1965 Matchless G15-CS

teazer

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Admittedly old forks are a little on the skinny side to try to ram a modern cartridge down inside, but how small are those legs on the ID? if they are more than say 25mm ID, then a 20mm cartridge could be made to fit - straight out of mant modern forks. I'm thinking early GSXR which are cheap or maybe early R6 Yamaha etc.
 

AgentX

Member
Admittedly old forks are a little on the skinny side to try to ram a modern cartridge down inside, but how small are those legs on the ID? if they are more than say 25mm ID, then a 20mm cartridge could be made to fit - straight out of mant modern forks. I'm thinking early GSXR which are cheap or maybe early R6 Yamaha etc.
There's lots of room inside; this variant of the roadholder has external springs, so the stanchion is only accommodating the damper tube, which is pretty bulky itself. I think it would be easy to fit a modern cart diameter in there.

The stock fork uses, or is supposed to use, the flared base (heh) of the stock damper tube as a hydraulic bump stop, so something would need to be done to replace that. Holes in the stanchion provide the top-out stop (after this mod anyhow) so that likely would not change.
 

teazer

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Tapered hydraulic bump stop is common in damper rod designs, but not so common in cartridge forks.
 

AgentX

Member
For a less-involved conversion, I have considered making a dummy pumping rod out of a Roadholder damper (different kind than my rare G15-CS ones) to put a Racetech gold valve atop...

1) elimination of the shuttle valve and damper rod entirely

2) modification of the stock damper tube to a dummy pumping rod with cupped top to support the gold valve and pass oil freely to the valve

3) use of your recommended internal spring at the appropriate length to accommodate the height of the combined emulator and pumping rod, plus a preload spacer as needed.

I would expect the hydraulic bump stop arrangements at top and bottom to of the stroke to continue to function (given that they’re already appropriately modified from the useless stock versions, anyhow), but I also see the possibility of incorporating a top-out spring under the “pumping rod” cup.

Do you think it could work? I assume it’d be best to have the same system in both legs?

I wrote to Racetech, but closed for the holidays so just musing here.
 
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teazer

Active Member
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Without checking all the components and design of your fork, I can't be certain, but to change to a conventional damper dor design with a gold valve emulator sounds like a smart and cost effective solution.

Triunph tried shuttle valves on some of their unit twins (think T100 Daytona) and that was similar to the designs used for years on CB72,350 etc. It's a crude system but worked as well as most things back when it was harder to hold tolerances and oil was way thicker than we use today.

I checked out that site you linked to and they have to use a special bottom screw to embody the lower needle valve and that goes back to the designs of say Suzuki GS1100 with variable damping.

I like your idea and instead of modifying the damper rod, it might be possible to use a pair out of a cheap pair of say Goldwing forks or something similar. That way it would be really easy to add a top out spring under the damper rod top and they come with bottom out cones. In fact I have a pair of goldwing fork legs here that I was just going to put on ebay that you can have to $25 plus shipping if that would work for you.

If you removed the shuttle valves, could you replace them with say a solid sleeve with teflon bushes and kill two birds with one proverbial stone?

Savor (Chris Livengood) www.chrislivengood.net is more of an expert on suspension than I am and may be able to add something to the discussion.
 

AgentX

Member
All very interesting...

I think the best rod to use would be the stock Roadholder rod, since it situates perfectly in the tube already and should be an appropriate length...shouldn't be hard to put a cupped cap on them, and a top-out spring, if needed, would be easily retained between that cup and the retaining nut on the bottom of the stanchion.

The right height for the rod cup would be essential, given the possibility of interference between the underside of the rod cup and the stanchion bottom nut. The stock arrangement fits completely through the hole, so that's not an issue...I really don't know how everything sits at rest and at full compression, but could start measuring to see...

I'm not sure I follow you on replacing the shuttle valve. What would the purpose be, and how would it allow the valve emulator to sit where it needs to? The normal shuttle valve damper rod is a main reason you can't put a valve emulator in.

Edit: also, with the goldwing forks, is the bottom-out cone you mention a hydraulic function, or is it a physical bumper as on a rear shock?
 
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teazer

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If the shuttle valve is on the bottom of the staunchion, the oil holes could be blocked off if changing to a damper rod design but it would still need to be valved for compression damping.

Goldwing forks use a "normal" tapered cone hydraulic bottom out.

BTW, what is the OD of your fork staunchions? You might be able to swap in a pair of other staunchions (legs) if there's enough meat to cut a top taper or enough in the top triples to cut a parallel hole with clamping bolt.

So many possibilities. The best is probably a modern cartridge from a cheap set of GSXR etc forks, followed by a complete damper rod re-design with emulators.
 

AgentX

Member
Internet says 1.357 to 1.359"; am away from the bike right now. Doing a taper on top of something else is the kind of thing I think I need to stay away from...the cost and trouble, lacking a buddy to do such work, will likely exceed just buying the kit from Cosentino (though that kid is likely to need modification to fit my G15-CS longer stanchion tubes, as well...)

Also not gonna be a way to cut the top yoke into a clamp arrangment...that'd end up needing custom triples, too.
 

teazer

Active Member
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That's 34.4mm in new currency. So RD350/400 legs might work with some modification but without access to a machine shop, a drop in kit would probably work best.
 

teazer

Active Member
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If your forks have more travel that regular Roadholders, the damper tube may need to be longer. if travel was the same but legs are longer for more clearance, they may need special recessed top caps - depends on how different they are. Those Lansdowne dampers look nice and appear to have rebound damping in one leg and compression in teh other which obviates the need for an adjuster at the bottom of both fork sliders. That in and of itself makes them preferable as long as you have a decent fork brace to spread load between both sides.
 

AgentX

Member
Dude's interested in possibly making me a longer damper unit to match my longer stanchions. His Commando damper already gives 25mm more travel than stock, which should be fine for my bike.
 

AgentX

Member
Of course, now I don't have the stock damper to take a measurement for the guy who makes the cartridge dampers, lol. Got a call out for info on Access Norton, but even then, these things aren't exactly super-common. Hoping an Italian guy in the middle of a G15 build has easy access to the parts to tape them for me. I've been nice and helpful to him on a few things so......
 
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