1971 911 Suspension help

[sebastianroher]

Evening,

I'm looking at installing a set of Bilstein RSR coilovers and 935 spring plates on my 71T. Does anyone know what all is involved in the setup? The coilover setup I was thinking about going with ( https://patrickmotorsports.com/products/sus91134019rsrpms ) says they fit 72-89, what will I have to modify or work around to get this setup to work on my car? Thanks for your help!

-Sebastian

[H-viken]

It should be bolt on, but you should reinforce the rear crossmember since it’s not designed to take the load from the coilovers

As an alternative to Bilstein, have you considered KW’s solution?

[sebastianroher]

Originally Posted by H-viken

It should be bolt on, but you should reinforce the rear crossmember since it’s not designed to take the load from the coilovers

As an alternative to Bilstein, have you considered KW’s solution?

I have purchased the kit from Elephant Racing to reinforce the crossmember while the car is in paint/body. What is the difference between the KW and the Bilsteins?

Thanks for your help,
Sebastian

[snbush67]

The kw’s are adjustable.

[sebastianroher]

Originally Posted by snbush67

The kw’s are adjustable.

Which model KW's?

[snbush67]

Im researching KW, this thread may help answer your question.

https://forums.pelicanparts.com/porsche-911-technical-forum/1069640-anyone-kw-v3-struts-shocks.html

[Tremelune]

The biggest issue is the 1971 cars had narrower rear shock towers and steel trailing arms with slightly different mount points such that the coilover springs will foul...

https://www.early911sregistry.org/forums/showthread.php?60673-Anyone-put-a-coilover-suspension-in-a-70-911

You might be able to get away with turning the rear dampers upside-down and using narrow springs or modifying the trailing arms...maybe replacing with aluminum arms?

I'm curious to know where you land, because I want to do the same on my '70 without welding in new towers and what not...

[Trackrash]

Originally Posted by Tremelune

The biggest issue is the 1971 cars had narrower rear shock towers and steel trailing arms with slightly different mount points such that the coilover springs will foul...

https://www.early911sregistry.org/forums/showthread.php?60673-Anyone-put-a-coilover-suspension-in-a-70-911

You might be able to get away with turning the rear dampers upside-down and using narrow springs or modifying the trailing arms...maybe replacing with aluminum arms?

I'm curious to know where you land, because I want to do the same on my '70 without welding in new towers and what not...

Also, note, up to '72 the rear shocks are shorter than the later ones. Make sure you have enough travel. Otherwise you will have to go to the aluminum trailing arms.

[sebastianroher]

Originally Posted by Trackrash

Also, note, up to '72 the rear shocks are shorter than the later ones. Make sure you have enough travel. Otherwise you will have to go to the aluminum trailing arms.

What is your advice on swapping to aluminum trailing arms? Certain year to look for in particular?

[Tremelune]

My advice is not to...The weight savings is like 10lb and the work to get the dampers, brakes, and axles to work with them can be onerous. You may just be able to remove the damper dust shield and whack the tower with a hammer a bit, or you might be able to grind/machine the trailing arm to position the dampers such that they no longer rub...or you might need new wheel bearings, something for the axles, new dampers, machine work, hammer work...

This is the thread that turned me off from it:

https://www.early911sregistry.org/forums/showthread.php?76735-Aluminum-trailing-arms-and-rear-Aluminum-S-Calipers

This is why:

https://members.rennlist.com/911pcars/911AlloySuspAll-a.pdf

I didn't know the dampers were different lengths...Is it enough that it really causes an issue? Like, does it bottom out or mess with the valving...? I now fear the hot setup is only available on '72+ cars...

[Trackrash]

There are a couple of differences. From '72 the shocks are about an inch or so longer, and the bottom mounting bolt is 14mm instead of 12mm. And the angle is slightly different with both the upper and lower mounting positions being moved slightly. You can see some old posts were the aluminum trailing arms had to be modified so the shocks don't hit the exhaust. Personally I would put bigger torsion bars in and call it good especially if the car is lowered. This compares two Koni shocks, the red is the older and yellow is the newer.

[sebastianroher]

Originally Posted by Trackrash

There are a couple of differences. From '72 the shocks are about an inch or so longer, and the bottom mounting bolt is 14mm instead of 12mm. And the angle is slightly different with both the upper and lower mounting positions being moved slightly. You can see some old posts were the aluminum trailing arms had to be modified so the shocks don't hit the exhaust. Personally I would put bigger torsion bars in and call it good especially if the car is lowered. This compares two Koni shocks, the red is the older and yellow is the newer.

I may do that...I just can't shake the idea of 935 spring plates and coilovers. I know Elephant Racing makes a coilover set for my car, just pricey is all!

-Sebastian

[Tremelune]

Originally Posted by sebastianroher

I know Elephant Racing makes a coilover set for my car, just pricey is all!

Wait, do they?? I strongly suspect they're subject to the same limitations, and that Elephant expects the customer to sort it out. I would love (love) to be proven wrong, because I absolute hate reindexing the rear torsion bars, and it seems like I do it every year for one reason or another...

[sebastianroher]

Originally Posted by Tremelune

Wait, do they?? I strongly suspect they're subject to the same limitations, and that Elephant expects the customer to sort it out. I would love (love) to be proven wrong, because I absolute hate reindexing the rear torsion bars, and it seems like I do it every year for one reason or another...

https://www.elephantracing.com/porsche/911/coilover-kits-parts-for-911/coilover-shocks-struts/

[Tremelune]

Interesting! The Elephant shocks have shorter spring perches so they clear the towers. I got in touch with them and Erik had this to say:

"The shocks are same length of travel as the later versions, the springs are shorter but have the an equivalent rate to them to compensate for the shortness. The only issue we have come across is the swaybars or axles possibly being a bit close to the springs, as well as the shock towers needing to be massaged a bit on the inside for clearance purposes. Hand built cars am I right."

I asked Motion Control the same questions:

"We are very familiar with the application and recognize the challenges with the narrow towers on the early model cars. We are in the process of producing a special rear upper spring perch (deeper) for eye-pin shock configurations for use in CO conversions that will work better in the tower. With that said, stock exhaust manifolds with heater boxes always introduce some level of interference, and like any application where a coil spring is being introduced to an area that it was not originally designed to fit, there can be some level of fitment exercising/massaging for a clean execution."

KW does not offer anything for cars earlier than '74.

[Trackrash]

Here is a thought, if you really are set on the 935 setup. Contact Koni racing and see if they can put together the correct coil over setup. They have any number of shock sizes and they can, I believe, re-valve for your car. Springs also come in a variety of sizes. https://www.koni.com/en-US/Cars/Products/Racing/

Then just add the trailing arm. But as mentioned, headers and other things might cause issues. If you search there have been some pictures posted showing rear coilover setups.

BTW, I got lucky and found a set of vintage Koni racing shocks for the rear of my car. Was very lucky, as they USED to make them for the older 911s.

[yelcab1]

Interference galore. Be prepared.

[dwa917]

depending on where you are and how far you want to go... you could consider changing the rear cross member - that is what I did for my 71 - converted to 73 RSR suspension with RSR coilovers, RSR steel trailing arms, RSR brakes, etc... albeit I was starting from a complete teardown and rebuild of the entire car...

I used the 964 part - designed for coil overs... part number is 964.501.075.00 or superseded to 964.501.075.02 (sold by our hosts) https://www.pelicanparts.com/More_Info/96450107502GRV.htm?pn=96450107502GRV&bt=Y&fs=0&SVSVSI=0834

It fits right in and plenty of room...

[Tremelune]

That is...somewhat alarming! How do you position the new crossmember to the millimeter? It looks like your chassis is sitting on a Celette bench.

[dwa917]

You're right. I had the same thoughts. That's why I found and paid a porsche expert with a Celette bench to do it.