Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

> Rear arms, to strengthen or not to strengthen!
Blue6
post Feb 14 2014, 10:32 PM
Post #1


Senior Member
***

Group: Members
Posts: 1,035
Joined: 3-October 13
From: SoCal
Member No.: 16,470
Region Association: Southern California
Looking for opinions on strengthening the rear trailing arms. Car is a '70 with a 2.7 that will be street legal but used for track days also. Ed914.com has a very nice set of arms, powder coated, new bearings etc, but have not been strengthened. My question is have any of you had trouble with broken/cracked arms from agressive driving ?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
 
 Reply to this topicStart new topic
Replies(1 - 13)
ConeDodger
post Feb 14 2014, 11:04 PM
Post #2


Apex killer!
***************

Group: Members
Posts: 23,601
Joined: 31-December 04
From: Tahoe Area
Member No.: 3,380
Region Association: Northern California
I think Chris Foley and Eric Shea both offer a method where holes are drilled and tubes welded in to strengthen them. The Porsche method from the 70's apparently doesn't do much.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Alphaogre
post Feb 14 2014, 11:14 PM
Post #3


Member
**

Group: Members
Posts: 460
Joined: 28-May 12
From: San Diego
Member No.: 14,487
Region Association: Southern California
Do the arms flex that much to where they need reinforcement? What is the benefit of strengthening them?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
ConeDodger
post Feb 14 2014, 11:18 PM
Post #4


Apex killer!
***************

Group: Members
Posts: 23,601
Joined: 31-December 04
From: Tahoe Area
Member No.: 3,380
Region Association: Northern California
QUOTE(Alphaogre @ Feb 14 2014, 09:14 PM) *

Do the arms flex that much to where they need reinforcement? What is the benefit of strengthening them?


More accurate suspension. They definitely flex and when they do, the tire surface changes it's relationship with the pavement. Handling suffers. It's a 10/10ths thing I guess...
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
McMark
post Feb 15 2014, 12:24 AM
Post #5


914 Freak!
***************

Group: Retired Admin
Posts: 20,179
Joined: 13-March 03
From: Grand Rapids, MI
Member No.: 419
Region Association: None
If you absolutely need to win a plaque for your wall, go for it. If you just wanna drive fast, don't bother. That's my perspective.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
jcd914
post Feb 15 2014, 12:38 AM
Post #6


Advanced Member
****

Group: Members
Posts: 2,081
Joined: 7-February 08
From: Sacramento, CA
Member No.: 8,684
Region Association: Northern California
(IMG:style_emoticons/default/agree.gif)
You probably need wide tires & wheels to put enough load on the arms to flex them significantly.

Jim
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Elliot Cannon
post Feb 15 2014, 01:07 AM
Post #7


914 Guru
*****

Group: Retired Members
Posts: 8,487
Joined: 29-December 06
From: Paso Robles Ca. (Central coast)
Member No.: 7,407
Region Association: None
If you leave them stock and bang something hard with a rear wheel, the trailing arm bends and you replace it. If you reinforce them and hit something hard with a rear wheel, the chassis bends and you have to....? (IMG:style_emoticons/default/smash.gif) (IMG:style_emoticons/default/sawzall-smiley.gif)
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Blue6
post Feb 15 2014, 01:10 AM
Post #8


Senior Member
***

Group: Members
Posts: 1,035
Joined: 3-October 13
From: SoCal
Member No.: 16,470
Region Association: Southern California
Sorry should have included that it is a wide body, and my track tires are 245/45-16's. I just remember reading somewhere that cracked arms were a problem. Thanx for all the input.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
CptTripps
post Feb 15 2014, 02:33 AM
Post #9


:: Punch and Pie ::
****

Group: Members
Posts: 3,584
Joined: 26-December 04
From: Mentor, OH
Member No.: 3,342
Region Association: Upper MidWest
I'm strengthening mine because I have them off and was doing a lot of welding. Skip the clamshell method, especially for a track car. I read up a lot on the unsprung weight. Do tubes!

I posted pics and measurements on my build thread recently how I did mine. Purchased 24" of 1" steel tube and a step bit. Took about 45min start to finish, and cost under $20.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
falcor75
post Feb 15 2014, 05:44 AM
Post #10


Senior Member
***

Group: Members
Posts: 1,579
Joined: 22-November 12
From: Sweden
Member No.: 15,176
Region Association: Scandinavia
QUOTE(CptTripps @ Feb 15 2014, 09:33 AM) *

I'm strengthening mine because I have them off and was doing a lot of welding. Skip the clamshell method, especially for a track car. I read up a lot on the unsprung weight. Do tubes!

I posted pics and measurements on my build thread recently how I did mine. Purchased 24" of 1" steel tube and a step bit. Took about 45min start to finish, and cost under $20.


So you just add two pieces of tube that ties the sides of the rear arms together?
Any special locations for them or just evenly along the length of the arm?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
J P Stein
post Feb 15 2014, 06:29 AM
Post #11


Irrelevant old fart
*****

Group: Members
Posts: 8,797
Joined: 30-December 02
From: Vancouver, WA
Member No.: 45
Region Association: None
QUOTE(McMark @ Feb 14 2014, 10:24 PM) *

If you absolutely need to win a plaque for your wall, go for it. If you just wanna drive fast, don't bother. That's my perspective.


I have lotso' plaques but never had the need to strengthen the trailing arms.....but I was only running 10 inch slicks. Spend your time/money on low striction trailing arm
bearings & good shocks instead.....just my .02
Attached Image
Attached Image
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
ChrisFoley
post Feb 15 2014, 09:07 AM
Post #12


I am Tangerine Racing
*****

Group: Members
Posts: 7,933
Joined: 29-January 03
From: Bolton, CT
Member No.: 209
Region Association: None
QUOTE(ConeDodger @ Feb 15 2014, 12:04 AM) *

I think Chris Foley and Eric Shea both offer a method where holes are drilled and tubes welded in to strengthen them. The Porsche method from the 70's apparently doesn't do much.

That's Eric's method not mine.
My stiffening process involves splitting the trailing arm and installing a bulkhead.
A corner gusset between the tube and body takes care of the crack sensitive area.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Blue6
post Feb 15 2014, 12:52 PM
Post #13


Senior Member
***

Group: Members
Posts: 1,035
Joined: 3-October 13
From: SoCal
Member No.: 16,470
Region Association: Southern California
Thanx Doug n Rob, thats exactly what im going to do. Ive reached out to socalandy so i can get a look and some measurements, as he has already done it. J P, yes i have already bought bilsteins and coil overkit. Looking forward to putting faces with names on 3/2 at Phoenix club.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
J P Stein
post Feb 16 2014, 08:47 AM
Post #14


Irrelevant old fart
*****

Group: Members
Posts: 8,797
Joined: 30-December 02
From: Vancouver, WA
Member No.: 45
Region Association: None
My home AX venue (PIR south pits) is rough as a cob......double vision rough.
I realigned at the start of each season. Any "flex" in the trailing arms must have been temporary as it held the previous alignment very well for 6-8 years.

The only place I had any cracking problems were at the bottom of the rear shock towers which (I was told) come with the territory when the rear spring rates are over 200lb.....I ran up to 300. Down tubes from the roll hoop to the shock towers tool care of that problem.
I am not adverse to mods......when they are meaningful.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
« Next Oldest · 914World Garage · Next Newest »
 

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 

Display Mode: Switch to: Standard · Linear+ · Switch to: Outline

Track this topic · Email this topic · Print this topic · Subscribe to this forum

- Lo-Fi Version Time is now: 27th May 2024 - 02:47 PM
Invision Power Board v9.1.4 © 2024  IPS, Inc.
All rights reserved 914World.com © since 2002
914World.com is the fastest growing online 914 community!
We have it all, classifieds, events, forums, vendors, parts, autocross, racing, technical articles, events calendar, newsletter, restoration, gallery, archives, history and more for your Porsche 914 ...