Author Topic: Stumped by a rear brake issue. (Read 879 times)

Pielz · « **on:** March 31, 2020, 11:50:55 AM »

I've tried searching the forums and followed all the directions but I feel like I'm missing something. I installed new brake shoes in to these old comstars. They clear fine, no dragging or anything. I go to hook up the brake lever arm to the pedal and I'm getting the right amount of play in the brake pedal, but if I turn the adjustment nut any farther, the brake engages and drags without depressing the pedal. Is this a normal amount of adjustment? Here are some pics that will hopefully prove something.

All levers are lined up with their respective dimples and the brake pedal height adjuster nut, as you can see, isn't even there so it should have maximum play.

I don't have the chain on yet by the way. Is it an issue of the rear wheel being too far back because it's not adjusted forward via chain? Although this was an issue on this bike before the new wheels when the original 630 chain was still on it

barrynoname · « **Reply #1 on:** March 31, 2020, 11:53:25 AM »

If the wheel cant move forward than this is not normal, check of everything is okey behind the cover.

Pielz · « **Reply #2 on:** March 31, 2020, 12:03:33 PM »

I wonder if somehow my brake lever arm is shorter than it should be? Hmm. Was planning on putting the new chain on today but ran out of time before work. There's probably some room for the wheel to move forward and I had a brain fart and as I said, it's sitting without a chain on it right now. I'll see if I can get the chain on and pop back in to update and see if I've just embarrassed myself more than usual by asking about this haha. I'm a newbie at this and still learning.

69cb750 · « **Reply #3 on:** March 31, 2020, 12:32:29 PM »

Move drum arm (ignore dots) so nut gets on rod.

ADW · « **Reply #4 on:** March 31, 2020, 01:13:27 PM »

Agreed to go ahead and move the brake arm at the wheel a notch or two off the dimples to get enough thread on the nut/rod. It won't hurt anything.

bryanj · « **Reply #5 on:** March 31, 2020, 01:27:59 PM »

Has the end of the rod been broken off?

Flyin900 · « **Reply #6 on:** March 31, 2020, 01:29:14 PM »

Possibly the splined cam that goes through the hub is 180 degrees out if it was removed did you or a PO put it back in correctly. The pictures are too close to tell, yet the brake arm off the splined cam on the rear shoe looks weird in that position, although it maybe just the picture.

BenelliSEI · « **Reply #7 on:** March 31, 2020, 02:15:33 PM »

Is the backing plate brace bolted on and the drum n the right place (rotationally)? We’re these Comstars original to this bike?

Pielz · « **Reply #8 on:** March 31, 2020, 02:26:07 PM »

The comstars are not original but were closely examined and compared with the original parts and are directly swappable. I've read everyone's replies and I appreciate it. Tomorrow evening I should be able to check on some of the things that you guys suggested. I'll make sure I update back even if it's something really stupid and embarrassing lol

And I don't believe the threads were broken off at any point. Although if it happened 20 years ago the evidence is probably buried under some surface rust

pjlogue · « **Reply #9 on:** March 31, 2020, 05:02:17 PM »

Not sure what year model bike you have but I had a similar problem with the same issue when I went to reassemble my rear break on my '76 750. Turns out I had the clevis end of the brake rod turned down instead of up where it attached to the brake lever. You might check the orientation of the clevis.

-P.

Pielz · « **Reply #10 on:** March 31, 2020, 05:08:06 PM »

Quote from: pjlogue on March 31, 2020, 05:02:17 PM

Not sure what year model bike you have but I had a similar problem with the same issue when I went to reassemble my rear break on my '76 750. Turns out I had the clevis end of the brake rod turned down instead of up where it attached to the brake lever. You might check the orientation of the clevis.

-P.

I'll do that! Thanks!!

BenelliSEI · « **Reply #11 on:** March 31, 2020, 05:48:16 PM »

+1 to JPL. I’v made that mistake too.

scottly · « **Reply #12 on:** March 31, 2020, 08:14:04 PM »

Quote from: Pielz on March 31, 2020, 11:50:55 AM

All levers are lined up with their respective dimples and the brake pedal height adjuster nut, as you can see, isn't even there so it should have maximum play.

Although this was an issue on this bike before the new wheels when the original 630 chain was still on it

If your bike originally had a 630 chain, it must be a '77 or 78 model (you didn't say?) which had a longer swingarm than earlier 750s. Is it possible you have the earlier, shorter brake rod? Measure the length from the center of the clevis pin to the threaded end of the rod.

Pielz · « **Reply #13 on:** March 31, 2020, 08:15:05 PM »

That's absolutely possible. This bikes history is questionable at best. I'll measure and check it out as soon as I'm able!

scottly · « **Reply #14 on:** March 31, 2020, 08:20:20 PM »

I'll measure a known K7 rod when I get the chance...

Pielz · « **Reply #15 on:** March 31, 2020, 08:20:58 PM »

Thank you I'd appreciate that greatly

Pielz · « **Reply #16 on:** April 02, 2020, 05:59:38 PM »

Sorry for the anticlimactic ending to this saga but I disassembled the rear brake pedal assembly to inspect it and when I buttoned it back up it fit up properly and I seem to have the correct amount of adjustment. Honestly I have no clue what I did or what I fixed but it's working now.

Is it possible the return spring was binding up or something?

The Lone Builder · « **Reply #17 on:** April 03, 2020, 03:53:48 AM »

Well done. It’s puzzling, but nice when that happens!

Pielz · « **Reply #18 on:** April 03, 2020, 08:30:12 AM »

Definitely! Lol

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Author Topic: Stumped by a rear brake issue. (Read 879 times)