calipers right before I put them on and they are not leaking so it's gotta be air or the master won't work with these calipers. Has anyone used the newer brakes and had to swap the master or does anyone know if the 81 calipers are compatible with the 79 master cylinder? Thanks.
 
Master should be comparable. Getting all the air out can be a pain. I've had the best luck pumping the fluid quickly so the bubbles are carried out before they can float back upward.
 
Take the brake lever off and push the piston all the way in with a phillip screwdriver or something similar. With the M/C cap off you should see tiny bubbles rise to the surface.
 
It works, I have the same calipers and MC on my '79 1000.
Stops better than the stock calipers, too.
 
i may be wrong

i may be wrong

i thought the rectangular mc was of a larger diameter than the round one, no?
 
I tried to put a set of drilled rotors off a Kat on my '79 'S.When I did up the rotor bolts , I found I couldn't do them up tight against the rotors.I found on close inspection and measurement that the rotor was about a mm thinner than the original only in the area that bolted to the wheel.The brake contact area of the rotor was the same thickness as the originals,same diameter,same bolt pattern etc.The only dimension that was different was as I've said.As my old rotors were still good,I put them back on.In effect what had happened was the Kat rotors were closer together and closer to the centre of the wheel and therefore closer to the fixed pad.I never tried to bleed them with this set up,but maybe this is causing your hassle.Cheers,Simon.
 
I have always had good luck putting a hose on the bleader screw & put it in a container with enough fluid to cover the hose. Then pump until their are no bubbles
 
Thanks guys, I tried bleeding a little more last night and the lever did get firmer but not near what it was. I'll try some of the suggestions today and see if gets all the air out. I'm pretty sure it just needs to be bled more. even though I waited to disconnect the lines from the old calipers until everything was together on the new ones to avoid draining the master but I guess air got up there anyway.
 
One other thing that can lead to soft lever feel is if the floating pins on the caliper are binding. You might want to make sure they are properly greased and the caliper slides from side to side easily.
 
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