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Shock length

Is there any difference in the total length of different brands of shock absorbers?
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Old 11-03-2012, 01:27 PM
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Clarification . . .

Hi Kent,

We all appreciate your very concise question. I am afraid you will need to elaborate a little, or clarify, in order to get some response. Maybe something like this:

" For a given car (like my 1972 911 for instance), do all the damper manufacturers (like Koni, Bilstein, Penske, Carrera) produce a "recommended" shock with the same fully-extended length? "

= OR, depending on your real question, maybe this =

" Which damper manufacturer produces the LONGEST fully-extended shock that will bolt right up on my 1972 911 ?"

Something like that . . .

[EDIT]: Is this a racing question?
Ed

Last edited by RaceProEngineer; 11-05-2012 at 05:17 PM..
Old 11-05-2012, 05:15 PM
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What he said^^

There are dozens of different shock lengths within each brand. Explaining what you have, and what you are trying to accomplish might encourage some useful information from the experienced setup guys here.

http://www.autosportgallery.com/bilstein_stock_car-june08.pdf
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Old 11-06-2012, 06:19 AM
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Your right it helps to explain the question.

I have a 72 911T that was lowered and corner balanced by Troy Sport in Orlando. I have always, since then had a clunk in the front when hitting chuck holes or hard braking and turning. The shocks are KYB. What I finally found out was the shock was bottoming out! Recomendations are to pull it all out and go to Bilstein, $2000. However my thought is if I can find a shock that's total length is shorter than the KYB I'm home free. I have added a large bump stop to the top of the shock shaft limiting the compression travel and all is good, except I only have about an inch and a half of compression travel. The car is stiff anyway and on the track (DE's) it works fine but rather stiff on the street.

Options are Bilsteins, cut the top of the shock shaft and rethread if possible or a shorter total length shock???

Any ideas?
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Old 11-06-2012, 02:42 PM
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I have not done it personally but I believe there is a VW Fox application of some sort that is an inch or so shorter overall then the Porsche insert for BOGE front struts. However, you will have to shorten the strut body the same amount. Really the way to fix this correctly is to raise the spindle first and then if you still want to go lower, shorten the shock body. I imagine RothSport can help you out with this or Elephant I understand will shorten Bilstein struts as well but there is no simple solution of just installing a shorter insert in the front without also shortening the front strut. At a certain point the front A-arm makes contact with the tub as well. The rear is easier and I believe the Koni Sport shock is a bit shorter then most but still the axle hits the body before you run out of shock so I am not sure this is a big issue. The only easy and cheap solutions are raise it up, live with using the bump stops as spring rate (I hate to admit is but I have had a few AX cars that sat on the bump stops at rest to get higher spring rates), or go stiffer.
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Old 11-06-2012, 03:01 PM
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Kent,

My reason for asking if this is a racing (or autocross) application is that dual-purpose 911s are a big bag of compromises.

If you are still using this car on the streets, then I can not immagine that the ride height is SO LOW that the suspension is bottoming -- UNLESS there is something else wrong.

KYB dampers are certainly not known for their quality, or their performance, or their longevity, particularly for track use. My bet is that the offending shock(s) have "lost their zoom" - in bump, AND probably in rebound. Another contributing factor, as Evan implied, will be relatively low-rate torsion bars - perhaps old ones.

We need to speak about this in terms of the track, since (hopefully!) that is where your car is seeing its most extreme use. For a track car, in the paddock, if one can push down on a front fender, and the body travels more than ~", then things need to be stiffer (bushings, torsion bars, dampers). And, obviously, the lower the ride height, the greater the need for stiffer suspension. Remember, extreme pitch can come from weakness in the rear suspension, even though it shows up in the front.

Your KYBs can be rebuilt and revalved. My guess is that, for the cost, you will be much further ahead with adjustable Konis or even monotube Bilsteins.
Ed

Last edited by RaceProEngineer; 11-06-2012 at 06:04 PM.. Reason: Revalving
Old 11-06-2012, 05:55 PM
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Quote:
Originally Posted by RaceProEngineer View Post
If you are still using this car on the streets, then I can not immagine that the ride height is SO LOW that the suspension is bottoming -- UNLESS there is something else wrong. Ed

What Ed says! I've seen this in the rear occasionally, but only when shocks were turned upside down with coilovers and had the clevis's isntalled shortening the total available travel.. I can't imagine bottoming out a front shock.

I suggest wrapping a few zip-ties tightly around the piston shaft, they will act as telltales for max shock travel. Either the clunk is something else (sway bar, ball joint, steering arm, a-arm bushing, etc..) or the shock is probably bad. Even on my extremely lowered 911 racecar (1970) we didn't have travel issues in the front...
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Old 11-06-2012, 06:13 PM
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Actually I picked the KYB without any research since my friend Sid Collins in Orlando uses them on his race car. But ever since he put them on I've had the clunk . After a year of changing ball joints and anything else I could find in the front suspension, not the torsion bar, I tried the zip tie trick the shock shaft is for sure bottoming in the unit. Raising the spindles on new bilsteins is the best step all bet $2000 for a winter project. My car is fairly light 2200 lbs (72T) and lowered/corner balanced (23" front/22" rear with me in the car). That's with 205X50 tires all around. There is very little travel in the front even before it hit the rubber stop so it may have had stiffer torsion bars added before I bought it.

It just feels and looks like if the shock shaft was about 1-1.5 inches higher in the cylinder everything would work???
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Old 11-07-2012, 01:50 PM
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Kent,

Currently installed, do you have Boge, Bilstein, or Koni struts?

Ed
Old 11-07-2012, 03:24 PM
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Brand new Bilstein RSR struts including shocks are 1400(Elephant Racing) for the pair (Raised 19mm+gussets)
Old 11-07-2012, 07:10 PM
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Quote:
Originally Posted by kent olsen View Post
Actually I picked the KYB without any research since my friend Sid Collins in Orlando uses them on his race car. But ever since he put them on I've had the clunk . After a year of changing ball joints and anything else I could find in the front suspension, not the torsion bar, I tried the zip tie trick the shock shaft is for sure bottoming in the unit. Raising the spindles on new bilsteins is the best step all bet $2000 for a winter project. My car is fairly light 2200 lbs (72T) and lowered/corner balanced (23" front/22" rear with me in the car). That's with 205X50 tires all around. There is very little travel in the front even before it hit the rubber stop so it may have had stiffer torsion bars added before I bought it.

It just feels and looks like if the shock shaft was about 1-1.5 inches higher in the cylinder everything would work???
23 inches front is extremely low. You do have a short tire so that's part of how you get that low.

But even with those short tires, at that height you should definitely do raised spindles.

We can also custom shorten struts and inserts if you still need more travel.
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Old 11-07-2012, 09:07 PM
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Oops, yes they are Boge struts. As I said, although I have never pulled them and checked, I believe I have larger Torsion bars as the car has always been stiff. Here's a couple pictures at the track here in Portland. If I sit on the front fender it drops about 3/4" , the rear only about 1/2". Corner balanced by TroySport in Florida and RennSport in Oregon, it's 49/51 front rear. A very predictible track car if I could just get another inch of shock travel.
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Old 11-08-2012, 06:11 AM
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Thanks for the Bilstein catologe. I didn't see anyone there that would slip into the Boge strut, hmm. I'm sure they do have them. I know I can go all the way to raised spindles and Bilstein but I hate start over with something that works fine except for the clunk.

On vacation next week so I'm pulling out the KYB's to measure and then some phone calls to look for something that may be just a little shorter.

This car has been a real pleasure to drive on the track after the corner balance both in Florida and Oregon. I've tracked it at Sebring, Portland, the new track in Shelton, Wa, and Oregon raceway park in eastern Oregon. With a power/weight of 9:1 and 49/51 front to rear it goes where you point it and if you get a little over your head, recovers without any embarassment.

I'm running soft Yokohama's on 7" rims with stock fenders so I could surely do more for more performance, but as long as I have a smile on my face when I come off the track all's well.
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Old 12-02-2012, 10:25 AM
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Kent - how about a summary of how you achieved 49/51? Is that 2200 lbs with you in it? My track car is at 1960 without me, but much closer to the usual 40./60 than it is to 50/50. And that with the 4 gallon oil tank up front, too.

I have Bilstein HDs for Boge struts in my SC (which is no where nearly as light as your car, but it has to make class weight). They replaced Koni Sport Adjustables, which I damaged by running the car too low. One of the shocks was bottoming, damaging the adjustment mechanism down in the bottom of things.

When setting ride height for track cars, one really ought to use Porsche's method for figuring out what is so low that there will be parts interference. It is easy to measure the distance between the CL of the torsion bar, and the CL of the axle, and use that. Just turn the wheel out, lie down on the ground with a tape measure, and measure to the ground for each, then subtrack the one from the other. I measured a friend's car, which seemed lower than mine, and used his measurements as a kind of safe harbor. Got the car down about an inch more than it was, and no bottoming.

Because the fender method will vary with your tire diameter (I'm using 225/40/15s up front now, mainly to get the car lower). And I have no trust at all in fender locations, especially in the front where it is easy to replace.
Old 12-05-2012, 09:51 PM
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Quote:
Originally Posted by Walt Fricke View Post
Kent - how about a summary of how you achieved 49/51? Is that 2200 lbs with you in it? My track car is at 1960 without me, but much closer to the usual 40./60 than it is to 50/50. And that with the 4 gallon oil tank up front, too.
We have run hundreds of 911s over setup scales. (As I am certain you already know) 49/51 is not achievable without moving the motor into the back seat, and the driver into the smugglers' box.

Ed
Old 12-06-2012, 04:09 AM
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Kent- How exactly did you come to the diagnosis of the shock being of issue? Did you do any of the testing recommendations above?

I had an aftermarket set-up on a previous car in my JDM phase and was getting a thunking noise as you described. I replaced the shock at the offending corner and still got the thunk. It turns out that the shop that installed the suspension and who also stated the shock was to blame, actually failed to re-install an anti-roll bar bushing in the first install and never said anything. Once I discovered the missing bushing and replaced it , not more thunk.

What I am saying is, check all your suspension fasteners and bushings as well.
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Old 12-06-2012, 04:50 AM
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OK here goes.

I"ve had this 72 911 since 98. Autoxed it right away and started tracking it in about 99.

It's a "T" so it's light to begin with and has the oil reservoir forward of the rear wheel. Here's the progression with the weight reduction which I always thought was cheaper than horse power. Front to rear.

1. Fiberglass hood
2. One jell battery in right front
3. No jack or spare
4. Camber plates and light weight strut brace
5. "M" brakes with drilled/slotted disc"s
6. Light weight seats
7. Door pockets removed
8. Aluminum trailing arms
9. "M" brakes with drilled/slotted disc's
10. Modified 240hp twin plugged 3.0L with 40mm webers(installed last winter, much more expensive)
11.European headers without heat exchangers
12. M&K 2 in 2 out early muffler, 10lbs
13. Fiberglass deck lid with ducktail

The car was aligned and corner balanced at TroySport in Orlando two years ago and then again at Rothsport in Portland last spring with the same results, 2210lbs with 1/2 tank, no driver and balance of 49/51.

Troysport installed the KYB shocks and I have had the clunk ever since. I've replaced the ball joints, tried the tie wrap around the shock strut and it all leads to the shock bottoming in the casing. I do remember now that I raised the front as high as it would go and driving over my favorite chuck hole still caused the clunk, hmmm!

I purchased an after market rubber snubber to slide over the shock strut, no help, then I fabricated another rubber donut I also slid over the strut an "NO CLUNK". Therefore my belief that the shock is bottoming in the housing and I need a shorter, not by much, shock.

Question: do some shocks have progressive resistance as they compress?
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Old 12-06-2012, 02:12 PM
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Kent

Like Ed, I am having trouble believing a front/rear distribution of weight of 49/51 for a 911.

What I can believe is that the left to right distribution is 51/49 with you in it (though usually that requires some ballasting). Or that the left/right distribution without you in it is 49/51 (or the other way round).

Might you have misread the corner balance printout, or misinterpreted what the shop told you?

And of course I believe you when you say it handles very well! Looks good, too.
Old 12-06-2012, 04:31 PM
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You took the wind out of my sail but your'e right. I went back and looked at both sheets and it is 49/51 left to right and 39/61 front to rear. Thanks now that's clear.

So back to the shock. I plan to take out the KYB's, measure them and try to replace them with something else. Any ideas for me like Bilsteins or something that fit the Boge strut?
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Old 12-07-2012, 07:43 AM
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This doesn't seem to be a common measurement. You'd want a guy with quite an assortment of different shocks to do the measuring.

With Koni shocks, you can cut the bottom peg down, and section out an equal slice of the upper strut and reweld, and you have the shock more extended as static height.

You can raise the spindle 19mm (more, if using larger than 15" diameter rims), which gets your shock more travel for a given ride height. Need to get a steering arm bump steer attachment. Other than the Bilstein strut, you have to cut the strut tube top and bottom, and add to the bottom what you cut from the top.

But measure your ride height the way Porsche does - the difference in height between the axle and the torsion bar. Easy to do with a tape measure and a bit of eyeballing to get in the eyeball park.

For an SC, this difference at ROW (Euro) ride height is 108mm, +/- 5mm. I found I was at 156, but a buddy was at 185 and had no bottoming issues. I figured I could lower an inch (25mm or so) and still be OK.

I measured the distance from T bar axis and ball joint at about 300mm. I measured the torsion bar adjuster at 53mm [re-edit - I thought I misread my scrawled notes,but I was confusing myself]. This meant I needed to loosen the adjuster about 4mm (close to 6 to 1 ratio). Thread looked to be M8x1.25, so three turns of the adjuster should be close. It was, and I came out at 178 and 181, the difference being from previous corner balance adjustment.

Anyone else ever used this method of calculating how to reset ride height? Was I just lucky?

But knowing this suspension centerline difference means not having to rely on rim and tire differences, or the vagaries of bodywork, to deal with the relationship between ride height and suspension interference.

Last edited by Walt Fricke; 12-24-2012 at 01:49 PM.. Reason: as above - goofed up
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