My "Solution" for no Bilstein Sports for E12 based Cars

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G03rt2
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My "Solution" for no Bilstein Sports for E12 based Cars

Post by G03rt2 »

In case anyone decides to lower their car, but then finds out that Bilstein only makes HD shocks for the E12's now. This was my solution.
See pictures.
Threaded shaft (it was definitely hardened and took a while) at M10x1.5 all the way down to the stepped edge on the strut shaft.
Then had a machinist at work bore out the collar on the inside of the tophat to only leave 3/8" at the top and leave a very thin wall through the rest. Essentially letting the top hat slide further down before it rests on the stepped edge.

We'll find out over the summer if I weakened the collar too much and have a shock come shooting through my trunk [-o<
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Klaus
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Re: My "Solution" for no Bilstein Sports for E12 based Cars

Post by Klaus »

It appears as if Bilstein does not plan on offering any more rear Sports for E12's or E12 based E24's. But they are still offering rear Sports for E3 and E9 chassis, and as far as I am concerned the specs are close enough to be interchangeable. Rear uses 24-008198, about $110 per side. Front is still available as 34-193020, about $130 per side. No modifications are required for installation and all the provided hardware is usable.

Klaus
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Brucey
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Re: My "Solution" for no Bilstein Sports for E12 based Cars

Post by Brucey »

the main problem with using a longer stroke shock with a (shorter) lowering spring is that the springs may become unseated on full droop. The normal way of addressing this is to use 'helper springs' which are compressed flat (and therefore work like spacers pretty much) until there is almost no load on the main spring, whereupon they extend with enough force to at least keep the springs seated. I don't know what the best way of implementing this scheme would be on these bilsteins though.

If modifying a shock externally I would consider machining back the shoulder on the shock shaft. The reason I think this will work is that (IIRC) the last part of the shaft never enters the shock body anyway; on full bump the springs go coilbound and/or the bump stop cannot be compressed flat, and this limits the shock travel anyway.

There are lots of options to look at. Does anyone know what the E3 damping rates are?

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
rhanley 635csi89
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Re: My "Solution" for no Bilstein Sports for E12 based Cars

Post by rhanley 635csi89 »

Have you looked into the Bilstein rebuild service?

SERVICE INFORMATION

BILSTEIN Technical Center - The official Bilstein Shock Absorber shop in the US offering complete rebuild of most A.M. dampers and customized valving of your aftermarket dampers for motorsports use.

http://www.bilsteinus.com/products/s...rvice/service/
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G03rt2
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Re: My "Solution" for no Bilstein Sports for E12 based Cars

Post by G03rt2 »

My original plan was to machine the shoulder of the shock shaft down like brucey mentioned. When I showed it to our machine shop foreman he had two comments: is the shaft hardend? And how to hold the shock in the lathe without it turning. The shaft is hardened. Which worried me when running a die over it. I think we could have figured out how to hold it in a lathe, but the main problem being is that the shaft is hardened. That is when plan B came alone to machine out the collar.

I also thought about using Bilstein rebuild services, and still might, but I'm going this route first since it was least expensive (cost of the m10x1.5 die)
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Brucey
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Re: My "Solution" for no Bilstein Sports for E12 based Cars

Post by Brucey »

IIRC the shock body is ~50mm dia (once the perch is off) and this is of a size that will fit up the headstock of a decent sized lathe (with suitable packing to stop it from flapping about if necessary), which means that the shock shaft can be held in a chuck so that the part you need to work on is easily accessible.


I don't think the shaft is hardened to the nth degree so a carbide tip ought to make light work of it. In case it doesn't work easily, there is a fallback position; once the part is mounted for turning it can equally well be ground in situ.

Another approach that will probably work is simply modifying the mounting eye on a set of E28 type shocks, and sorting out springs and perches/mounts to suit one end or the other. I think the only difference in the eye is that the E28 bush is long on one side; this is easily changed, or the E28 shock can be mounted in an E12 with the eye round the other way using a longer bolt than normal perhaps.


Also note that it isn't that difficult to strip and rebuild Bilstein rear shocks. You can see the insides here;

viewtopic.php?f=17&t=16878

To open them you can (carefully) drill a hole in the base (near the shock eye) to discharge the nitrogen (which is at about 200psi IIRC). The shock then comes apart easily by removing snap rings from the top of the body. You can either weld the hole up in the base (and give it to a shock rebuilders to recharge/fill with oil) or you can install a tank valve in the base and then use a suitable pump (eg a bicycle shock pump) to repressurise the shock. Fitting an additional spacer on the shock shaft can turn a long stroke shock into a short stroke one.

The pressure inside the shock and the oil fill level become shock tuning parameters; higher oil fill levels give an additional rising spring rate in bump and adjusting the pressure can give a different threshold for a plateau in the bump damping (i.e. if you hit a very big bump very fast the shock deflects not just by pushing oil through the piston but additionally by pushing the floating piston downwards; this is what enables gas shocks to work well over big speed bumps etc).

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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