Trailing Arm - Bent/Damaged?

[Magnum]

Hi All

I'm in the middle of upgrading the steel trailing arms (on my 3.2 engined hot-rod) to aluminum arms, which I've had vapour blasted and sorted out the pre-73 ball-pin mounting for roll bar (on the later arms), thank you Mike Bainbridge for some helpful hints!

So my question - when standing the arms on the flat mounting face of the bearing retainer plate and comparing end to end, one appears taller than the other. I am obviously concerned that one (unlikely both) is bent or damaged.

So:

1) Would you continue to use these arms and take confidence that bushes etc will permit proper settings to be achieved?
2) How would one determine this as I'm sure that Porsche service centres (well at least in Cape Town, South Africa) no longer carry related jigs to measure these?

Photographs:








Your help/thoughts most appreciated!

[911hillclimber]

That is a big difference for a bush to accommodate, and a difference in the wheel base as a result.
I doubt Porsche would have such a discrepancy.
Imho one is bent.
How do the other connection points measure esp where the spring plates mate?

[Magnum]

Thanks Graham

That's what I would have thought but two very experienced folk in South Africa have suggested they'll be fine - one suggesting the bushes and inbuilt "adjustability" will take this problem away, the other suggesting that arms are different such that the car "pulls straight under power".

Frankly confused and seriously wanting to avoid finding out, after all the work involved in swapping over, that there is a problem!

Further thoughts welcome! Further actual experience/knowledge begged of you

Cheers

[hot66]

you're just relying on how they are sat on a flat surface .. not the most accurate method. You really need to somehow measure exactly the relative postions of the hub centre line to the bush centre line to get a true idea of wether they are bent or not

[Gary71]

Questions:

Is your surface you’ve set them on flat?
A tiny difference in angle at the bottom will make them appear misaligned.

Can you physically measure the arm with a tape measure edge to edge? Mine are off the car at the moment so I’ll have a look tonight to see if measuring would be useful.

Can you beg borrow steal another arm or two to compare?

Also I suggest the ‘expert’ that says they are like that to pull straight under load isn’t an expert! (I’m not either, but it’s not an Indy car that just turns left)

Best of luck

[inaglasshouse]

For your purposes you probably don't need a specific jig.
As others have mentioned - if I were you I would just start with a proper flat surface table / surface plate (found at pretty-much any place that does machining). Bung them on there and see how they look.

[Magnum]

Thanks Chaps

I measured on a flat granite work surface and the pictures show the results - worryingly I don't think one can one get flatter than that? Next step is to measure as suggested above, although it'll be rudimentary.

Stop Press! I've cracked and put though a call to Porsche Centre Cape Town....let's see if they can help but not holding my breath sadly.....If not then a lot of work ahead.... tracking down arms to compare, perhaps make my own simple jig (out of wood......) to measure etc.

This upgrade has become a major, major ball-ache, however, with all the parts and a helpfull dose of stubbornness it'll happen! And i'll have learnt a great deal....in fact the last frontier on these older 911s is an engine build.....maybe too much....

[fetuhoe]

You really do need to establish a datum to see which arm is bent otherwise you could be chasing this problem for a while.

The alternative is to locate a P295b (Items 5 & 6)

[911hillclimber]

I think I would simply buy another set of arms.

If the one arm is bent that must have been a mighty impact. Not sure I could trust the cast arm is not cracked somewhere?