Rear Suspension Reinforcement Options

[kdfoust]

This spring I'm wrapping up completely rebuilding my suspension. Right now I'm working on the rear end.

First off, what do ya'll think about the weld on trailing arm reinforcing plates (like PP and a number of other places sell for ~$100). The reinforcing plates seem like a reasonable thing to do, right? All these kits look like the same stuff to me. Is there a mo-better way to do the job, allowing that I can fabricate anything I need?

Secondly, I'd like to go ahead and reinforce the suspension consoles while I'm at it. The problem I've got is that I've never had a good look at the underside of a teener (laying on my back on my creeper in the garage doesn't count). I've looked at the PCA GGR picture for the reinforcment setup. Is the GGR setup state of the art OR is something else the hot ticket? Any recommendations for SoCal shops to do this for me - ones you've used in LA/Orange/San Diego county area?

Have fun,
Kevin

[Brad Roberts]

Here is my take on the control arms reinforcement:

1. If it doesnt bend in a off course excursion..where does the energy go ?? (The control arm mounts on the tub)

2. Do I really need to ad weight to a unsprung component ??

3. Control arms are cheap.. if I bend one (without the stiff kit on it) replacement can be made in about 2 hours and 50$.

4. I know of many many club racers that dont run the stiff kit (guy's that race on 10inch wide slicks... and win) Guy's who have been racing for 12-15 years.

I do suggest you stiffen the control arm pickup points. About 4 pieces out of the chassis stiff kit actually do anything when installed on the tub. The rest are worthless and just ad weight. I'm not the only one to share this view... The 914 IMSA racers of the early eighties figured this out way back when running 12+24 hour events in 914's.

TonyC is the fabricator here.. let him show you what he came up with on one of our 914's for the control arm pickup points. It involves a few tubes all tied to the main hoop.

B

[Jeroen]

Brad wrote: "...About 4 pieces out of the chassis stiff kit actually do anything when installed on the tub. The rest are worthless and just ad weight..."

Ok, so which four pieces would that be? Saving weight is cheap hp (IMG:style_emoticons/default/biggrin.gif)

Any pics from Tony would be great as well
I've got a fairly good idea of what to do, and have seen some, but more "btdt" info and pics is always good!

Cheers,

Jeroen

[Tony C]

Here are some pics of the re-enforcement of the rear control arm pick-up points. I don't have any of the innear pick up, but it was done very similar.

TC Design outer pick-up point

TC Design 914-6 Project

-Tony

[Gint]

Thanks Tony. I was just looking at those pics yesterday. I need to have a closer look when I'm not a work. I may have some questions.

Mike

[drew365]

kdfoust; If you try to box your trailing arms yourself be aware that you can warp them with too much heat. I believe the good shops use a jig to keep them true while welding. I didn't want to take a chance and ordered rebuilt ones through Patrick Motorsports. They exchange new for old. I also would like to know which parts of the stiffening kit should be used and which trashed. I have a kit here waiting to go on my car when I have time.

[Brad Roberts]

I need a pic of the kit laid out. I'll circle the ones you can use. If you have a cage that passes through the rear window or ties the rear shock towers together.. you wont need it at all. The chassis cracks on the tub right where the centerline of the shock goes up (draw a virtual picture inside the fenderwell following the shock) The only reason the chassis' crack is when you add more spring (225 and up will start the process within a few months of TT or RR) The problem is: the tops of the shock towers are not strong. They are only held in place on 2 sides (both of which are weak) The actual frame rail ends in front of the shock tower....leaving the sides vulnerable to cracking.

The outside mount normally wont crack until the inside one lets go.

B

[Jeroen]

Here's a pic of the kit
Call the numbers, just like bingo (IMG:style_emoticons/default/biggrin.gif)

Cheers,

Jeroen

[Brad Roberts]

5,2,4,3

B

[Brad Roberts]

2+4+3 are questionable.

4+3 dont do anything. Several old school racers figured out that the chassis will still crack even under number 5. Number 5 helps support that increase in spring rate that I spoke of above.2 right above 5 (when mounted on the car) really doesnt do anything. The piece below it is whats left of the frame rail.

I think people install these pieces (because the factory did) (because so and so has it) (they think it increases the value)

After seeing factory race cars from that era (they where designed in the early 70's) Porsche hacked together whatever they could to get the cars on the tracks. They where the factory.. they didnt expect this stiff kit to last..they would throw the chassis away and build a new race car. I even doubt that the factory designed this kit. I'm finidng more and more that they listened to racers and adjusted accordingly.

B

[Jeroen]

here's a pic of how the frame-rail is actually attached to the rear shock tower
(or better, how it is NOT attached)

Cheers,

Jeroen

[Brad Roberts]

Correct. Its more like 1.5 sides of support. Run a tube to that spot... and stiff kit pieces numbers 2+5 become 100% worthless. The fram rail ends right there.

B

[Gint]

Jeroen,
Can you take or post another pic of that area with the camera 1/2 a meter or so back from that same area?

[Jeroen]

Like this?

Cheers,

Jeroen

[Brad Roberts]

Great shot. This really shows how the frame rail ends in front of the shock tower.

The idea from here would be to triangulate to the front side of the shock tower (if your rules permit) Think of the frame rail as one side of the triangle and the main hoop of the cage as another "side" of the triangle. Then from the top of the main hoop go down to the front of the shock tower to complete the triangle. Several of our classes dont allow us to pass through the back window (or bulkheads) This is when we have to get creative with a tube that runs forward to the firewall and ends... doesnt exactly work as well as the tube running from the main hoop.. but it works well.

B

[brant]

Brad, Jeroen, et. all.....

Dang....
great shots, great explanation.
I heard brad talk about not using the full kit in the past... but those shots are great...

I want to truly thank you for the info...
sometimes you see something like this at the perfect time (right when you need it)...

Thanks for the site... and the expertise...

brant

[drew365]

Jeroen; thanks for the good pics.
Brad; thanks for the good info. Since I just reinforced my trailing arms and console ear and installed 250# springs I now know what area of the car to keep a close eye on.

[Gint]

Perfect Jeroen. Thanks!

[Gint]

Hey Brant (and anyone else interested),

Take a look at the first shot on this page (thanks Jeroen). See that rust hole at the bottom of the long just after where it curves up ad before it reaches the console? The hole on my right long I was telling you about last night is about 2" directly above the hole in that picture.

[brant]

Mike,

perfect... timing wise...
and great shots...
so what is the group consensus...
Mike, I think you could cut out, or cut back to good metal and then weld in a patch... or piece of the silver car....

it depends upon how far you would have to cut back.
but in an ideal world, you may not have to remove the entire floor pan (as Jeroen did)... if you don't mind it being less than concours.......

Using heavier than stock gauge metal... you should be able to make a patch that would restore the original strength...

yep.. I agree that the motor would need to come out.. but with that fancy lift of yours... and the chassis supported correctly.... it should be doable...

what's the group consensus...
and how do we talk mike into firing up that fancy new welder he bought and jumping in with both feet...

brant