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Syncro Body Creases forward of rear shock towers
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kryptkat
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PostPosted: Thu Mar 12, 2015 3:30 pm    Post subject: Reply with quote

I'm a simple guy so I have a simple theory, maybe its "weight"? I do alot of offroading, even crashed into the side of a mountian last year but my quarter panels are as straight as a ruler. I try and keep my van as light as possible (3700lbs). Maybe thats the key but I also have double sliding doors, maybe my body is alittle more ridgid than the average Syncro?
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Chugach
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PostPosted: Thu Mar 12, 2015 3:38 pm    Post subject: Reply with quote

Quote:
I also have double sliding doors, maybe my body is a little more ridgid than the average Syncro?

or more flexible? doesn't this panel deformation occur on both sides of van?
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SyncroGhia
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PostPosted: Thu Mar 12, 2015 3:52 pm    Post subject: Reply with quote

My experience of twin sliding vans is that they're more flexible than the single sliding door vans.

If you think about the extra panels that Syncro 16s get around the sliding door... that should tell you enough Wink

Here's the thing though, this is less about the sliding door though as I don't think that this has any effect the area in question.

I think that this is more about the area behind the C-pillar with loads, spring rates, shock absorber damping rates etc.

MG
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syncromike
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PostPosted: Thu Mar 12, 2015 4:22 pm    Post subject: Reply with quote

rmcd wrote:
Yes I'm a dork with too much time during my lunch break.

I'm having a hard time understanding how the plating might work to reinforce my syncro from body creases.

This is my attempt at a free body diagram to simplify the forces in two dimensions. Yes, I know the geometry is infinitely more complicated than this. Maybe this diagram will help someone smarter than I develop a solution or explain how the existing Syncro 16" plating (aka lipstick on a pig) or the newly suggested triangular body plating might help reinforce the rotational forces acting across the Hinge from Hell.

The more I look at this the more I think that the Syncro 16" plating may actually help firm up the subframe area into a huge rigid block (motor, bumper weight) that enables more rotating force across the Hinge from Hell.

Thoughts?

Image may have been reduced in size. Click image to view fullscreen.

I think you nailed it. the pivot point on the trailing arm acts as the fulcrum and when you land hard on the rear wheels it bottoms out the spring and puts a massive force up on the load point where the shock attaches to the frame while pulling down on the pivot point. That lines up with the other picture showing that the rear end actually gets pushed *UP* on that hinge.
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syncrodoka
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PostPosted: Thu Mar 12, 2015 5:00 pm    Post subject: Reply with quote

Hmm...
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rmcd
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PostPosted: Thu Mar 12, 2015 5:02 pm    Post subject: Reply with quote

I think this should affect all Vanagons. Does the geometry of the engine subframe connect to the body frame the same?

Only place I can see, short of an internal roll cage, that MAY add some counter rotational force around the Hinge from Hell is in front of the engine firewall.

Maybe the Syncro 16" reinforcing plates do help to counter this bending?

Look at the moment arm multiplying factor when you put more weight further out on the bumper.

Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Thu Mar 12, 2015 5:50 pm    Post subject: Reply with quote

syncrodoka wrote:
Hmm...
Image may have been reduced in size. Click image to view fullscreen.


Holy heck where is that build? lol
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PostPosted: Thu Mar 12, 2015 6:05 pm    Post subject: Reply with quote

A rally vw t3.
Image may have been reduced in size. Click image to view fullscreen.

http://www.syncro-bernd-jaeger.de/DEUTSCH/html/rallyebus.html
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PostPosted: Thu Mar 12, 2015 7:53 pm    Post subject: Reply with quote

A couple comments as one who has studied vehicle chassis stress.

First, the diagram with the colored markings showing the forces needs to have the red upward force arrow on the forward suspension pivot removed. The chassis loads rest upon the spring mounts and transient forces both up and down rest on the shock mounts. The pivot is just that - a pivot.

Secondly, the small red triangles recommended on March 10 are too small in terms of resisting flex. When a reinforcement is too small, it will result in very concentrated stress right at the new parts. This is a pretty tricky game - adding stiff reinforcements to a large thin walled unibody structure.

Rather than add reinforcements to the hinging area of two long arms that are showing unwanted movement, it is better to go to the ends of the arms where the reinforcement will more easily prevent unwanted movement.

I think VW's approach to reinforcing the 16s was a good one. Not enough, but adding more sheet metal similar to the existing structure's materials is a safe way to reinforce - lowering the risk of having concentrated stress at a new way-too-stiff added part. This is a thin-walled monocoque structure. So either add more thin walled metal, or go to the ends of the levers for attachment of something heavier such as the tube frame structure shown.

I don't have the answer but I just don't want to see someone start adding small stiff bits that may cause serious damage when the structure continues flexing.

Doug
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PostPosted: Fri Mar 13, 2015 3:48 am    Post subject: Reply with quote

Re: Free body diagram. The left hand arrow should point downward, shouldn't it? (if the frame rail junction is being considered as a pivot)

Edit: or am I considering the rear rail as a uniformly loaded beam, with the "pivot"on the left, spring load in the middle and the body load on the right?

I didn't get a great grade in college physics and that was 25 years ago...

Has anyone noticed distortion in the engine hatch perimiter frame or top of the engine bay side panels i.e. the spring towers have also been pushed inward slightly?

Edit #2 Is it possible/probable/more likely that the rear spring towers are doing what the front suspension is known to do under high load/big impact/high rate springs & damping, which is that the top spring mounts slowly creep inward at their tops? The symptom being the inability to correct front camber to factory settings.

Hence my earlier question about the transverse flatness of the rear deck.
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PostPosted: Fri Mar 13, 2015 7:27 am    Post subject: Reply with quote

Ok, I quickly studied my syncro before I headed into work. I also took a couple pictures with my phone. Here is a picture of where the inner panel is cracking in the beginning of this thread. If you look closely at the inner fender, there is a factory bend, and I would bet if you carried that bend out to the outer fender, that is where the outer panel is buckling. That does not help.

Image may have been reduced in size. Click image to view fullscreen.



Second, I looked underneath and the rail that supports the spring top, bump stop and shock is about 6 inches or more inward of where the chassis is bending. Technically if it was the suspension bottoming out, the forces would be against the radius of the support which is the opposite of the failure.

Image may have been reduced in size. Click image to view fullscreen.


Also say you did try to gusset that area, because it is boxed steel, any loads of the gusset would collapse the box.


So is there a bolt on solution? I don't believe so. I think you could add some strength using roll bar tubing but that would require quite a bit of custom fabrication.
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PostPosted: Fri Mar 13, 2015 7:53 am    Post subject: Reply with quote

interesting subject ...
i`m looking to buy a Syncro , and ill definitely watch for this concern ....
well , Pedro will lolllllll...........


I`ve been hard offroading for 35 years , mostly in Jeeps and
what I can say is : if nothing flexes , it will crack !

originally my old CJ frame was twisting so much that body panels would crease as the syncro shows .....
I had to change the frame for a YJ`s because my frame would crack at many stress points .......
consequences: I had to work on the suspension intensively to get the wheel travel that I had before .....

Another point , when putting weight on these carriers at the back , support part of the weight with some binder straps attached to the top of the rear hatch ...it takes the bouncing to a minimum ....it did a lot of benefits to mine !

Dan ,
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PostPosted: Fri Mar 13, 2015 10:40 am    Post subject: Reply with quote

Slight side issue that I experienced a while ago: I bought a NOS Caravelle rock'n'roll hinge frame from VW, but I had one hell of a job to get all four bolts in. Nothing seemed to line up right. I put it down to the frame maybe being a "second" but because of the proximity of the mounting bolt plate to this problem area, maybe my '85 syncro isn't so straight after all.
The LH rear wing had already been changed before I bought it, maybe this was hiding something?
I would turn out the back of the bus to inspect the rear deck for deformation but it's full of all sorts at the moment...
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PostPosted: Fri Mar 13, 2015 10:53 am    Post subject: Reply with quote

From where I sit, the crease is caused by twist. Westys and sunroofs will be prone to twisting more easily, imo. Vehicles with heavy rear ends will be more prone to twist damage creases.

To avoid body creases, avoid twist… Anything that puts a wheel in the air, creates twist. So imo, only vehicles that spend time on 3 wheels will have the creases.

A heavy westy with lots of rear weight, offroad, is an ideal candidate for body creases. Note Syncro Jael is the poster child for that feature set.
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derekdrew
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PostPosted: Fri Mar 13, 2015 11:08 am    Post subject: Reply with quote

I have a heavy westy that goes on 3 wheels a lot and it is badly creased. I am sure that you could measure the flex in the van when off-roading if you really wanted to with some kind of laser jig, and then experiment with what reinforcement would stop the flexing, and then sell "reinforcement kits" to prevent it.
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MarkWard
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PostPosted: Fri Mar 13, 2015 11:21 am    Post subject: Reply with quote

On all 3 of my vans with them on a lift supported at the jacking points, the front doors do not close easily. That tells me there is certainly some flex going on with one or more tires in the air. Trying to brace from above, you will loose interior space and I don't think the difference between the bottom of the van and the two rails is enough to triangulate from below. Plus you'd have the CV shafts and suspension in the way. Curved tubes loose some strength vs straight ones.
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PostPosted: Fri Mar 13, 2015 12:46 pm    Post subject: Reply with quote

Jon_slider wrote:
From where I sit, the crease is caused by twist. Westys and sunroofs will be prone to twisting more easily, imo. Vehicles with heavy rear ends will be more prone to twist damage creases.

To avoid body creases, avoid twist… Anything that puts a wheel in the air, creates twist. So imo, only vehicles that spend time on 3 wheels will have the creases.

A heavy westy with lots of rear weight, offroad, is an ideal candidate for body creases. Note Syncro Jael is the poster child for that feature set.


I will submit a photo of the poster child crease if it occurs. Wink

Now that have an idea of what causes it I will be more careful on what trails I embark on. It just hurts to see a beautiful "Syncro Bo" with that crease in it. And it's not even mine! Shocked

This has been an informative thread.
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PostPosted: Fri Mar 13, 2015 2:48 pm    Post subject: Reply with quote

djkeev wrote:
I'm NOT a syncro guy at all, yet I find this thread fascinating!
Who Knew that these rigs deform like this?
Is this a new phenomenon? Or has it been around for years but not spoken about much?
Dave
'Popcorn'


I'm guessing that VW knew about this problem from early on or else they wouldn't have bothered to add the reinforcement to the 16" and also the added strength to the later Syncros.
I've driven my Syncros pretty hard on logging roads, etc. but I don't have much added rear weight other than a spare tire carrier. No deformation at all on mine.
But then again, I've never "jumped" mine either! Very Happy
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PostPosted: Fri Mar 13, 2015 6:54 pm    Post subject: Reply with quote

BigDan1 wrote:
interesting subject ...
i`m looking to buy a Syncro , and ill definitely watch for this concern ....
well , Pedro will lolllllll...........


I`ve been hard offroading for 35 years , mostly in Jeeps and
what I can say is : if nothing flexes , it will crack !

originally my old CJ frame was twisting so much that body panels would crease as the syncro shows .....
I had to change the frame for a YJ`s because my frame would crack at many stress points .......
consequences: I had to work on the suspension intensively to get the wheel travel that I had before .....

Another point , when putting weight on these carriers at the back , support part of the weight with some binder straps attached to the top of the rear hatch ...it takes the bouncing to a minimum ....it did a lot of benefits to mine !

Dan ,


Hi Dan!

Yes we will go check out that syncro westy asap. I am very curious to see what we will find. My main concern is driveshaft vibrations, if the tranny and viscous coupling works as it should, rust issues, and of course this syncro crease!

Cant wait to see that syncro!


In regards to all the theories elaborated so far, its really nice to see a lot of people shiming in and brainstorming to the ways it probably created that body crease.

I would like to add that the picture shown straith from the side only shows a rectiline forces applyed to the top of the spring tower. You need to add the 3 dimensional way because:

1- of the angled spring tower
2- the bottom of the spring tower is not directly under the frame but on the side.
3- and the very small surface that it attaches to the top engine floor, to a flimsy C channel... Wow!

Image may have been reduced in size. Click image to view fullscreen.

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MarkWard
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PostPosted: Sat Mar 14, 2015 10:01 am    Post subject: Reply with quote

Ok, we discussed this over breakfast this morning. We believe what is causing the bending is actually when the front end gets light. Think of it as pulling a wheelie. At the point that the front is unloaded, the fulcrum becomes the unibody area above the rear axle. Since the engine weight etc is behind the fulcrum, the unibody is bending above the fulcrum because it can't support the weight of the other 2/3rds of the van. The suspension is designed to support the unibody with the loads distributed between both axle lines. Experts?
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