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914World.com _ The Paddock _ Rear chassis flex. What do you think?
Posted by: vintage914racer Jul 7 2023, 08:34 PM
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.
Posted by: gms Jul 8 2023, 07:10 AM
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.
Posted by: vintage914racer Jul 8 2023, 07:37 AM
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.
Posted by: brant Jul 8 2023, 07:58 AM
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
Posted by: vintage914racer Jul 8 2023, 08:23 AM
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.
Posted by: rick 918-S Jul 8 2023, 10:18 AM
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..
Posted by: SirAndy Jul 8 2023, 10:28 AM
That's a lot of flex and it's not just in the mount, the whole upper long part seems to be moving/twisting.
Posted by: Bullethead Jul 8 2023, 11:29 AM
That's a scary amount of movement... first thought was the mount, but there must be more to it. Like way more than this:
Posted by: vintage914racer Jul 8 2023, 01:06 PM
Pulling the trailing arm tomorrow and investigating further. Stay tuned.
Posted by: rick 918-S Jul 8 2023, 07:17 PM
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.
Posted by: Krieger Jul 9 2023, 08:39 AM
That looks scary to drive! I can't imagine how much flexing occurs from the cornering forces the car can generate.
Posted by: vintage914racer Jul 9 2023, 06:38 PM
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!
Posted by: vintage914racer Jul 9 2023, 06:38 PM
Posted by: Bullethead Jul 9 2023, 06:54 PM
Great job!
Posted by: infraredcalvin Jul 9 2023, 09:55 PM
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.
Posted by: SirAndy Jul 9 2023, 09:55 PM
Great job! 
Posted by: SirAndy Jul 9 2023, 09:58 PM
I wonder if you can do some creative cross bracing to prevent this from happening again?
Posted by: rick 918-S Jul 10 2023, 04:20 AM
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..
Posted by: gms Jul 10 2023, 09:14 AM
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).
Posted by: slivel Jul 10 2023, 01:04 PM
Is this a crack?
Posted by: vintage914racer Jul 10 2023, 02:17 PM
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).
Thanks, Glenn. Rick should get all the credit for a job well done.
See you in a few days.
Posted by: sixaddict Jul 10 2023, 07:14 PM
This thread helped a lot as have similar issues …..not quite as easy to get to.
Posted by: vintage914racer Jul 11 2023, 08:11 PM
Is this a crack?
That's not a crack. That's the factory overlap where the two panels are spot welded together. I knew it wasn't, but wanted to wait for the car to return from the alignment shop to look at it to validate.
Posted by: vintage914racer Jul 11 2023, 08:16 PM
Following Rick's miraculous short notice repairs on Sunday afternoon, it was a race to find a local shop to align the car before my planned departure for Road America on Wednesday. My regular alignment guy was booked solid, as were the other local usual suspects I trust with the car. Fortunately the folks at https://www.werksautomotive.com/ were able to sneak it in.
I dropped the car off yesterday afternoon and they worked it in this afternoon. From there it was a scramble to get the car home, buttoned up and loaded for the trip to Road America in the morning. 
Put back together, loaded in the trailer and ready to go!
Posted by: gms Jul 12 2023, 01:40 PM
Is this a crack?
No that is the lower edge of the targa reinforcement panel
Posted by: infraredcalvin Jul 12 2023, 09:28 PM
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..
Seems like this fix might be good preemptive measure when installing gt reinforcement kit in wheel wells if planning on heavy tracking or autox…
Posted by: vintage914racer Jul 19 2023, 10:31 AM
Quick update after attending the WeatherTech International Challenge at Road America last weekend.
The car ran and handled phenomenally. Road America was repaved last fall and is incredibly smooth. And fast. I consistently ran my best laps there ever.
Not a huge surprise, but the cars handling was as consistent as ever, now that it's no longer a flex-flyer. 
Posted by: brant Jul 20 2023, 08:28 AM
That is awesome
Brant
Posted by: SirAndy Jul 21 2023, 08:41 PM
Quick update after attending the WeatherTech International Challenge at Road America last weekend.
The car ran and handled phenomenally. Road America was repaved last fall and is incredibly smooth. And fast. I consistently ran my best laps there ever.
Not a huge surprise, but the cars handling was as consistent as ever, now that it's no longer a flex-flyer.
Posted by: Charles Freeborn Jul 22 2023, 09:36 AM
Quick update after attending the WeatherTech International Challenge at Road America last weekend.
The car ran and handled phenomenally. Road America was repaved last fall and is incredibly smooth. And fast. I consistently ran my best laps there ever.
Not a huge surprise, but the cars handling was as consistent as ever, now that it's no longer a flex-flyer.
Well done!
When you have a chance could you post some pics of how your cage connects - I'm especially interested in how your "Halo Bar" goes from the top of the main hoop into the footwell as I'd like to add a similar one to mine.
Thanks!
Posted by: blabla914 Sep 3 2023, 07:06 PM
glad to hear you got it fixed and were able to get out on track.
I broke my car on the left side in very similar fashion years ago from many years of autocrossing on rough lots. This is definitely a spot to keep an eye on. On mine I could see from inside the engine compartment the frame rail had separated from inner fender.
nice bus 
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