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Posted by: John Oct 31 2010, 12:24 PM

I'm considering strengthening the trailing arms.

I have looked at the steel plates people add to wrap around the stock trailing arms and I can understand that this may increase the strength of the trailing arm some, but the weight it adds seems counter-productive and a band-aid solution at best.

I know that this is how dad did it and it's been working pretty good up until now, but I keep thinking there might be a better way.

My idea after looking at my trailing arms for the better part of the last 2 days is to add some stiffeners through the arm box similar to the tube running through the arms to access the inner brake pad adjuster.


The tube is welded to both sides of the box and would serve to keep the two sides from deflecting. This is a brace, and would stiffen the tube member significantly without adding much weight.

I'm thinking the addition of 2 additional tubes would decrease deflection more than the plate stiffeners and will be no where near the weight.

Anyone else think this?

I'm sure in the last 40 or so years, someone else has had this same idea.

I would love to see some pictures or see some results (I hate to reinvent the wheel if I don't have to)


Thanks for reading.

Posted by: SirAndy Oct 31 2010, 01:05 PM

Many times in fact.

I know of tubing added vertically and horizontally as far back as 20 years ago. I'm sure people have done it even earlier.
It's a simply way to add strength without cutting the whole thing apart.

Racer Chris did some with added plates, there's a thread here somewhere.
And i believe Eric Shea offered the arms with additional tubes at one point.

Posted by: burton73 Oct 31 2010, 01:48 PM

Eric Shea did the trailing arms on number 41 with tubes just like that. Sorry but I do not have a picture of the arms at home.

Bob Burton

Posted by: Eric_Shea Oct 31 2010, 02:00 PM

Some pics of the process. This adds only ounces and really stiffens the arms. More so than the factory kits.

First, 1" holes are milled into the arms. The pattern is triangulated off the original inner adjuster tube for the stock handbrake:


Here you can see a test fit of a 1" steel tube through the arm:


The next step (not shown yet) is to have the arms media blasted to bare metal:


Once we have fresh metal to weld with, the tubes are welded into place and trimmed. After the welding the entire arm goes into powder coating:


Prototype gussets should help shaft tube flex:


Sneak peak on the car:

Posted by: gothspeed Oct 31 2010, 06:23 PM

I like it !!!!

Posted by: John Oct 31 2010, 09:02 PM

Perfect!

Thanks Eric!

The pictures are great. Thanks a bunch.

I spent the past 2 hours looking through 5 year old threads where Chris added a bulkhead sheet metal stiffener then went through 5 or more pages of FEA that may or may not have supported any stiffness increase.

I still think this has to strengthen the arms without adding much work or weight (regardless of the neigh-Sayers).



You wouldn't have any dimensions for the triangular gusset plates do you? (now I'm being real lazy).

Thanks again.

Posted by: strawman Oct 31 2010, 09:44 PM

I've done it; go to post #98 at http://www.914world.com/bbs2/index.php?act=ST&f=2&t=83031

Posted by: Eric_Shea Oct 31 2010, 10:38 PM

Stats I heard were 50%for these.

I don't have the measurements for the gussets but I think RonS had a drawing that may help. Easy to eye up otherwise.

E.

Posted by: RJMII Oct 31 2010, 11:11 PM

link to post 98: http://www.914world.com/bbs2/index.php?showtopic=83031&st=80#

Posted by: Spoke Nov 1 2010, 05:15 AM

I strengthened the rear trailing arms by inserting 3/8 inch rods at diagonals in 2 places.

Drilling the holes:



Holes Drilled



Finished product:

Posted by: ChrisNPDrider Nov 1 2010, 02:12 PM

Spoke - thanks for sharing
I had not seen this version yet...what do the gurus have to say?

Posted by: dflesburg Nov 1 2010, 02:26 PM

totally tubular dudes!

Posted by: sixaddict Nov 1 2010, 02:43 PM

I have a set that have external triangulated tube for strength done by race shop from Eastern PA. Would be happy to send photos although I would need to take them.PM your address as I can never get photos posted.

Posted by: McMark Nov 1 2010, 03:15 PM

Chris, I had a similar idea to Spoke, but never followed through. I think it would be beneficial, although I would keep an eye out for stress cracks. The welds on the end of the rod are small compared to the welds on the tube method.

Posted by: Racer Chris Nov 1 2010, 08:41 PM

Regardless of my friend's FEA work,
my empirical test data totally supports the fact that adding a single bulkhead gives a substantial torsional stiffness increase.
Thats why it's part of all the Upgraded Trailing Arms we sell.

I'm sure welding a 1" tube crosswise through a trailing arm adds stiffness but the real value there is that its easy to do.

I'm a little doubtful of the 3/8" rod method.

Posted by: John Nov 1 2010, 09:51 PM

That's just what my wife and I are discussing right now. We're both engineers.

While the 3/8" rod method may add some stiffness, the bulkhead or plate would offer the greatest resistance to collapsing of the tube in twisting, and the 1" tubing would offer some benefit with the ease of installation (don't have to cut the tube in half to install).



I'm going with inserting (2) 1" tubes as this makes the most sense to me and is light weight. (and doesn't introduce a bunch of heat into the part).



Thanks for responding Chris. (Your input probably means the most as it was you doing the empirical testing way back...)