Restoring a 1983 Trek 720
 

Hi folks--
I'm restoring a 1983 Trek 720. The bike was in disarray in the corner of someone's garage when I bought it. I've got it all stripped down to frame and components, cleaned everything up nicely, did a little paint touch up, and am now starting to think in detail about starting to build it back.
The current puzzle I've got is the drive train, and it's only a puzzle because I just don't know much about it.
Here's the "known" parts:
* I'm going to use a Suntour Cyclone GT rear derailleur
* the bike came with a Campagnolo front derailleur
* the bike came with a Sugino AT triple crankset, with a 50-tooth chainring, a 45-tooth, and a 28-tooth "granny". I plan to use all that.
* came with Suntour bar-con shifters, which I plan to use

The bike came with a 5-speed Regina freewheel. I'd like to replace this, but don't know what I can/should be looking for. Can I put a six-speed freewheel on? What about a seven?

I also don't know what I should be looking for in a bottom bracket. I guess the main thing to consider is total length?

Thanks for any help/info. (And if this is the wrong place for this post, please let me know).

First things first..... You need to quickly make enough posts so that you can upload photos!

The crankset determines BB spindle length (usually.....), so if you're keeping the cranks, get a BB with the same spindle length. It's possible the length is embossed on the spindle that's in there. And if you haven't dismantled the BB, maybe a cleaning and new bearings/grease are all you'll need.

If the rear hub is 126mm you should be able to fit a 7sp freewheel. But since it's got a 5sp on there, it's more likely that it's 120mm. If it's 120mm, you could fit a narrow 6sp.... Or spread the dropouts to 126mm, get a longer axle and spacers to make the old hub 126mm (you'll have to re-dish the wheel), or build up a new wheel with a 126mm hub.... Then you can use a 7sp.

some inspiration

https://cargocollective.com/BRAZENBI...ek-720-Touring

My 1985 720 takes a 6 speed no problem but it came with 5.

Ha, I'd be glad to post pics when I'm able.

I've already disassembled the bottom bracket, and it was not original--what I pulled out of it was a Shimano sealed-cartridge unit, which I'm really confident was not original on this bike. And when I compare that shimano to a couple of bb spindles I have lying around, one of which came out of a late 1980s trek touring frame, the Shimano is noticeably shorter. So i'm suspicious of it.

Also, I don't know why I hadn't tried this already, but I also have a rear-wheel from a late-80s/early 90s Trek "hybrid," with a 7-speed freewheel. And the 720 frame accepts that wheel, so I guess I now know its 126mm. Still not sure I know if the Suntour Cyclone will cope with a 7-speed, though...?

Also, I've read just enough about chain length to know that with that 28-tooth granny gear on the front, I will be limited as to the biggest sprocket I can have on the back. So that makes me think 7-speed freewheels might be ruled out by that math.

Ah, that's lovely.

The 83 Trek catalog shows a 6 speed heliocomatic 13-28 six speed rear setup which has probably been replaced although they were also made in 5 speeds. 720s are very respected here.

After a little careful measuring, I think the rear dropout spacing is 120mm, not 126. (The wheel with the 7-speed freewheel did go in, but it didn't just slide right in, it needed some help.)

Steel is pretty forgiving. There's plenty of debate about the stresses involved in 'shoe-horning' a 126 into a 120-spaced rear triangle..... Personally I think if it doesn't require serious muscle to get it in, it's fine. But for peace-of-mind, resetting is pretty easily done.

How large to you want to go with the biggest rear cog? IIRC a Cyclone GT (long-cage) can handle quite a bit of chain. And should be able to handle 7sp, regardless. Check Velobase or Sheldon Brown for the correct BB spindle length for the Sugino crankset.

I've never used a half-step plus granny setup and I want to, so I intend to keep the 28-tooth granny gear that is currently on the crankset. And I think that implies very linear (?) differences in size for the sprockets on the freewheel...?

Firstly, I am assuming restoration means keeping the same wheels and rear dropout spacing. If you wanted to respace and get new hubs/wheels, the options open up considerably.

I think you can get an ultra 6 on there (120 spacing hub), and keep the existing hub. Might need a different wheel-set to go 7 speed, but since you are restoring, might as well find an ultra 6 (I assume the hubs are Maillard?), though finding them unworn and wider range is often tough.

Far as I know, the only Ultra 6s are the SunTour versions, Atom 77 Compact, and Regina BX-6 (I think that is the 120 mm hub version). @pastorbobnlnh will know better.

If you are not wanting to spend the $60-80 to get an Ultra 6, having 5 speeds is okay too!

Suntour Cyclone FDs are relatively easy to come by.

You should definitely fully explore the 1/2 step+ granny and the 5 speed FW you got might be lovely. Play with one of the online gear calculators. 6 sp can work ok and forget about 7.

You can go as low as 24 on your granny. A 14-28 five speed freewheel and 24-45-50 would cover a ton of ground. Personally my 720 wears 24-40-45 and 14-17-21-26-32 freewheel. Either way you'll be in good shape with the right length chain.

https://cimg4.ibsrv.net/gimg/bikefor...4497de68a0.jpg
Hippy camo 720.

I've found this online gear calculator to be great. A good way to visualize your setup (note that you can hit the 'compare' button and add a second setup to the page, and also if you want to bookmark your setup you need to click on "link to the currently selected setup'). I've got a half-step + granny on my PX-10 and really like it (first 1/2+g I've ever had). I'm building up a Holdsworth now, and trying to keep it a double up front and it's a bit of a challenge to evenly cover the range I need!

How close are you adhering to 'restoration'? Staying as original as possible, or more resto-mod? The roads where I live are so uniformly awful, and the Appalachian-steep hilliness meant if I wanted to actually ride my PX-10 it was going to have to be a resto-mod.

It's not 120 unless someone has messed up the spacing on the rear wheel.

Exactly. I would guess an 83 is spaced at 128. I'm using a 10 speed, 130 spaced cassette hub in mine and it just slides right in.

My goal is just to get this bike up-and-running, as economically as possible. I _did_ splurge on the Cyclone derailleur. But having, for instance, to build out a new rear-wheel would kill this project for me.


I wanted to replace the Regina freewheel because I had a heck of a time pulling it off, and I wasn't the first. The "tabs" that form the notches the removal tool fits into are chewed up; if I put it back on it might be for the last time. (And by the way, it's 13-15-18-21-24.)


I might have gotten overly ambitious, because I removed the axle and ball bearings from the rear hub (the hubs are Campagnolo) and after I was done I looked at it wondering how I'll ever get it reassembled. ;) I have not disassembled the front hub yet, and am thinking I might not.

you do want to overhaul the hubs, bottom bracket, and headset plus replace the consumables.

So... the Trek 720. An 83 would be first year with cantilever brakes and last year with the old school Trek styling.

The Sugino AT is one of the best, and best looking triple cranksets ever made. Check out Sheldon's database- https://www.sheldonbrown.com/bbsize.html.
I seem to remember it being 127- but there's other values in there. I've had several half step/granny crank sets but don't use them exactly in that context- but I will use the half step to find a more comfortable cruising gear- and only with 5 or 6 speed. I'm running 10 speed so my crank rings are 28-38-50. But I probably should be running a 48.

As mentioned- a 1983 Trek will not be spaced at 120- most likely 128 and you can use 126 and 130 with none of that "cold setting" nonsense- on top of it only being 2mm- it's 2mm with 47cm chainstays.

Yes you should be able to use a Cyclone GT (either first gen or MII) with 7 speed. The suntour barcons will work with that. I'd suggest getting real shift housing rather than the metal springy stuff it came with. I haven't used the old barcons with anything over 7 speed- you might have a bit of an accuracy problem at 9 and over. Again, half-step with 7 speed is dicey- someone can figure that out with a gear calculator.

Me, personally- if you're running the original DC960 brakes, I'd replace those with something cooler- XT M732, Deore MT62 or MT60 or XT MC-70- in that order.

I have a 1985 Trek 720- I've replaced most everything on it- but it's running a 10 speed triple. It's really a great great bike.

https://live.staticflickr.com/1740/2...32f42d0f_b.jpg1985 Trek 720 by Dave The Golden Boy, on Flickr

https://live.staticflickr.com/65535/...13909bc7_b.jpg85720Yard by Dave The Golden Boy, on Flickr

https://live.staticflickr.com/4646/2...28f7ddf0_b.jpgIMG_0616 by Dave The Golden Boy, on Flickr

https://live.staticflickr.com/4643/3...96ca1e65_b.jpgIMG_2402 by Dave The Golden Boy, on Flickr

https://live.staticflickr.com/4646/3...b177c0b7_b.jpgIMG_1728 by Dave The Golden Boy, on Flickr

https://live.staticflickr.com/4731/3...a59b967d_b.jpgIMG_1715 by Dave The Golden Boy, on Flickr

Beautiful 720

Thanks for all this info. Your 720 is lovely.
I had been wondering about that metal cable housing--I'd never seen it before. Lately I had been pondering how to clean it up, so I guess maybe I won't have to solve that.

Rear wheel / frame mismatch
 

It appears to me that the rear wheel I bought with the bike is for a 120mm setup, not the 128 that would be correct for this frame.
It's been so long now that I just don't remember if the wheels where on the bike when I bought it all, or not. Would the bike be rideable if you squeezed the rear triangle to hold that smaller-than-it-wants rear wheel?
:(

Thanks for any info--

So I guess the thing to do would be to find a replacement axle of the correct length, figure out what freewheel I want to use, and then redish the wheel to accommodate those changes?

You could also just pick up a 5 or 6 speed rear wheel with the 128 spacing that you need, they're pretty common.

I used CR18's on my '83 Trek 720 with no complaints.

https://www.treefortbikes.com/Qualit...MaAlweEALw_wcB


https://cimg8.ibsrv.net/gimg/bikefor...e3a8def81.jpeg
https://cimg9.ibsrv.net/gimg/bikefor...983effdf3.jpeg