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Torsion Tube Reinforcement

I am in the process of rebuilding the suspension in my 911 IROC replica.

One option I am looking at is to move to coil over suspension front and rear, using 935 style rear 'spring' plates, which opens up a much bigger range of spring rates and easier ride height and suspension geometry changes.

The need to reinforce the rear shock towers and cross member when going to coil over is well understood and documented on various threads.

However, I was wondering if I need to be worried about reinforcement of the Torsion Tube area where the 935 style spring plate will connect to the chassis - this area was known to crack sometimes when upgraded torsion bars are fitted.

I was thinking that since all the spring and shock loads will now be going though the shock tower, is there still the need to reinforce the torsion tube area now it will become just a pivot point.

Tim
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Old 12-21-2017, 06:12 PM
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Will be curious what others have to say, but I'd say that there should be less stress on the torsion tube if you are no longer using torsion bars. Because without the torsion bar in there, that area is now just a pivot and no long subjected to the torsional stress from the suspension. Not to say there won't be substantial stress there still, but it should be less.

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Old 12-23-2017, 03:52 AM
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I would suspect the same, much less stress or close to nothing now when just a pivot joint
Old 12-23-2017, 01:50 PM
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What year is your car?

I think some reinforcements were added in 1974. If your is older you might want to look into my build thread.

There is an illustration on this page half way down.

You can also see some welding near the beginning of the thread

Saving a 73 from the crusher...

and just for fun, here is the continuation if you are bored and get to the end of the first one


Saving a 73 from the crusher...AGAIN
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Last edited by wayner; 12-23-2017 at 02:28 PM..
Old 12-23-2017, 02:20 PM
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Car is a 1983SC which due to extensive rear left damage in a racing accident is getting a new shell from a 1976 donor.

While I am in there I am updating the suspension - hence the question as it much easier to do all the strengthening updates now rather than later.
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Old 12-24-2017, 12:31 AM
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Did the picture in my thread help you or are you still looking for more info?
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Old 12-24-2017, 09:12 AM
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I have the ERP (Eisenlohr Racing products) 935-style spring plates and run coilovers in my race car.Installed in 2015.

I bought the ERP parts from Tarett, which is a company I recommend. Prior to those plates, I ran modified factory plates with plastic bushings. On those I modified the bushings and housings so I could grease them from time to time (Zerk fittings).

I ran those for 15 years-- for sale in classifieds. The allow for lower camber settings for bias ply tires, or higher camber settings for radials on a very low car.

Anyway, when I inspected the torsion tube area prior to the 935 style plate install, I noticed some cracking around the plate bosses. So I fabbed up some metal reinforcement plates and had them welded in.

Not mandatory for coilovers, but if you see cracks (which can be pretty common) it is a good idea to deal with them. And if you are thinking ahead and have the resources, not a bad idea to be proactive.

Elephant Racing Products actually sell parts for this-- convenience. They are pre-cut and ready to be welded into place. But you can make some using a cardboard/tape template and some scrap metal. All it takes is a jig saw.

These forums have some threads wwherein this type of reinforcement is discussed/described.
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Last edited by Mahler9th; 12-30-2017 at 03:02 PM..
Old 12-30-2017, 02:58 PM
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Example of crack:


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Old 12-30-2017, 03:01 PM
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When I converted my 912 (which had been converted to a 911 engine, and coilovers, and raced in SCCA's GT3 or thereabouts) to 935 style spring plates (for their adjustability)I had slugs made up with two drilled and tapped holes to attach the Heim. I think maybe the odd 8mm bolt receptor had minor cracking, easily welded. Haven't had any more trouble there (the camber boxes for the inner mounts, which moved those pivots up, put extra torsion on the center of the tube, which eventually cracked just outboard of a mount and had to be welded back up - I think those should be reinforced to the tub to counter the extra lever arm).

So I second the approach of inspect, fix if any fixing needed, and then inspect from time to time (like when changing tires, which in a race car is very often).
Old 01-01-2018, 09:34 PM
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On my car, we cut away a lot of the center anchor for the torsion bars. It's heavy. We added reinforcements fore and aft. My car has the raised-and-relocated mounting points for the trailing arms.



Old 01-02-2018, 11:20 AM
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Jack did u raise the pick up points to the higher 930 location or more? You are running larger diameter tires than stock 930 and mostly likely had to compensate for the added tire height and lowered ride height ?
Old 01-02-2018, 08:56 PM
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It's the Smart Racing setup. I don't remember exactly where we ended up. But my wheel/tire combination is only 3.2% larger in overall diameter than the Turbo's.
Old 01-02-2018, 09:17 PM
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Did you raise the outer pickup points (spring plate pivot location) too or just the inner?
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Old 01-02-2018, 10:02 PM
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Quote:
Originally Posted by wayner View Post
Did the picture in my thread help you or are you still looking for more info?
Yes it did - thank you. The diagram was showing the need for webbing around the centre of the torsion tubes to stop them deflecting - something that was fixed permanently in SC models and later - given my donor shell is 76 it ensured I checked.

Jack - I'm not planning on going that extreme but the photo from Mahler9th is exactly what I have had to repair previously on the old shell - hence why I raised the question as I prepare to change to coil-over style suspension on the new shell.

Given it's stripped bare, I'll probably go ahead and reinforce just to be safe.

Thank you everyone for the input - keep an eye out for a build project which I plan to document over the coming 6 months.
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Swapped my WRX Sti MY02 for a Porsche 911SC '83
Keep buying parts to make it look older.
Mid life crisis is now in its 12th year.
Old 01-04-2018, 03:57 AM
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