Rear chassis flex. What do you think?, Discovery prepping for Road America next week Options

[vintage914racer]

Paranoia has set in as I'm nut and bolting the 914 before Road America next week. I'm hoping I can some second opinions.

A little background. My 914 has been a track car for nearly the entirely of it's life. She's been used and abused, but generally has been a reliable steed. Over the years chassis reinforcement and modifications have been made. Notably, the RR (pass) rear suspension console was replaced after the original tore (which is seemingly pretty normal).

What I'm noticing. After getting my car up on stands and prepping/inspecting for the next event I noticed a small amount of tire wear on my inner driver's left fender. I initially attributed it to bumping up to wider tires last Fall (225 Hoosiers vs. 205 Kumhos), but started investigating further to make sure there wasn't something else upstream.

When I have the car on jack stands and put pressure on the LR wheel, there's what I consider quite a bit of flex at the outer A-arm mount and forward into the rear long. You can see it in the attached video. As a point of comparison, when I do the same on the RR/passenger rear wheel there is some flex, but not as much. It should be noted that I had the inner suspension console replaced on the passenger side a few years ago after the old one tore, so in theory it should be stronger. 

The LR doesn't show any signs of tearing. It's also reinforced with stress bars on the outside and inside. 

Left Rear Flex Video (the side I'm worried about): https://youtu.be/NZDbDg22dFI

https://www.youtube.com/watch?v=NZDbDg22dFI


Right Rear Flex Video (the "control" if you will): https://youtu.be/bQMBecKZ6Yc

https://www.youtube.com/watch?v=bQMBecKZ6Yc



My questions are as follows:

1) How much flex is normal? Is this outside what is normal?

2) My flex test doesn't necessarily translate to how torsion is applied to the chassis when the car is on the ground, so am I worrying about something that isn't relevant? Wouldn't the applicable stress while driving get suppressed in part by the rear shock?

3) Would you be concerned about running the car?

Mid-term I'm going to get the LR console replaced for peace of mind, get the reinforcements cleaned up and tidy. The question is, should I forego my race and get it repaired before running.

[gms]

It is very hard to tell what is loose from the video but it looks like the outer suspension mount is moving? you need to examine the bottom of the longitudinal in that area for cracks or seam separation. I would say any lateral movement will make the cars handling unpredictable.

[vintage914racer]

It is very hard to tell what is loose from the video but it looks like the outer suspension mount is moving? you need to examine the bottom of the longitudinal in that area for cracks or seam separation. I would say any lateral movement will make the cars handling unpredictable.

I agree. Unfortunately I don’t see anything that’s glaring when I’ve inspected it.

[brant]

thats scary looking..

really unpredictable rear steering when that happens..
can't think it would be very safe..

could this be ovaled mounting holes?
also hard for me to see where the flex is from.

I'd pull those rear swing arms for inspection

[vintage914racer]

thats scary looking..

really unpredictable rear steering when that happens..
can't think it would be very safe..

could this be ovaled mounting holes?
also hard for me to see where the flex is from.

I'd pull those rear swing arms for inspection

I think pulling my swing arm is the next step.

[rick 918-S]

Definately metal fatigue. Drop the suspension. I am sure you will find cracks in that mount. If I wasn't neck deep at work I would take a day and come down. Let me know what you find. Sent you a text..

[SirAndy]

Definately metal fatigue.

(IMG:style_emoticons/default/agree.gif)

That's a lot of flex and it's not just in the mount, the whole upper long part seems to be moving/twisting.
(IMG:style_emoticons/default/unsure.gif)

[Bullethead]

(IMG:style_emoticons/default/agree.gif) That's a scary amount of movement... first thought was the mount, but there must be more to it. Like way more than this:

[vintage914racer]

Pulling the trailing arm tomorrow and investigating further. Stay tuned.

[rick 918-S]

I'm heading down to see if I can assist Ben. That crack photo is what I was thinking may have happened. We shall see.

[Krieger]

That looks scary to drive! I can't imagine how much flexing occurs from the cornering forces the car can generate. (IMG:style_emoticons/default/unsure.gif)

[vintage914racer]

A huge thank you to Rick (rick918-s) for coming down to the cities from Duluth today to assess and ultimately fix my flex issues. He’s a true asset to the 914 community. It took him just a few minutes to determine that the factory spot welds that connect the flange in the inner (engine compartment) flanges to the exterior sheet metal were compromised and not connecting the inside and outside.



Following an afternoon of drilling, temporarily fastening with self tapping screws and stitch welding the drivers and passenger sides were back in business. No more flexible flyer. Now I just need to get an alignment before leaving town on Wednesday.

Huge shoutout and thank you to Rick. He’s one of the hood ones!

[vintage914racer]

[Bullethead]

(IMG:style_emoticons/default/smilie_pokal.gif) Great job! (IMG:style_emoticons/default/smilie_pokal.gif)

[infraredcalvin]

(IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif)

That is so awesome! Thanks for posting the issue and fix. Kudos to Rick for taking the time to head over, identify and fix the issue.

[SirAndy]

(IMG:style_emoticons/default/smilie_pokal.gif) Great job! (IMG:style_emoticons/default/smilie_pokal.gif)

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/beerchug.gif)

[SirAndy]

Following an afternoon of drilling, temporarily fastening with self tapping screws and stitch welding the drivers and passenger sides were back in business. No more flexible flyer.

I wonder if you can do some creative cross bracing to prevent this from happening again?
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[rick 918-S]

It was a nice day. When I arrived the suspension was off so it wasn't real easy to see what happened. Ben made up a quick lever out of some square tubing and bolted it to the three point mount. With a little pressure it was clear what was moving. The upper spot welds had completely unzipped from the bottom to the top of the inner rail.

I went over and checked the right side and the same thing had occurred. The right side was not as obvious as the suspension console had been replaced and it was tied into the roll bar.

The easies fix was to use Drill Screws to pull the flange back in place. As I removed one screw at a time I used a 1/4 drill to flare the hole and expose the inner flange. I just plug welded both sides. Should be good to go.

If you race or AX alot you may want to check to see if this is happening. Just stick a screw driver or pry bar between the panel and the flang and see if moves. My 6 is stitch welded from the engine bay side along the top edge of the inner flange as it used to be a race/AX car. Even with this method and a poor welding job I can see some of the welds did not hold like a spot weld thru the flange would.




It was nice to see Ben again. It has been a few years. Time flies..

[gms]

Great work Ben & Rick! See you at Road America!

Unfortunately the after market chassis stiffening kits do not extend around the bottom of the inner wheel house to the longitudinal pinch weld like the factory kit does (below).

[slivel]

Is this a crack?