1971 Rear Shock Geometry

[Danimal16]

I am in the process of switching the steel rear arms to the later aluminum. I am evaluating the shock options for this modification and am familiar with the known information regarding the change in size of the shock mounting bolts between the 71 and the 74's, i.e. 12mm v. 14mm.

I also looked at the dimensions of the Bilstein shocks for those two years. The 71 uses a B46-0167 with an extended length of 555mm and a compressed length of 378mm. The 74 uses a B46-0169 with an extended length of 582mm and a compressed length of 396.5mm (thank you Bilstein).

The situation that I am requesting has to do with the proper length of the shocks for the modified set up. I understand that the post 74 911s had a change in the location of both the upper and lower shock attachment point, relative to the 1971. In order to calculate the appropriate shock length I need the data on the shock attachment geometry.

Can anyone please provide the information or point me to the source of this information that shows the change in the rear shock attachment points?

Thanks in advance.

[djdsc]

Excellent thread on the 911 S Registry:

Swap steel trailing arms with alu trailing arms? - Early 911S Registry Bulletin Board

[Danimal16]

djdsc,

I saw that article before. Excellent post along with Sherwood's famous 1996 write up. What I am looking for is actual information showing the change in the upper and lower attachment points.

DanB

Originally Posted by djdsc

Excellent thread on the 911 S Registry:

Swap steel trailing arms with alu trailing arms? - Early 911S Registry Bulletin Board

[Flieger]

Clint at Rebel Racing does coil-overs and has a setup for early cars with Aluminum arms (he has a 1970 911T with coil-overs and Aluminum trailing arms). For that, he uses an inverted Bilstein damper and reports no geometry issues or binding. I would advise you to contact him to see if his dampers can work for your torsion-bar car.

clint@rebelracingproducts.com

(805) 440-9849

Home

[BURN-BROS]

My opinion is to retain the shorter shocks and buy/make a 14mm/12mm step down stud to mount the early shock to the aluminum trailing arm. A minimum of 1/2" has to be taken off of the trailing arm to prevent the dust cover from rubbing on the shock body. We just converted a car and found that the longer shocks can run out of travel depending on ride height.