How Too - Fit Aluminium Trailing arms to a pre 1974 911

[Luke]

The pre 1974 911’s had steel trailing arms, they are heavy and they dent quite easily. As part of a full suspension rebuild I decided to replace mine with aluminium versions as they are both lighter and stronger, and don’t suffer from the dreaded rust. As this modification is something I think quite a few early 911 owners might consider and one I’ve completed I thought I’d run you through the procedure and what parts you’ll need.

Parts required:

Aluminium Trailing Arms – Preferably from a 1974 car, these arms will accept the existing CV joint and half axle set up without modifications. They also have the “nipples” required to attach a OEM anti-roll bar. Arm’s newer than 1974 require you to change all or part of the CV joint/axle assembly so it’s worth hunting out a 1974 pair. I got mine for 100gbp I believe (they required a little work as PO had stripped the thread for the shock absorber bolt, then welded a bolt in place, so I needed to drill out the old bolt and heli-coil the thread, hopefully you won’t have a similar experience)

Hubs – You will need to get a pair of 1974 onward hubs, as the pre 74 hubs have an offset 5mm deeper than the later hubs. In effect if you fit the pre 74 hubs your brake discs will sit too far out and your brake callipers wont fit (which you’ll agree is rather irksome) My hubs came from http://www.early911.co.uk/ for 50gbp

Bushes – After much research there are only 2 options to replace your trailing arm bushes: OEM or monoball, monoballs are very expensive and give a hard ride so unless you’re racing OEM are the thinking man’s choice. Poly bushes are not viable in this application as the trailing arm joint actually moves in 3 dimensions which leads to poly bushes squeaking like a bag of stoats. OEM bushes are around 15gbp + vat each and you require 4. Monoballs are much more, check out http://www.elephantracing.com/suspensio ... noball.htm

Wheel Bearings - You will have probably knackered your wheel bearings removing the hubs from the assembly, if not they’re over 30 years old and will be in need of replacement, may as well change them while you’re in there, they’re about 30gbp + vat.

2x Accentric camber adjust bolts – The pre 1974 accentirc bolts to adjust camber are considerably shorter than the 1974 onwards bolts. Whilst your pre 74 bolts will fit one of the adjusters you will need to buy 2 of the newer type (1 each side) from your OPC (17.50 + vat each)

Non Essential Items – Whilst you’ve got the arm off, there are a lot of items you can replace, parking brake shoes, brake lines, brake pads, brake discs, rear shocks, spring plate bushes, torsion bars etc

So how do you get the old arm off and the new ones on?

Firstly jack the car up and put it on stands, you’ll be using a fair bit of force to move some of the parts so you don’t want it falling off the jack.

Remove the rear wheels, then you will need to loosen the large castle nut that holds the stub axle in place, you’ll need to remove the existing split pin and then get a very large (34mm I think) socket and a very, very long, strong bar and undo the nut, you’ll need to do this BEFORE disconnecting the brakes as you require an awful lot of force to budge that nut. Now unbolt the callipers, remove the brake discs,and baffles and disconnect the brake lines from the connections on the trialling arms. Ensure you also disconnect the parking brake cable from the brake assembly.

You will now need to remove the 2 accentric bolts and 2 standard bolts securing the trailing arm to the spring plate. Make sure you keep all the bolts and washers, and note the order the washers are arranged in (a digital camera always helps) Note that you will not have to reset the ride height of your car unless you remove the spring plate, spring plate removal is NOT necessary to get the trailing arm off, however “while your at it” now is a good time to replace worn spring plate bushings.

The next step is to unbolt the shock absorber from the arm, there is one, large bolt running through the base of the shock into the steel trailing arm, simply remove the bolt and the trailing arm should now swing free (now’s a good time to replace the shocks too if you want).

Now here’s the tricky bit, the arm is attached to the body way up near the engine firewall, either side of the gearbox. The pivot bolt holding the arm in place cannot be removed without dropping the gearbox (I don’t care which way around the bolt is located, head toward centre of the car, or head toward wheel arches, there is NO WAY to remove the bolt without dropping the gearbox, some people suggest that you can remove the bolt without dropping the gearbox but it just ain’t true)

So you need to lower the gearbox, make sure you disconnect the speedo cable , clutch cable , and shifter coupler (inside the hatch in the middle and in front of the rear seats), you may also need to disconnect the earth strap going from the engine mount/body to the gearbox. Place a jack under the gearbox, ensure you’ve got a bit of wood on top of the jack so as not to damage the gearbox, then carefully undo the engine mounting bolts at the gear box end of the car. DO NOT remove the engine mounting bolts at the cross member (fan end of car) as obviously this will result in an entire engine drop, what you want to do is tilt the gear box downwards enough to be able to extract the bolts, you’ll need to tip it to about 30 degrees (at least I did)

Once you have the bolts out, Bob is your father’s brother, the arm should, with a little persuasion, drop out.

To install the new arm just do the reverse of the above. You’ll need a new Nylock nut for the trailing arm pivot bolt for safety’s sake, and make sure you insert the stub axle into the hub before you bolt the arm to the spring plate otherwise it just plain won’t fit.

The trickiest part of the installation is readjusting the parking brake and getting the pre-requisite 235nm torque (or some such ludicrous value) on to the stub axle castle nut. I used a HUGE torque wrench and 2 burly men. (no comments from Cubist)

Note: SWB cars need not apply.

[hot66]

nice write up Luke.

I think we need a seperate section for technical articles like this.

[Miggs]

yes sounds good any takers to moderate it

[Nick Moss]

Nice article Luke. I could not have written it better myself.

Miggs, count me in as techie moderator if you need one