How to tell difference between trailing arms?
 

I bought a twin turbo wide body conversion (based on a 1975 911) with some pretty aggressive suspension modifications and I am trying to figure out if the rear trailing arms are the stock 1975 pieces or something more stout.

Are there any easy visual ways to tell the difference from underneath the car?

Also, the front end seems to 'clunk' over bumps in the road - very unlike my 911 SC. I have coil over shocks in the front. Is this noise indicative of mono ball or other race suspension?

Thanks for the help.

All the aluminum rear trailing arms from 74-on are basically the same. So unless they swapped them out for 930 trailing arms they wouldn't be more stout than stock. To install 930 trailing arms would require changing the torsion tube or relocating the mounting points. If you have 930 rear arms the brake caliper would be mounted on the back of the rotor and with the standard trailing arms the caliper is mounted on the front.

If the '75 was a Carrera it would have come with turbo trailing arms.

See if the brake mounts are forward or behind the axle line.

Not true. The '74 had ball type drop link mounts. Later SC have bolt on drop links.
-C

Trailing arms.........
 

Charles,

You are correct. The '74-'76 CIS cars have the ball type drop link mounts. While the '78 SC and later have the bolt on drop links.The cars in the garage are '77S, '78 SC, and '89 cabriolet.

Tony

Talking about a clunk or thud, it is most likely the firewall (oil canning) I'm going through the same drama in my hot rod 77 coupe with mass suspension work, my car being rhd and non boosted the firewall flexes, I'm thinking of putting a dimple in it to slightly compress the sheet metal.

There a part number and date on trailing arm should be easy to know what you have.

Ahh, I don't think so...

JR

My statement was absolutely true in answering his question. He asked if his suspension was more stout not if he had early or late aluminum trailing arms.

My apologies. It was late and I was thinking of the later M491 turbo looks.

Thanks for the info. I will check caliper placement tonight.

Also, the clunk is definitely in the front end. If it was an old muscle car I would say the ball joints were worn out - same type of sound.

Also, the part number will be cast on it

I agree that neither is likely stronger than the other, but I've never sawn one of each in half to see if the wall thickness is different (more or less stout) But for the sake of clarity and interchangeability they are not the same. The later SC rear suspension used a heavier swaybar, which is also not interchangeable with the earlier style suspension.

Ironically the earlier CV's are larger and stronger than the later SC era joints, and to switch out to the SC trailing arms on my '74, I also had to change the output flanges on the transmission to accommodate the SC CV's.

Here's the write up on my rear suspension re-build:
http://forums.pelicanparts.com/porsche-911-technical-forum/821403-were-off-74-rear-suspension-rebuild.html

-C