Bilstein & Others Shock Lengths

[Sixty's Guy]

Hi all. I thought I would share some info that I have learned over the last year or so about shock lengths to suit the 60 series Cruisers. I have included info on Ironman shocks, OME and some Bilstein info. Maybe someone can use this info for their benefit and not have to research as much as I have.

BTW, I have included some info on 80 series rear shocks that bolt onto the front of the 60 series. I have never done this, but MAF use rear 80 shocks in their shackle reversal kit and Rancho in Aus list rear 80 series shocks for large lifts in the front of a 60. According to the Bilstein valving reference chart the valving should be similar.

 

[ntsqd]

All of the Universal Fit Bilstein's (those sold by length rather than application) come with 255/70 valving unless special ordered with something different (if possible?). That is their standard valving for leaf springs. 360/80 is more appropriate for coil springs, but even that may not be enough for coils if high speed dirt roads are on the mix of uses. And 255/70 is a bit soft for the GM 63's. I've gone to 275/78 for those, but testing is still IP.

Did you find a valving spec sheet for the stock application dampers? If so I would be very interested in seeing it.

 

[ntsqd]

BTW, have you seen this file?
http://northwest.2bigbroncos.org/technical/shocks_files/shock_specs.xls
I created it years ago, but it might still have some useful info in it.

 

[Sixty's Guy]

All of the Universal Fit Bilstein's (those sold by length rather than application) come with 255/70 valving unless special ordered with something different (if possible?). That is their standard valving for leaf springs. 360/80 is more appropriate for coil springs, but even that may not be enough for coils if high speed dirt roads are on the mix of uses. And 255/70 is a bit soft for the GM 63's. I've gone to 275/78 for those, but testing is still IP.

Did you find a valving spec sheet for the stock application dampers? If so I would be very interested in seeing it.

I have the Bilstein 5125 installed front and rear in mine. Going by this; http://www.bilstein.com/ValvingQuickReferenceChart.pdf theoretically the rear 80 series shocks might be ok for the front of a 60. I say 'might', because I don't know for sure.

I found some specs of the original shocks for the FJ40, FJ45 and FJ55, but they list the compression and rebound stats differently to Bilstein.

 

[Sixty's Guy]

BTW, have you seen this file?
http://northwest.2bigbroncos.org/technical/shocks_files/shock_specs.xls
I created it years ago, but it might still have some useful info in it.

Yeh, I have that one too! Thanks!

 

[Norris Marshak]

Anyone interested in a set of Bilsteins for a 60(not much use) should drop Stainless 40/45 an e-mail. I'm sure the price will be right.

 

[lehiguy]

Bilstein numbers

Bilstein is the only manufacturer I have even encountered that publishes a value for shock performance or resistance. Unfortunately, it's only one number to try to quantify something that is speed sensative, meaning there is a progressive curve when it comes to resistence vs. shaft speed. The way you feel dips in the freeway (slow speed dampening) has absolutely nothing to do with the way the shock reacts to a square edged hole or a tree root (high speed dampening). I found virtually all Bilsteins to be very nice on the road but over dampened on high speed. This can be remedied if you want to rebuild and revalve them, anybody who has ever done a motorcycle shock will immediately figure out these shocks, they are fairly simple. I built about five different shim stacks before settling on one that worked for my Cruiser. Untimately I ended up with about the same slow speed dampening, less mid range and tons less high speed with more rebound dapening on the rear shocks. Now The jolts from rocks, roots and the occasional Honda Civic, are absorbed and not transfered into the vehicle nearly as much. This is probably useless info for most people, I just thought I'd throw it out there. If I get extremely motivated I may even post the shim dimensions for those stupid, er, brave enough to build their own shock.

 

[ntsqd]

I want to say that I've seen actual damping force numbers for one other shock mfg., but to my best recollection it was for Penske shocks, which has no off road application at all.

I would be interested in which shims you used. I've a feeling that I'm not going to be happy with the off the shelf valving.

FWIW if you can find the Penske Damper manual pdf out there somewhere, it has some excellent damper tech in it. Among other topics, it talks about what the difference btwn progressive, linear, and digressive pistons is. As I understand it, Bilstein mostly uses digressive pistons in off road applications.

 

[lehiguy]

I want to say that I've seen actual damping force numbers for one other shock mfg., but to my best recollection it was for Penske shocks, which has no off road application at all.

I would be interested in which shims you used. I've a feeling that I'm not going to be happy with the off the shelf valving.

FWIW if you can find the Penske Damper manual pdf out there somewhere, it has some excellent damper tech in it. Among other topics, it talks about what the difference btwn progressive, linear, and digressive pistons is. As I understand it, Bilstein mostly uses digressive pistons in off road applications.

Bilstein claims "digressive, self adjusting" but I'm not sure that's really true. The piston itself doesn't do much other than seal against the shock body and direct the fluid through the valve stack, a different one for rebound and compression, there really is no other way to do it. They are, in fact, progressive since resistance increases with shaft speed. This can be decreased by reducing the thickness of the final two or threee shims in the stack. I think I took out some that were .35 mm and ended up with some that were .20 mm thick. This allows the shim stack to "blow open" easier when a sharp impact occurs. The rears require a different set of shims than the front since the springs are stiffer, the shock orientation is different, and the dynamic forces of the vehicle are different on the rear. I have more slow speed and more rebound dampening on the rear than I do in front; it just worked better this way. Any Bilstein with a silver body, except the 5150s, can be rebuilt. I like to outfit them with remote resevoirs, as you can pick up two inches more travel by getting rid of the dividing piston that keeps nitrogen and oil separated, and installing a shaft that is two inches longer. The parts are fairly cheap, I usually rob resevoirs from old motorcycle junk and build the plumbing myself.

 

[ntsqd]

The geometry of the piston around the ports thru it can determine whether it is digressive or not, and by adding a small OD shim or two btwn the largest OD shim and the piston you can revert a digressive piston to be linear. There are some really good diagrams of this in that Penske manual.

It is really rare, from what I've read and seen, for a damper to be truly progressive as reportedly that ride is miserable. At most they are linear. But "linear" labeling is misleading since the slope of the line can be very steep. A simple linear would be if you doubled the shaft speed the damping force would also double, but the damping force could also increase by 6.708 times and still be called linear. A progressive curve would increase the damping force by some exponential power. Digressive is when the damping force tapers off with an increase in shaft speed and is usually some sort of Root function (square root, cube root, e^3.1415*S root, etc.). Believe it or not there are guys who enjoy doing that sort of math modeling. I'm glad they're out there and I'm glad I'm not one of them.

Self adjusting and Digressive are not mutually exclusive. Though I'd call it velocity sensitive rather than 'self-adjusting' but that's marketing fighting off the erroneous perception of the superiority of Rauncho 9000's.

LOL, I'm just recalling reading a primer, written by a gal, for gals going desert racing with their boyfriends/husbands/etc. She said "Guys can talk shock valving forever, bring a book."

 

[lehiguy]

The geometry of the piston around the ports thru it can determine whether it is digressive or not, and by adding a small OD shim or two btwn the largest OD shim and the piston you can revert a digressive piston to be linear. There are some really good diagrams of this in that Penske manual.

It is really rare, from what I've read and seen, for a damper to be truly progressive as reportedly that ride is miserable. At most they are linear. But "linear" labeling is misleading since the slope of the line can be very steep. A simple linear would be if you doubled the shaft speed the damping force would also double, but the damping force could also increase by 6.708 times and still be called linear. A progressive curve would increase the damping force by some exponential power. Digressive is when the damping force tapers off with an increase in shaft speed and is usually some sort of Root function (square root, cube root, e^3.1415*S root, etc.). Believe it or not there are guys who enjoy doing that sort of math modeling. I'm glad they're out there and I'm glad I'm not one of them.

Self adjusting and Digressive are not mutually exclusive. Though I'd call it velocity sensitive rather than 'self-adjusting' but that's marketing fighting off the erroneous perception of the superiority of Rauncho 9000's.

LOL, I'm just recalling reading a primer, written by a gal, for gals going desert racing with their boyfriends/husbands/etc. She said "Guys can talk shock valving forever, bring a book."

Good one! I'm not much for numbers, I just start with what I have and make incremental adjustments. Dirt bike shocks are where I started all this, it just happened to come in handy on the Cruiser once I found out about Bilsteins and how they are made. Simpletons like myself usually refer to the small shim between the piston and the actual shim stack a "bleed shim". Bilsteins have them, bikes do not, they use an adjustable orifice. I used to desert race motorcycles now that you mention it.