[Gridds]

So, today you can buy some pretty decent dampers for mountain bikes. Units like the CCDB etc. which have fully independent high and low speed compression and high and low speed rebound...
These dampers are configured to work primarily in compression. This got me randomly thinking...

I ask this: Could one of these dampers be valved/re-valved such that if you were to remove the spring it would work as a 'pull' shock. i.e the usual rebound damping circuit becomes the 'compression' and the compression circuit becomes the 'rebound' meaning that at rest the damper is fully compressed and when fully worked the damper is fully extended. Or does the air/nitrogen pressure etc. mean that this cannot be done.
How would the shock body construction and internals hold up to this reverse loading configuration?

 

[w00dy]

I don't know the answer to that, but there is rebound damping already built in. You could play with the rates and use the shock to damp something in traction. Reversing the channels so you have high and low speed rebound would take some major modifications to the shock I imagine.

Pull shocks have been tried, though.

You might be able to get your hands on one of these. Plenty of those frames cracked and (as far as I know) no other frame uses this particular shock.

Edit: Rock shox made it, I remember that much.

 

[boogenman]

I had a Rock Shox pull shock on my Yeti back in the day, it was a turd.

 

[IH8Rice]

I had a Rock Shox pull shock on my Yeti back in the day, it was a turd.

as did i on my Schwinn (same bike as the Yeti)

it was poop, but yet still better than the other offerings at the time it seemed.

 

[Sandwich]

There's no reason something like that wouldn't work, since all a shock really does is move viscous oil through a controlled orifice to slow down the shaft and therefore spring. Think about an object in water, it moves the same backwards and forwards. I assume you would need to reverse the rebound and compression assemblies to retune them to their appropriate motions. Nitrogen or air is usually used as pressure to keep the shock oil at the same volume and prevent foaming...if it gets too hot, it will expand...the nitro takes up that space until the oil does....I think. Some modern shocks use that air for different purposes (bottom out/propedal, again I think), but the original use is still there. Shouldn't matter what direction the shock is moving.

The rockshox are a good example of this, it's the same damper methodology, but the shaft continues through the valving and out the other side, kind of like what you've thought of, only the spring is on the other end of the shock and not elsewhere on the bike. The internals are otherwise pretty similar.

 

[Gridds]

Yeah, I'm aware of previous incarnations of pull shocks. I was just wondering if the latest generations of decent dampers could be modified now that they have good damping for compression and rebound.

The shock on that old Yeti is also bloody huge! One of the reasons I'm asking about this is to maybe reduce the package size of the damping unit.

 

[iRider]

The Scott Genius is using a pull shock. Not downhill though.

 

[Udi]

Not sure if I'm stating the obvious here, but to use an ordinary shock as a pull-shock would require a complete or drastic redesign. The pull shock has the shaft coming out of both sides of the shock rather than just one.

Basically, revalving will be the least of your worries. If you mean building one from scratch on the other hand, then yeah, I'm sure it'd work fine, but not without compromises. Dual entries/exits for the shaft = twice the number of seals = lots of extra stiction to give you one example... a big reason why air shocks don't feel as nice as coils.

 

[Gridds]

Not sure if I'm stating the obvious here, but to use an ordinary shock as a pull-shock would require a complete or drastic redesign. The pull shock has the shaft coming out of both sides of the shock rather than just one.

Basically, revalving will be the least of your worries. If you mean building one from scratch on the other hand, then yeah, I'm sure it'd work fine, but not without compromises. Dual entries/exits for the shaft = twice the number of seals = lots of extra stiction to give you one example... a big reason why air shocks don't feel as nice as coils.

Why would you need a shaft to have two entries/exits? Why could it not be made geometrically like a conventional compression damper, but just work in tension?

 

[Sandwich]

you would need a place for the spring, for one. I don't know if anybody has tried a "pull spring" that works in tension rather than compression. A leaf spring might be a novel idea.

 

[Gridds]

Yeah the spring would be elsewhere in the suspension/frame geometry.

 

[mtg]

Current dampers most definitely "work" in rebound as well as compression- they provide damping force in both directions. I think what you're referring to when you talk about the shock being "at rest" at full extension is the fact that there's an air spring inside of a damper, and the pressure of that air extends the shock.

The internal air spring is necessary to allow for oil displacement as the shock is compressed and the damper shaft takes up volume inside the damper. Without the air spring in a conventional damper, it would be hydro-locked and not move. As mentioned above, if you made a through-rod damper (like the Ohlins TTX40 that the Double Barrel is based on), you don't need an air spring inside the damper because the shaft volume inside is always constant.

Pull springs are possible and quite common- they even look very similar to compression coil springs. Leaf springs, depending on how they are used, tend to have a falling rate, which is probably why you don't see many of them.

 

[time-bomb]

Yeah the spring would be elsewhere in the suspension/frame geometry.

Scott did this years back but both units where push rather than pull. One unit was a spring and no damping and the other unit had no spring and controlled the rebound. I don't remember if there was a compression control or if it was just built into the damper. This was done around the same era as the Yeti/Schwinn pull shocks and GT Lobo. I don't recall why Scott decided to separate the shock into two different units though.

 

[Gridds]

Scott did this years back but both units where push rather than pull. One unit was a spring and no damping and the other unit had no spring and controlled the rebound. I don't remember if there was a compression control or if it was just built into the damper. This was done around the same era as the Yeti/Schwinn pull shocks and GT Lobo. I don't recall why Scott decided to separate the shock into two different units though.

I remember. In fact my brother actually had one of those double shock Scotts!

 

[Sandwich]

probably foar moar shimz

 

[time-bomb]

I remember. In fact my brother actually had one of those double shock Scotts!

Cool. Do you know what the rationale was behind separating them like that? (sorry to get off topic a bit).

Aside from moar shimz

 

[Gridds]

Cool. Do you know what the rationale was behind separating them like that? (sorry to get off topic a bit).

Not really, though it might have been something to do with one dealt with the normal stuff and one for big hucking hits... I think... (?)

Or actually, thinking about it it might have been one for compression damping and the other for rebound. I remember he took one of them out after the rocker link bust, and rode it, but the rebound damping was then pretty non existant so, yeah, probably this.

 

[Pslide]

To answer the original question...

I don't know much about shock internals, but going by the difference in shaft speeds between compression and rebound, you need very different valving / orifice sizes / shim-stacks. I'm pretty sure orifices are machined into the shock, I don't think you can just swap them if you wanted to make a pull shock. So IMHO, the answer is no...

 

[troy]

Turn the piston with shimstacks over so the rebound is on the compression side and compression on the rebound side . Set the IFP 1-2cm deep . Insert the shaft assembly . Push it all the way in . Fill it with oil . Suck out the air from ifp chamber to make underpressure . Install a pull spring, custom machined spring seats and some goooood seals . Maybe it will work.

 

[IH8Rice]

didnt i read somewhere that the Ancilotti is a pull shock design?

 

[time-bomb]

didnt i read somewhere that the Ancilotti is a pull shock design?

you would be correct.

 

[Steve M]

To answer the original question...

I don't know much about shock internals, but going by the difference in shaft speeds between compression and rebound, you need very different valving / orifice sizes / shim-stacks. I'm pretty sure orifices are machined into the shock, I don't think you can just swap them if you wanted to make a pull shock. So IMHO, the answer is no...

I think possibly with the CCDB you might be able to get pretty close by whipping out the compression and rebound assemblies and installing them into the opposite sides (if that's possible) but you still have the issue of the compression shim stack being on the wrong side of the piston. If it's easy enough to flip that around then it'd be possible.

Turn the piston with shimstacks over so the rebound is on the compression side and compression on the rebound side . Set the IFP 1-2cm deep . Insert the shaft assembly . Push it all the way in . Fill it with oil . Suck out the air from ifp chamber to make underpressure . Install a pull spring, custom machined spring seats and some goooood seals . Maybe it will work.

You would still need to have positive air pressure in the reservoir, not a vacuum. You would definitely need very good seals though - normally they don't actually see that much pressure in compression because there is a pressure drop over the piston, and the maximum pressure that can be generate in rebound is nowhere near as high as in compression, but if you reversed that so the entire compression stroke pressure was acting directly on the seals... you'd want good ones.

didnt i read somewhere that the Ancilotti is a pull shock design?

They're Italian and I think something is lost in translation compared to our normal vocabulary - the shock itself is a conventional push-shock, but the linkage relies on a dogbone link that's in tension, ie "pulling" the shock link to compress the shock rather than "pushing" the shock link to compress the shock.

 

[IH8Rice]

They're Italian and I think something is lost in translation compared to our normal vocabulary - the shock itself is a conventional push-shock, but the linkage relies on a dogbone link that's in tension, ie "pulling" the shock link to compress the shock rather than "pushing" the shock link to compress the shock.

kinda really misleading, but it could be the translation difference.

if it was sold in American, im sure someone would sue them over that

 

[Pslide]

kinda really misleading, but it could be the translation difference.

if it was sold in American, im sure someone would sue them over that

I would hope not.

They are a tiny family run Italian firm. There was a good article in Dirt about them. The suspension has roots in older moto designs. They're not trying to pull the wool over anyone's eyes.

 

[Pslide]

PS - And when you see it in person, it's blatantly obvious it's not a pull shock.

 

[time-bomb]

Must be lost in translation. Looking at their site it says pull shock all over the place and they aren't referring to the linkage in many cases. At a closer look at some photos it does become more obvious it is a push shock. However, in stock photos and with the shock being tucked away as it is, it is difficult to tell.

 

[IH8Rice]

I would hope not.

They are a tiny family run Italian firm. There was a good article in Dirt about them. The suspension has roots in older moto designs. They're not trying to pull the wool over anyone's eyes.

if they make no mention that the "pull shock" is actually a term for their linkage, than that would be false advertising. it even says pull shock on the swingarm

 

[troy]

You would still need to have positive air pressure in the reservoir, not a vacuum.

Why ? When You will compress the suspension , shock should extend, so there will be more space for oil (volume of the "missing" shaft/rod) -> ifp will go deeper in the chamber . Vacuum/underpressure should cause proper damping (like a minimum pressure in non modified shock). When You will add some air into the ifp chamber , You will lose some part of the travell or damping in the begining of stroke i think .

 

[mtg]

Why ? When You will compress the suspension , shock should extend, so there will be more space for oil (volume of the "missing" shaft/rod) -> ifp will go deeper in the chamber . Vacuum/underpressure should cause proper damping (like a minimum pressure in non modified shock). When You will add some air into the ifp chamber , You will lose some part of the travell or damping in the begining of stroke i think .

Low pressures in the damper increase the chances for cavitation

 

[Steve M]

Why ? When You will compress the suspension , shock should extend, so there will be more space for oil (volume of the "missing" shaft/rod) -> ifp will go deeper in the chamber . Vacuum/underpressure should cause proper damping (like a minimum pressure in non modified shock). When You will add some air into the ifp chamber , You will lose some part of the travell or damping in the begining of stroke i think .

Yeah but as soon as the shock rebounds, there'll be no pressure opposing oil flow = severe cavitation, no damping at all.

 

[Pslide]

if they make no mention that the "pull shock" is actually a term for their linkage, than that would be false advertising. it even says pull shock on the swingarm

Perhaps pull is a verb, not an adjective.

 

[IH8Rice]

Perhaps pull is a verb, not an adjective.

"pulling" a shock isnt a verb?

 

[dump]

Edit: Rock shox made it, I remember that much.

This looks different from the Rock Shox shock on my DH-8. Mine didn't have a separate reservoir. If I recall correctly, a few were made by Fox. Stikman would know.

Looks great in that color combo though!

 

[Sandwich]

there were two different versions...the original straight 8 had a bassboat paint scheme and the no-resi super deluxe. The next year dropped bassboat and added the DKG linkage, which gave it a rising rate instead of straight, and the resi on the super deluxe, which I think became the pro deluxe.

You can tell the difference between frames by looking at the shock mount. On one, the front of the mount is curved, on the other, it's straight. I think the latter frames are curved, as above.

 

[IH8Rice]

This looks different from the Rock Shox shock on my DH-8. Mine didn't have a separate reservoir. If I recall correctly, a few were made by Fox. Stikman would know.

Looks great in that color combo though!

yep, my Straight 8 had no resi either

the newer ones had a straight front shock mount

 

[Pslide]

I'm just saying that everyone assumes "pull shock" to be the kind on an old Schwinn Straight 8, where pull is used as an adjective to describe what kind of shock is used.

But that's just a convention. "Pull shock" could mean a shock that is pulled, where pull is acting like a verb - as in a shock that is pulled by a linkage, which is what is going on with the Ancilotti. It's just that the pulling is coming from a different direction than most people think.

Sorry, this is a really lame conversation...my bad!

 

[xy9ine]

Yeah the spring would be elsewhere in the suspension/frame geometry.

that sounds tastily exotic. is this in conjunction w/ a gearbox configuration? i'm salivating already.

 

[time-bomb]

I'm just saying that everyone assumes "pull shock" to be the kind on an old Schwinn Straight 8, where pull is used as an adjective to describe what kind of shock is used.

But that's just a convention. "Pull shock" could mean a shock that is pulled, where pull is acting like a verb - as in a shock that is pulled by a linkage, which is what is going on with the Ancilotti. It's just that the pulling is coming from a different direction than most people think.

Sorry, this is a really lame conversation...my bad!

I know what you are saying. However, I think the shock is still being pushed in this case. It is the link that is being pulled to drive the shock through its compression. For example, Mountain Cycle 9.5, Superco Silencer, and many others have a linkage system that is pulled by the swing arm and drives the push shock. That seems to be the case with this frame too.

 

[Gridds]

Thanks all, but I really don't need to know about ancient pull shocks and erroneous naming conventions.

I just want to know if any modern compression shocks can be converted in to a tension/pull shock. Other than flipping the compression and rebound shim stacks to work the other way round, what else would be needed and/or why would this not work?

 

[Sandwich]

that sounds tastily exotic. is this in conjunction w/ a gearbox configuration? i'm salivating already.