Vintage Mountain Bike Disc Brake Conversion

This bike got a Readers Ride feature in the Radavist! https://theradavist.com/vintage-mtb-disc-brake-conversion/

This is my 1993 Specialized Rockhopper that I converted into a 650b disc brake do-it-all bike. I've always had an affinity for 90's era Rockhoppers with their steel frames, clean lines, comfortable geometry and cheap price tags. And I've always wanted to weld some disc mounts onto one - because the factory cantilever brakes leave something to be desired, but also because it's an outlet to do engineering things and fab things and bike things all at the same time, and that's pretty fun.

I designed the disc adapters in CAD after modeling the fork, frame tubes, and wheels as best I could with calipers and a tape measure. I used printed plastic prototypes of the adapters with the brake calipers mocked up on the bike to dial the design in and to build confidence that it could work. In the end, the solution features a flat mild steel adapter for the fork and frame (welded) and a flat aluminum adapter for the caliper (bolted). The aluminum adapter plate is drilled and countersunk from the bottom such that the caliper mounting bolts are invisible when installed; these bolt heads rest flush against the steel plate. Outboard bolts then join the aluminum plate to the steel plate via thru-holes and tapped holes, respectively, such that the caliper and adapter plate subassembly gets installed onto the welded plates on the bike. The design is common for both the front and rear brakes. I stripped the paint with sandpaper and used my MIG welder to join the adapters (cut on a laser) to the bike. Automotive wheel paint and clearcoat were used for the finishing touches.

A modern 1x gravel drivetrain with drop bars and an internal dropper post were installed to complete the transformation. The dropper post was a real struggle to figure out since I'm using Rival road brifters with a OneUp post - both of which take the cable head of the shift cable; requiring the use of a set-screw cable clamp or "knarp" on the non-cable-head end. It was a lot of trial and error of fishing the cable through the housing, frame stops, and seat tube to get the cable length exactly correct for my saddle height. The margin of error on this is equivalent to 1/2 the total adjustment of an inline barrel adjuster. I drilled a hole in the frame above the bottom bracket for the cable exit from the seat tube, which then routes externally through the front shift cable path up to the brifter (since that path is vacant with the 1x drivetrain).

The bike is incredibly versatile and is the one I reach for most. Commuting to work, gravel rides, singletrack, bikepacking, grocery shopping, this thing can do it all!

Build Spec:
Frame and Fork: 1993ish Specialized Rockhopper Sport (19" CTC)
Disc Adapters: Custom!
Brakes: SRAM Rival Hydraulic
Wheelset: Hunt/Mason 650b Adventure Disc QR
Tires: Rene Herse Umtanum Ridge 55's or Conti Terra Speed 40's
Cranks: Truvativ Stylo 172.5
BB: SRAM DUB BSA 73mm
Chainring: 32T, 36T and 40T options (but always 6mm non-boost offset chainline)
Cassette: Velo Orange 11-46T 11spd
Derailleur: SRAM Rival 11spd
Bars: Salsa Woodchipper 460mm
Stem: Nitto x Crust UI Quill 60mm 15deg

Dropper Post: OneUp V2 Internal 27.2 x 120mm travel

Saddle: Brooks C15 Carved

Frame Bags (usually): Field & Forest Custom Half Bags

Rear Rack (sometimes): Tumbleweed T Rack (355mm)

Front Rack (sometimes): Sunlite eBay special with Wald 137 basket

Conversion Photos: