Bilstein Race Shocks for the 6

[Tomas]

This is probably more geared toward the race section but I'll leave it here for those interested in suspension in general.

About a year ago I acquired Bilstein SN series take-apart dampers for the rear suspension on the 6. Part#B46-LTA6-DTA6S for the steel cap version (SN) . For the aluminum cap version (SNS) the part number would be different. Part number is for a 6" stroke shaft which is what is needed as per my measurements. From the driving I've done so far, I have no reason to believe this shaft length is incorrect. There is no contact on the stops inside the damper when the rear suspension is in full droop or when fully compressed. At least not that I can tell. The Billstein cataloge is attached. The dampers are on page 15.

If you go this route, there is a list of components Bilstein recommends you get:

(1) digressive or linear valving kit or both.
(6) c.o.b. check plates (if digressive)
(6) c.o.b. check springs (if digressive)
(1) beaker
(1) gas fill tool
(1) gal Bilstein shock oil
(1) disassembly collar
(1) seal saver needle

In addition, you will need to source a small tank of Nitrogen to fill up the shocks. Not sure about all Bilstein's but for these units, you always fill up to 125 psi. Oil quantity is 272 milliliters which you can mark on the scale of the beaker. You will also need a digital caliper to ensure the shim sizes you are using are the correct ones.

Both the Bilstein dealer here in FL and Bilstein directly provided an immense amount of support considering I am just some lone schmuck with absolutely zero prospects of ever achieving any sort of fame and glory on Bilstein's behalf. I can understand why the dude from Far North Racing is such a die hard Bilstein fan. They really are incredible as far as helping their customers. The person at Bilstein I dealt with is named Jim and he provided the valving specs listed below. He also always explained, or least tried to to the uninitiated such as yours truly, what the different valving specs mean. Unfortunately I am not yet at a stage where I can exactly tell how the different shim diameters, thicknesses, and locations on the stack affect all the different damping characteristics.



Once you receive the dampers, make sure they come with the Piston you asked for. The linear piston IS NOT the same as the digressive piston. Also ensure there are snap rings sitiining on the inside of the damper tubes just on top of the shaft caps. As much as I have become a Bilstein fan boy, regrettably their inventory / shipping department is atrocious. On almost every order I made there were mistakes in the parts being delivered. When I received the dampers the snap rings were missing. Also on the digressive shim kit one of the shim sizes was labeled incorrectly.

After you remove the snap rings, take two slotted screw drivers and pry the cap off making sure you don't damage the inside of the damper housings. First you pry the cap to the edged of the housing, and then you take the disassembly collar and continue prying until the cap is completely out of the housing.



Next clamp the shaft upside down on a vice and remove the top lock nut.



Then remove all the shims till you get to plate B4622 or the doughnut type rubber stop at the end of the stack. That would be the blue stop on this pic.





I have used 3 different shim configurations/stacks so far. The first one was on 300 lbs rear springs and it didn't feel much tighter than stock. The floaty feeling was still there. On the second iteration I didn't feel much of a difference either. Others may have noticed it but I have a fairly insensitive ass (insert ghey note here). Jim then made what he considered a large decrease in bleed for both compression and rebound (increased damping force for both directions) to see how I would perceive the change. This change really made a difference. The floatiness is completely gone and at least in my opinion, it does not feel overdamped. Just generally solid. I also happened to find 350 lbs springs that would fit the perches on the LCA's of the 6 and that is what I am currently running. 350 lbs rear springs with 7.2 compression and 3.6 rebound bleed. If it weren't for how tired I am of taking the dampers in and out of the 6 and revalving them I'd send them to get shock dynoed. I might still do that. For now however I am fairly saturated of rear suspension work on the 6. Fumbling with the top plates holding the shocks to the unibody will never cease to bring tears to my eyes.



This is somewhat what the shim stacks listed above will look like when you put it together.



If you are using a digressive piston like I am, you need to make sure the piston is pointing the right way. They are directional. The piston face sitting against the check spring fingers needs to look like this.



This is the check spring. So the shim you see laying inside the piston on the pic above rides against the fingers of the check spring below.



Make sure you measure all the shims you are using with a digital caliper. Do not rely on the markings on the box / bags. Once the shim stack is together, fill the shock tube / housing with 272 milliters of shock oil and insert the rod. Make sure you pump the rod up and down a few times to evacuate all the air in the stack. Let it sit for a few minutes till all the bubbles are gone from the surface of the oil.






Next push the cap down on the housing and insert the snap ring. Now you are ready to fill this thing up with 125 psi of Nitrogen.





That should be it.
The dampers come standard with spherical bearings. They clank like crazy. I machined aluminum bushings for both top and bottom mounting points to try to isolate the range of movement of the damper but they didn't help. I even used o-rings between the bushings and the bearings and that didn't help either. It's not like the clanking will make the car fall apart. But it's fairly annoying. I ended up pressing out the spherical bearings and using the OEM damper bushings which I ripped out of joints on the stock dampers. Then used some heater hose to secure their sideways movement. Not the most elegant solution but works like a charm. This is the fail.





By the way, the blue boot you see is just something I got off ebay to protect the shaft from dirt etc. It is not part of Bilstein's delivery.

This is what they ended up looking like after the bushing mod.

[Tomas]

I was able to convert the stock Bilsteins to take aparts. Both for the fronts on the 6 and the rears on the 3. Pretty sure you can convert all OTS Bills into take aparts. All it takes is drilling and taping a 1/8 NPT on the gas side of the shock as per the pics and then installing some scraeder valves.

Both Bills have digressive pistons with compression only bypass valves. Pretty neat. Not sure if all HD or Sport have that but I would bet there is a good chance they do. I measured the shims on both and added them to the list. From there, I increased the thickness of the shims, or changed them, according to what I wanted to achieve.

The epoxy secured shraeder valves might not be the most elegant solution but they work. I scrapped welding for two reasons: 1x I couldn’t find shraeder valves made of steel - they were all brass. And 2, ain’t nobody got time pho dat. As of today it seems to work.

Drill and tap here



Take dust cap off with knife, remove snap ring for shock cap, saw some slits into shock cap so you can remove with screw driver, and then pry cap off.





Push cap down so you can take off snap ring







Take out shim stack and shaft.



Pour oil out into container, and then tap and glue shraeder valve in place.





I disassembled the valve stack and measured all the shims. They are listed on the attached file.



I have looked through the interwebz trying to find of information on how to valve shocks but failed. There are plenty of sites telling people what valving combinations to use but none really explain what all the individual shims do. Either there really isn’t anything out there on how to do this or I hais the retards. Both are distinct possibilities. Bilstein has a very simple explanation of their shim stack but it is ambiguous IMO.
When I am more initiated into the shim stacks I will post what I believe they do at the different forces and velocities. As of now I am only about 90% sure so I’ll hold off.

[phate]

I've been eyeing this recently:

http://www.shimrestackor.com/index.htm

@zenit; says he has used it.

[Tomas]

Thanks.
But that doesn't help me much for what I am trying to do.
I need to equate valving changes to driving characteristics of the car. Not just how the valving changes will affect damping forces on a dyno plot. I have a pretty good idea right now just by looking at the list of shims on a stack how the plot would look like if I were to put the damper on a dyno. Don't really need software for that unless I were to have target force and velocity points on a plot. That is not what I am trying to do. At least not now.

[zenit]

Originally Posted by phate I've been eyeing this recently: Shim ReStackor, Finally software to tune a shim stack @zenit; says he has used it.

Yup.

[Tomas]

9 rear re-valvings and 4 front re-valvings later I am still experimenting with different stacks. I am getting better at this though. Fronts feel almost 100% for the 750/200 springs and the rears need more for low speed rebound I think.

A note to those experimenting with this: Don't change the compression damping from the original damping. The ride will get very harsh very quick with very little increases in damping force. Rebound is a whole different animal however. At least from the perspective of my seemingly insensitive arse small changes in rebound are barely noticeable. Generous increases are needed here.