Help needed on differences of aluminum trailing arms.

[enzoducoing]

Hello fellow pelicaneers !
I would like to summon the collective knowledge that moves this most excellent forum, with a question to a matter that eludes me.
Does anyone know if there are differences in length between 1974-1989 aluminum trailing arms? (not counting the turbo arms, which I know to be significantly different)
Do 2.7,3.0, SC and 3.2 Carrera trailing arms have different part numbers?
If there are differences, what would be the best choice for an aluminum upgrade for a 1971 narrow body?
I would appreciate any and all knowledgeable answers and guidelines to this mystery (at least to me) that will help me to identify the arms I need for my project.
Thanks for the help.
MD

[Shaun @ Tru6]

74-75 would be your best bet if the pair came with the 4-bolt, 2-pin stub axles. Early Al control arms will also have the sway bar ball stud like the steel arms if you have a rear sway bar. Not sure how far that design went before it was changed over the bolt on style drop links.

[chris_seven]

There are no difference in lengths with any LWB Trailing arm expect for the Short Turbo Arm which also significantly increases rear track and won't fit a narrow bodied car.

As Shaun says above the earlier arms with the ball pins seems to make sense but the conversion is not easy.

Your 1971 Shell will most likely have the narrow rear seat pans. These changed for a wider rear seat pan in 1972.

The potion of the shock mount beam also changed at the same time and this means that the shock absorber angle will not work very well.

The shock towers are also smaller diameter and the result is that the shock absorber dust shields will foul on the towers and will need to removed or modified by cutting them away.

You will also need to change the position where the shock absorber mounts on the arm by re-drilling the mounting bolt hole lower down or the bottom bush will tend to bind and cause problems.

You are also most likely to have to modify the engine oil cooler as the shock absorber body will rub due to the change in angle so you will have to gently re-shape the cooler with a small mallet.

Your driveshaft arrangement will also need some changes as the flanges differ between the two trailing arms.

I would tend to add an RSR style stiffener to the steel arm and leave it alone.

[frankc]

[QUOTE=Shaun 84 Targa;8473240Not sure how far that design went before it was changed over the bolt on style drop links.[/QUOTE]

FYI, '77 was the last year for ball & socket sway bar drop link.

[enzoducoing]

Thank you all for the information, It is very helpful to know there are no differences in length that I must account for. I have heard that is easier to use the bolt on drop link trailing arms (78-89 if you plan on using aftermarket sway bars like the ones from Tarrett, so that's what I would like to move on.

MD

[wayner]

If I can add a question here as well,

Is the rear brake calliper bolt spacing the same on the steel and aluminum arms?

[chris_seven]

Yes 3"

[Bird911]

Originally Posted by chris_seven

There are no difference in lengths with any LWB Trailing arm expect for the Short Turbo Arm which also significantly increases rear track and won't fit a narrow bodied car.

As Shaun says above the earlier arms with the ball pins seems to make sense but the conversion is not easy.

Your 1971 Shell will most likely have the narrow rear seat pans. These changed for a wider rear seat pan in 1972.

The potion of the shock mount beam also changed at the same time and this means that the shock absorber angle will not work very well.

The shock towers are also smaller diameter and the result is that the shock absorber dust shields will foul on the towers and will need to removed or modified by cutting them away.

You will also need to change the position where the shock absorber mounts on the arm by re-drilling the mounting bolt hole lower down or the bottom bush will tend to bind and cause problems.

You are also most likely to have to modify the engine oil cooler as the shock absorber body will rub due to the change in angle so you will have to gently re-shape the cooler with a small mallet.

Your driveshaft arrangement will also need some changes as the flanges differ between the two trailing arms.

I would tend to add an RSR style stiffener to the steel arm and leave it alone.

Enzo, I'm also doing this on my 1970 project with a 1986 trailing arms set. Chris is right on with his comment. I would only add that the amount of material you have to remove from the shock point on the arm is 20mm to 25mm or 3/4'' to 1''. It's not a problem as the tread in the trailing arm start deeper than this.

For the shock absorber dust shields, you can just remove it and add replace with a rubber one if you are still too close from the tower.

[Bird911]

Just found what I was looking for !
This is a good article that appear in Excellence many years ago about this modification:

UpgradeAlloyControlArms