View Single Post
Old May 27th 2015, 03:05
graham's Avatar
graham graham is offline
Registered User
Join Date: Feb 2004
Location: surrey England
Posts: 273
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.

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.
gee dub
Reply With Quote