So a few of you would have read Udi's shimmed Boxxer thread, this is basically a similar thing, though instead it's a full TPC+ conversion rather than a home-made compression assembly. Basically the reason for doing this stems from a few issues with the stock Motion Control (Moco) damping. First of all and most importantly, the rebound damping is pretty crap - ported rebound means you have to run it quite fast for it to track well, which then makes it very fast in the top part of the stroke. The Moco LSC/floodgate adjustment provide a pretty useful compression damper in the sense that you can run tons of LSC without too much harshness, but there is another issue here - you can't fine tune properly because the range of adjustment is way too big for how far you're turning the LSC knob. Even with the blue ano knob removed (no detents) like I've had mine for ages, it's very hard to get the LSC bang on, because moving it even 1 degree substantially affects the amount of damping. On top of this, because of the way the Moco damper works, there is a bit of a "dead zone" before the damping kicks in, for better or for worse. And last but not least, you can't tune the high speed curve at all, only its blow-off threshold in the form of the floodgate. TPC+ solves all of those problems.
I've had shimmed rebound running in the Boxxer (first using my own piston, later using a Manitou one) for about 6 months or so now, only recently did I get around to completing the compression assembly to match. It's in a workable form right now but the shim stacks in the compression assembly need tuning because frankly they're way too light (and I'd already added a few shims from the stock setup, the original setup must have had between zero and f**k all damping).
This conversion is made possible because of a lot of similarities between the RS and Manitou gear (at least from the TPC+ Sherman I ripped my spares out of). The general layout of the damper is obviously the same, and the rebound assemblies are very similar. The rebound pistons share the same ID, as do the check valve shims, and all 3 of the Manitou pistons in the TPC+ damper are actually the same as far as I can see, which is handy if you're pilfering spares. The OD of the Manitou pistons with glide rings is a bit bigger than the RS stuff, which indicates thicker stanchions in the Boxxer than the Sherman (as both have a 32mm OD).
The rebound assembly was made by modifying a plastic Manitou TPC+ rebound piston. This involves taking off the axial flange on the ID, and countersinking the hole a bit because the piston height is a bit bigger than the RS one - the countersinking allows it to sit down a bit further on the rebound shaft, which means you get more thread insertion on the locknut. This is necessary (as is loctite!) because, as I found out during my race run on the weekend, the nut holding it all together can come off pretty easily otherwise. Doing 2/3rds of a race run with no rebound damping and some hardcore topout is not cool at all (anyone who was watching at Eildon probably saw/heard this!), so if you decide to make yourself one of the rebound pistons like this, do it all properly. I also filed the faces down so the total thickness was 8.0mm instead of the original 8.4 or so, and used the Manitou locknut because the RS one is pretty silly. The rebound piston OD is also turned down to 25.20mm (I think the stanchion ID is probably 25.4mm ie 1" but I haven't been able to measure it accurately) and run without a glide ring or o-rings - this is because it's nylon and acts as its own lubricated glide ring anyway. You can probably go for a slightly tighter tolerance (maybe as high as 25.30mm) but the 25.20mm works well regardless. For reference, the OD of a Rockshox rebound piston incl glide ring was, as best as I could measure, 25.18mm. The glide ring also has a split in it which allows some oil through, so the tolerance isn't tight to begin with.
The compression assembly... now this was a bit of a bastard thing. Manitou, being Manitou, decided that it was a great idea to mix metric, imperial, and custom sized threads. Manitou top caps don't have the same thread as Boxxer ones, so I modified a Boxxer top cap and create a threaded insert for it, which was bonded in. Naturally, being Manitou, the thread for the main shaft to screw into the top cap wasn't a 12mm, nor was it a normal 1/2" UNF - it was a 1/2" by 24tpi which is not a recognised size, so it's obviously custom cut - you bastards Manitou. I then made up a brass extender for the assembly, that threaded into the topcap insert, because the stock TPC+ comp assembly was about 70mm shorter than the MoCo cart it was going to replace. This was then bonded to the outside of the original main shaft, I had to cut off the bit that threaded into the original top cap in order to do this. This meant that the internal adjuster needle was too short, so I cut down a length of 4mm allen key, cut up a super cheap 4mm socket head (you shouldn't be able to get through tool steel with a blunt hacksaw at all, let alone as quick as that - that's what you get when you buy a 40pc socket set for $7.20!) and bonded the length of 4mm hex rod to the original top cap adjuster rod. The top cap is sealed up with the same o-rings as the original one was, so hopefully there won't be any problems there.
Sooo... only put it together tonight. Quick test ride reveals that it's extremely smooth but lacking low speed compression damping even with the LSC turned right in, so the shim stacks are too light. Predicted issues are mainly to do with sealing and initial contamination of oil from whatever swarf and stuff wasn't completely cleaned out of the bits I made up.
Big thanks to my boss for spending way too much time helping me out with the machining, giving good practical advice, and letting me use his tools! Also many thanks to Udi for kicking me up the arse enough times to actually get the thing done, cos I just kept putting it off for months on end. All told, this should be more or less the ultimate DH fork once it's dialled in, especially once I get an air leg for it - lightweight, smooth, and well damped.
I've had shimmed rebound running in the Boxxer (first using my own piston, later using a Manitou one) for about 6 months or so now, only recently did I get around to completing the compression assembly to match. It's in a workable form right now but the shim stacks in the compression assembly need tuning because frankly they're way too light (and I'd already added a few shims from the stock setup, the original setup must have had between zero and f**k all damping).
This conversion is made possible because of a lot of similarities between the RS and Manitou gear (at least from the TPC+ Sherman I ripped my spares out of). The general layout of the damper is obviously the same, and the rebound assemblies are very similar. The rebound pistons share the same ID, as do the check valve shims, and all 3 of the Manitou pistons in the TPC+ damper are actually the same as far as I can see, which is handy if you're pilfering spares. The OD of the Manitou pistons with glide rings is a bit bigger than the RS stuff, which indicates thicker stanchions in the Boxxer than the Sherman (as both have a 32mm OD).
The rebound assembly was made by modifying a plastic Manitou TPC+ rebound piston. This involves taking off the axial flange on the ID, and countersinking the hole a bit because the piston height is a bit bigger than the RS one - the countersinking allows it to sit down a bit further on the rebound shaft, which means you get more thread insertion on the locknut. This is necessary (as is loctite!) because, as I found out during my race run on the weekend, the nut holding it all together can come off pretty easily otherwise. Doing 2/3rds of a race run with no rebound damping and some hardcore topout is not cool at all (anyone who was watching at Eildon probably saw/heard this!), so if you decide to make yourself one of the rebound pistons like this, do it all properly. I also filed the faces down so the total thickness was 8.0mm instead of the original 8.4 or so, and used the Manitou locknut because the RS one is pretty silly. The rebound piston OD is also turned down to 25.20mm (I think the stanchion ID is probably 25.4mm ie 1" but I haven't been able to measure it accurately) and run without a glide ring or o-rings - this is because it's nylon and acts as its own lubricated glide ring anyway. You can probably go for a slightly tighter tolerance (maybe as high as 25.30mm) but the 25.20mm works well regardless. For reference, the OD of a Rockshox rebound piston incl glide ring was, as best as I could measure, 25.18mm. The glide ring also has a split in it which allows some oil through, so the tolerance isn't tight to begin with.
The compression assembly... now this was a bit of a bastard thing. Manitou, being Manitou, decided that it was a great idea to mix metric, imperial, and custom sized threads. Manitou top caps don't have the same thread as Boxxer ones, so I modified a Boxxer top cap and create a threaded insert for it, which was bonded in. Naturally, being Manitou, the thread for the main shaft to screw into the top cap wasn't a 12mm, nor was it a normal 1/2" UNF - it was a 1/2" by 24tpi which is not a recognised size, so it's obviously custom cut - you bastards Manitou. I then made up a brass extender for the assembly, that threaded into the topcap insert, because the stock TPC+ comp assembly was about 70mm shorter than the MoCo cart it was going to replace. This was then bonded to the outside of the original main shaft, I had to cut off the bit that threaded into the original top cap in order to do this. This meant that the internal adjuster needle was too short, so I cut down a length of 4mm allen key, cut up a super cheap 4mm socket head (you shouldn't be able to get through tool steel with a blunt hacksaw at all, let alone as quick as that - that's what you get when you buy a 40pc socket set for $7.20!) and bonded the length of 4mm hex rod to the original top cap adjuster rod. The top cap is sealed up with the same o-rings as the original one was, so hopefully there won't be any problems there.
Sooo... only put it together tonight. Quick test ride reveals that it's extremely smooth but lacking low speed compression damping even with the LSC turned right in, so the shim stacks are too light. Predicted issues are mainly to do with sealing and initial contamination of oil from whatever swarf and stuff wasn't completely cleaned out of the bits I made up.
Big thanks to my boss for spending way too much time helping me out with the machining, giving good practical advice, and letting me use his tools! Also many thanks to Udi for kicking me up the arse enough times to actually get the thing done, cos I just kept putting it off for months on end. All told, this should be more or less the ultimate DH fork once it's dialled in, especially once I get an air leg for it - lightweight, smooth, and well damped.
Attachments
Last edited:
I guess I'll have to stick with stock products
