Rebuilt front brake binding on the brake piston side: single disc '77 GS750

[nickjtc]

So I finally managed to get around to rebuilding the front brake caliper. Replaced all the rubber bits and the piston seal. Even managed to finagle getting the piston boot into the finicky little slot on the inside of the caliper. Brand new pads, installed into their respective places as deeply as they will go.

Problem is that even with the piston pushed all the way into the the cylinder the brake pad on that side binds on the disc. And on the other side, even with the caliper 'slid' over towards the disc there is a gap between the pad and the disc. It's almost as if the whole caliper is offset to the left. I am scratching my head because I cannot figure out what I am missing.

Obviously the brake didn't bind back before I stripped it off the bike...

The pic shows the gap on the wheel side. I cannot get a clear pic of the binding side.

What am I missing?

 

[salty_monk]

The rubbish bin maybe... Just yanking your chain but unless originality is really important there are many better options than the original caliper. That one is the worst of all of them

If the sliders are free then either it's spaced incorrectly (unlikely) or the piston is not seated correctly I would think. The piston controls the sliding half not the other way around.

 

[Rich82GS750TZ]

I?m guessing you have a spacer(washer?) in a different position when you threaded your axle back through the speedo drive, wheel, and various spacers than it was before you took everything apart. Unless you never removed the axle and wheel. If you didn?t, then never mind. Ignore me.

 

[nickjtc]

Hmmm, an alternative caliper. Do tell... are there simple bolt-on options?

 

[Grimly]

Hmm... not sure about yours, but I can tell you that the 79 GS850 uses the same hockey-puck calipers and they can be replaced directly with the 80-onwards calipers which are far better.
Yours, being the single disc version likely uses a different caliper mounting bracket to mine, but there's a very strong possibility that the later caliper body itself will bolt straight on to the carrier bracket. But it might not... you need to look for a single disc 80-up model to see if there's a difference in carrier bracket.

 

[nickjtc]

I?m guessing you have a spacer(washer?) in a different position when you threaded your axle back through the speedo drive, wheel, and various spacers than it was before you took everything apart.

I thought that, too, since I did have the front wheel off to change the tyre. And yes, the situation makes it look like the wheel itself is off-set. Apart from having the axle bolt through from the wrong side in the first instance, the spacers under the fork end caps are exactly the same length and the only washer is the one under the castellated retaining nut, which is outside the forks.

So I am flummoxed as to what's happening.

 

[Rich82GS750TZ]

When reinstalling the wheel, did you make sure that the tabs of the speedometer drive meshed with the grooves that turn with the wheel, in turn turning the speedo drive. You can check by spinning the wheel and seeing that the speedo drive turns. Seems impossible to get wrong but I have read of this happening to people where they didn’t align the tabs properly and then had fitment issues and of course their speedo no longer worked.

 

[nickjtc]

When reinstalling the wheel, did you make sure that the tabs of the speedometer drive meshed with the grooves that turn with the wheel, in turn turning the speedo drive. .

Yes. I had thought of that too. The speedo works fine.

 

[salty_monk]

One of the later ones off a 550E should be a straight bolt on I would think.