Is it REALLY necessary ? I've done a couple of these but have yet to understand why. I have NEVER seen a trailing arm bent from anything otther than a hard collision. I see no way they could be twisting or flexing in any way in hard cornering. I'm curious if any of the hardcore racers have seen a true need for them. Anyone ever seen a ARM crack from use not rust ? Sure the consoles crack, the body cracks but the trailing arm ? Seems like unneccesary weight to me


Talk amongst yourselves I'll check back in later

I think a lot of the Noticeable flex that was attributed over the years was probably mistakenly attributed to the swing arm when it was actually the chassis and swing arm mount that was flexing....


however they do still flex
a truly skilled builder and racer who is 10 faster in his 914 than I ever will be, insists that he can tell the difference on a car with or without trailing arm reinforcement.

he has built 20-30 914 race cars and always installs both the mount brace bars on the chassis and also the swing arm reinforcements.

Additionally... Chris ran actual flex tests on a bench of trailing arms to design his brace kit that he sells. The thread is one of the best threads that has ever been on this site. It shows that there is flex and that sticky race tires could produce that flex.

So in summary.... a little flex
although the chassis mount brace kits are equally responsible for a little racing flex.


brant

i wonder it is better to have the trailing arm be the weak link. they are replaceable. instead of transferring the load to the chassis. my opinion is that if the trailing arms are going to be reinforced than the pickup points must be reinforced also.

Yep, Chris' thread testing the arm is pretty damn extensive. And I think this is why he sells both the trailing arm stiffening as well as the mount stiffening itself.

I think when racing its better to have neither be flexible...
the same reason race cars are built to be as stiff as possible and use roll cages to develop a stiffer chassis.... to allow the suspension to work better


on the street, if your building for failure zones with the knowledge that eventually you will hit a curb and you want a failure point then developing a failure point because you know as a manufacturer that some of the drivers are bad drivers, then it kinda makes sense...? in the same way that modern cars have crumple zones?

but no flex is better for racing period!

I designed the trailing arm stiffening procedure I now use during those tests.
The metal we add weighs far less than the boxed reinforcing kits, and doesn't over-strengthen the arm.

I think that welding the box reinforcements warps the trailing arms, adding toe-out.

Previously I had determined that the chassis around the suspension mounts and the outer console bracket both twist in hard cornering.

There are documented failures of trailing arms cracking where the box meets the pivot tube.
Gusseting there provides a significant benefit.

I don't understand Chris. Why are you bad-mouthing the box reinforcements. You seem to take every opportunity to put them down.

I just don't learn.

We do a very simple and easy mod for our customers that almost anyone can do.

I was told it added nearly 50% in stiffness and the bonus is, there's no weight penalty. I like it because it's inexpensive, simple, it works and it's fairly noninvasive.

Get a long bit and drill two holes straight through the arms. Then get a Step Bit and drill those holes out to 1" like so:


Weld in two 1" tubes to add lateral stiffness:




Paint or powder coat the arms:


We also add gussets to the shaft tube:


I also added the bulkhead to inner mount bars on my car. Not sure of the overall effectiveness for a street car but, the car feels like it's on rails.

Nice, Eric. I like this - thanks for sharing.

I made the mistake of putting those old school clunky stiffeners on my first 914. I hated them. Way too heavy and a ridiculous thing for a regular street car.

I have some pics of the popsicle stick and hot glue gun treatment that I did on my sunflower yellow car, Mr. Sunflower. I'll see if I can post them later.

I glad you mentioned this. Before my time so I looked it up. Good reading. http://www.914world.com/bbs2/index.php?showtopic=42873

I went with Eric's solution and it was easy to do

Well played.

Thanks Woodster!

Nice

JW aka Otto, RIP, who holds track records in 914's was a firm believer in the trailing arm stiffening kit. I bought his kit and installed them on my car.

Andy, did you use .060" or .090" tube?

All of the fastest drivers who know the difference, prefer a stiffening kit. But for full race not street.

Kent, I bought 0.125 , 1/8" wall tubing. The vendor had a min. purchase so I got 4ft.

Your welcome to have what you need and borrow my step drill if you want or bring your arms over and we can do them here

Second in line

Kent has what he needs Mark so your up!!

Yup. On to Scotty's original question; I think a simple kit wouldn't hurt on a street car but, as Brant mentions, most gains will come on the track if that's your thing.

The factory kits only weigh 4-5 each and do stiffen the arm quite a bit but; why have a weight penalty if you can get better (and easier) results without it?

I like that idea of adding two 1" tubes through the trailing arm box.

The tubes don't triangulate at all, so I would wonder how much they help. I'm not sure they would help the arm not twist.

I can easily see how adding stiffener tubes and gussets would help keep them from flexing. Like adding a cross-member to a ladder chassis.

Correct the tubes do not triangulate. What they do is keep the box from collapsing or buckling in on itself (deflection) under loading.

As far as the box reinforcement kits if you weld the outer vaneer first (laying the heat on) it will toe in. Then weld the inner vaneer it comes back... Mine did (Chris did you weld the inner first?)

In the end the chassis sheetmetal is the weak link.

AFAIK, the boxed kits cover 3 sides only - top, bottom, and inside face. No welding on the outer surface makes for net toe out.
I'm not familiar with the outer veneer you're referring to.

Vaneers![size=4]

***UPDATE***

Here's a variation on this mod we did for the 914 ORV project. Thought I'd keep them all in one place.

You can "see what we did there..."

Click to view attachment

Click to view attachment

Click to view attachment

Click to view attachment

Click to view attachment

Click to view attachment

Click to view attachment

Click to view attachment

I love this latest idea. I'm going to try that. Looks easy peasy and great with the black powder coat.

Well played.

I drilled through the arms at places that will give me rigidity from a couple of different angles. I still need to weld and cut but these should work without excess weight.

Click to view attachment