5280Racer

Hey Guys I bought some Penske 7500's from RXBen which He had never used and purchased them from Hardbar. I have talked to Gary quite a few times and did what he told me " Break them in and then let me know how they are" Of course I have had them on for a few weeks and run them decently hard and they did change a bit but I still have questions. And I'm not a suspension person yet so these are learning questions. First off holy crap my rear end is bouncy as hell!! When I'm going slow or fast the *** will bounce up so hard and fast I can hit my head on the roof and if I'm cruising over a bump or crack sounds like the hardest thud ever. I understand the coil overs and what not a bit, but adjusting them so its not so bouncy is what I want to learn. I have very heavy springs like 700 lbs I think he said. And also according to Gary the shocks are shorter then normal but I still can't et it to drop at all to achieve my desired right height even with the collars all the way up till no threads are showing. Experts please chime in school is in session.! Michael.

fatbillybob

I'm not an expert but sounds to me a mismatch with front and rear springs. Shocks control the springs but you got to be in the ballpark to get the most out of the shocks. For example you tune the chassis frequency front and rear for comfort and anti-porposing (bouncing up and down) by having the front frequency 10-20% less than the rear. You can violate that which is often done in tintop racecars upping both front and rear frequencies without a good split but then need shocks to control what would be porposing. This is done so that you can have a stiff ride and still get the power down and launch out of corners. Also, racetracks are pretty smooth vs. streets. As to rideheight the springs control that. So if you got the collars full lowered and you still are too tall you either have to go to a shorter spring and or adjust height by preloading the spring with both upper and lower collars. Springs are cheap about 60 bucks ea.. Hardbar has to tell you what springs go with those shocks as they are valved. If you change the springs the first thing a good shock rebuilder will do is ask for your corner weights and desired chassis frequencies and or purpose of the car and help you pick springs and then revalve the shocks for those wheel rates. If you don't know what you are trying to achieve then all you can do is rely on the guy you buy the set-up from and hope you both have a meeting of the minds and he understands what you want.

froggy47

Those are built in non/single/double adjustable I believe. Which do you have? Did you check the gas pressure?

5280Racer

They are supposed to be built in regards to track only... when I have taken the car out on the twisties it behaved extremely well. at 70 mph on very tight corners I could feel what I think is the lack of lateral grip due to the Nitto Invos I use on the street. but the car feels very solid and braking and acceleration in corners it behaves very well too. I recently had it at the drag strip and launching the car around 4000 rpm's it squats and goes which is very firm feeling too. Gary did say it was valved for hard track use and there are few things I can do.. With single adjustable shocks. My biggest issue is just the normal whoops in a road really make it compress down and bounce back up.

5280Racer

I pretty sure the only adjustment I saw is a small allen head at the bottom of the shock.

Olitho

I bet they have no nitrogen pressure. Go to 150 PSI on the front and 100 on the rear and go from there.

5280Racer

Ok, where can I get it filled at?

Olitho

I personally have a nitrogen bottle I keep in the race trailer. I can tell by the suspension behavior right of the bat when the pressures are not right. Bouncy = low nitrogen pressure.

I suggest at least a small bottle, regulator and hose from one of the gas suppliers like Airgas. If you don't want to buy a bottle I am not sure what to tell you. Maybe a fellow racer or local tire shop that has nitrogen can help you out.

If you don't have the special shock pressure gauge go the winging-it route by setting the pressure on the regulator and pushing the air-chuck onto the shock and holding it there firmly and then snapping it off the valve quickly so minimal pressure is lost on the chuck removal. That will get you real close.

My shocks leak over the month. They shouldn't, but they do....

Supercharged111

I believe Leary's will service Penske shocks, and he's local to you.

5280Racer

What does the gauge look like you use to check them?

Olitho

http://www.powersportsplace.com/part...FeU5QgodfCwAhg

http://www.summitracing.com/parts/is...3/media/images

5280Racer

Thanks so much... They are literally 10 minutes from my place!

5280Racer

Thanks a lot you have been a big help! Michael.

autoxer6

So is this a single adjustable shock? If so, just turn the adjuster in more to increase rebound damping. Penske at full soft will have less damping than a stock shock and will be really bouncy.

Olitho

With the kind of bouncing 5280 is reporting I seriously doubt it is the adjuster. I will wager strongly he has no gas pressure in the shock. Without gas pressure they simply don't work right.

MySR71

Could be. I found this interesting....

Have you talked to Gary about what ride height the shocks were designed for? If you adjust the ride height too low for the shocks lengths, you will be into the bump stops too much. The result can be what you are describing in terms of weird handling over bumps/dips. If you are already resting on the bumps stops, you won't be able to adjust the ride height any lower with the spring perch. I know you said they were "shorter then normal" but maybe it still isn't what you want/need.

Just another thought....

fatbillybob

Great replys guys. I got a little chuckle out of them. I assumed the OP knew what he was doing and suspected organic set-up issues not being the original purchaser. Your guy's first thoughts are user error and both your theories hold water. I guess that goes back to the whole "loose nut behind the wheel" thing. I got to think more like chess not checkers. We will have to wait for the OP to enlighten us.

Pfadt Racing

5280Racer

Well sorry I haven't gotten back to ya'll sooner. On Friday I went over the Leary's which is literally 10 minutes away and spoke to Mike Leary the owner... I asked him about charging my socks which he said he would do for free.. Also only charger me $10 a shock to run on the dyno and compare to my original dyno numbers. Hopefully there isn't anything wrong with the valving and I can just charge and reinstall. He carries a wide variety of hyperco coils in stock so once I know I want to keep whichever spring rate I can get a 2" shorter so I can effectively use my shock body to adjust ride height unlike right now. I still haven't received any calls or emails back from Gary so I guess I'll just write him off.

5280Racer

Thanks everyone for texting Gary!!! he called me this morning calling me a dirty little poop talker! My plan worked flawlessly! Just to be clear with everyone... Gary is the go to guy for any suspension information.