Broken A-arm Brackets
Joined: Jul 2002
Posts: 2,724
Likes: 42
From: Orlando
Originally Posted by Windscreen,Aug 4 2004, 12:47 PM
Ian,
In my engineering opinion, the brackets fail due to the loads from repeated, heavy braking. Going off road or airborne doesn't apply stress to the brackets like the brakes do. When you use the brakes, a moment (torque) is created about the lower ball joint due to the distance between the tread contact patch and the lower ball joint.
This moment is reacted to by the upper control arm, which gets "pushed" forward and places the welds of the upper a-arm rear mount in tension. If someone can draw me a free body diagram to show how running stiff shocks or a stiff bar increases the load on only the rear upper a-arm mount, I'd like to see it.
I've seen a friends car with stock shocks, Hoosiers, and a Gendron bar crack the welds this past spring. I believe a local competitor that runs exclusively on stock everything, including S02 tires, also has the early signs of the welds failing (can see cracks in the seam sealer around the bracket).
I ran my car since June '01 and first saw the failure begin at a test & tune in spring '03. That test & tune course was particularly braking intensive as I could only take 3 runs in a row before needing to cool the brakes down or deal with fade. I'll also add that I have a deserved reputation for using brakes hard. This was also the first event I ran the Penskes at.
Rumor has it that Honda is close to releasing a bulletin describing the acceptable repair method for this failure.
As for the E36 M3, I'm quite sure they will fail the rear strut mount even if driven exclusively on the street with stock shocks. It is just a poor design.
Steve
In my engineering opinion, the brackets fail due to the loads from repeated, heavy braking. Going off road or airborne doesn't apply stress to the brackets like the brakes do. When you use the brakes, a moment (torque) is created about the lower ball joint due to the distance between the tread contact patch and the lower ball joint.
This moment is reacted to by the upper control arm, which gets "pushed" forward and places the welds of the upper a-arm rear mount in tension. If someone can draw me a free body diagram to show how running stiff shocks or a stiff bar increases the load on only the rear upper a-arm mount, I'd like to see it.
I've seen a friends car with stock shocks, Hoosiers, and a Gendron bar crack the welds this past spring. I believe a local competitor that runs exclusively on stock everything, including S02 tires, also has the early signs of the welds failing (can see cracks in the seam sealer around the bracket).
I ran my car since June '01 and first saw the failure begin at a test & tune in spring '03. That test & tune course was particularly braking intensive as I could only take 3 runs in a row before needing to cool the brakes down or deal with fade. I'll also add that I have a deserved reputation for using brakes hard. This was also the first event I ran the Penskes at.
Rumor has it that Honda is close to releasing a bulletin describing the acceptable repair method for this failure.
As for the E36 M3, I'm quite sure they will fail the rear strut mount even if driven exclusively on the street with stock shocks. It is just a poor design.
Steve
Registered User
Joined: Sep 2002
Posts: 2,677
Likes: 0
From: Upland, CA
Tomorrow (or thereafter), go to your local Honda dealer and ask them to search for "Pop noise at front upper control arm mount." You just might be pleasantly surprised at what turns up on their electronic service information system. 
Registered User
Joined: Sep 2002
Posts: 2,677
Likes: 0
From: Upland, CA
http://pamelaarden.hn.org/AArmRepair.pdf
Enjoy, and don't forget to thank someone at Honda! We can't say they never did anything for us!
Enjoy, and don't forget to thank someone at Honda! We can't say they never did anything for us!