Need help from GS'r with '78 750 - brakes

[Pearson]

Somethings not lined up with my rear caliper. My rotor's hitting the caliper and caused the almost total destruction of my rear brakes. I'm hoping someone with an identical '78 750 as mine will help me verify I have my rear axle put together right. It's as if I'm missing a spacer almost the size of the one up against the axle nut on the right side. Looking at the fiche, I'm not sure my spacers are on the correct side of the wheel. Here's pics of what I have on the left and the right. Help!

[Bopi]

Mine might be a little grainy but here you go. 78 750GS-C

Nice Paint by the way.

[Pearson]

Mine might be a little grainy but here you go. 78 750GS-C

Nice Paint by the way.

Thanks Bopi! Far as I can tell, and from some of the other pics I've seen, all the parts are in the right order. Don't suppose your in the Fairfax area of Virginia and wanna ride over lemme put an eyeball on the bike? Supposed to be decent riding weather this weekend.:-D

I'm not sure I'm seeing the right side correctly, kind of hard to make out for me but you notice anything different?

[Bopi]

Sure, I'm in Christiansburg ( about 5 hours away) and my bike is still in a few pieces (soon to be remedied) but other than that.......


I did download your pic and took it to the basement (we have walk-out basements here) for a comparison and your set up seems in order. My brake mounting bracket is first in line from the swing arm in,followed by a coned bushing and then the rotor.

Maybe a pic of the actual rotor and caliper would help solve the problem as I can't discern anything wrong at this point.

[deves3000gt]

is it the calliper that is hitting the rotor or is it the two calliper bolts?

[deves3000gt]

Is it the calliper it's slef that is hitting or is it the two calliper bolts. From your pic. the washers look right (al least that is how i just put mine back together) mine is close to the roter but not touching if you change the spacers around then the calliper would be two far away right?

[Pearson]

Sure, I'm in Christiansburg ( about 5 hours away) and my bike is still in a few pieces (soon to be remedied) but other than that.......

My brake mounting bracket is first in line from the swing arm in,followed by a coned bushing and then the rotor.

Maybe a pic of the actual rotor and caliper would help solve the problem as I can't discern anything wrong at this point.

Thanks very much. So much for seeing you up North, maybe on the blue ridge, right? The caliper is off already but what I seem to have is swingarm, spacer, caliper bracket then the coned bushing up against the rotor. Check this shot:


You sure you don't have a spacer between the bracket and swingarm?

[Pearson]

is it the calliper that is hitting the rotor or is it the two calliper bolts?

Definitely the caliper Deves. Got me stumped. My neighbor is suggesting adding another spacer in there. Check this thread that started things, where mine looks just like lukehan's:

http://www.thegsresources.com/_forum/showthread.php?t=105475&highlight=pearson

[Boondocks]

If a caliper is gummed up with residue from dirty brake fluid, it can stick with the pad(s) constantly rubbing the rotor under pressure. This will quickly reduce a pad(s) to bare metal, which will then start gouging or transferring metal to the rotor.

Can you put the caliper on with the brake pads removed? Does it drag with no pads? As long as the caliper doesn't touch the rotor with no pads installed, there is no spacer or misalignment problem.

It doesn't matter if the rotor is off-center in the caliper. That's the beauty of hydraulic brakes. In a clean, properly functioning caliper the pads are self adjusting and will put equal pressure on both sides of the rotor whether it is centered in the caliper or not.

It is normal for the pads to lightly touch the rotor before the brakes are applied. There is a minimal amount of drag and friction with this light contact. If there is heavier dragging, the caliper is probably dirty and the pads are sticking. Cleaning the caliper and replacing the seals will allow it to reduce pressure to the pads when the brakes are not applied.

[Pearson]

Thanks boondocks

I can't say for sure if the caliper touches without the pads. I will have to reassemble and check, but I don't think so and here's why:

I had previously noticed some dragging, but with a mere 50 mi. on this bike, (and completely overhauled brakes/pads) I failed to realize what was causing the dragging until wayyyyy too late. Using the only tool I had with me at the time, my ignition key, I was able to poke at the pads and apparently free things up enough to let me get the 10 mi. home. I stopped and checked a couple times and everything was fine

That leads me to believe you may be right...perhaps one or both of the pistons were not moving and got stuck against the rotor causing the build up of way too much heat & then damage. I was able to get the pistons to retract which led the caliper to start touching the rotor since it wasn't being centered by the pads any longer. My head hurts.

[Steve]

If the caliper is touching the rotor, there is a definite alignment problem. It will not "be centered by the pads" at any time. What happens when pressure is applied, is the pads move to where pressure is applied equally to both of them and they squeeze.

Sounds to me like there is a spacer missing or mis-placed. Assemble the rear wheel with the caliper in place, but no pads. The disk should be approximately in the middle of the caliper opening. If it's not, check the loacation and sizes of your spacers to see if something can be moved to align the disk to the opening.

Don't know if it's possible at all, but...is the disk on the wheel backwards? There is usually an offset, and, if it's not much in your case, putting the disk on backwards will cause your problem.


.

[Pearson]

Don't know if it's possible at all, but...is the disk on the wheel backwards? There is usually an offset, and, if it's not much in your case, putting the disk on backwards will cause your problem.
.

Regardless, I'll be reassembling soon so I'll check everything again. The disk was never removed so it's not on backwards. Wish I'd thought to check brake alignment before the rebuild. Arrgh.

[deves3000gt]

hey pearson how are the brakes? i did some research on the axle and spacers you have it right. I would say that it has to be something with the caliper it's self. keep use posted

[Pearson]

hey pearson how are the brakes? i did some research on the axle and spacers you have it right. I would say that it has to be something with the caliper it's self. keep use posted

Haven't yet dug into them due to a coooold garage. A buddy (with a lot more experience than I) is thinking we're going to have to get a 2mm spacer made up since we both think I have it right. I'll keep you posted, appreciate the support.

[Pearson]

Brake and Caliper Alignment - Solved

I like to close out my posts in case another GS'r comes across the same problem in the future so here's what I found:

After packing in 4 ea. .5mm spacers, the caliper aligns perfectly over the rotor. A spin of the tire and it turned and turned and turned: silence. Nice.

I rebuilt the caliper with all new parts and slipped it over the rotor. Now the tire would barely spin at all. WTF?

Taking a look this afternoon, I realized I had almost no play in the rear brake pedal. I adjusted the freeplay and the wheel began to spin again. So to celebrate I took her for a 15 mi. jaunt. I love this little 750. Once good and warmed up, she pulls!