Shortening Strut Housings

[Britain Smith]

Everyone always talked about raising the spindle (which I have done), but another issue when lowering a car to extremes is the strut body running to to the top of the shock body and ultimately hitting the bottom of the tub. On my Bilstein struts, I have about 1/4" of travel left before the strut body runs out of shock to travel on.

I am now looking at sectioning the strut housing and shorten it about 1 to 1.5inches to gain the additional shock travel. An additional part of the mod could also include shortening the actual shock shaft where it fits inside the strut housing and then machining it to re-accept the roll-pin. This would put the shock back in the middle of it travel range.

I am sure that people have gone down this path, however I did not come up with anything when I searched. Anyone have any experience with this?

Thanks,
Britain

[Britain Smith]

Ok, everyone should be back now, any insight to this?

-Britain

[Porsche84]

I have a buddy who likes his 72 track car real low. When I corner balanced it I noticed that the struts were sitting on the bump rubbers at rest. I had the shock shaft shortened about 1 inch to avoid bottoming out during hard compression. I raised the car a little and I cut off part of the bump rubbers. If your strut tube hits the tub your shock shaft will blow out through the bottom of the strut or bend like a pretzle. In addition to this, as the shock goes solid, the spring rate increases to infinity, making the car diabolical in a corner.

[Steve@Rennsport]

Britain,

This is a somewhat complex subject as there are several variables and some limitations.

There is a finite amount one can shorten a Bilstein shock shaft before there is insufficient travel for it to function correctly and thats about 1-1.25". The strut body cannot be practically shortened beyond the above figure for the thing to contain the insert and still function.

FWIW, Porsche & Bilstein knew all this and thats why the 935 struts are two-piece assemblies where the strut tubes can be raised and lowered within the clamp-on spindle forging as needed.

Naturally, these cars had different pickup points for the A-arms as well as longer ones to correct the camber curve at low ride heights since OEM A-arms are too short. ERP makes their 935 front suspensions in two versions (long & "regular") for these very reasons.

Anything is possible, however some creative and extensive fabrication may be needed to reach your objective.

[Chuck Moreland]

There are actually 3 things at play when shortening; strut body, insert body, and rod.

Strut body

Neglecting the bump stops, the strut body is the first limiting factor for compression travel. It will achieve metal-to-metal contact with the bottom of the strut dust cover (or camber plate if dust covers removed) before the internals bottom.

So shortening the strut body is the first step.

Shortening the strut body by machining as you suggest is limited as it requires you to move the upper linear bearing down, reducing its leverage and increasing its side load. This means more friction and shorter life of the bearing.

An easy way to accomplish this is to replace the wiper seal housing with this shortened version from Elephant Racing. No cutting, this is a simple press off the green wiper seal housing, press on our replacement. This simple procedure shortens the strut body by 19mm. And it doesn't impact the linear bearing.



This is essentially what was done to the RSR struts.

Combined with a raised spindle, this provides adequate compression travel for most any car.

Insert body

If you really need to go further than the above, the next thing that bottoms out is the insert body, against the inside of the strut body. The strut insert body can be shortened by machining. We can do this at Elephant Racing.

Insert rod

Does not need shortening for any practical insert body length. When we assemble the insert with the shortened insert body, we position the rod (more precisely we position the divider piston) such that the rod has full travel in the shortened housing.

Shortening the insert rod without shortening the insert body is non-productive because the body will continue to bottom first.


Another thing to pay attention to is the articulation range of the ball joints and tie rods. Don't exceed their range or bad things will happen.

[Janusz]

Great insight. So at what point does shortening the strut and raising the spindle become recommended, meaning do you start looking at this type of change once you are below euro height (for lack of another reference) and is so how far below? Also, is this type of change only something one would benefit from under racing conditions (besides reducing bump steer)?

[Flieger]

Chuck, what is the general range of motion for ball joints + tie rods, etc.? Do the stock ball joints have the same range as your de-cambered ball joints?

[Brad Roberts]

Chuck?

Can he just yank the wiper seal housing off? This is an AutoX car that only sees 10-12 days a year of 60second runs. I know his linear bearings were replaced about 1.5 years ago when the shocks were sent back to Bilstein to be revalved. I *know* this will promote premature wear, but exactly how much wear will he see? I'm guessing not enough to make a difference.

FYI: VW Rabbit Bilsteins have shorter shock bodies. I'd have to do some digging to come up with the part numbers, but their OD measure exactly the same and the Porsche Bilstein, but the body and the "stick" are shorter. It allows you to cut the top off and install new linear bearings.


B

[Chuck Moreland]

Raising the spindle is meaningful even at Euro height. By raising the spindle, the camber curve is improved to better match the needs of modern radial tires. Consider that the original spindle height was a compromise by the factory to accomodate 14 inch wheels.

The range of motion for the stock shock/strut length is +/- 19 degrees (if my memory is working). Shortening the strut increases this.

Our ball joints and tie rods support +/- 24 degrees of articulation. I can't recall the factory numbers off the top of my head.

Brad, one could leave off the strut wiper seal provided they are prepared to deal with wear accelerated by extra grit and contaminate introduced into the strut body. The degraded strut bearing lubrication will also increase friction of the strut.

[Britain Smith]

Alright, here is the top of my shocks as it sits on the car. Under full load, the dust seal rides all the way up to the top of the chrome. Should I be ok or should I start modifying stuff.



-Britain

[Britain Smith]

Another source of issue is clearance between the ball joint/control arm and the rim. I have already had to raise the car about 3/8" because the inside of the rim was rubbing and removing aluminum. What other mods can I do and what can I clearance and get away with to not rub the rim?

-Britain

[Chuck Moreland]

You have the early style bilstein struts, and they can't be shortened using our seals. Shortening of the strut would require machining.

For ball joint clearance, you have a few options;

Take a grinder to the ball joint retaining ring to clearance for the wheel. It's the retaining ring that normally hits first. You may also find some interference from the arm itself, and it to can be clearanced a bit.

Decambered ball joints created clearance by moving the wheel out a bit. This may be enough by itself.

Wheel spacers can also be used to move the wheel out.

[Janusz]

"Raising the spindle is meaningful even at Euro height. By raising the spindle, the camber curve is improved to better match the needs of modern radial tires. Consider that the original spindle height was a compromise by the factory to accomodate 14 inch wheels."

So is the improvement gained by raising the spindle due to the use of radial tires or was the geometry never changed by the factory when it went to 15" and 16" wheels or both? If it's primarily due to wheel size, how has this been confirmed, through track time or validation through layouts, with bump steer measurements, etc? Not debating what is being posted, just interested in the details. Thanks.

[Britain Smith]

So, Chuck, my only opition is to shorten the housing itself? Would this require cutting the housing down and welding it, shorting the bronze insert, and shorting the shaft of the shock and remaching the roll pin?

I am not sure I need to go down this path, as it looks like I won't completely run out of strut to hit the body. However, will shortening the shock put it in a more optimum location in the range of motion?

Regarding the de-cambered ball joints or spacing the wheel out, that is the last thing I want to do because it would increase the scrub radius and that is the last thing I want to do on a AX car. I also run Bias-Ply tires and don't need a lot of camber.

-Britain

[RWebb]

and... I have a follow-up to Janusz's question:

is that only for racing or will there be meaningful/significant improvement even for street hotrodding?

[Brad Roberts]

Lose the safety catch and cotter pin. Put a paint mark on it after you modify and re-install the nut. I'd machine new nuts down 3-4mm's on the face (not the end for the special socket) and run with it. It is easy to see in the pics how the safety plate and nut would hit the wheel with different ride heights. Removing 3-4mm's from that nut is not going to compromise safety.

[Brad Roberts]

What the hell is all that seam sealer and undercoating still on the tub?? LOL If it weighs more than ZERO.. remove it.

[J P Stein]

It's not hitting on the retainer or nut but on the A arm when the suspension gets near full compression. Pic #3 bottom center....note the shinny spot where I buffed off the aluminum shavings.
A very tight AX corner......right about apex the front end washed out......OOPS, the outside front "brake" went on.....come to find out.
Add that to the traction circle.

[jimmcc]

Originally Posted by Chuck Moreland

An easy way to accomplish this is to replace the wiper seal housing with this shortened version from Elephant Racing. No cutting, this is a simple press off the green wiper seal housing, press on our replacement.

Chuck,

Went looking for this seal housing on your site with no luck. Direct me to the page please and thanks.

Jim

[Walt Fricke]

Great pictures showing how there is a limit, based on rim dimensions, on how far a spindle can be raised.

One aspect of Koni strut inserts: they have a steel peg on their bottom end. As best I can tell, this is designed to make the insert long enough for stock Porsche Koni, Boge, or Sachs struts. Which means that you can saw it off (it is solid, so it takes some sawing) flush, and then section an equal amount out of the upper part of the strut and reweld the housing (so you keep the threaded part). Now you can lower the car by that amount without reducing shock travel.

I'd put a zip tie around that exposed upper shock shiny cylinder down low, drive and stress the car, and then see if you still have any room above where the zip tie ends up. With big bars you may not need as much travel as stock, but you do need travel. Preferably enough that you can keep a rubber bump absorber in there and seldom hit it.

Walt Fricke