Adding compression adjustment to the OEM Showa shock
I'd recently had my YZ forks revalved, shortened etc. by an MX suspension specialist and mentioned to him that I was going to buy a new rear shock. He offered to rebuild mine and commented that as it already had rebound adjustment, remote preload and remote reservoir, the only thing it lacked was compression adjustment.
After much scouring of ebay for a suitable remote reservoir I took a punt on a CBR600 shock which I managed to steal for £15 delivered. No great shakes if it didn't work out.
This is what arrived in the post.
Doesn't look great but the important thing is the remote reservoir is a Showa unit with a compression adjuster. It looked to be the same size as the BMW one. I was also lucky enough to be given a thirty thousand mile Dakar shock to try it out on. I took it all over to his workshop and we degassed them and took the reservoirs apart.
The Dakar one has a schrader valve to enable it to be regassed. The CBR one didn't so we ended up only needing the top part of the CBR reservoir. It originally had the bladder acting as the seal whereas the BMW one has the bladder at the other end. We found a suitable new O ring and reassembled.
Schrader valve on the BMW reservoir.
This is what's left over apart from the CBR shock. BMW top, CBR body and CBR base.
The hose connection was slightly different between the 2 reservoirs. To make things as simple as possible we used 3 Dowty washer to take up the longer thread of the Dakar hose. As yet this is untested on the bike but it's held perfectly so far. If it does fail then I'll get a new hose made up.
Once it was oiled and gassed up and we knew it had held it was time to sort the Dakar shock.
I had it rebuilt with new seals etc. I also had the shim stack redone to take in to account the compression adjustment on the reservoir and my riding.
Rebuilt and ready to go on the bike.
Hope this is useful information for others but bear in mind that if you're going to add the adjustable compression then you'll also need to get the shock revalved to make the most of it. The suspension chap I used spent a lot of time designing the new shim stack so I'm not going to publish it here. If anyone wants it done, I can thoroughly recommend Kevin Bancroft of KB Racing in Malvern, Worcestershire, tel 01684 568555. He doesn't really do the internet so call and leave him a message.
Thanks Dansin, all great info.
Just to add the info you pm'd me. 5wt Oil, and 150psi nitrogen charge?
I've managed to get a reservoir from a older piggyback showa shock ( type with dual shocks on a bike ). Same outside dimensions and bladder size, but attachment to the shock body is different. However uses a standard banjo bolt, so could concievably be conected to our shock with a pipe with banjos at each end. photo 1.jpgphoto 4.jpg
However the bladder (and end cap with valve ) should be a direct fit to our reservoir so will be a spare in case mine is damaged.
Racetech Suspension in the US does list replacement bladders, seals and bushes for our shocks. However they've not yet replied to my emails so I haven't ordered yet. I'll add some photos of the seal body, and stock piston and valve stack when I get the spares and replace the seals.