Rear coilovers on supers
 

I have maxx struts on the front and wanted to install the rear coil over kit. Does anyone know who would have the best quality kit out there. i have found several kits but i haven't really found the actually coilover shocks. Just the adapter kit.

Loads of companies sell coil-overs, AVO, Spax, Protech, Bilstein etc etc, we are spoiled for choice in the UK! Just measure up to see what you need. Personally I will (and have before) be going for protechs...

I've gone for Spax on the rear in anticipation of adding a threaded sleeve for coil overs. However, I will be retaining the torsion bars as well using the coils just to up the overall spring rate. I would be very nervous about relying on the 12mm bolt at the top and the aluminium housing at the bottom to withstand the stress of providing the fixing for 500lb/in + springs. Remember that the bolts are in cantilever bending that creates a moment that is around 4 times that of a bolt suspended between two fixing points. I can't see any good reason unless of course you would require a full progressive spring rate instead of the linear one that was imparted by the torsion bar.

evilC

Whenever I see coilovers mounted that way it always makes me nervous too. If you can fab up a double-shear situation, I think it would be just fine, but that single-shear situation is a little scary to me too.

Jason

can we get a bunch of various coil setups in reference pics explaining the various differences / pros & cons? the gallery isnt that great at explaining the variences between each, just a thought

I posted some over here, it's in Dutch though
http://www.keversite.nl/forum/viewtopic.php?f=5&t=16351
(Achterkant = rear)

Is it for steel trailing arms or for 944 Alu trailing arms?

About the single shear:
It's a good point, but in the Käfercup they raced with the single-shear setup and it didn't break. And they did push their cars to the limit.

To a degree it doesn't matter if its the steel or alloy arm since the connection of concern is the top mount, which is the same for both. The top mount has a single 12mm bolt that is in single shear but also has a significant element of bending that is compounded if the top bush is rubber rather than a ball joint. The shear value of the bolt is well within the bolts capability but it is the cyclic bending that is problematic IMO. Because of this cyclic bending NEVER use a stainless bolt because it will prematurely fail.
the lower mount on a steel arm is actually much better than the alloy arm because the bolt is only in shear, which it can cope with very easily. The alloy arm however, uses a 14mm bolt again in cantilever, this time with a substantial lever arm as the threads are well buried in the housing.
Remember, both VW and Porsche designed these fixings only to take damper loads that are minimal compared to the loads imparted by a spring.

evilC

Sorry, I forgot to comment on the single shear in racing. Most/all Kafercup cars used the rear cup brace that in general connects to the top damper mount. This point is then triangulated back to the frame horns at their front and rear so that the damper mount now becomes a simple double shear point not the single shear/cantilever bolt arrangement thus doubling the shear capability and quadrupling the bending moment capability (although as previously said there is very little bending moment imparted by this set up.

evilC

Sorry, my post was inclomplete again, I ment single shear on the trailing arm, since the upper mount can be made into a double shear mount.
Anway, thanks for your answer!

Why does the bolt in the alloy arms work in cantilever (and why doesn't it with the stock arms?)
Is the damper under a different angle compared to the stock arm?

And only the topmount is of concern, since it's the one that gets a bending load?

The steel trailing arm can be fabricated with thin metal to create a two sided cup that supports the bottom bush of the damper. The alloy arm is a complete casting and to creat a double sided support would be difficult without adding fabricated bits. Since the loads are relatively small through the damper (only) mount having a single cantilever bolt is no great problem. I don't think the angle of the damper changes between steel and alloy trailing arm.

The bending load is in both bolts equally but the bottom bolt of the alloy arm is M14 and the top bolt is M12 a difference of 36% in bolt strength but the M14 is a longer bolt and therefore the bending moment is greater (PL/4).

evilC

the mo30, 951 ALLOY ARM, USES A COIL OVER SHOCK, WITH THE TORSION BARS

I completely agree and it's why I will stay with the torsion bar set-up.

hello 951 - m030 option
 

look

rear coil over = stock
m030 option
http://www.weissach.net/968_M030-Opt...ocksAndSprings

Yes, but what else did Porsche do besides just bolt that "shock" on there? What other modifications were made, in support, of the M030 option?

it tells you on that link

-fat bars
adjustable koni's

there isn't much else you could do is there?

ooh i almost forgot, i have a used pair of avo adjustable coil over shocks - eyes both ends, but me thinks 13mm eyes
-2 and a quarter inch springs, may fit an ally arm better than a steel turret
£100

he does have a point (unfortunately) as the M030 option used that coil-over spring in addition to the torsion bars. Not instead of the torsion bars as we intend to do...

This option is the addition of the "shock/spring", not a replacement, you just add it to the suspension as a supplement; it's not a "coil-over" as you're thinking like the MBT and other set-ups out there.

My point is, if Porsche didn't remove the torsion bars then neither should you. The rear coil-over is "neat" and it's "pretty" but it's very very dangerous because the entire weight of the rear of the car rests on that one bolt (on either side). I would not feel comfortable driving a car that if one bolt was to break something like this would happen.

http://www.superbeetlesonly.com/foru...10_8_36166.jpg

I have been driving mine with 944 arms and coilover, with single shear bolt on the bottom for several thousand miles now. mostly track drag and autocross.
No problems at all!

The 14mm bolt is probably the strongest on the whole car! its a 14-9 bolt, that is it wil hold 140kg pr square mm! that will give you a couple of tonn's to spare even if you take all the weight on one wheel.

I have no worries using it like this.

the pic's show what happen if you try to drill holes in the brakedrum to make it lighter... :D

and even if the bolt should break-your car wil only be lowered a bit.

Why not just run the 924/944/968 bars?
cheap and easy to get. Relatively easy to install.
many options to choose from.
http://www.germanlook.com/Html/Tech/...Suspension.htm
and a full list of all at http://www.924.org/techsection/technical.htm (suspension section)


Rob

If there were a million cars that drove a million miles each, then I'd do it but I'd rather never ever take a chance with a safety issue. However, on a track car running single autocross you cut the risks down a lot.

The 030 upgrade was to add a coilspring to the rear damper in addition to the torsion bar to increase the wheel rate. I see that spring (anyone know the rate?) as a light helper spring on the rear of a front engined car. My concern is in discarding the torsion bar and fully relying on a coilover spring that needs to be around 500 lb/in. The forces in compression will then go into the mounts that were not designed for anything near the 1000lb loads that could be experienced.

evilC

I honestly never did any research on the 968 because it was my understanding that the 968 was nothing more than the latest model 951 and 952, as far as suspension and brakes are conerned. The 951 and/or 952 has this M030 option now that I remember, in fact, that webpage of the 968 M030 optional parts are all 944/951 part numbers sans the 964 (911) bushing.

This would work safely, as long as the torsion bar was not removed.

Does anyone know if this would work with the early 944 steel arm conversion? I have the entire rear from a 1985 944 for my 1303.

Does anybody know how the Remmele uni-ball kit gets around this problem? I believe that eliminates the torsion bars and puts the full weight of the car on the coil overs.

The German TUV certificate is very strict though so I cant imagine there being any chance of a failure just through a bolt shearing! anybody own this kit or seen one close up?

No, but 'we' (as in: not me, haha) found out that H&R has a claim on their site somewhere saying they did the research and found out the mounting points were strong enough!
HR is quite a respectable company...

H&R supplied the springs from the (Bilstein) cup suspension used in the Porsche 944 cups, which is how they ended up creating a tüv-approved coil-over set for the rear. They do still offer a complete coil-over set for the 944 with a tüv certificate stating that it is to be used without the torsion-bars.
http://www.h-r.com/bin/RSS-37-827.pdf

For the beetle however they only offer a coil-over for the front and non-coilover dampers for the rear, so they keep the torsion-bars in place, see: http://www.h-r.com/bin/29581.pdf

This basically means

• removing the torsion bars and running coil-overs on the rear of a beetle officially isn't legal in Germany
• The 944 aluminium trailing arm and the 12(?)mm bolt for mounting the damper is strong enough to handle the loads it is subjected to
• The upper damper mount on the beetles chassis could be the weak point (at least it hasn't ever been tüv approved to handle the loads from a coil-over)

Thanks for the excellent summery Simon!

It is weird though as the 944 top bolt (12mm) is the same size as the bug's...

Maybe nobody has Tüv'd it because of the high cost involved wrt being a 'low-cost' beetle...