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Pics of my Trek 728 project + centerpull brake question

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Pics of my Trek 728 project + centerpull brake question

Old 02-03-21, 10:09 AM
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uprightbent
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Pics of my Trek 728 project + centerpull brake question

I'm lucky to have scored this barley ridden 1982 Trek 728. After stripping it down completely, I'm almost back to a complete bike keeping it mostly original. I've never had these "grail" brakes I've read about, the Gran Compe 450's, mostly have cantilever experience on other touring rigs. First, they seem to have lots of play in the arms while at rest, even with the black pivot bolts tightly screwed in. Secondly, when pulled, the arms don't see to lift in an even plane, spreading a bit when fully squeezed. The last 2 pics shows the gap at full squeeze versus at rest. Maybe this is not unusual for centerpulls, don't recall this happening on those Weinmanns' on my old Raleighs. Thanks in advance for any advice on these brakes, safety being my main concern since they're 40 years old, and I'm nearing 60.




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Old 02-03-21, 10:21 AM
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Very nice!
I am not familiar with those calipers. Is there a bushing between the fastener and the caliper arm?
id you lubricate the pivots or is there a plastic bushing?
They should pull evenly, if not then one side of the spring is stronger than the other or the yoke is not in the center of the cable.

If the spring force is different from on side to the other, you may be able to bend the weaker one out further to match the other side. This is really grasping at straws but maybe worth a try. Springs do resist bending but they all have a yield point.

Check the symmetry of the spring too.

Do you know the year? The SN will tell you when you check out the Vintage Trek site.
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Old 02-06-21, 10:09 AM
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I don't entirely understand why this thread hasn't gained a whole lot of traction- that is a supremely cool bike!!

Welcome to the Trek 720 Club!

Your bike looks beautiful and it looks to be in really beautiful shape- components and all. About the brakes... I have a set, but they're on a 1978 Trek TX700 that's still in the queue to finish getting built- so I've never actually USED them. I think as long as they're assembled tightly, they're safe- while they are relatively rare brakes, I've never heard of a set exploding under load. By the way- yours still have that beautiful Gran Compe sheen to them- that's awesome- for people that haven't seen that, the pix do not capture that 'velvet-y' finish to them.

The 82 720/728 is a great bike these days because it doesn't have cantilevers- and you can get longer reach brakes to use the bike with 650B wheels. Which would mean larger volume tires that will fit under fenders better than any "vintage" Trek will accept with fenders. I think I've gotten lucky with my 720 fitting 35s and SKS fenders. And it's *just* squeaking by.

What fenders do you have on there? They look beautiful and seem to fit under your fork crown really well.

I'm really looking forward to more pix of the bike- I'd suggest maybe getting down on the same level as the bike- and not just taking pix of the bike looking down at it. I think that might be detracting from the glorious pr0n-ness of it.
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Old 02-06-21, 04:35 PM
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Originally Posted by uprightbent View Post
I'm lucky to have scored this barley ridden 1982 Trek 728. After stripping it down completely, I'm almost back to a complete bike keeping it mostly original. I've never had these "grail" brakes I've read about, the Gran Compe 450's, mostly have cantilever experience on other touring rigs. First, they seem to have lots of play in the arms while at rest, even with the black pivot bolts tightly screwed in. Secondly, when pulled, the arms don't see to lift in an even plane, spreading a bit when fully squeezed. The last 2 pics shows the gap at full squeeze versus at rest. Maybe this is not unusual for centerpulls, don't recall this happening on those Weinmanns' on my old Raleighs. Thanks in advance for any advice on these brakes, safety being my main concern since they're 40 years old, and I'm nearing 60.




I suggest taking one of the pivots apart to see if you can eliminate
play by adding a thin spacer between the arms. Keep the other one as a model of where you came from.
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Old 02-06-21, 04:48 PM
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Originally Posted by uprightbent View Post
I'm lucky to have scored this barley ridden 1982 Trek 728. After stripping it down completely, I'm almost back to a complete bike keeping it mostly original. I've never had these "grail" brakes I've read about, the Gran Compe 450's, mostly have cantilever experience on other touring rigs. First, they seem to have lots of play in the arms while at rest, even with the black pivot bolts tightly screwed in. Secondly, when pulled, the arms don't see to lift in an even plane, spreading a bit when fully squeezed. The last 2 pics shows the gap at full squeeze versus at rest. Maybe this is not unusual for centerpulls, don't recall this happening on those Weinmanns' on my old Raleighs. Thanks in advance for any advice on these brakes, safety being my main concern since they're 40 years old, and I'm nearing 60.
Something is bending or moving. Either the pivots have too much play or the arms are too thin. Play in the pivots can be reduced with a spacer if it is end-play, but that does not usually result in the misalignment shown; that's from play at the bearing surface (or bearing seat if there is one).

Often times the problem with "grail" parts is that that status is determined by what you see, not what it does.
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Old 02-06-21, 04:56 PM
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I think the real question is whether there is any play in the bushing. If not the gap is a cosmetic issue.
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Old 02-07-21, 11:14 AM
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Push the bike forward when looking at it. The force exerted on the arm by the wheel when actual braking should counteract that. Does it shudder or squeal in actual use?

Supremely nice bike, by the way...
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Old 04-24-21, 09:01 PM
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Originally Posted by The Golden Boy View Post
I don't entirely understand why this thread hasn't gained a whole lot of traction- that is a supremely cool bike!!

Welcome to the Trek 720 Club!

Your bike looks beautiful and it looks to be in really beautiful shape- components and all. About the brakes... I have a set, but they're on a 1978 Trek TX700 that's still in the queue to finish getting built- so I've never actually USED them. I think as long as they're assembled tightly, they're safe- while they are relatively rare brakes, I've never heard of a set exploding under load. By the way- yours still have that beautiful Gran Compe sheen to them- that's awesome- for people that haven't seen that, the pix do not capture that 'velvet-y' finish to them.

The 82 720/728 is a great bike these days because it doesn't have cantilevers- and you can get longer reach brakes to use the bike with 650B wheels. Which would mean larger volume tires that will fit under fenders better than any "vintage" Trek will accept with fenders. I think I've gotten lucky with my 720 fitting 35s and SKS fenders. And it's *just* squeaking by.

What fenders do you have on there? They look beautiful and seem to fit under your fork crown really well.

I'm really looking forward to more pix of the bike- I'd suggest maybe getting down on the same level as the bike- and not just taking pix of the bike looking down at it. I think that might be detracting from the glorious pr0n-ness of it.
Thanks for your compliments Golden Boy, I somehow missed yours and several other replies. The fenders are Velo Orange smooth in the 37mm width which were on sale for only $50.00. I really wanted some fluted or more decorative fenders on this special bike but I guess the narrowest versions are mostly smooth. However, they ended up looking great and fitting well, although with limited clearance. Here's a few more shots on a recent shakedown ride:





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Old 04-24-21, 11:38 PM
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Are these the Gran Compe brakes that have bearings at the pivots instead of bushings? Beautiful bike!
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Old 04-25-21, 05:51 AM
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Originally Posted by daka View Post
Are these the Gran Compe brakes that have bearings at the pivots instead of bushings? Beautiful bike!
I pretty sure those brakes have ball bearings at the pivots too. I remember wanting to get a pair for that reason and then they took them off the market before I bought them. Be really careful if you decide to take them apart
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Old 04-25-21, 07:59 AM
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That's a really beautiful build. I'm really impressed by the brown tape, housings and especially the brown Brooks saddle; extremely classy. I would look for a Campagnolo smooth shaft seat post (would be the two-bolt type, which I love and others hate) so you don't have relieved flutes disappearing into the seat tube -- that's a Laprade, right? Suntour also made a more modern-looking smooth-shaft seatpost with two bolts that are adjusted from beneath (easier), and I think one of Nitto's expensive models has two bolts too, and is also smooth shaft. But I've never had a problem adjusting the Campagnolo type -- just need a long-handled 10 mm box-end wrench, and a little patience. I can even do it with an Acorn medium-size canvas saddlebag mounted to a Brooks B17.

A centerpull that looks nearly as nice as the GC 400, and performs really well too, is the MAFAC Competition, with reach 44–54 mm for the "petit étrier" and 49–59 for the "grand étrier" (they came with different arch heights, not different arm lengths from pivot like the Weinmann 610 and 750, and like Weinmanns there's often one of each in a set). There was even a (very rare) "étrier reglable" version with a slotted arch mount for 51–66 mm reach. I like Weinmanns a lot too, but the MAFAC brakes are a cut above in terms of finish and appearance, plus they take the same brake shoe as your GC 400s. Another venerable and good-looking centerpull is the Universal Mod. 61, which also came in two reaches: 49–60 and 56–72, though some have characterized them as being brittle, mainly because they don't seem to tolerate bending the arms to adjust toe-in. I never bend centerpull arms, but use Kool-Stop adjustable tilt shoes on those brakes with forward-facing shoe mount holes, and filing carefully the washers for the arms with forward-facing shoe mount holes, like the MAFAC and the brakes you have. René Herse sells such washers with built-in toe-in too; and brass bushings for the MAFAC brakes (along with a reamer; can get expensive) -- that might work for your brakes if it comes to that. I believe the operative shaft dimension is 8 mm.

MAFAC Competition brakes are harder to find these days than they used to be, unfortunately -- but nowhere near as scarce as your GC 400s. The MAFAC Racer is probably just as good in terms of operation as the Competition, just not as smart looking; but still very much available. Then there are Paul's non-vintage ones, pricey, probably pretty bulletproof, but not really my cup of tea.

I've never seen or handled, much less used, the GC 400 brakes, but the arms, while very appealing in the looks department, do seem to have a profile that would not be as strong in bending (section more half moon than rectangular, with less material at the highly-stressed tension and compression boundaries) as it seems to me the Weinmann and MAFAC ones are. Of course, alloy chosen affects ability to resist bending stresses too.

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Old 04-25-21, 08:39 AM
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Originally Posted by Doug Fattic View Post
I pretty sure those brakes have ball bearings at the pivots too. I remember wanting to get a pair for that reason and then they took them off the market before I bought them. Be really careful if you decide to take them apart
Perhaps there was a reason they were taken off the market. Bushes may well be better for the size of the bearing (small), the load (high), and the rpm (fractional).
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