Failed (bent) WEVO Spring Plate - cause? - Page 2

jaydubya · 10-08-2006, 03:51 PM

Quote:

Originally posted by ZOANAS
Great thread. I just looked at my Weltmeister adjustables, and they are indeed flexed a tiny bit, resulting in an increasing gap between the main plate and the adjuster arm.

What kind of spring plate bushings/bearings are you using? Any evidence of rubbing on the tub? Could you take a photo or two?

Thanks!

Jeff

Grady Clay · 10-08-2006, 04:26 PM

The steel spring plate twists along the long axis.

Yes the OE rubber bushing at the torsion bar also deforms. With more rigid bearings (anything from plastic to metal bearings) then more of the twist is in the spring plate and less in the bearing(s) at the torsion bar.

The coil-over 935 eliminated the twist (and the spring plate) by having a spherical bearing link. The 2-axis spherical bearing allows for the twist where a single axis bearing at the torsion bar requires the spring plate to twist.

Best,
Grady

jaydubya · 04:45 PM

Quote:

Originally posted by Grady Clay
The steel spring plate twists along the long axis.

Yes the OE rubber bushing at the torsion bar also deforms. With more rigid bearings (anything from plastic to metal bearings) then more of the twist is in the spring plate and less in the bearing(s) at the torsion bar.

Thanks Grady, that helps a lot. I appreciate you taking the time to explain this in detail.

With this information, it seems clear that a rigid or nearly rigid single-axis articulation at the torsion bar in combination with the Sway-A-Way or WEVO style adjustable spring plate is a recipe for the problem that I have encountered.

This makes me wonder whether polybronze or needle bearings with a standard spring plate are really the best solution for this application. Although these approaches have become nearly standard in our older 911 race cars, an ideal design would combine a metal articulation with two axes of rotation like the 935 "spring plates".

Cheers,

Jeff

911ctS · 10-08-2006, 05:00 PM

Everyone seems to be right on in their statements of how the rear suspension functions.

Grady - The 356 swing axle is a great analogy due to the pronounced range of travel and camber change throughout its arc. These spring plates do twist quite a bit. Also, you pointed out the fact that the adj. allen screw is adjusted almost all the way up (giving the car much potential to be lowered in the future). I think this is a significant factor here when you look at the curve of the outer plate (one that bent) and where it bent. Had the adj. been more in the middle, the plates would have shared more contact area and the outer plate would have resisted the twisting motion much more. Right?

Quote:

In the OEM configuration with rubber bushings, why would the plate deform in torsion? Wouldn't the rubber bushing deform first? Why would Porsche use both a rubber bushing at the torsion bar end AND a spring plate designed to deform under torsional loading? Seems redundant.

I have always understood that even with rubber bushings the spring plates are designed to "deform" or better put conform to camber change with suspension travel along its arc. The springs plates were not designed to deform in the manner that they would take away from the spring rate (T-bar), although they do very very slightly (not noticeable). The rubber bushings are soft enough to allow movement and absorb sound yet hard enough to keep the spring plates somewhat centered relative to their axis. A car with stock suspension abuses this suspension arc much more resulting in the need for more multi-axis articulation.

Jeff- hope it all works out! Have you tried checking (prying) for lateral movement with both the car at static height and with some of its weight taken off?

Plavan · Plavan's Garage

With all this talk about springplates etc, Have you had a chance to check your bearings on the bananna arms? Check your bolts to make sure they are still there

jaydubya · 10-08-2006, 05:05 PM

Quote:

Originally posted by 911ctS
Jeff- hope it all works out! Have you tried checking (prying) for lateral movement with both the car at static height and with some of its weight taken off?

Thanks!

So far I have only tried to pull laterally by hand with the wheels off the ground. Felt very solid. Depending on what WEVO says and my shop's schedule, hopefully the car will be on the rack sometime this week.

Cheers,

Jeff

jaydubya · 10-08-2006, 05:07 PM

Quote:

Originally posted by Plavan
With all this talk about springplates etc, Have you had a chance to check your bearings on the bananna arms? Check your bolts to make sure they are still there

The (brand new) ER monoballs looked fine on both sides. And yes the bolts were there too

Elombard · 10-08-2006, 05:44 PM

Wow amazing what you learn here. I never realized the spring plate has to twist a bit...I thought all the movement was in the bannana pivot. Makes you realize what a "compromise" the whole set up is. I thought that with the ER Polybronze and monoball Bannana pivots everything would move smoothly with know bindingif the T bars were removed. Not the case at all. I wonder how much "rate" the twist adds. Makes me really want 935 coil overs. Interesting to learn the root cause here. I remember a post exactly like this where a guys Sway-a-ways failed in a similar way. I wonder if it was a similar cause. Everyone wrote that off to poor quality IIRC. Obviously not the case with WEVO parts.

ZOA NOM · ZOA NOM's Garage

Quote:

Originally posted by jaydubya
What kind of spring plate bushings/bearings are you using? Any evidence of rubbing on the tub? Could you take a photo or two?

Thanks!

Jeff

I just bought the car from another Pelican, and there are poly urethane bushings with zirt fittings in the outer t-bar cover. There is no evidence of rubbing, but the car has only been used for DE at this point, and the engine is stock. I didn't wanna jack it up and take off the wheel right now, but I will tomorrow. You can barely see the gap between the plates in the second pic. Note that the outer (adjust) plate on mine seems to have much more width than yours. I wonder if the narrower WEVO unit is weaker with regard to restricting lateral movement of the plate?

JP911 · JP911's Garage

I spoke to a well-respected mechanic in So Cal a few years ago about which direction to go with adjustable spring plates (my 76 targa had the fixed stock plates). He strongly urged me to avoid the aftermarket stuff that used the "perched" bolt ride height adjuster (Weltmeister/Sway Away); he claimed to have seen several failures.

ZOA NOM · ZOA NOM's Garage

When were you gonna tell me, Jon?

JP911 · JP911's Garage

When Cliff and I came by to check out your new sled the day you brought it home I made a comment about them. The thing is that it was one guy's opinion (albeit an experienced guy) and when I searched the issue here on the board nobody had posted anything about any failures.

Besides, I need something to slow your a$$ down so I can catch you!

ZOA NOM · ZOA NOM's Garage

I'm considering swapping them with my daily driver stock carrera plates. Or I may just drill the hole and clamp them like Grady suggested.

jaydubya · 10-09-2006, 04:38 AM

Found another thread that describes the same problem with the Sway-A-Way adjustable spring plate:

Bent my Weltmeister adj spring plate at the track

Elombard · 10-09-2006, 05:49 AM

I refuse to believe Wevo did not think of this, Interesting to hear what they say.

ZOA NOM · ZOA NOM's Garage

There's probably a disclaimer in the package that says not to exceed 60mph.

DW SD · 10-09-2006, 08:06 AM

I'm guessing the tech may not have aligned the parts correctly when they were installed. It is important that there be no side loads when the springplates are installed. With the large bolts used to tie the springplates to the banana arm, it would be easy to conceive that the lateral load could have been pre-loaded, if the springplate wasn't in perfect alignment with the banana arm, prior to bolting the springplate to the banana arm.

I would believe that it would be necessary to shim and grind (likely both) on the four mounting points for the torsion bar bearing carrier to bring things into alignment as part of the installation. (I did this with the elephant racing spring plate bushing kit.)

In other words, I'm guessing there was too much space between the spring plate and the banana arm, before they were fastened together. This would have made the alignment of the ride height adjuster and springplate incorrect. With some heavy loads from the track, this may have been the straw that broke the camels back. And forced this something to bend.

It is also very possible that the banana arm monoballs weren't installed properly. There was no press-fit on mine when I installed the ER monoballs. I used a loctite bearing retainer product to ensure that they were solidly mounted. If this were not installed properly forces on the springplates, for which they are not intended, could result.

I suspect I wrote what has already been offered.

shbop · 10-09-2006, 08:16 AM

Having just installed adjustable spring-plates on my car, DW SD's post concerns me. When I removed the stock plate there was definitly tension between the banana arm and the spring-plate. The last bolt removed, popped-out. When I installed the adj. plates, I used a clamp to bring the two together in order to easily install the bolts. Is the spring-plate supposed to meet-up with the banana arm flush, and without any tension?

DW SD · 10-09-2006, 08:24 AM

Quote:

Originally posted by shbop
Having just installed adjustable spring-plates on my car, DW SD's post concerns me. When I removed the stock plate there was definitly tension between the banana arm and the spring-plate. The last bolt removed, popped-out. When I installed the adj. plates, I used a clamp to bring the two together in order to easily install the bolts. Is the spring-plate supposed to meet-up with the banana arm flush, and without any tension?

Jon,
It may not meet up with zero tension, but my view is it shouldn't be great amounts. Having to clamp may be an indication that things are too out of alignment. Looking at the springplates themselves, they are not designed to carry side loads, only vertical loads.

Are your adjustable plates like the factory or the like the WEVO / Sway Away design, with a threaded height adjuster?

The factory style stay bolted together by their design. While it may not be ideal to load the springplate bushings with all of the side loads, at least things will stay together.

Doug

shbop · 10-09-2006, 08:30 AM

Doug, I'm using the Sway Away design. Even the factory plate required some twist, in order to bolt-up. The new plates don't require any "more" twist. I could have squeezed them together by hand, but it was easier to clamp them. I even tried moving the assembly ( both spring plate and control arm) up and down to try and find a sweet spot. there wasn't any.