lowered 911, shorter rear shocks?

[Elombard]

I am thinking about raising the spindles on my 84 hot rod to have a lower ride height while retaining suspension travel. I always thought that if I lowered the front to approximately level lower control arms with raised spindles on 15" fuchs I would be a bit over 24" at the fender with the tires I run. Then assumed I could lower the rear to whatever it needed to be with a bit of rake (using the scruggs alignment specs).

The other day I was reading about a high end build here and the owner sent his rear bilstiens to bilstien to have them shortened so that suspension travel would be preserved.

Any body have more info on this? I had not heard that before, are the ER (Von?) shocks for the rear shorter? Any body know how much suspension travel you have on the rear of a lowered T bar car?

I need to go out an look under mine and see what I have now.

[Elombard]

Pelican Parts.com - Von Sealed Rear Shocks (Single Adjustable)

In the description here you can see indeed that they are advertised as shorter for more suspension travel for lowered cars.

How much shorter I wonder?

[Trackrash]

Some things to consider, HBTDT.

Make sure the new shocks you get really are shorter than stock, and if you really need shorter shocks.

Make sure that the shocks you end up using allow you complete suspension travel.

Make sure that your bump stops keep your CV boot from hitting your oil lines when at full bump.

You should use stiffer than stock torsion bars.

[Elombard]

Hey Gordon, I was actually hoping to stick with my fairly fresh bilstiens and not have to buy or shorten the existing shocks. I expect you might have to use shorter shocks on a full race car but not a DE street fun car

[Trackrash]

Originally Posted by Elombard

Hey Gordon, I was actually hoping to stick with my fairly fresh bilstiens and not have to buy or shorten the existing shocks. I expect you might have to use shorter shocks on a full race car but not a DE street fun car

You could be right. Most guys who lower the rear only need to cut the bump stops. Depends on how low, the shocks, and which torsion bars.

[gestalt1]

I actually cut the tops off the shock mounts and raised them about 3/4". I don't recommend this because it is a lot of work. Much better to just get shorter shocks.

[Driven97]

You might want to measure and see if shortened shocks are even necessary.

When I bought my car, it was on 17" (25" tall overall) tires and soft OE bars. On full length struts with intact bump stops the LR tire would contact the wheel well on hard acceleration. I do not know if I was hard into the bump stop or not at that point, but considering that people can (and do) shorten the bump stop says to me there is a lot of compression travel in the stockers.

[Tom Elder]

Hi Erik

I don't know for sure if this info will help you, I am not knowledgeable in the detail differences between my 1970T and your 84. But I am working on a similar issue.

I have been dialing in my stance and suspension settings. I have raised front spindles and lowered the rear. I don't have my notes here to tell you the exact number but around 24" at the rear. I could feel I was riding on the bump rubbers. The rear Bilsteins HD came with 30mm packer and the bump rubber. I parted off the packer roughly 60/40 in a lathe, and put the new cut down 17mm packer back in. Ride has been improved. I do not run any dust shields on the rear dampers, no room in the '70 body. I have put a little bit of plasterzine on top of the damper body to check to see if I am getting into the bump rubber during my casual daily commute to work. I have not rechecked this yet and if I find I am still getting into the bump rubber, I may try a 10mm packer or no packer but will retain the stock bump rubber.

How much do you plan to raise the front spindles? When I did my initial research on this, I had read different suggestions, 17, 18, and 19mm was possible with the 15" wheel. I decided to go for the middle ground at 18mm. At 18mm the control arm does interfere with the wheel at bump and lock. I trimmed the flange back on the leading edge of the control arm and it still inferred with the wheel. I then added 6.35mm (1/4") wheel spacers. Wheels are 7" x 15", boge struts and the car has rolled fenders.

In the process of resolving the inference issue I did some more googling and found that maybe 16mm is the limit for raising the spindle with a 15" wheel, without additional control arm trimming and spacers.

[Elombard]

Thanks Tom for the info.

Yes my plan was to be conservative on raising the spindle so 16 or 17mm maybe.

I did not get a chance to look at the measurement on the rear shocks yet. The next question then is do you get good damping out of the rear shocks when only using an inch or two of travel at the compressed end of its reach. I am thinking about shock dyno charts and it seems like they are pretty linear until you get to the very end but I need to do more research.

I am running fairly stiff T bars and adjustable sway bars, I will not tolerate wheel rubbing so I will have to raise ride ht if that becomes an issue.

[Driven97]

Originally Posted by Elombard

The next question then is do you get good damping out of the rear shocks when only using an inch or two of travel at the compressed end of its reach. I am thinking about shock dyno charts and it seems like they are pretty linear until you get to the very end but I need to do more research.

Oooh, I'll take this one as I'm ankle deep in researching shocks right now.

The piston in a shock should not care where it is in the stroke range. You just absolutely DO NOT want to bottom one out.

If you're talking about shock dyno charts like this:


These plot shock forces vs speed, not position.

The chart above is of a digressive valved shock. The upper part is bump (compression) and the lower is rebound (extension.) Notice the forces ramp up very quickly at low shock velocities. Up to about 4"/sec or so is transitional stuff. Turning in, getting on the gas, getting on the brakes. The higher forces at these shock speeds control the body motions much better than if you have an old-school linear valved shock.

~10"/sec is stuff like tar filled expansion joints in bump, pavement cracks in rebound, or even larger bumps with a more round profile like track curbing. The valving on the above shock "blows open" at these higher velocities and the slope either severely decreases or even flatlines at a maximum, absorbing the bump without excessive damping.

My buddy was telling me he was testing a damper for an off road military vehicle to shaft speeds of 40"/sec (!). That seems nuts, I wonder what shaft speeds Baja trucks see:

[tirwin]

Erik,

I recently did a rear suspension refresh. I did 28's for the torsion bars, ER polybronze bushings, ER adjustable spring plate and Chuck re-valves my rear Bilsteins on a digressive curve. I have the dyno charts at home but I am on the road the next couple of weeks. When I'm back home I could post it for reference. Since you're local, you're more than welcome to drive my car.

The rear shocks were shot before and I must not have realized how bad it was. The rear end bounce test before I did the work was pretty bad. People always say that it's a harsher ride when you increase the size of the t-bars but I increased my t-bar size, and with the other stuff, it now handles better and is much softer when hitting potholes and dips in the road. The shocks probably had the most to do with it.

I've been futzing around with the rear ride height to get it to the right height AT the middle of the spring plate adjustment so it can be properly corner-balanced later. My first try I was at 24" at the wheel well and I think that's about as low as you could reasonably go. I have spacers on the rear wheels so they "fill" the wheel arch. Any lower and the tire would rub on the fender when the rear end sits down. Optimal is probably closer to 25" in the back. I run 16x6 & 7 Fuchs by the way.

I'm seriously considering raising the front spindle height by 30mm too. I *think* you need either spacers or adjustable tie rod ends to achieve what you're looking for, but maybe not. FWIW, I was just looking at my front suspension the other day (mine is lowered already) and I noticed that the tie rod end seemed like it was at a really severe angle to the horizontal plane at the spindle. I don't see how the ride height could be lowered any further without changing the rest of the geometry in some way. I think raising the spindle height would help make the angle more to the neutral plane, if that makes sense. A picture would probably be better than my lame explanation.

Don't know if that helps or not.

[Ferrino]

Great thread. I've also wondered about bottoming out rear shocks on lowered cars. When I set up my ride height, I'll make a note to figure out where the stock shocks sit relative to the center of their travel...

[Elombard]

your right Matt those are the graphs I was thinking about and I remembered what they show incorrectly. Thanks for the info

I have bump steer spacers on the front tie rods already so I should be all set if I raise the spindles.

[john walker's workshop]

Bilstein rears have nylon spacers that can be removed.

[safe]

Bilstein Club Sport (B46-0967) ARE 20 mm shorter than normal HD.

[KTL]

Shortening the front shocks is worth considering for those who have not raised the spindles. Even if you have not lowered the ride height much at all. Reason I say that is because I used to have a set of single adjustable Koni front shocks and one of them apparently bottomed out, jamming the adjuster.

My car was not excessively low and I made a point of keeping the ride height not too low. The bump stops were not removed. Stock suspension is pretty soft and allows for a lot of suspension travel. My Koni actually bottomed out with stiffer 23mm torsion bars.

Also, 30mm raised spindles is pretty tight on 16 in. wheels. The wheel pictured below is a 16" BBS RS 3-piece wheel mounted on a Bilstein spindle raised 30mm by Clint at Rebel. That's pretty tight clearance. Especially considering the BBS rim shell provides about as much clearance as you'll find, due to it's modular/3-piece construction.

[will hung]

Originally Posted by KTL

Shortening the front shocks is worth considering for those who have not raised the spindles. Even if you have not lowered the ride height much at all. Reason I say that is because I used to have a set of single adjustable Koni front shocks and one of them apparently bottomed out, jamming the adjuster.

My car was not excessively low and I made a point of keeping the ride height not too low. The bump stops were not removed. Stock suspension is pretty soft and allows for a lot of suspension travel. My Koni actually bottomed out with stiffer 23mm torsion bars.

Also, 30mm raised spindles is pretty tight on 16 in. wheels. The wheel pictured below is a 16" BBS RS 3-piece wheel mounted on a Bilstein spindle raised 30mm by Clint at Rebel. That's pretty tight clearance. Especially considering the BBS rim shell provides about as much clearance as you'll find, due to it's modular/3-piece construction.

I can vouch for this. I had Chuck raise my spindles 30mm and I had to have my wheel weights moved inward to clear the bottom of my ball joints. I'm running 16x7 Fuchs.