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  #1  
Old May 16th 2015, 14:27
effvee effvee is offline
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Coil overs shocks

Hi everyone, concerning my rear suspension. please note, none of the pictures shown, are of my suspension. I have collected three sets of the 944 rear trailing arms, but time has moved on and I still have not completed anything. There was talk concerning the 6 cylinder Subaru engines being installed in VWs, with the deck lid down. On one of the threads I noted the use of what I believe are height clearance trailing arms, for something like dune buggies.
This typo of trailing arm is what I have collected.

However adding the coil over shocks has shown itself to be not been easily done. one of the reasons in my opinion is, the trailing arm already made in its configuration. And then adapting this trailing into a IRS beetle. Placement, and angle of alignment is problematic to say the least.

In this pic, of the off road trailing arm. I think because of the part being steel and its configuration, maybe its possible, to get that more correct alignment of the coil over shocks. This pic is from a person adapting the 6 cylinder into a earl bug. I think he may have hit on something, for me




adapting a shock mount and its alignment look more easily done with this trailing are, what do thing will be some of the hang ups?

Last edited by effvee; May 16th 2015 at 21:14.
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Old May 20th 2015, 16:53
spannermanager spannermanager is offline
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It depends on the agenda you have for the car, generally, for all but very smooth surfaces, there is insufficient travel before the shock bottoms out, ideally the travel needs to be increased by using longer shocks and springs, to do that, the top mounts need to be re engineered, turrets in the wheel wheel arches or fabricating new top mountings into the roll cage, or a combination of the two is preferable to trying to use the stock chassis mountings with a network of brace bars. The off road boys have led the way, and the blue Japanese racer follows a similar rout to my own set up with re positioned over slung lower mountings and the upper mountings off the roll cage rear triangle, here is where steel a arms offer more versatility than alloy Porsche ones, being easier to modify.
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Old May 20th 2015, 23:04
effvee effvee is offline
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Hi, after your eye opening facts, I will scratch that ideal, thank you very much. Ok I see where the coil over shocks are in alignment, I have read where the lower bolt/stud is a Porsche part. Is it a stand alone chassis support, or does it rely on help for the torsion bars?
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Old May 21st 2015, 08:47
spannermanager spannermanager is offline
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I should add my remarks concern race circuit cars were you can give nothing away concerning running as low as possible, you won't beat a Porsche unless you gain the advantage in set up and handling, as they can be drastically
lowered without suspension alignment problems, VW road cars running at a raised or stock ride height just about have enough travel but there are still the clearance problems you correctly spoke of, and the debatable strength of the single shear fixings, both top and bottom, and it's only me that hates 5 bar braces, just a band aid to me, and a heavy space grabbing one at that, although in some cases, there are restrictions to moving the shock mounts to inside the car etc, as to your question, the lower bolts most folk are using are aftermarket and very high quality, but they can and do break in the imperfect world we all have to work in, some folk run the bolts with coil overs AND torsion bars, less load on the lower bolts , others remove the T.Bs and just use heavier springs on the coil overs, far higher loads on the bolts, I would not go racing like that, tho many do, which is why all my fixings are re located and in double sheer.
Just a note, the coil overs above look to be 2 1/2" units, if I HAD too, I would use 2 1/4". There are also 1.9 inch units, which would offer better clearance, but the maximum spring rate available for that size is 400 lb/inch, do able WITH torsion bars though..

Last edited by spannermanager; May 21st 2015 at 08:55.
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Old May 21st 2015, 09:00
effvee effvee is offline
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Quote:
Originally Posted by spannermanager View Post
I should add my remarks concern race circuit cars were you can give nothing away concerning running as low as possible, you won't beat a Porsche unless you gain the advantage in set up and handling, as they can be drastically
lowered without suspension alignment problems, VW road cars running at a raised or stock ride height just about have enough travel but there are still the clearance problems you correctly spoke of, and the debatable strength of the single shear fixings, both top and bottom, and it's only me that hates 5 bar braces, just a band aid to me, and a heavy space grabbing one at that, although in some cases, there are restrictions to moving the shock mounts to inside the car etc, as to your question, the lower bolts most folk are using are aftermarket and very high quality, but they can and do break in the imperfect world we all have to work in, some folk run the bolts with coil overs AND torsion bars, less load on the lower bolts , others remove the T.Bs and just use heavier springs on the coil overs, far higher loads on the bolts, I would not go racing like that, tho many do, which is why all my fixings are re located and in double sheer.
Just a note, the coil overs above look to be 2 1/2" units, if I HAD too, I would use 2 1/4". There are also 1.9 inch units, which would offer better clearance, but the maximum spring rate available for that size is 400 lb/inch, do able WITH torsion bars though..
One of my major problems is, not knowing the suspension stuff. Circuit racing and the likes, I just don't know.. I'll keep both the 944 trailing arms and, try the coil overs as a secondary.
Thank you
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Old May 21st 2015, 11:06
spannermanager spannermanager is offline
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Interesting the two separate setups above, one using a 6 rib bus box with torsion tube intact, the other with much longer Subaru 'box with a sectioned and overhead 'bridge' plate reinforced torsion tube.
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Old May 21st 2015, 13:43
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The chassis with the H6 is shortened in a way to move the torsion housing forwards in the car, the lengthened trailing arms put the wheel back to the original position...
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Old May 21st 2015, 14:55
effvee effvee is offline
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I was going to use the stock lengths. I thought by using steel I would be able to mod the coil overs more in line. Question is the 944 trailing arms holding up pretty good?
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Old May 21st 2015, 17:41
spannermanager spannermanager is offline
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There are no question marks over the Porsche or VW a arm strength, steel or alloy, but again, the steel arms are more versatile for fabricating a decent double sheer lower shock mount as Dave has done on his rally replica, we all minimise the increased loads on them for racing by lateral thinking and tying the drive train down solid, the shock mount problem remains open to individual interpretation for your own requirement, the 6 cyl Subaru drivetrain will be well into the diminishing returns area with weight and complexity, drive shaft angles have already been compromised and it breaks my own KISS and lightweight rules, it's almost worth giving up on the rear engine layout and mid engining the whole deal, but I can't imagine the agenda for the project anyway other than a good road touring car, as it's easy for a 300 hp four banger rear engine VW motor in an 800kg Beetle to be an unbeatable missile that will out brake and out turn 400 hp in an 1100 kg build, at least as far as track use is concerned.
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Old May 26th 2015, 03:47
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Coil overs shocks

Spanners what are your views on the possibility's of designing and welding a double sheer mount onto the ali arms ? I know ali is difficult to weld but it is possible by the right person.Has anyone ever tried welding anything onto a Porsche arm ( I would imagine the casting is pretty good ? )

When my car goes off to have the gearbox cradle fabricated I want to add double sheer top mounts off the cage so whilst I am at it I may as well sort the bottom mount's out if its doable ?? the thought of shock mount bolts letting go is worrying to say the least.

Also Spanners what would YOU choose for coil overs with the scooby 4 cyl engine,no T.B's and uniball ? i.e. lengths,widths,lb's etc.(if I have to have the top mounts raised into inside the car then so be it, I am just interested in getting it set up as best as possible )

Lots of questions I know but your thoughts are always appreciated
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Old May 26th 2015, 15:15
spannermanager spannermanager is offline
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Cool

Hi Graham, well I've never actually modified the Porsche ally a arms, but yes, it must be doable, firstly, from the pics above, it looks as if the lower fixing offers more ground clearance then the steel arms, VW or Porsche being the same in dimensions, it's always clearance to the spring from the outboard end drive shaft/cv over the range of travel that is tight, I would use 2 1/4" spring units, but as to a brand name? Well there are many top quality products out there, Koni are right up there for quality if the budget is high end, cheaper quality? Spax or protech are both very helpful, I would only say stick to a simple adjuster spec, 4 way adjusters are just overkill for all but race teams, 2 way are plenty enough, bilstein don't adjust and will work brill straight out the box, the engineers did the work, your application is a little different tho!!
Have a look at the Japanese blue bomber, moving the lower damper mount to the top of the a arm is a smart move, the higher compression loads are easily supported, something similar would be doable in alloy, and the top mountings are cage mounted, I don't like the opposing fixing bolt axis they've used but it must work for them. NVH may be a problem to consider, even with rubber bushings, solid spherical eyes will be a mare on the road, we have it easy for track only, but I'm now deaf as a post from it all lol..
Watch for wheel/tyre clearance over the full travel, there's a fair old swing on the dampers, damper length? Probably best measured once it's all been mocked up, upper/lower bump stops can be built into the units if needed, a lot depends on the mechanical/existing droop and bump stops, if any, provided by whatever type of spring plate and trailing arm fixings you use?
The downer to modifying stuff away from the brilliant original conception, is that it becomes a major mechanical exercise to do what was originally easy, a rear shock Change now takes me an hour at least, colour code the bolts/ nuts for shock or roll cage members if they are different specs.
You will need a fair old spring rate for stock location dampers with no torsion bars, less spring rate if they are moved outboard towards the wheel, considerably less in fact, less leverage acting on the spring/damper units.
Wally will shoot me in the head now, he's done OK with Billy's in the stock location, not sure if he uses torsions or not, but they do take the load off the shock bolts.
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Old May 27th 2015, 03:05
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Nice one Spanners great input/advice,and once again lots to consider.

Ive done a bit of digging around and found that failure of the racers edge lower shock bolts is very rare.The couple that have failed where on heavier porsches and one was running no TB's with 700 lb springs.

Not to say it wouldn't happen on a lighter beetle but maybe the concerns on them actually failing on a beetle are not as likely ?

Here is something I found re lower shock bolts,the last paragraph is particularly interesting.He is talking about track cars but it is food for thought.



Quote:
The stock lower shock mount bolt for the alum. trailing arms is an M14 (14mm). Two reasons for the racer's edge type bolt adaptors: 1) the offset/width of the spherical bearing require a standoff distance from the trailing arm. 2) the spherical bearings are 1/2" (12.7mm) so the M14 bolt will not fit through the hole in the bearing. The adaptors are exactly that, they adapt the 1/2" to the 14mm trailing arm.

So the standard/stock bolt is larger diameter (potentially stronger?) than the aftermarket adaptor sets.

If you use the bilstein turbo cup suspension or the older koni double adjustable coilovers (not the 2800 or 3000 series), you need to use the factory bolt. Any shock with a spherical bearing lower mount requires the adaptors.

I have setup my cars to run both with the torsion bars reindexed and without torsion bars using bilsteins (so I used the factory bolt). I cant say that one setup is dramatically different feeling than the other. W/o is a little easier to install and allows more and easier adjustability in the future. I did not have any failure problems with either setup.

I have never heard of the factory bolt shearing, but that does not mean that it has not happened. I also have not heard of the racer's edge part failing. I have seen a Kelly Moss adaptor bolt break, but this was on an old Firehawk car, which had thousands of endurance racing miles on it - so that might not be a common example.

For you guys that do all the suspension calculations, how much loading is on the rear shock mounts? Probably a high speed bump or pot hole will be the largest loading, and idea? For a 14mm bolt: cross section is 0.239 sq. in. and a pretty standard shear strength is possibly up to 60,000 psi for a hardened bolt, so it will handle over 14000 lbs force. Even if the strength is 30ksi, thats still 7000 lbs, which is almost 10 times the static weight of the car acting on the corner.
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Old May 31st 2015, 09:26
spannermanager spannermanager is offline
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My concern is More the cyclic loads suspension components have to contend with, rather than a calculated yield point, it wouldn't be too difficult to calculate the yield point of the bolts, even from a simple torque test to yield point, thats if they are not manufacturer published as a matter of course, I would think the info is generally in the public domain, but any installation problems such as misalignment, too short on travel and bump stops and/or bottoming out, or a bending moment applied to the shock body by contact with the a arm as it arcs upwards, a stack up of all these led to Dave's problem on his Porsche Salzburg car were he had to re design his shock mountings, but he overcame his with re engineering the lower mounting and a arm work.
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Old June 3rd 2015, 01:49
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Quote : any installation problems such as misalignment, too short on travel and bump stops and/or bottoming out, or a bending moment applied to the shock body by contact with the a arm as it arcs upwards, a stack up of all these led to Dave's problem on his Porsche Salzburg car were he had to re design his shock mountings, but he overcame his with re engineering the lower mounting and a arm work.[/QUOTE]

Spanners do you think that by relocating the top mounts alone could solve the problems you mention above ? As I have the cage to tie into i have the option of fabricating/designing something.If this means having the top mounts inside the car then so be it.On the surface this seems to be an easier option rather than getting into fabricating and welding something onto the bottom of the ali arms ? This part of my build is something that does concern me and I do obviously want to get it right.The main thing thats holding me back on design is I don't have a clue about suspension geometry or any experience with any of this .
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Old June 3rd 2015, 02:05
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Coil overs shocks

Also,in first the picture at the beginning of this thread the Red Coil Over is tied into the cage,the top mount is on the left of the cage,this has thrown the shock and adds to the obscure angle on the lower mount/bolt,if that top mount where on the right of the cage and higher up would this help things ? Sorry if Im rambling on here and Im not sure if anyone else is paying attention to any of this apart from you,but it would be great for me to get this sorted as I am planning on getting back at the build as funds and life should soon allow.
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