rear Penske shock

[Jean-Sebastien Stoezel]

Hello,

Can somebody identify what shock model this is?



Apparently it's a Penske, and it's connected to a remote adjustment cannister (black, in the background) with a 6 positions (rebound?) selector.

What type of spring is this?
Can I service this shock myself? What needs to be done to it?
Any other information on how to set it up is appreciated.

Thanks,
Jean

[samiam520]

I believe it is a Penske 7500

Looks like about a 150-200LB spring. Don't know the manufacture.

Yes, you could service the shock yourself but I wouldn't. Parts are available and there are a ton of shock shops that will rebuild it and then dyno it for a very fair price.

I would recommend that whoever rebuilds it has FV shock experience. Our valving tends to be different then other formula cars.

[Matt King]

Bob Lybarger is one of many vendors who can rebuild and dyno a Penske Vee shock for you. He did my 8100 for under $100.

[Gary_T]

Hey Jean,

I have some 7100's apart in the garage right now - similar, except no external canister. They aren't difficult to take apart, but you'll want to keep everything extrememly clean as you re-install.

The Penske website has some very good documents on the various shocks, track them down and you should be able to do anything on them yourself.

Gary

[Bruce]

Check the ID on your spring. It may be worn since it seems to bend in an arc, or it could be, the ends seem to over hang the mounting plates on the shock. Most Penskes use a 2.25 ID spring.

[DaveB]

That is a old 8100 series Penske.

Dave

[S Lathrop]

I know something about the rear setup you have there. If I did not build it, it is a good copy of ones I built. The design is an Ed Zink's original.

The droop limiter is not something that I produced though. I used a rubber die spring that was about 1" to 1.25" dia and 1" to 1.5" long. This is a tuning issue. I would get that part right before going to the track.

The shock valving is not difficult but it is not what most people would expect. Most of the units I sold used Fox shocks. That was what was available at the time. You can rebuild the shock yourself with very simple tools. You can down load instructions from the Penke web site.

I will bet the spring is dead. It apperars to be very close to coil binding. I switched to 2.5 ID springs to avoid this problem. The rate should be something around 150 #/in. and needs to be 10 or 12 inches long. You will absolutely have to make a spring compresor to install the spring.

PM me for more information if you want.

[Jean-Sebastien Stoezel]

Hi,

Thanks for everyone's contribution.

I don't think there's any shop where I leave that has any experience with FV. There's a few motorcycle shops though that seem to specialize in Fox shocks. They may be able to do something.
I'm just tired of sending parts to the US to get them fixed/serviced, it costs me more in shipping/custom fees than in actual performance improvements.

Thanks for the heads up Gary, I got some documentation from the Penske website.
Bruce, it's interesting you mention the spring may be worn. I had never noticed it is arced...

Steve: the setup came with the car and this is one of the few zero roll setups I have ever seen. I ran with this all last summer and I wouldn't mind fixing it to whatever it should be.
I'm interested in figuring this out with you, thank you for the offer. You have a PM.

Thank again to everybody,
Jean

[racerdan]

You can always send them to David Clubine in Ontario. I know he does Penske shocks

Britain West Racing
519-756-1610

[gmac]

Hey JS it is an 8100, call Bill Vallis 905-384-0016 and he can give you the advice you need. I threw out all my notes on that car last spring, I did not think to send it along to you. Anyway he got me the part numbers I needed when I rebuilt it in 2003. Another thing to check is the nitrogen pressure. The cold wheather seems to make them leak over the winter. Every spring I would find it down a couple of pounds, after filling it up and it would hold all season.

Cheers

gmac

[Jean-Sebastien Stoezel]

Hi,

I got a macpherson strut spring compressor to remove the spring and evidently this is not the tool for this type of spring.

This is what I have:
http://www.princessauto.com/workshop...ing-compressor

It seems the coil spacing is just too small for this tool to fit.

What does the right compressor look like?

Alternatives I saw at the store are:
http://www.princessauto.com/workshop...ing-compressor
http://www.princessauto.com/workshop...ing-compressor

I'm thinking the first one would work, and would make use of the opening in one of the shock spring stop (?). Though it seems a bit big for that shock.

Steve mentioned in his post I will have to build one... Could anybody post pictures of what the compressor should look like?

Thanks,
JS

I know something about the rear setup you have there. If I did not build it, it is a good copy of ones I built. The design is an Ed Zink's original.

The droop limiter is not something that I produced though. I used a rubber die spring that was about 1" to 1.25" dia and 1" to 1.5" long. This is a tuning issue. I would get that part right before going to the track.

The shock valving is not difficult but it is not what most people would expect. Most of the units I sold used Fox shocks. That was what was available at the time. You can rebuild the shock yourself with very simple tools. You can down load instructions from the Penke web site.

I will bet the spring is dead. It apperars to be very close to coil binding. I switched to 2.5 ID springs to avoid this problem. The rate should be something around 150 #/in. and needs to be 10 or 12 inches long. You will absolutely have to make a spring compresor to install the spring.

PM me for more information if you want.

[racerdan]

you dont need any of these tools to remove the spring. just unwind the spring pearch.

Likely the spring is too short for your car. when it is removed check the length and consider a longer one or a spacer between the bottom of the spring and the spring pearch.

Dan

[Bruce Livermore]

I don't think I could remove my springs (safely) without a spring compressor. The collar is still under some tension with the platform backed all the way off. I think it depends on the stiffness and length of the spring vs. the length of the shock.

I purchased a spring compressor specifically built to deal with coilover spring/shock units like we use, probably from Lybarger. I'd assume that other FV specific race suppliers would also have something similar. They hold the shock as the spring is compressed and are designed for our small diameter springs (vs. street car springs).

[S Lathrop]

I don't have a drawing for the spring compressor that I use. But I will try to describe what I made.

I build mine out of an old style bumper jack. The kind that cars were delivered with years ago,

Next I took a piece of tubing about 4 to 6 inches long and large enough to fit around the spring. This is a major safety feature. Keeps the spring from bending and shooting across the shop.

I welded the tube to the stand portion of the jack, near the top. On the movable part of the jack I made a clevis to attach the bottom eye of the shock.

To hold the spring I made 2 hooks out of 3/16 angle iron. I drilled a 1/2 in hole in one side of the angle. The hole is tangent to the undrilled leg. On either side of the tube I welded some 1/2 all-thread. You slide the angle down the all-thread and engage a coil on both sides. Any thing that will hook a coil will do. This was the best idea I had at the time with the stuff I had laying around the shop.

Be careful. You will have hundreds of pounds of force when you compress the spring.

[Jean-Sebastien Stoezel]

Does it look like this one:

http://cgi.ebay.com/ebaymotors/Motor...-/380302775542

I don't think I could remove my springs (safely) without a spring compressor. The collar is still under some tension with the platform backed all the way off. I think it depends on the stiffness and length of the spring vs. the length of the shock.

I purchased a spring compressor specifically built to deal with coilover spring/shock units like we use, probably from Lybarger. I'd assume that other FV specific race suppliers would also have something similar. They hold the shock as the spring is compressed and are designed for our small diameter springs (vs. street car springs).

[Bruce Livermore]

Jean,

No mine is not like that. However, that might work.

Check your pm's.

[Hardingfv32]

If you only due this once in a while, why not just use hose claps and applied them when the spring is compressed by the collar?

I use a hydraulic press with some carefully spaced bar stock.

You show consider this little project a test of whether it is wise for you to be working on this car by yourself.

Brian

[Tiago Santos]

Hehe.. Brian, some of us don't have a choice. We might not know exactly what we are doing (yet) but we need to learn somehow. I wish I had a couple of nice FV race shops around here to take care of my car - actually, no, I wish I could afford to do that!

I did think of hose clamps when I wanted to remove my spring, or ratchet straps. But a loaded spring is not something I want to have to worry about, and man would I worry if I wrapped it with hose clamps!

Springs are happy bouncy things, even when they seem to have little tension.. Had one jump out at me at a junkyard while trying to scavenge upper spring mounts from the rear of an old Volvo. Got lucky that one time - maybe I'm overly careful as a result. But I still got all my fingers though, so it may be working!

[Hardingfv32]

Well, at least you know your limits. All you can do then is keep posting with your questions.

Brian

[Jean-Sebastien Stoezel]

What's a typical size for a shock with this setup? This one looks a bit long for my setup.
As this shock stands installed, at the droop limiter it measures about 13" eye to eye.

I'm looking to sell this one and get a newer style (Penske 8300(?) or equivalent in other brands). What's a fair asking price for it (will come professionally rebuilt by a shop... It's a the shop right now).

What size should I go for the replacement one? We don't have a FV shop here so I'll get the new shock through a motorcycle shop. They've asked about valving and spring rate, as they have no idea what it should be for a FV.
What do you guys recommend?

Thanks,
JS

[Tiago Santos]

I don't think it matters that much, as long as it fits and you can get the correct ride height/camber angle you want. My old carrera shock was 12" spring perch to spring perch.. Can't remember from end to end. The "new" fox is 10" perch to perch, so probably about 12 or 13" end to end. The 2" difference between shocks was easily compensated for with a couple turns of the push rods (or whatever they're called, the rods that go from the leading arm to the zero roll rocker thingamajiggies.

Sorry, my terminology is all over the place

[Bruce Livermore]

As long as the shock gives you the travel required without hitting it's limits, it's not "too long" (or too short). In fact there is a school of thought that for ideal operation, the shock piston should not run near either end of the shock body.

The only thing wrong with a shock that is a bit longer than necessary is a tiny increase in unsprung weight. On a Vee this is hardly worth considering.

A properly set up 8100 works pretty well.

[Jean-Sebastien Stoezel]

Hi Bruce,

Thanks for the reply.

Yes the main motivation is weight reduction. Also as seen in the picture, the threading on this shock stops half way through the body. I can't really lower the car more than that. As well the pushrods are adjusted as short as they can be. Still I barely make the "proper" camber adjustment. In this sense, isn't this shock running at its limit?

Another thing with this setup: since the shock seems long, the angle between the pushrods and the bellcranks(terminology?) seems a bit more "open" than other setups I've seen on the net. I wonder how this affects rates.

Newer shocks have threading all the way through the body, and both length and weight seem to be better used.

As long as the shock gives you the travel required without hitting it's limits, it's not "too long" (or too short). In fact there is a school of thought that for ideal operation, the shock piston should not run near either end of the shock body.

The only thing wrong with a shock that is a bit longer than necessary is a tiny increase in unsprung weight. On a Vee this is hardly worth considering.

A properly set up 8100 works pretty well.

[DaveB]

The set up on your car has been used for years. How are you setting the car up? The push rods set the droop the spring sets the camber. That yellow spring is probably 25 years old. But if you insist on pitching money at it I will give you $100 for the shock.

Dave

[Matt King]

I think the problem is your spring, not the shock. It looks way too short.

[Jean-Sebastien Stoezel]

Hi Matt:

A longer spring will not fit. Again check the threading on the picture, it does not extend to the end of the body of the shock. The adjusting crown/bolt is at the end of the threading in the picture.

JS

I think the problem is your spring, not the shock. It looks way too short.

[Matt King]

I couldn't tell that from the photo. But those shocks are pretty modular, so it may be worth a call to a shock specialist to see if you can have it swapped for a fully threaded body. It may cost less in the end than a completely new shock.

[Hardingfv32]

1) Why do you have to be lower the car? Are you getting the proper rear camber setting at this time?

2) Would it not be cheaper to modify or maybe replace only one push-rod?
Don't worry about the rocker geometry. It is not that important, particularly at your level.

Brian

[Jean-Sebastien Stoezel]

Hi Brian:

Thanks for your reply. All this got sorted out by quite a few very detailed PMs and emails I've received.

To answer your questions quickly 1) I couldn't make the recommended camber settings, I'm not worried about ride height. 2) Certainly, though at this point I mainly wanted to know if it was worth for me to keep this shock. There's been quite a few bogus parts on this car, which keeps me on my toes.

JS

1) Why do you have to be lower the car? Are you getting the proper rear camber setting at this time?

2) Would it not be cheaper to modify or maybe replace only one push-rod?
Don't worry about the rocker geometry. It is not that important, particularly at your level.

Brian

[gmac]

The car had 6 degree of camber in the rear when I sold it to you, you don't want to go more than that or you will burn through swing axles end diffs and other various transaxle parts. Vees are vw with out fenders and just like production based race cars you have to live with the limitations.

Cheers

GMAC

[Tiago Santos]

I think you should easily be able to find a spring that'll work for you. Might have to be shorter than the current one, or just shorten the push rods like Brian said, or buy a new shock body.. You have a pretty good shock to begin with, so I'd look for a cheaper, easier solution than selling that and buying a different one!

[Jean-Sebastien Stoezel]

Hi Greg:

I'll say the car doesn't seem to go as low with me in =].
Also I've installed a ride height adjuster at the front, which transfered more weight towards the front.

JS

The car had 6 degree of camber in the rear when I sold it to you, you don't want to go more than that or you will burn through swing axles end diffs and other various transaxle parts. Vees are vw with out fenders and just like production based race cars you have to live with the limitations.

Cheers

GMAC

[Hardingfv32]

1) I assume the 6 deg in the rear is because of street radials?

2) If the Penske is in good work order and setup correctly you will not be able to realize any difference with a new model shock.

3) Shortening the rods (or rod) is the most inexpensive solution.

4) AND... just how much weight do you think you can transfer by lowering the nose?? Do not avoid an answer, I need a good laugh.

Brian

[Jean-Sebastien Stoezel]

Aaaah Brian the point is the car doesn't go as low now. I got what I was looking for with this thread, I have no incentive going further.


Thanks for your replies.

1) I assume the 6 deg in the rear is because of street radials?

2) If the Penske is in good work order and setup correctly you will not be able to realize any difference with a new model shock.

3) Shortening the rods (or rod) is the most inexpensive solution.

4) AND... just how much weight do you think you can transfer by lowering the nose?? Do not avoid an answer, I need a good laugh.

Brian

[Hardingfv32]

Ok, how much weight transfer from nose movement up or down? You might learn something by discussing your answer to the question.

Brian

[Jean-Sebastien Stoezel]

So... Tonight I got the shock back from the shop and I guess this is not over.

The shock is re-valved, thank you to those who've helped off-forum to figure this out. The help is greatly appreciated.

Also, I got a new spring since the other one seemed worn and too soft.

Now... When looking at the whole assembly I can see a few things that seem wrong, and that the shop either missed or did not think was worth mentioning...

Bruce remarked in a previous post that the spring was arced, potentially because it was worn.
I checked this on the reworked shock and realized this is because the shock retainer and the ride height adjuster are 2 different sizes... The ride height adjuster is 2.25", while the spring retainer is 2.5".

By the way, I ordered a spring of the same diameter of the old one, that is 2.5". I wanted to go with a 2.25" but the shop insisted I needed a 2.5", I guess that's another story.

This is the maximum gap on the spring retainer side (pretty small):



This is the maximum gap on the ride height adjuster side (gap looks close to 0.25" to me):




All in all, the spring is not seated on the ride height adjuster and moves quite a bit around the shaft - I guess I need a replacement 2.5" ride height adjuster.


Now take a look at the spring retainer again, there's a fatigue crack all around the shaft, where the jamnut seats... Never really looked at the spring before but I think this is severe enough that the shop should have mentioned it.



So... What's with the crack? Is this typical?... I don't have experience with shocks - maybe it's normal, I don't know. Looks quite bad from my side though.

Does this spring retainer require replacement?

I guess the crack may have developed because there's no proper droop limiter spring... Who knows. Lybarger is sending me a rubber droop stop.

If I need to replace the spring retainer then I would like to switch a 2.25" retainer, and get into the 2.25"x8" spring market. This way I won't need a spring compressor and will have access to rates that I believe are more appropriate for my setup.

All that to say that this brand new never raced spring could be for sale if somebody is interested. It's a 10"x2.5" 175# Hyperco.

Lets see first if this spring retainer is garbage. Is it?

Jean

Check the ID on your spring. It may be worn since it seems to bend in an arc, or it could be, the ends seem to over hang the mounting plates on the shock. Most Penskes use a 2.25 ID spring.

[Tiago Santos]

I was under the impression most fox/penske shocks used 2.25" springs.. Mine sure does. That gap looks way too big for sure..

[Jean-Sebastien Stoezel]

Penske 8100s come with either 2.50 or 2.25 adjusters/retainers (items 2 and 32 on page 2 of http://www.penskeshocks.com/files/Adjustable_Manual.pdf)

I was under the impression most fox/penske shocks used 2.25" springs.. Mine sure does. That gap looks way too big for sure..

[Tiago Santos]

Well there ya go I'd definitely try to match everything together, do whatever ends up being cheaper - either replace the broken retainer with a 2.25" piece and a spring to go with it, or both the retainer and the adjuster with 2.5" pieces..

edit: I couldn't find 2.25" springs in the rates I wanted locally and either had to wait a few months (which I did) or have it shipped from the US. Considering the size and weight of these springs, I'd seriously consider buying the 2.5" retainer and adjuster and be done with it. I haven't given it much thought, but other than weight (??) and packaging (...??) I'm not sure there are any other advantages to a 2.25" spring, are there?

[Jean-Sebastien Stoezel]

Thanks for the general advice, that's a good sum up of what I stated in my post.

Well there ya go I'd definitely try to match everything together, do whatever ends up being cheaper - either replace the broken retainer with a 2.25" piece and a spring to go with it, or both the retainer and the adjuster with 2.5" pieces..