IRS alignment setting for wide rear tires

[Hebster52]

I just wanted to ask if it acctually works to file up the holes and twist the trailingarm in the suspensionplate? I mean doesn't it twist the inner bushing out of line then so it wear out in no time?

Anyone who has done this and proved it to work?

[Hebster52]

Ok. Here is the deal... I did some theoretical pictures.

When the suspension is lowered the alignment of the torsionarm and trailingarm gets offset as on picture 1. This would mean that the trailingarms should be angled as stated earlier.



The best option would in my oppinion be to lift/turn the inner TA mount in proportion to the wanted lowering. In other words keeping the inner TA aligned to the torsionarm. (picture 2)



Opinions? Comments?

[Bruce2]

Originally Posted by Hebster52

I just wanted to ask if it acctually works to file up the holes and twist the trailingarm in the suspensionplate? I mean doesn't it twist the inner bushing out of line then so it wear out in no time?

Anyone who has done this and proved it to work?

This adjustment is exactly how Porsche adjusts camber on the 944, so yes it has been proven to work.

I've never heard of anyone who's worn out the inner pivot. When I used to modify stock Beetle TAs, the final step was powdercoating. This meant the inner bushings had to come out. Every one I removed was in perfect condition.

[Hebster52]

Thanks Bruce!
I definitly will have to look into the tech regarding this when I start fitting in the 944 trailingarms on my T-34 this summer.

However the rear frame have been swapped from the swing to IRS (T-3 versions without the gearboxhorns) and the torsionarms(plates) on it is the double version... I've heard that those were a 1969 one year only feature I wonder if I would benefit in using the single 1303 torsionplates instead that I have in the back on my garage?

[Bruce2]

All IRS Type 3s used the double spring plates, while Beetles went to singles in 71. I guess they thought the extra weight of a T3 warranted it. They were wrong. This has been proven by looking at a stock 944 that has single spring plates.

Instead of using Beetle spring plates, use stock 944 adjustable spring plates. Then you can use the camber adjustment Porsche designed. I adapted the 944 spring plates into my Beetle without the camber adjustment.

Single spring plates weigh less.

[Hebster52]

I'll see which springplates I'll use. I dont have any 944 springplates so it will be either the double T-3's or the 1303's

The T-3's have the same hole pattern as these 944's



The only difference is the height adjustment and the middle hole (the one with the vertical arrows). On the T-3's that hole is only adjustable horisontally. The 1303's doesn't seem to have that hole at all..

[G-force]

Moving the inner pivot bolt for the trailing arm upward raises the roll centre upwards considerably, so the car may handle more like a swing-axle bug if you did that.

May also have a strange effect on the rear toe curve. i.e. Lots of toe change on bumps, and excessive toe-in induced by body roll when cornering. Likewise, straight line stability would probably suffer for the same reasons (ie wind buffeting causing more rear end steering).

Hebster, considering you don't have the frame horns in the way, it may be easier for you to fit the 911 rear suspension onto your type3.
Would move the rear wheels back 57mm but give a smoother & more predictable ride. Plus you'd get the 911 brakes too.