944 Control Arm Discussion - Answering Bill Seifert's :-)
02-06-2004, 05:28 PM
#61
Race Director
Originally posted by Bill L Seifert
I just talked to Markus about his steel a arms. He forwarded a letter from Porsche that approves his arms for PCA racing. (of course I allready figured that.) I am going to send that to the SCCA. He also said that there is a Porsche Tech Bulletin that says that stock alloy arms are not to be used for racing. The Bulletin says that if they are used for racing they are subject to failure. Hopefully SCCA will take that into account when they make their decision on my request of last month.
I just talked to Markus about his steel a arms. He forwarded a letter from Porsche that approves his arms for PCA racing. (of course I allready figured that.) I am going to send that to the SCCA. He also said that there is a Porsche Tech Bulletin that says that stock alloy arms are not to be used for racing. The Bulletin says that if they are used for racing they are subject to failure. Hopefully SCCA will take that into account when they make their decision on my request of last month.
When you get that, call me at (713) 206-0666. That is my work cell phone and it's never turned off. I will need you to get that to me ASAP. Your letter is being reviewed this month and if you want that to be considered, you will need to get it to me ASAP so I can pass it on to the ITAC.
02-06-2004, 08:31 PM
#62
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Here is a repost of the letter from Alwin Springer, Director of Porsche Motorsport N. A. found at
http://www.connact.com/~kgross/FAQ/944faq10.html
To: All Porsche 944 & 968 Competitors
Re: 944 & 958 Control Arm Usage In Racing Applications
The following A arms should be installed in 944 and 968 Series vehicles according to the conditions noted:
944 341 027 02 L/S Production version arm (round groove 360 degrees on ball joint)
944 341 028 02 R/S Production version arm
These parts are good for moderate competition. (Time trials etc.)
951 341 027 32 L/S Competition version arm (slotted groove on side of ball joint)
951 341 028 32 R/S Competition version arm
These parts are recommended for long distance races or heavy competition.
Neither set of arms noted above pose a problem, as long as:
1. The ride height is not lowered beyond the point which causes binding of the ball joint when the suspension reaches full travel,
2. The front sway bar is not greater than the M030 package sway bar in either 0.D. or wall thickness,
3. The lower bore in the strut is not worn out and 4) the parts are assembled following the steps outlined in the Porsche Service Manual. (Despite the fact that this may be slightly contrary to the Service Manual, it is imperative that the bolt and nut (original Porsche Parts) be replaced each time they are removed.
As always in racing, it is important to inspect the arms for nicks or cuts from road debris after each event to avoid development of any cracks. Please note that the leading cause of failure we have seen on both the Production and Competition version arms, in racing applications, is the failure to follow the instructions I have listed above. Please call PMNA with any racing preparation issues.
Alwin Springer
Director of Porsche Motorsport N. A.
NOTE: that some of the parts are no longer available from Porsche.
http://www.connact.com/~kgross/FAQ/944faq10.html
To: All Porsche 944 & 968 Competitors
Re: 944 & 958 Control Arm Usage In Racing Applications
The following A arms should be installed in 944 and 968 Series vehicles according to the conditions noted:
944 341 027 02 L/S Production version arm (round groove 360 degrees on ball joint)
944 341 028 02 R/S Production version arm
These parts are good for moderate competition. (Time trials etc.)
951 341 027 32 L/S Competition version arm (slotted groove on side of ball joint)
951 341 028 32 R/S Competition version arm
These parts are recommended for long distance races or heavy competition.
Neither set of arms noted above pose a problem, as long as:
1. The ride height is not lowered beyond the point which causes binding of the ball joint when the suspension reaches full travel,
2. The front sway bar is not greater than the M030 package sway bar in either 0.D. or wall thickness,
3. The lower bore in the strut is not worn out and 4) the parts are assembled following the steps outlined in the Porsche Service Manual. (Despite the fact that this may be slightly contrary to the Service Manual, it is imperative that the bolt and nut (original Porsche Parts) be replaced each time they are removed.
As always in racing, it is important to inspect the arms for nicks or cuts from road debris after each event to avoid development of any cracks. Please note that the leading cause of failure we have seen on both the Production and Competition version arms, in racing applications, is the failure to follow the instructions I have listed above. Please call PMNA with any racing preparation issues.
Alwin Springer
Director of Porsche Motorsport N. A.
02-06-2004, 09:16 PM
#63
Three Wheelin'
Neil,
I think the competition arms that Springer put in the Bulletin cost about $1,200 apiece not a pair, when they were available. Markus said they are scarce as hens teeth now.
Geo, I will get the Tech Bulletin that Markus talked about to you ASAP. He said he would either email it to me or tell me the number so I could get it from Porsche. I would not be surprised if it is the one the Neil quoted in the thread above me. As of when I logged on I have not received it. If I don't have it by monday, I will call Markus again.
:You will get the first copy. Do you want a copy of the thing Markus sent me about Porsches approval of his steel arms|?
Bill
I think the competition arms that Springer put in the Bulletin cost about $1,200 apiece not a pair, when they were available. Markus said they are scarce as hens teeth now.
Geo, I will get the Tech Bulletin that Markus talked about to you ASAP. He said he would either email it to me or tell me the number so I could get it from Porsche. I would not be surprised if it is the one the Neil quoted in the thread above me. As of when I logged on I have not received it. If I don't have it by monday, I will call Markus again.
:You will get the first copy. Do you want a copy of the thing Markus sent me about Porsches approval of his steel arms|?
Bill
02-06-2004, 10:25 PM
#64
Race Director
Originally posted by Bill L Seifert
Geo, I will get the Tech Bulletin that Markus talked about to you ASAP. He said he would either email it to me or tell me the number so I could get it from Porsche. I would not be surprised if it is the one the Neil quoted in the thread above me.
Geo, I will get the Tech Bulletin that Markus talked about to you ASAP. He said he would either email it to me or tell me the number so I could get it from Porsche. I would not be surprised if it is the one the Neil quoted in the thread above me.
Originally posted by Bill L Seifert
Do you want a copy of the thing Markus sent me about Porsches approval of his steel arms|?
Do you want a copy of the thing Markus sent me about Porsches approval of his steel arms|?
02-07-2004, 01:17 AM
#65
Nordschleife Master
Originally posted by M758
I have seen the ball joint pins on Fabcar arms break.
dmoffitt bought Chris Cervelli's old 951 race chassis. He drove it on the street after installing a street motor and broke the ball joint pin. This was on a car with Fabcar arms. I know the Charly arms have a pin that is 2mm thicker. The pics of the failure looked just like a the binding falure. I believe the Fabcar arms have rebuildable ball joints.
Do remember that Chris's Car was pushing 450 to 500 rwhp, had something like 10" wide wheels in front with slicks, was lowred as much as possible and was driven hard.
I have seen the ball joint pins on Fabcar arms break.
dmoffitt bought Chris Cervelli's old 951 race chassis. He drove it on the street after installing a street motor and broke the ball joint pin. This was on a car with Fabcar arms. I know the Charly arms have a pin that is 2mm thicker. The pics of the failure looked just like a the binding falure. I believe the Fabcar arms have rebuildable ball joints.
Do remember that Chris's Car was pushing 450 to 500 rwhp, had something like 10" wide wheels in front with slicks, was lowred as much as possible and was driven hard.
02-07-2004, 06:17 AM
#66
Race Director
Originally posted by Premier Motorsp
It is all metal fatigue. Yes, in unusual cases the ball joints can get bent over by over travelling. I doubt they would snap off instantaneously, but being bent over does nothing good for the fatigue life.
The harder you work thse parts, the shorter the fatigue life. On 225/50 15 tires and stock brakes, your parts are probably going to last a while, maybe a few seasons. On 285 slicks on 10.5 inch wheels, you will be lucky to complete a race weekend.
It is all metal fatigue. Yes, in unusual cases the ball joints can get bent over by over travelling. I doubt they would snap off instantaneously, but being bent over does nothing good for the fatigue life.
The harder you work thse parts, the shorter the fatigue life. On 225/50 15 tires and stock brakes, your parts are probably going to last a while, maybe a few seasons. On 285 slicks on 10.5 inch wheels, you will be lucky to complete a race weekend.
Maybe it's splitting hairs, but fatigue would seem to imply something that happens over time while the failures at the balljoint or swaybar mounts would seem to indicate some other causal relationship. The one failure that I could see as fatigue would be the separation at the inboard mounting point on the steel arms.
Can you elaborate?
02-07-2004, 10:46 AM
#67
Three Wheelin'
I think anything can break. You just don't hear about the FABCAR and Charlie arms breaking as much. Yesterday I talked to Denny Voss, a NASA 944 driver from Mich. He told me again about the 2 ball joint failures at Putnam last fall. He told me he knew of 5 drivers with alloy arms that had the ball joints fail, though not all of them in the same place. Some broke, some pulled out etc.
Markus says absoulutely none of his have broke. But, because they are man made, we all know something could happen. I just think they are safer in the long run.
Bill
Markus says absoulutely none of his have broke. But, because they are man made, we all know something could happen. I just think they are safer in the long run.
Bill
02-07-2004, 10:56 AM
#68
Race Director
Originally posted by Bill L Seifert
I think anything can break. You just don't hear about the FABCAR and Charlie arms breaking as much. Yesterday I talked to Denny Voss, a NASA 944 driver from Mich. He told me again about the 2 ball joint failures at Putnam last fall. He told me he knew of 5 drivers with alloy arms that had the ball joints fail, though not all of them in the same place. Some broke, some pulled out etc.
I think anything can break. You just don't hear about the FABCAR and Charlie arms breaking as much. Yesterday I talked to Denny Voss, a NASA 944 driver from Mich. He told me again about the 2 ball joint failures at Putnam last fall. He told me he knew of 5 drivers with alloy arms that had the ball joints fail, though not all of them in the same place. Some broke, some pulled out etc.
02-09-2004, 10:13 AM
#69
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Gents,
Chris makes a very good point about the durability of front end parts in general on the pre 87 cars. There have been a number of failures of the spindles on these cars, especially those which have the mechanical drive speedometers and hence the larger hole (for the cable) in the left spindle.
I have my 924S spindles magnafluxed at regular intervals and, when I started using 225-16 hoosiers with a stiff suspension, they developed fatigue cracks in very short order. I have also noticed much reduced wheel bearing life since I started running wider/stickier tires (by the way a hoosier 225 is as wide as most 245's so that is a lot of tire for an early front end).
I recall front spindle failures on 1986 944 Turbo's at Watkins Glen and Nelson Ledges PCA races a couple of years ago and we also had one (Tony Sciarrino) on an early 944 at the Mosport PCA Club Race last year. I adivse anyone running these parts to stock up on good ones (i.e. have them inspected) at the wreckers. The consequences are at least as bad as a failed control arm.
Another point, I'm a Mechanical Engineer who in a past career did stress analysis in the nuclear and aerospace industries. The fatigue life of any part does not have a linear relationship with stress. If your alternating (i.e. fatigue) stresses double, then the fatigue life will be cut by much more than 1/2. If you incorporate a stress riser (like the ball joint shaft groove in the late control arms) this increases your fatigue stress even more and decreases the fatigue life of the part by a multiple of that increase in stress. For these reasons you should never machine, replace or modify parts (like those discussed in this thread) without being sure that you are not increasing fatigue stresses and you should always be sure to regularly inspect and test, if necessary, parts which are subjected to higher than design loadings. Our cars are getting old, and by fitting wide, sticky tires, big swaybars, better brakes etc etc, we are putting loads on the front end parts that they were never designed to handle. Mix in the fact that these cars are now getting to be 20+ years old and that the original parts appear to have been marginally designed and you have some serious concerns. Be vigilent!
gd
Chris makes a very good point about the durability of front end parts in general on the pre 87 cars. There have been a number of failures of the spindles on these cars, especially those which have the mechanical drive speedometers and hence the larger hole (for the cable) in the left spindle.
I have my 924S spindles magnafluxed at regular intervals and, when I started using 225-16 hoosiers with a stiff suspension, they developed fatigue cracks in very short order. I have also noticed much reduced wheel bearing life since I started running wider/stickier tires (by the way a hoosier 225 is as wide as most 245's so that is a lot of tire for an early front end).
I recall front spindle failures on 1986 944 Turbo's at Watkins Glen and Nelson Ledges PCA races a couple of years ago and we also had one (Tony Sciarrino) on an early 944 at the Mosport PCA Club Race last year. I adivse anyone running these parts to stock up on good ones (i.e. have them inspected) at the wreckers. The consequences are at least as bad as a failed control arm.
Another point, I'm a Mechanical Engineer who in a past career did stress analysis in the nuclear and aerospace industries. The fatigue life of any part does not have a linear relationship with stress. If your alternating (i.e. fatigue) stresses double, then the fatigue life will be cut by much more than 1/2. If you incorporate a stress riser (like the ball joint shaft groove in the late control arms) this increases your fatigue stress even more and decreases the fatigue life of the part by a multiple of that increase in stress. For these reasons you should never machine, replace or modify parts (like those discussed in this thread) without being sure that you are not increasing fatigue stresses and you should always be sure to regularly inspect and test, if necessary, parts which are subjected to higher than design loadings. Our cars are getting old, and by fitting wide, sticky tires, big swaybars, better brakes etc etc, we are putting loads on the front end parts that they were never designed to handle. Mix in the fact that these cars are now getting to be 20+ years old and that the original parts appear to have been marginally designed and you have some serious concerns. Be vigilent!
gd
02-09-2004, 01:50 PM
#71
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Hey GeoffD -
Thanks for your expertise. So that's why Fabcar arms are built like a Sherman Tank! Safety pays, but it also costs, as in $100's per pound!!
Thanks for your expertise. So that's why Fabcar arms are built like a Sherman Tank! Safety pays, but it also costs, as in $100's per pound!!
