On a short ride this week, I noticed a pretty serious rebound issue on my Penske 8900 shock, and ultimately found that the rebound adjuster had backed itself completely out when I had some time to stop and check it. When I attempted to adjust it back in, I ended up with no detents until it was all the way tight.
This is a shock that KFG Racing "rebuilt" last year, with less than 10,000 miles on it since, so I decided to go in a different direction to look into the issue: I enlisted the assistance of Escapefjrtist.
To get to the rebound mechanism, we started by disassembling the shock as far as you would normally go for a rebuild. We noted a fair amount of rusty crud in the shock, as well as a very worn out bushing. We ultimately discovered that the dowel pin that sits below the rebound needle/metering rod was broken in half and needed to be replaced. If you get into this pickle, here are some photos and notes to help you deal with the problem (there's nothing in the manual, and nothing on the internet that we could find until now).
These parts will all look pretty familiar once the shock is opened up. The important points are that the spring retainer (brass disc with 3 holes) threads onto the shaft mount (brass piece at bottom of photo). One of its purposes is to limit the rotation of the rebound adjuster knob. To get the shaft mount off, loosen the jam nut first, then clamp the shaft carefully in a wood lined vise and hit it with an electric impact to back it off. Next, the knurled clear anodized rebound cap just sits on top of the red rebound adjuster knob with a tight press fit, and you can pop it off with your fingers or work it off with soft jawed pliers. With the cap off, you have access to the dowel (or what was left of it in my case) which rides against the detents of the adjustment knob and is held in place by the 150Psi of nitrogen in the reservoir.
Bused dowel pin. George had a stroke of genius and recommended replacing this with stainless steel, which we were able to obtain fairly easily from Metal Supermarkets. We noted that on some diagrams, this O-ring isn't shown, though I do see it on the current online PDF (page 6).
While we were at it, I removed the metering rod and needle to clean all the rusty gunk out of there. I do not recommend removing the circlip to gain access to the jet unless you have a replacement available (it's 1/4", tiny!). Replace the seal on the needle if you have it out.
It can also be inferred from this process that the O-rings that are present around the rebound adjuster knob aren't doing a whole heck of a lot more than keeping dirt and debris out of those threads and possibly providing some extra resistance to rotation, so if you don't have replacements, that's not a huge deal breaker.
Broken dowel pin penske 8900, broken pin, broken rebound
This is a shock that KFG Racing "rebuilt" last year, with less than 10,000 miles on it since, so I decided to go in a different direction to look into the issue: I enlisted the assistance of Escapefjrtist.
To get to the rebound mechanism, we started by disassembling the shock as far as you would normally go for a rebuild. We noted a fair amount of rusty crud in the shock, as well as a very worn out bushing. We ultimately discovered that the dowel pin that sits below the rebound needle/metering rod was broken in half and needed to be replaced. If you get into this pickle, here are some photos and notes to help you deal with the problem (there's nothing in the manual, and nothing on the internet that we could find until now).
These parts will all look pretty familiar once the shock is opened up. The important points are that the spring retainer (brass disc with 3 holes) threads onto the shaft mount (brass piece at bottom of photo). One of its purposes is to limit the rotation of the rebound adjuster knob. To get the shaft mount off, loosen the jam nut first, then clamp the shaft carefully in a wood lined vise and hit it with an electric impact to back it off. Next, the knurled clear anodized rebound cap just sits on top of the red rebound adjuster knob with a tight press fit, and you can pop it off with your fingers or work it off with soft jawed pliers. With the cap off, you have access to the dowel (or what was left of it in my case) which rides against the detents of the adjustment knob and is held in place by the 150Psi of nitrogen in the reservoir.
Bused dowel pin. George had a stroke of genius and recommended replacing this with stainless steel, which we were able to obtain fairly easily from Metal Supermarkets. We noted that on some diagrams, this O-ring isn't shown, though I do see it on the current online PDF (page 6).
It can also be inferred from this process that the O-rings that are present around the rebound adjuster knob aren't doing a whole heck of a lot more than keeping dirt and debris out of those threads and possibly providing some extra resistance to rotation, so if you don't have replacements, that's not a huge deal breaker.
Broken dowel pin penske 8900, broken pin, broken rebound
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