Metal bikes. They just hit different. Even those older 1990s metal full suspensions can be repurposed with a bit of love as Harrison exhibits in this week’s Readers’ Rides with his 1996 Specialized Ground Control…

Hey y’all! I’ve got a fun one for you!

So, a couple of years ago, I went down to the Cola Town Bike Collective to look for a couple of wheels for my grocery-getter (it’s an old Hardrock, in case you’re wondering); that I found a pair of old 26” wheels at a bike co-op is unremarkable, but where they were is the good part: attached to the bottom of a trashed 1996 Specialized Ground Control.

I remember seeing these things in my LBS as a ‘90s shop rat, and there was something way cool about the straightforward look of the rear suspension design. To me, then, they seemed almost exotic in their visual simplicity, like a Euro-market/alternative reality version of an FS design (ironically, the actual Euro version looked like a GT LTS, if memory serves). It was decided that the clapped-out remains of the Ground Control, its blown proprietary rear shock and the stuck-down Quad 21 with its sludged elastomers but still-on-point graphics would remain attached to the wheels I was there to purchase, and so began this project.

I’ve serviced a few forks over the years, and while it’s hardly a comprehensive list, I think it’s safe to say 3.5” drywall screws aren’t in the manuals for any of those forks or any others on the market. They are, however, the best tool I have for removing elastomers that have turned to Jolly Ranchers. The elastomers in these things are arranged in stacks, so the removal procedure was to drill into each piece one by one and pop out or break off whatever the screw bit into or broke. Eventually, most of it came out, though small sticky crumbs that fell into nooks and crannies worked their way loose during subsequent shakedowns and caused the fork to perform like the piece of trash that, to someone, it literally was. Ultimately the fork required at least four teardowns, though IYKYK a complete overhaul of a Quad 21 can be done in less than 20 mins once the elastomers are sorted. This has a spring kit (undamped!) in it now, which amazingly can still be purchased new on eBay.

The front shock was gross, sure, but the rear was the hard one to figure out. I figured somewhere out there in all of the vastness of cyberspace, maybe not even in the top 5 Google hits, would be the information I needed to rebuild this thing. I mean, it’s a Specialized, right?

Well, if someone out there knows, then they’re not manning the proverbial phones at Specialized, who “do not have any documentation on repair or upkeep of shocks or bikes from the 90’s” (which was a while ago, I guess) and suggested Pinkbike, where threads pointed to Retrobike, where threads tend to fizzle when someone asks for specifics. My crew at my local Specialized dealer were amused and enthusiastic but equally clueless about the shock (again, understandably so) and referred me to Risse.

Amazingly, they still sell a replacement unit for this but were less than forthcoming with advice about repairing the factory unit. Also understandable. RST (who made the shock) Europe suggested contacting their Asian branch where the unit would have been manufactured, which was another dead end. Operating under the assumption that although the chassis, damper, and metal bits were probably proprietary, the consumables (seals and rings) probably weren’t, I figured it was time to pop this thing open, measure some stuff, and produce this unfindable TSB. I’m working on saving a species here!

This brings us to this diagram. Basically, this thing’s just a basic monotube shock: gas on the bottom, oil on the top, spring on the outside. The pressurized chamber probably might contribute something to the suspension feel and tuning, sure, but really, in this thing, it just needs to keep the damping fluid in the right place: at the top of the shock. If the seal on the free piston fails, there’s no damping at the top of the stroke, and the system alternates between undamped clatter and hydrolock. The same happens when the “valve” at the bottom of the shock, which is just a rubber bung plug, fails, and the free piston is stuck down.

So, anyway, how about that rebuild procedure (a genuine scoop!):

1. Undo the hex bolts to remove the shock from the bike. Fun fact: studies show that this setup was a Horst Leitner creation, so I looked for hints in old AMP manuals. The manual for the Mongoose Amplifier notes that riders can adjust the geometry of the bike by partially sliding the shock out of the collar if they want to make the head angle steeper (!)
2. Unload the spring and remove it.
3. If replacing the head seal (you probably are), the top shock mount will need to be removed so that the seal can slide off the shaft. Clamp the shaft in a shaft clamp (you can make one by drilling a hole in a piece of wood, cutting the piece of wood down the center of the hole, and then using a bench vise with your new semicircular-notched blocks around the shaft. Then you can unscrew all that stuff at the top.
4. Use a pin spanner or a small strap wrench to unto the top cap. I use a strap wrench, though this will ruin the sweet Specialized x RST sticker on the cap.
5. Pull out the guts. The head seal is a 10 x 20 x 9.5mm type TC4 shaft seal. This is a standard thing. Good luck finding it locally if you’re in the states (I am!), but the internet’s got ‘em.
6. The seal on the damping assembly/piston valve is, well, I’m not sure. But I measure it at 19.6mm OD x 1.5mm thick. I’m not sure how much it matters, though, because if this one’s not working right then, as far as I can tell, it’s just going to shift the damping to the faster end of the turtle-bunny spectrum. It’s paired with an undamped fork on the front anyway; mine might be blown, but it feels consistent.
7. The seal on the free piston, at least mine, measured at not-quite 14.8mm ID x 2.4mm thick. This one’s really important. It’s kind of hard to consistently measure an old O-ring, and they change size as they absorb oil and wear. These numbers, though, correspond to a size that you can order from McMaster Carr, and mine’s held up for a season. However, I have a hunch that, based on the square-profile channel on the free piston, the original design intent might have been for something like a square TetraSeal, which our aforementioned pal Horst used in his AMP bikes that preceded this. Maybe one day I’ll make a free piston where this channel’s a bit wider so I can fit some backup rings and an x-seal on there…
8. If you haven’t already removed that mysterious hex bolt on the bottom of the shock, then do it now. Then slide the free piston and the piston valve into the shock. Push them down until they bottom out (if your new seals are good then this won’t be possible with that plug on the bottom screwed in: it plugs the hole for the air chamber at the bottom of the shock.
9. Once everything’s down there at the very bottom, you can replace that screw with the bung plug through it. Then fill the shock with damping fluid until it reaches the seat for the top seal (the 10×20.9.5 TC4). I use the lightest damping fluid I can find, which is from a dusty bottle of Push 3 weight my LBS keeps on the way back.
10. Charge time! That rubber plug at the bottom is for a charging needle, which is basically a hypodermic needle with a Schrader valve on the bottom of it. They’re easy to find online. Recommended pressure? Beats me. I just pump it up until there’s enough pressure down there so that the shock can extend without the spring attached. If your plug is dry-rotted like mine, then a piece of 3/8” buna-N cord will do just fine. Pro tip: if you make a replacement cord and it’s a little too stiff to self-seal the hole from the needle, then inflate it with the plug/screw assembly partially unscrewed. Tighten it up after you pull the needle out, and it’ll crush the plug (assuming you made it long enough) and seal the hole.
11. Put everything back together, get out there, and shred (lightly, of course). You weren’t expecting a sag figure, were you?

So there you have it! A proper tech tip! The most exclusive manual and diagram on the whole internet, maybe! And did I mention it’s a single-speed now?

I remember there was an old episode of The Simpsons where one of Marge’s sisters said something like, “This was originally a Halloween costume, but it found its way into my regular rotation.” That’s how this turned out, too. Schedules get tight, local trails start feeling a little too familiar, and something needs to make the whole scene a ‘lil more peppery. This bike does the job. In fact, I’ve found myself grabbing this bike more than any other over the past year, and it’s not just because I don’t have a spot for it in the workshop and it’s in the way of all the other bikes, though that might be part of it. Sometimes, things don’t need to be really good to be really great, and this bike is one of those things. The treasure:trash ratio of this thing is indeterminable; that it still rips is undisputed.

Build Spec:

• Frame: 1996 Specialized Ground Control (Aluminum front triangle, steel rear triangle)
• Fork: RockShox Quad 21 R w/ Kronos spring kit
• Shock: Specialized x RST (w/ special guest appearance by McMaster-Carr)
• Wheels: Velocity Atlas 36h x Velocity hubs
• Tires: WTB Velociraptors. Old ones.
• Cockpit: OE Specialized stem, Nitto B814 bar, Dia-Compe grip shift levers matched to Oury high-flanges.
• Pedals: Sometimes old Specialized clipless, sometime Shimano XT flip flops.
• Drivetrain: Surly x Surly x those ‘90s Specialized cranks. You know the ones. And a Paul Melvin.
• Brakes: Alivio and LX cantis with Kool Stop (because this thing actually gets ridden) pads.

Best,

Harrison Floyd
@harrison.floyd on IG