Snapped an RE trailing arm bolt.. *UPDATE* With better pictures
09-30-2012, 08:53 PM
#31
Rennlist Member
SLAMMED!!!
Please come back to us with what Karl's assessment is Jason.
Please come back to us with what Karl's assessment is Jason.
09-30-2012, 08:54 PM
#32
09-30-2012, 09:49 PM
#34
I bought a spare set of RE bolts
should be good unless analysis is bad and it wasn't just a one off event.
10-01-2012, 02:50 AM
#35
Rennlist Junkie Forever
First... not that it really matters now, the rear bottom shock mount is supposed to be mounted such that the shock body is away from the trailing arm. That's why it's offset. Yours is backwards.
The reason is to get clearance between the shock collar & spring and the trailing arm.
The stiffer spring, the bigger the OD, the more clearance needed.
No matter... this isn't the reason for the failure. I'm just point this out.
Personally... unless you're fully converted to a solid spherical suspension, there's no real reason to run those lower shock mounts. And even if you were converted to a solid spherical suspension, the benefit from that lower shock mount is probably never going to be realized.
That said... I run the rubber bottom mount with a grade 12.8 bolt with zero issues.
TonyG
The reason is to get clearance between the shock collar & spring and the trailing arm.
The stiffer spring, the bigger the OD, the more clearance needed.
No matter... this isn't the reason for the failure. I'm just point this out.
Personally... unless you're fully converted to a solid spherical suspension, there's no real reason to run those lower shock mounts. And even if you were converted to a solid spherical suspension, the benefit from that lower shock mount is probably never going to be realized.
That said... I run the rubber bottom mount with a grade 12.8 bolt with zero issues.
TonyG
10-01-2012, 09:04 AM
#36
First... not that it really matters now, the rear bottom shock mount is supposed to be mounted such that the shock body is away from the trailing arm. That's why it's offset. Yours is backwards.
The reason is to get clearance between the shock collar & spring and the trailing arm.
The stiffer spring, the bigger the OD, the more clearance needed.
No matter... this isn't the reason for the failure. I'm just point this out.
Personally... unless you're fully converted to a solid spherical suspension, there's no real reason to run those lower shock mounts. And even if you were converted to a solid spherical suspension, the benefit from that lower shock mount is probably never going to be realized.
That said... I run the rubber bottom mount with a grade 12.8 bolt with zero issues.
TonyG
The reason is to get clearance between the shock collar & spring and the trailing arm.
The stiffer spring, the bigger the OD, the more clearance needed.
No matter... this isn't the reason for the failure. I'm just point this out.
Personally... unless you're fully converted to a solid spherical suspension, there's no real reason to run those lower shock mounts. And even if you were converted to a solid spherical suspension, the benefit from that lower shock mount is probably never going to be realized.
That said... I run the rubber bottom mount with a grade 12.8 bolt with zero issues.
TonyG
Minus the top eye in the rear shocks it's fully spherical suspension.
Last edited by jasonlp; 10-01-2012 at 09:20 AM.
10-01-2012, 09:42 AM
#37
Rennlist Member
First... not that it really matters now, the rear bottom shock mount is supposed to be mounted such that the shock body is away from the trailing arm. That's why it's offset. Yours is backwards.
The reason is to get clearance between the shock collar & spring and the trailing arm.
The stiffer spring, the bigger the OD, the more clearance needed.
No matter... this isn't the reason for the failure. I'm just point this out.
Personally... unless you're fully converted to a solid spherical suspension, there's no real reason to run those lower shock mounts. And even if you were converted to a solid spherical suspension, the benefit from that lower shock mount is probably never going to be realized.
That said... I run the rubber bottom mount with a grade 12.8 bolt with zero issues.
TonyG
The reason is to get clearance between the shock collar & spring and the trailing arm.
The stiffer spring, the bigger the OD, the more clearance needed.
No matter... this isn't the reason for the failure. I'm just point this out.
Personally... unless you're fully converted to a solid spherical suspension, there's no real reason to run those lower shock mounts. And even if you were converted to a solid spherical suspension, the benefit from that lower shock mount is probably never going to be realized.
That said... I run the rubber bottom mount with a grade 12.8 bolt with zero issues.
TonyG
10-01-2012, 09:45 AM
#38
10-01-2012, 12:18 PM
#39
Drifting
I've been running a grade 12.9 bolt as my lower shock bolt for 6 years of track duty. Stiffer springs than you're running and my T-bars are only adding minimal force. No issues in my car. I'll spin each bolt on occasion looking for bending but so far I'm on the original set.
10-01-2012, 12:37 PM
#40
Rennlist Member
hopefully you installed it incorrectly so you can it blame on that. Instead of trying to figure out what happened if you know what i mean
10-01-2012, 12:58 PM
#41
10-01-2012, 02:28 PM
#42
Addict
Rennlist Member
Rennlist Member
Deja vu all over again … sort of:
https://rennlist.com/forums/944-turb...roke-bolt.html
As I recall the bolt screws into a steel insert, cast into the banana arm. That steel insert may not be designed to handle the extra axial (pulling) load well enough, so with time the bolt may lose some tension, loosening it. Once that happen the 14mm stud with threads is not strong enough to handle the extra bending moment from the weight of the car.
In other words, check the torque of the bolt after some use and re-tighten if necessary.
Also, the larger the diameter of the contact area, the less the peak stress in the material, so the custom bolt design is far from optimal with respect to strength.
Laust
https://rennlist.com/forums/944-turb...roke-bolt.html
As I recall the bolt screws into a steel insert, cast into the banana arm. That steel insert may not be designed to handle the extra axial (pulling) load well enough, so with time the bolt may lose some tension, loosening it. Once that happen the 14mm stud with threads is not strong enough to handle the extra bending moment from the weight of the car.
In other words, check the torque of the bolt after some use and re-tighten if necessary.
Also, the larger the diameter of the contact area, the less the peak stress in the material, so the custom bolt design is far from optimal with respect to strength.
Laust
10-01-2012, 09:30 PM
#43
Three Wheelin'
10-01-2012, 09:58 PM
#44
Racer
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I had (sort of) the same issue, mine bent. They were the supplied mounts with JIC Cross coilovers.
Being an engineer, I determined the base of the mount (where it mates with the arm) was insufficient diameter to use the threaded section solely in tension, with the resulting bending moment causing failure. The mount in the picture looks like fatigue failure to me, caused by the same condition.
My fix was to fabricate new mounts (shouldered studs really) with a base circle matching the diameter of the boss on the arm, and with a longer threaded section. I bottom tapped the arm to match the new threaded length, and potted the part in the hole with epoxy (JB Weld) to prevent fretting.
I made the parts from 4130 and heat treated them to Rc 43, hard enough for high tensile strength, but tough enough to prevent brittle fracture.
5 racing seasons later with 850 pound springs - no problem.
Being an engineer, I determined the base of the mount (where it mates with the arm) was insufficient diameter to use the threaded section solely in tension, with the resulting bending moment causing failure. The mount in the picture looks like fatigue failure to me, caused by the same condition.
My fix was to fabricate new mounts (shouldered studs really) with a base circle matching the diameter of the boss on the arm, and with a longer threaded section. I bottom tapped the arm to match the new threaded length, and potted the part in the hole with epoxy (JB Weld) to prevent fretting.
I made the parts from 4130 and heat treated them to Rc 43, hard enough for high tensile strength, but tough enough to prevent brittle fracture.
5 racing seasons later with 850 pound springs - no problem.
10-01-2012, 10:07 PM
#45
Banned
Maybe you have to swap out the left side shock and install it on the right side. The offset may correspond then. Just a thought.