Resurrecting a Vintage Trek 3700: Budget 1x Conversion & Restomod
- Jace
- Jun 30
- 3 min read
What started as a simple, bare-minimum flip quickly turned into a massive mechanical headache.
I pulled this vintage Trek 3700 out of the back patio with a clear mission: get it up and running as a bulletproof campus commuter for the Bicycle Rescue initiative. The goal was simple: strip off the unnecessary weight, give it a clean 1x drivetrain conversion, and get it into the hands of a local student.
But old bikes have a funny way of fighting back. From a waterlogged suspension fork to a drivetrain gremlin that almost ruined the trail test, this build made me earn every single pedal stroke.
Here is exactly how this budget restomod came together, the parts I used, and the massive mechanical mistakes to avoid on your next vintage MTB build.
The Setback: A Dead RST Suspension Fork
When I first got this bike, it had been sitting out in the rain. I suspected the water had seeped in, and I was right. The original RST 191 fork was completely dead. The internal elastomers had either dry-rotted or turned to mush, locking the fork up entirely.
I refused to let the project stall out. After aggressively scouring local listings, I managed to score a massive upgrade: a RockShox Judy (and an old GT Outpost) for just $30. After swapping the crown race and cleaning up the headset cups, the front end of the Trek was completely transformed, giving it a much more aggressive, classic stance.
The Budget 1x Drivetrain Setup
To make this a reliable commuter, I wanted to ditch the clunky front derailleur. Thanks to a backpack full of parts from a Costa Mesa swap meet and a free 32T FSA Grid crankset from my buddy Nigel, the 1x conversion was on.
Here is the drivetrain setup that brought this 26er back to life:
Front Crankset: FSA Grid with a 32T chainring.
Rear Gears: Shimano 7-Speed Freewheel (swapped down from a massive 14-34T MegaDrive).
Chain: Shimano CN-HG40.
Everything shifted beautifully on the repair stand. But the real test happens on the dirt.
The Trail Test: Diagnosing a Violent Chain Slip
I took the Trek out to the Fullerton Loop for a shakedown ride. The bike flew up the climbs, and the 16-inch frame geometry felt phenomenal. But on the high gears (the smallest cogs), the chain violently slipped under heavy pedaling.
At first, I thought the rear derailleur's B-Tension screw needed adjusting because of the new, smaller freewheel. Then, I checked the index limiters. But the culprit turned out to be a classic DIY mechanic trap: a mismatched master link.
How to Fix a Stiff Master Link on a 7-Speed Chain
I had used a 9-speed master link on a Shimano CN-HG40 chain. Here is why that causes a massive issue:
A 6/7/8-speed chain has an outer width of 7.1mm.
A 9-speed master link has an internal pin width of 6.6mm.
When I squeezed that 9-speed link onto the chain, the pins were literally too short. It clamped the plates together like a bench vise, creating a rigid "stiff link" that physically could not bend around the tiny cogs of the freewheel. The fix? Swapping in the correct 7.1mm (6/7/8-speed) master link. The stiffness instantly vanished, and the slipping stopped completely.
A Costly Reminder: Torque Your Crank Bolts!
Just when I thought the gremlins were defeated, the trail claimed one more victim. During the shakedown, I noticed the crank arm wobbling back and forth.
The FSA QR-20 Self-Extracting Crank Bolt had completely vibrated out and vanished into the dirt. Crankset bolts require a massive amount of torque (usually 40–50 Nm) to stay seated. Because I used a parts-bin crankset without fresh blue threadlocker, the trail chatter backed it right out.
Pro Tip: Always apply blue Loctite to your crank bolts and use a proper torque wrench or a long cheater bar. Under-torquing these will strip your aluminum splines and ruin your entire crankset!
The Final Verdict
Despite the hurdles, the Trek 3700 is officially dialed in, bulletproof, and ready for its new life. You might notice I didn't talk much about the tires I went with for the build. It's because I am testing some top-secret rubber.
Watch the full build video above to see the mechanical troubleshooting in action, and make sure you subscribe to the channel so you don't miss the dedicated tire review video!
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