Classic & Vintage - Suntour GPX Brakes

Well... last night I was looking around on my Panasonic. I haven't ridden it, or anything, much lately. No particular reason, and I really should. But, anyways. I was checking the brakes and noticed that my back brake wasn't working. Check the cable and lever, fine. Check the caliper, it wouldn't spring back. Wonderful. Well... I'm lucky enough to have GPX calipers (thanks to a Mr. Robbietunes), and me being the enterprising type when it comes to pulling stuff apart, I grab a Y-wrench and an adjustable and get to work. I pull it apart quite easily. There's a lot of parts in this one little brake.
http://lh6.ggpht.com/_Os80BGPtmH8/TEmhTdqXU3I/AAAAAAAABxI/tBwSzZZ-icU/s720/GPX%20Caliper%20Exploded%20View.jpg
Well... I clean it all up, figuring that there was just too much friction for the springs to overcome. Well, got it all nice and cleaned up, left some grease on the pivot points and started to put it back together. Get it put back together and... it springs in reverse. So I pulled it apart again. Checked. It all over again, and put it back together again... Same deal, except this time it's not springing as strong as it was. So I got frustrated and put it aside.
This morning I tried it again. For a few seconds I had it. I tried tightening it a different way this time and it was springing like brand new. Only problem was that it wasn't sealed like it should be, not all of it was tight enough. Wonderful. So I keep tightening... and same deal as last night.
So I'm stumped.
I don't know what to do. Has anyone else taken one of these or the Superbe Pro hidden spring calipers apart before and had success putting it back together? Cause if not, I'm beginning to thing this was just a product that once it went out it wasn't fixable cause something happens to the springs... or something. I don't know.
Can anyone help?
-Gene-

Bump. Anyone?
-Gene-

Hi Gene!

If it makes you feel any better, I've been down this road many times. :)

I've got a set of these on a bike and I'll take a look see in the morning.

I'll post some pics as well if that would help you at all.

.......and if all else fails, I'll be at the shop tomorrow working on my Zullo.

I'll take the bike in (Montagner w/ GPX) and show 'em this thread.

They may only be 25 year old mechanics, but they certainly know more than I do at times.

Check the shaft of the main bolt. It may have a side that has to be inserted in just so, in order to grab and hold the inner spring in place.

Also check that the spring horns are seated in the proper holes. This is the most likely cause. I believe there should be return tension on the spring as you assemble it. Every GPX caliper I've loosened up has sprung back pretty blatantly; one of the reasons I like their feel.

The same principal applies to the return spring on 8-sp STI's. It's likely coming out while you're stacking and packing. I can't stop in any time soon, but sure wish I could....

Tell me what pics might be helpful!

http://farm4.static.flickr.com/3587/3473611611_de4c102ef3_o.jpg

http://farm4.static.flickr.com/3625/3474419328_b8c760213b_o.jpg

I rebuilt some of these a few months ago. As Robbie says, the position of the spring horns is critical. I can't recall on the GPX's but I have seen cases where the length of the horns on rotational springs differs from end to end - as in the case Robbie cites for the 8 speed STI's. This would come to bear on getting them to lay flat if a horn bottoms out prematurely in a too-shallow hole, as. Result could be binding.

:-/
Alright. I think I may have missed a washer, honestly. I found one on my floor and that might be holding all of this up. And if so... I'm not sure which side it goes on. The springs are distinct in which half they go to. One has smaller horns than the other, but they're the same either way you flip them, which is what's confusing me so. I'll try pulling them apart again soon. I'm FINALLY getting the urge to go riding more, so hopefully it'll get used again soon. Just wish there were people around here I knew to ride with.
Thanks for the help all. And sorry, Gomango, but those pics aren't too helpful. I appreciate the concern though. Beautiful bike in any case.
And as an aside, I'm considering Khatful'ing the calipers. I think these would be beautiful brakes polished to a shine.
-Gene-

I have the original instruction page for these brakes but there is no exploded diagram on them.
Also its in japanese.
Sorry

Is this any help?
http://i284.photobucket.com/albums/ll34/rackfocus/gpx1.jpg

Did you ever figure this out? I took mine apart and am having a hard time getting the calibers to spring back sufficiently to overcome the cable drag (rear brakes only).

From what I've gathered, it takes an extra half turn of the spring when re-assembling. Just lining up the horns and turning 1/4 turn won't do, you have to turn them about 180 past where they fit easily. I recommend insert the spring, mount the other arm upside down, and turn 1/2 turn. Get someone else to hold them, or wrap them somehow, to prevent them springing back when you reassemble the washers and tighten it down.

This is a lot harder to describe than do, but it takes 3 hands. Actually, with a wheel on the bike, the "3rd hand" tool may be the ticket to hold everything together until you get all the other parts lined up and tightened down. With no cable tension, a "3rd hand" should be able to hold the arms against a rim and allow you to finish the job.

This actually sound like fun.

I have a pair in my tool box....but built. They are nice.

Did you ever figure this out? I took mine apart and am having a hard time getting the calibers to spring back sufficiently to overcome the cable drag (rear brakes only).

Best I could figure out was to put it all back together, but hold it open as far as it can while you reassemble it and tighten it down. It will only spring to the max it was tightened down to, so if its pushed further than that after being tightened, it surprisingly doesn't spring. So hold it open, put a 2x4 or something in if you cant hold it yourself, and crank that lock nut down. Should work fine after that.
-Gene-

Thanks guys! I was turning it only the 1/4 turn and thought I needed to get it further but couldn't do it without something loosening up. Good idea on using the 2x4! I'll try that tonight.