Be Careful How You Box Steel 944 A-Arms!
09-29-2006, 11:01 AM
#31
Three Wheelin'
I wish to heck we could get the sanctioning bodies, especially SCCA, let us used the Charlie Arms, Fabcar, etc. They just won't see breaking arms as a problem.
By the way, where did the failure happen?
Bill
By the way, where did the failure happen?
Bill
10-01-2006, 08:43 PM
#34
Originally Posted by Bill L Seifert
I wish to heck we could get the sanctioning bodies, especially SCCA, let us used the Charlie Arms, Fabcar, etc. They just won't see breaking arms as a problem.
By the way, where did the failure happen?
Bill
By the way, where did the failure happen?
Bill
10-02-2006, 10:32 AM
#36
I personally do not know. Your suggesting that it might be due to binding or a suspension issue is interesting. I plan on replacing the entire suspension soon, so hopefully I will not gain any more data points on this topic.
10-02-2006, 10:53 AM
#37
Race Director
Originally Posted by tinman944
Do these arms break on cars that have not been modified. (lowered, stiffer springs, and bigger sway bars)
I think the steel arms just fatigue over years of driving. Most stock 944's with steel arms have very small cracks in these areas. Most of the time it takes a LONG TIME to actually fail. I really think TD's failed much sooner due to racing stress and the stiffening of the rest of the arm put all the load in the weakest spot.
10-02-2006, 11:37 AM
#38
Addict
Rennlist Member
Rennlist Member
Hey;
I've never heard of one breaking on a street car. It is not all that uncommon for track cars. Obviously all the stiffenening we do to joints, damping, and springing takes its toll.
I've never heard of one breaking on a street car. It is not all that uncommon for track cars. Obviously all the stiffenening we do to joints, damping, and springing takes its toll.
10-02-2006, 12:00 PM
#39
Race Director
The stock ones on my 83 parts car were cracked. So were the ones on my 84. Not sure about the 88 924S. I think so, but I can't remember. I think the only ones NOT cracked were on my 84 944 that was a 60k mile car and had been a show car.
The cracks are just hairline stuff and you need to clean the crap off the arms to really see it. Even then they just look like scratch in the paint on the arm. It typically occurs on one side of the arm. Meaning top or bottom. Since these are used both left and right side the weak spot is "up" one side and "down" on the other.
The cracks are just hairline stuff and you need to clean the crap off the arms to really see it. Even then they just look like scratch in the paint on the arm. It typically occurs on one side of the arm. Meaning top or bottom. Since these are used both left and right side the weak spot is "up" one side and "down" on the other.
10-02-2006, 12:50 PM
#40
Addict
Rennlist Member
Rennlist Member
Join Date: Jun 2001
Location: Claremont,NH
Posts: 586
Likes: 0
Received 0 Likes
on
0 Posts
I have seen in the past that someone was beafing up the area where the sway bar bolted on. there idea was the stiff bars are breaking the arm in half. I cant say I have ever heard of one breaking in half.
The photos that stated this post show that there was a bushing failure. either the bolts there to tight or something got in there to bind it up.
when you think about it there is really not a lot of movement on a control arm.maybe 10 degrees each way???
I crack tested 5 sets of control arms this weekend and do not see one that has any stress cracks at all. now theses are all from track and street cars with tons of miles. the least miles would be from my car that is around 70K.
John, Joe, are the ones that you have seen all look like the ones in these photos??
The photos that stated this post show that there was a bushing failure. either the bolts there to tight or something got in there to bind it up.
when you think about it there is really not a lot of movement on a control arm.maybe 10 degrees each way???
I crack tested 5 sets of control arms this weekend and do not see one that has any stress cracks at all. now theses are all from track and street cars with tons of miles. the least miles would be from my car that is around 70K.
John, Joe, are the ones that you have seen all look like the ones in these photos??
10-02-2006, 12:56 PM
#41
Race Director
Tinman944,
The cracks I have seen are in the area that TD shows. I have never seen on failed like TD's, just the initial cracking that would eventually lead to this type of failure.
The cracks I have seen are in the area that TD shows. I have never seen on failed like TD's, just the initial cracking that would eventually lead to this type of failure.
10-02-2006, 01:33 PM
#42
Addict
Rennlist Member
Rennlist Member
Join Date: Jun 2001
Location: Claremont,NH
Posts: 586
Likes: 0
Received 0 Likes
on
0 Posts
I still think it is more of a bushing problem than anything else.There is not a lot of stress on a control arm.
my personal set up for my car is for everything to move free enough that gravity lets it fall straight down all by itself. if it is not square with the floor it has to much bind.
I do this with sway bars, control arms ,front and rear.
my personal set up for my car is for everything to move free enough that gravity lets it fall straight down all by itself. if it is not square with the floor it has to much bind.
I do this with sway bars, control arms ,front and rear.
10-02-2006, 01:38 PM
#43
Addict
Rennlist Member
Rennlist Member
Join Date: Jun 2001
Location: Claremont,NH
Posts: 586
Likes: 0
Received 0 Likes
on
0 Posts
TDin DC,
what have you done for mods on this car.
I think I can see you are running the later sway bar mounts..
what size sway bar are you using?
where they stock bushings or did you press in aftermarket.
what have you done for mods on this car.
I think I can see you are running the later sway bar mounts..
what size sway bar are you using?
where they stock bushings or did you press in aftermarket.
10-02-2006, 01:45 PM
#44
Race Director
I personaly think the problem is a stress concentration in the control arm. That spot has tight bend and a stress riser. Thus any load is amplified there. This then exceeds the normal fatigue level and as the car brakes and turn the cycles built until a crack froms. In time the crack grows and can fail the arm.
So racing introduces extra loading and a stiffening for the rest of the arm directs more load in to this spot causing faster development of the initial crack.
So racing introduces extra loading and a stiffening for the rest of the arm directs more load in to this spot causing faster development of the initial crack.
10-02-2006, 01:58 PM
#45
Addict
Rennlist Member
Rennlist Member
Join Date: Jun 2001
Location: Claremont,NH
Posts: 586
Likes: 0
Received 0 Likes
on
0 Posts
if the stress and loads of driving was the cause dont you think the ball joint end that is weaker would break first.
Plus with the ball joint 11 1/2 inches out further the stress would be more.
unless the three bolts absorb the stress . (it is very posible)
The stress on theses control arms are linear not vertical . If the load of the break was vertical the bushing housing would be egg shaped.
The way I see it the break was vertical from the arm going up and down. if that is so either the car was setup to low so it was bottoming out or the bushings where so tight that every movement was stressing the weld joints
Plus with the ball joint 11 1/2 inches out further the stress would be more.
unless the three bolts absorb the stress . (it is very posible)
The stress on theses control arms are linear not vertical . If the load of the break was vertical the bushing housing would be egg shaped.
The way I see it the break was vertical from the arm going up and down. if that is so either the car was setup to low so it was bottoming out or the bushings where so tight that every movement was stressing the weld joints