kasturbo

I was one of the ones that thought an upgraded lower shock bolt would be strong enough, but I broke one today. Luckily I was on a service road with no traffic. The bolt broke in half and dropped the whole right rear of the car.

Any one know where the best price on the Racers Edge lower shock mounts are?

Pictures to come when I get the car home.





http://forums.rennlist.com/upload/dsc00009.jpg

turbite

wow, thats scary.
You don't have T-bars?

What do you mean by "upgraded bolt?"

sl951

Paragon-Products

Sam Lin

Chris White at 944 Enhancement. How did you make a different bolt work though?

Sam

Peckster

What do you mean upgraded? Who did you buy it from? Doesn't sound like an upgrade to me if it broke!

kasturbo

I bought 10.9 grade bolts to replace the standard 8.5 grade. I was told that these would be fine and strong enough. I had my buddy at True Choice make my Koni 3012's with 14mm specrical bearings as apposed to the 1/2".

Ski

Racers Edge.

GWTurboS

Don't mean to freak you out, but if you've removed the rear torsion bars and are just supporting the weight of the car with the upper and lower mounting bolts and the coilover assembly, I'd set a service life on the lower bolt and replace it just like motor oil, timing belts, etc.

That lower shock mount has a single sheer design because the factory probably did not anticipate torsion bar removal as a possible suspension setup. When you apply a heavy load on the end of an undersized bolt that is fastened in single sheer, eventually it will snap.

Back in '93-94 I was campaigning an ex-World Challenge Mazda RX7 Turbo II in SCCA Club Racing. The rear suspension was also coilover with the lower mount set in single sheer. The guys from Metalcrafters who had the car before me made a note of that bolt being a service item.

Glad to see you were not hurt though!

Best Regards,
Greg W.

kasturbo

Thanks for the advice Greg. These were a M10 bolt. That's why I thought they would be fine. Do you think I would have to change the Racers Edge adapters that often?

Laust Pedersen

About a year ago on Willow Springs Raceway I heard a loud bang on the straightaway and after that the car was handled funny. I immediately pulled into the pits and looked the car over, especially the engine, but couldn’t find anything wrong until Tony G, who happened to be there, came over and expressed surprise “how much I had lowered the car”. After looking at it yet another time, I was surprised too and sure enough my 14mm bolt had broken. Luckily I could spin the broken stub out with my fingers and after buying washers and a new bolt at the local hardware store (which they apologetically charged a full $2 for) I was back in business.

It later turned out the other bolt was bent and ready to brake as well. This was a few months old installation by Huntley.

There obviously has not been done any stress analysis on that set-up, but here is my simple analysis and solution:
By lengthening the bolt (relative to OEM), stiffening the shocks and adding the cars weight (no torsion bars), the bolt has a much higher bending moment applied. Since the breakage did not occur immediately after the installation, only minor changes needs to be made, but in my assessment a stronger bolt is not enough.
The trick lies in the design of the spacer between the “banana arm” and the “shock eye” so that it shares the stresses from the bending moment. First make the spacer as short as possible (minimize coil/shock clearance) and secondly make the spacer conical with the large diameter toward the “banana arm”. That way the effective cross-sectional diameter, where the moment is the largest, becomes half the sum of the spacer’s large diameter and the bolt diameter.

As the attached picture shows, my simple solution was to go to the local hardware store and buy a cast iron pipe converter and drill and grind it a little bit to fit. It has worked flawlessly for more than a year. When time permits I’ll make a pair of better looking stainless spacers instead.

Laust

Dave E

What do you mean by M10? I thought the bolt was 14 mm. I have my coilovers installed with a 14mm bolt, and there is about .007 thousanths between the bolt shank and the inner diameter of the insert in the trailing arm, so I figured the fatigue load at the root of the first thread wouldn't be all that high. How much distance did you have between the bolt diameter and the insert? How long had you used the bolt for (miles) Spring rate?

Dave E

Laust, is the spacer resting on the aluminum or the steel insert? Seems like the load on the bolt and the spacer pulling on the insert may eventually pull the insert out of the arm, although I would guess its in there pretty good...

kasturbo

Nice write up Laust. I guess I'll be making a trip to the Hardware store this weekend.

kasturbo

M10 is the grade of the bolt meaning the bolt is a 10.9 grade. The stock bolt is a 8.5. I had 500lb springs with a one inch spacer on the lower bolt.

Sam Lin

The Racer's Edge adaptors won't have to be replaced as service items, they're designed properly as described and they're a better material with better heat treat.

Sam