Shock(ing?) experience
Posted: Thu Dec 29, 2011 5:54 pm
Hey all,
I figured I'd pass on a bit of experience that I've had with my Penskes over the past couple of years of owning them. Take it as one data point in what should be a much larger sampling size, but here it is.
After finally spending the coin to get a set in '08, I discovered last year that my RF was locking down to full stiff constantly. If I "popped" it up with quick velocity it would "break loose" and go back close to where I felt it should be, but I couldn't get it to match the LF. I don't have a shock dyno, so I did this with the not-incredibly-accurate but very-hard-on-the-back method of lifting a wheel and letting it fall (I knew that there was minimal to zero difference in the rocker movement, which would be the only large variable). I figured this was probably not a problem on the track as the hard rolling of the car should have "popped" the shock out of full stiff, but after that weekend I decided I might as well get them rebuilt.
So I took the shocks out, marked them with a permanent marker at each corner, and sent them off to be rebuilt late in the summer of '10.
When I got them back, the marks were gone so I had no idea which one came off of which corner. No biggie, though I wanted to monitor that problem child.
So I slapped them on the car and ran them all season in 2011. The car never felt exactly "right" but I couldn't put my finger on it. It wasn't terrible, but it just felt like it took a bit more work than I thought it should. This season I went with a widly different setup (like almost 3 degrees difference in caster, significant ride height changes, etc.) just for fun so I just always blamed it on the setup or me getting used to something new. Then at the Runoffs I really felt like something odd was going on (if you haven't seen the video, you can on youtube - search for phantom9192, my username).
At TWS in November the car still didn't feel right so I decided to check the shocks. Lo and behold, the RR shock was locked down at full (or at least VERY) stiff. It could not be adjusted. Full soft setting yielded an identical rebound rate (low velocity, which is all I could "test") to full hard, and that rate was very similar to full hard (or 1-2 flats off) on the LR shock. I have no idea if it's the same shock I had the "full hard" problem with before, but I figured it was definitely worth replacing, so I did. The car was much more predictable afterwards. A full stiff RR shock would certainly explain some of the handling issues I felt at the Runoffs, and since we found it the next time the car was on the track, I have to assume it was part of the problem.
Moral of the story is this: no matter how recently you've had your Penskes rebuilt, if the car feels "off" and you can't pin down what it is, check the shocks. The way I did it was to run the spring perches down as low as I felt was safe (keep count!), disconnect the sway bar, then with the car jacked up, just raise the wheel to full bump and let it fall. You should be able to see a difference in droop timing with just a couple of flats adjustment. You can really only compare side to side between fronts or rears, but that's enough IMO to catch anything egregious.
Hope this helps someone else down the road!
Oh and "Shock(ing?)" wasn't meant to imply anything negative here... it was just a silly play on words.
Denny
I figured I'd pass on a bit of experience that I've had with my Penskes over the past couple of years of owning them. Take it as one data point in what should be a much larger sampling size, but here it is.
After finally spending the coin to get a set in '08, I discovered last year that my RF was locking down to full stiff constantly. If I "popped" it up with quick velocity it would "break loose" and go back close to where I felt it should be, but I couldn't get it to match the LF. I don't have a shock dyno, so I did this with the not-incredibly-accurate but very-hard-on-the-back method of lifting a wheel and letting it fall (I knew that there was minimal to zero difference in the rocker movement, which would be the only large variable). I figured this was probably not a problem on the track as the hard rolling of the car should have "popped" the shock out of full stiff, but after that weekend I decided I might as well get them rebuilt.
So I took the shocks out, marked them with a permanent marker at each corner, and sent them off to be rebuilt late in the summer of '10.
When I got them back, the marks were gone so I had no idea which one came off of which corner. No biggie, though I wanted to monitor that problem child.
So I slapped them on the car and ran them all season in 2011. The car never felt exactly "right" but I couldn't put my finger on it. It wasn't terrible, but it just felt like it took a bit more work than I thought it should. This season I went with a widly different setup (like almost 3 degrees difference in caster, significant ride height changes, etc.) just for fun so I just always blamed it on the setup or me getting used to something new. Then at the Runoffs I really felt like something odd was going on (if you haven't seen the video, you can on youtube - search for phantom9192, my username).
At TWS in November the car still didn't feel right so I decided to check the shocks. Lo and behold, the RR shock was locked down at full (or at least VERY) stiff. It could not be adjusted. Full soft setting yielded an identical rebound rate (low velocity, which is all I could "test") to full hard, and that rate was very similar to full hard (or 1-2 flats off) on the LR shock. I have no idea if it's the same shock I had the "full hard" problem with before, but I figured it was definitely worth replacing, so I did. The car was much more predictable afterwards. A full stiff RR shock would certainly explain some of the handling issues I felt at the Runoffs, and since we found it the next time the car was on the track, I have to assume it was part of the problem.
Moral of the story is this: no matter how recently you've had your Penskes rebuilt, if the car feels "off" and you can't pin down what it is, check the shocks. The way I did it was to run the spring perches down as low as I felt was safe (keep count!), disconnect the sway bar, then with the car jacked up, just raise the wheel to full bump and let it fall. You should be able to see a difference in droop timing with just a couple of flats adjustment. You can really only compare side to side between fronts or rears, but that's enough IMO to catch anything egregious.
Hope this helps someone else down the road!
Oh and "Shock(ing?)" wasn't meant to imply anything negative here... it was just a silly play on words.
Denny