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Help me rebuild my '78 Trek TX 900

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Help me rebuild my '78 Trek TX 900

Old 03-22-20, 11:27 AM
  #1  
bikemig 
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Help me rebuild my '78 Trek TX 900

It's time for me to rebuild my '78 Trek TX 900. I robbed the parts off the original build for other bikes. Here's the problem: I've decided on the gearing and now I need to figure out the derailleurs. I'm going to use an IRD wide compact crank (46/30) with a 7 speed 12-28 Maillard freewheel. I have three options:

(1) Simplex retrofriction shifters, Campy NR front derailleur, and Campy SR rear derailleur. I'd love to get away with this but the max chain capacity on a Campy SR is 26 teeth and I've far exceeded that on this set up (32 teeth). I could try to get this to work but I suspect I won't be happy with the results, right?

(2) To heck with keeping the bike campy and/or European and just run as (1) above but with a shimano crane long cage rear derailleur. It's a pretty rear derailleur and it can handle this. The problem with this set up is that if I run a crane RD, I'll be sorely tempted to pick up first gen dura ace front derailleur and downtube shifters. I was hoping not to spend xtra cash on this project. BITD of course no one would have cared if you mixed parts like this (simplex retrofriction shifters, campy NR FD, and crane RD).

(2) (a) I guess I could run the long cages for a campy RD as well but it wouldn't surprise me if that crane shifts better than a campy RD retrofitted with long cages. This set up would be simplex retrofriction shifters, campy NR FD, and Campy RD with a longer cage from Soma.

(3) I could run huret new success rear and front derailleur and simplex retrofiction shifters. That has a capacity of 30 teeth which will work if I change out the freewheel to 13-26 7 speed. I like this because it keeps the drivetrain European (and the parts on the bike are almost all European). I like sachs new success stuff but it's not the best RD out there.

This is the sachs huret new success I'm thinking of using in option 3:
Sachs-Huret New Success derailleur (47.1D)

Here is the bike before I tore it down. The brakes (campagnolo nuovo record) and wheels (mavic hubs, mavic ma40 rims) are staying. I'm only changing the crank, freewheel, and derailleurs.



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Old 03-22-20, 11:59 AM
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Well the stuff you took off was perfect. Faced with the remaining choices, I'd pick door number 2(a).
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Old 03-22-20, 12:06 PM
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Old 03-22-20, 12:07 PM
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Originally Posted by Hudson308 View Post
Well the stuff you took off was perfect. Faced with the remaining choices, I'd pick door number 2(a).
I don't disagree. The cyclone derailleurs are likely better than any of the above 3 options. What can I say, I needed those derailleurs for an early 70s Fuji Finest I rebuilt.
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Old 03-22-20, 12:23 PM
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You should be fine with Option #1 . I ran an SR RD on 50/34 + 12/28 (also a total of 32 teeth) on a couple of bikes and they shifted just fine, even at Eroica in the gravel and in Wisconsin on those steep hills.

Different data point but same result: ran 50/28 with a 12-28 freewheel at Coppi using Dura Ace 7400 6 speed in friction setting. That's 38 teeth and it also worked just fine. Biggest problem is getting the small/big combo right so the pulley wheel doesn't hit the big cog but judicious use of horizontal dropout position and chain tension usually takes care of that.

Or you could sell me that sweet, sweet Trek 900 frame and stop worrying about it!
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Old 03-22-20, 01:16 PM
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Originally Posted by rccardr View Post
You should be fine with Option #1 . I ran an SR RD on 50/34 + 12/28 (also a total of 32 teeth) on a couple of bikes and they shifted just fine, even at Eroica in the gravel and in Wisconsin on those steep hills.

Different data point but same result: ran 50/28 with a 12-28 freewheel at Coppi using Dura Ace 7400 6 speed in friction setting. That's 38 teeth and it also worked just fine. Biggest problem is getting the small/big combo right so the pulley wheel doesn't hit the big cog but judicious use of horizontal dropout position and chain tension usually takes care of that.

Or you could sell me that sweet, sweet Trek 900 frame and stop worrying about it!
I like every idea in this post except the last paragraph,

You're right the 46/30 crank, 12-28 freewheel (which is your old freewheel btw!) is designed for those Wisconsin hills. I wasn't sure I could get option 1 to work but I'll give it a shot.

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Old 03-22-20, 01:49 PM
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I take it you haven't considered a modern drivetrain? The 11-speed stuff is amazing, not because of the 11 speeds but because they've made changes to the design so they work better than anything ever.
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Old 03-22-20, 01:53 PM
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Originally Posted by noglider View Post
I take it you haven't considered a modern drivetrain? The 11-speed stuff is amazing, not because of the 11 speeds but because they've made changes to the design so they work better than anything ever.
Yeah that would be plan 4, lol. I could go with something silver in Campy. I'd have to spread the frame though. It's currently set at 123 and I'd have to spread it to 128. Not a big deal but a consideration. Good idea for sure.
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Old 03-22-20, 01:55 PM
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'modern drive train' on this bike = gross, blasphemy, punishable by public shaming and banishment from the C&V forum! and then be burned at the stake!

I run a 28 rear with a SR derailleur, no problems.
I vote for option 1.
Or sell the frame to me (I did ask a while ago............ )
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Old 03-22-20, 02:36 PM
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My '78 930 runs 53/39, 13-28, and the SR RD does fine, with room to spare. +1 on retrofriction, and a Campy FD. And yours must be slightly earlier than mine which has tt cable guides.

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Old 03-22-20, 04:13 PM
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Originally Posted by jeirvine View Post
My '78 930 runs 53/39, 13-28, and the SR RD does fine, with room to spare. +1 on retrofriction, and a Campy FD. And yours must be slightly earlier than mine which has tt cable guides.

Beautiful bike. Dura ace crank? I have no doubt that the SR RD can handle a 12-28 freewheel, I'm a little skeptical that it can handle enough chainwrap but I guess I'll find out.
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Old 03-22-20, 05:31 PM
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I miss my 930.
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Old 03-22-20, 07:13 PM
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Nice bike, I’d opt for choice #1 and keep the Campy. I was able to keep the NR rd on my 77 TX900, switching to a Sunrace 12-28 freewheel, and a newer chain. Shifts as well as a NR normally does, which is not near as well as a long cage Cyclone GT would. Possibly my next upgrade.
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Old 03-22-20, 08:44 PM
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Retrofriction shifters and the Cyclone derailleurs.
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