I am doing some fit checking on the steering rack with a 911 cross bar. I noticed the cross bar angle wasn't at 90 degrees for the A-Arm. The body is level and I seated the cross bar so the bar and braces fit into the body nipples and are flush. I used a level and calculated the angle to be 86.3 degrees or 3.7 degrees off center to be going straight across to the front of the A-Arm. I can't find a reference to verify this angle is correct and since I'm using a 911 cross member and aftermarket brackets, I'd like to know if this is correct or something I need to fix. The pictures below will help explain the angle I measured.

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The above picture is the 911 cross bar and steering rack bolted flush to the body


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The above photo is the end of the cross bar that fits into the A-Arm.


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I used a feeler gage and level to determine the gap at the bottom. It's not exact but close enough to get a measurement. Both sides had the same angle which was 3.7 degrees off center.

Anyone know if this angle is correct?

Thanks,

DaveB

You need to install the 12mm bolts that hold the cross member to the body. That should sqrare it up.

Also loosen the bolts to the brackets then torque the 12mm bolts and then tighter the bracket bolts

Once the control arms are installed it will probably pull the 3.7 angle out.

Control arms don’t usually run parallel to the ground. Standard practice is to tip the arm slightly - higher in the front to create wheel recession (backward movement) as the wheel goes into compression and moves upwards. This improves ride quality and reduces impact loading to the suspension.

I don’t have a spec for you and i don’t believe I’ve ever run across something like it in print.

if you look closely I believe you’ll find the front control arm mounting point is slightly higher vertically than the rear.

I would not expect a 90 degree angle to the ground.

What you want is the front and rear control arm bushings on the same axis.

Here is a photo
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That sure is one clean chassis. What method was used?

have the factory spot welds been brazed over?

Thanks Bruce.

This is part of my concern. When I removed the control arm from the car last year, the tension bar was off center and wore unevenly.

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I'll use the 80mm length bolts on both sides and install the old control arm without the torsion bar to check the fit on the front suspension. I was hoping there was an easy button and someone would say 3 to 4 degrees is good. Plus I got the crossmember for you so I figured it was a sure fit and any issues are in the body.


DaveB

It was chemically dipped. I can see the factory brazing on the car but what you see in the picture is a repair.

This is the wheel well:


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This is from the workshop manual on a cutting line for a sectional repair:


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DaveB

FWIW the 930 has built in spacers on the front a arm mount. Consensus is that lowering the front of the arm helps with brake squat/nose dive handling. ER and others sell spacers (conical washers) that act as spacer and provides alignment so the whole a arm/tbar assembly rotates freely.

https://tarett.com/products/self-aligning-a...ies-914-2071600

This is typical bushing wear after 50 years, replace as needed…

Finally, the aluminum 911 cross member is known to warp/bend after many years service. There should be enough play in the an arm mounts to get smooth rotating action, which is all you’re really looking for. Use the conical washers as mentioned above to further refine.

You will not get and do not want a friction free, rotation from rubber bushings. However. As previously mentioned the rear and front LCA bushing mounts should be on the same axis. When installed you will not be able to rotate the LCA very far at all just using hand force.

The rubber bushing is not designed to have the LCA rotating freely within the bushing. Elephant Racing (ER) sells rubber bushings that are designed to grip the LCA properly.

The rubber bushing is designed to provide some initial rising rate to the suspension as it twists in torsion between the bushing can and the LCA.

As mentioned, ER and others sell various other bushings intended for track use like poly bronze and the spherical, Delrin, and needle bearing bushings mentioned that will minimize rotational friction of the LCA. These will come with a pretty significant ride harshness and road noise penalty. There is no free lunch regarding the engineering tradeoffs of rubber vs other bushing and bearing types. There is nothing wrong with these solutions for track use. But, be aware that what is best for track use is not always what is best for street use.

I always recommend rubber bushings for street use. There are solid engineering reasons all the major OEMs (including Porsche, Ferrari, Lamborghini, etc) use rubber bushings in their suspensions and it isn’t because they are too cheap to use poly bronze or spherical bushings. In addition to the NVH degradation, hard bushings intended for track use, increase the impact loads the body structure has to absorb and degrade body durability in some cases contributing to early fatigue of suspension mounts. Similarly, without some rubber in the suspension, wheel recession is reduced which degrades ride quality.

Regarding the bushing cans that utilise the self aligning conical washers, I am under the impression that these are for use only with solid (rigid) bushings (i.e. not rubber).

It would be nice to guarantee precise alignment between the front and rear bushing but I suspect that when used with rubber bushings you end up with too many degrees of freedom in the part and probably end up with difficulty keeping the LCA fasteners properly torqued.

To be clear, I have not talked to the manufacturer of these parts regarding use with rubber bushings. Curious if anyone else has?

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