A-Arm Pin Failures on track - Printable Version
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A-Arm Pin Failures on track - frogisland - 09-01-2008
Thanks for balanced reply John - fully appreciate that if you strengthen something, the next week link will show up. Perhaps my main concern is the catastrophic failure that occurs, potentially mid corner etc....but saying that, i have had some fairly hairy spins that were simply down to driver error!
I will ensure i keep an eye on mine, and perhaps swap over the pin for a 19mm over the winter.
JP
A-Arm Pin Failures on track - Anchorman - 09-01-2008
This is raising a little "tingle" for those of us that have basically daily drivers that we use for the occasional DE event.
A-Arm Pin Failures on track - wonko - 09-01-2008
[quote name='frogisland' post='58742' date='Sep 1 2008, 12:26 PM']Thanks for balanced reply John - fully appreciate that if you strengthen something, the next week link will show up. Perhaps my main concern is the catastrophic failure that occurs, potentially mid corner etc....but saying that, i have had some fairly hairy spins that were simply down to driver error!
I will ensure i keep an eye on mine, and perhaps swap over the pin for a 19mm over the winter.
JP[/quote]
The only two instances that I am aware of that have specifically analyzed the break, Eric's and our red car, had breaks over several incidents. If you look at the image of mine (earlier in the thread) there were several distinct zones. My impression is, at this point, the pins won't just break suddenly with no provocation. Either it will break during an incident, or it will be damaged and only later have a seemingly random catastrophic failure. Proper maintenance should almost eliminate the instances of catastrophic failure based on the information reported thus far. If an incident is harsh enough to break the pin wholesale, I'm just speculating here, but the pin will probably be the least of your worries.
More than anything it is being aware of the issue and respecting it.
John
A-Arm Pin Failures on track - wonko - 09-01-2008
[quote name='Anchorman' post='58744' date='Sep 1 2008, 01:17 PM']This is raising a little "tingle" for those of us that have basically daily drivers that we use for the occasional DE event.[/quote]
It is well worth considering. One more consideration to add to the list, probably above this one, are the front hubs. Under race conditions the front hubs have had numerous catastrophic failures, to the point that PCA Racing put out a bulletin in their newsletter warning people about it. If you are tracking a 968 (or 944 for that matter) you need to get the front hubs upgraded as soon as possible.
The summary here is the front end of a 968 takes a serious beating on the race track, particularly with oversized wheels and sticky rubber. Many of the components can be overstressed under these conditions. As you DE more frequently and more aggressively, these issues should float up to your field of view and become a priority so you don't have any issues going forward.
Also remember, these cars are 15 year old cars. In most cases we don't know everything that has happened to them in their street lives, so a healthy skepticism is warranted when pushing it.
John
A-Arm Pin Failures on track - 333pg333 - 09-01-2008
You can purchase brand new billet alu hubs also from RE.
A-Arm Pin Failures on track - Eric_K - 09-02-2008
Here are a couple of quick pics of my broken pin. This is something I should have caught because it obviously gave way over a period of time. Pablo's failure is the puzzling one since the part had relatively little time on it and apparently hadn't been bashed into anything.
A-Arm Pin Failures on track - wonko - 09-02-2008
That is really interesting Eric. It looks like yours broke at the little divot. Mine actually broke much closer to where it exits the spindle.
I have the RE hubs on both cars. I'm not aware of any other supplier for those, though I'm certain there must be one.
Pete reiterated to me that the RE A-arms have had no known failures yet. The one question I have is where, in at least two of the cases, the breakage was within the spindle, how would you remove the threaded part? I'm leaning towards them, but it would seem to severely complicate repairs should they be necessary. I suppose it is possible, even probable, that the additional 2mm diameter solves the problem enough that it is an irrelevant question.
Any thoughts? Am I beating a dead horse?
A-Arm Pin Failures on track - Big Dave - 09-02-2008
Interesting reading...+ somewhat concerning...
I have on my car a pair of "billet charlie" arms...I fitted them thinking/hoping, they were a upgrade over stock alloy arms...
These "charlie,s"have the longer 19mm pins fitted. + the spindles have been machined out to accept them...
Can anybody tell me if the 19mm pins have been known to fail. OR is it just the 17mm ones.??
And can i get a spare pair of 19mm pins from anywhere.??? Just in case...
The car is very similar to JP,s car in that it gets used predominently on Track days, and driven hard, in much the same way as his does,,,Its also lowered considerably...
A-Arm Pin Failures on track - Eric_K - 09-02-2008
The ones discussed in this thread have been 17s. Has anybody broke a 19? I don't know. I stayed with 17 because the M030 spindle looked like it was going to be pretty thin when bored to 19.
Are the spindles for the RE pins bored and then threaded? What happens with the retaining bolt? Anyone have a close up picture? Sounds interesting.
Quote:It looks like yours broke at the little divot.
Yes, it cracked in the middle of the retaining bolt dimple. The bolt probably makes for a good leverage point.
A-Arm Pin Failures on track - wonko - 09-02-2008
[quote name='Eric_K' post='58823' date='Sep 2 2008, 05:08 PM']The ones discussed in this thread have been 17s. Has anybody broke a 19? I don't know. I stayed with 17 because the M030 spindle looked like it was going to be pretty thin when bored to 19.
Are the spindles for the RE pins bored and then threaded? What happens with the retaining bolt? Anyone have a close up picture? Sounds interesting.[/quote]
From the Racer's Edge installation instructions:
Drilling the spindle bore: The spindle pin bore is approximately .84” long. Ideally you want the first .40” (as the pin enters the bottom of the bore) to be bored to .750” and the remainder of the bore to be tapped to accept a .750” by 16 TPI bolt. This process is a minimum 3 step process. First, after the spindle has been indicated in true to the existing bore, it must drilled using a 11/16” bit as this is the dimension needed for a ¾” 16 TPI tap. Second, the first .40” of the bore must be counter bored to .750”. Third, the remaining 11/16” bore must be tapped to .750” 16 TPI. This basically sets up the bore so that there is a .750” bore to the centre of the pinch bolt hole, and beyond that, it is tapped at ¾” 16 TPI.
If nothing else it sounds like it is in there securely <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />
John
A-Arm Pin Failures on track - pmcrespo - 09-04-2008
[quote name='Eric_K' post='58769' date='Sep 2 2008, 03:06 AM']Pablo's failure is the puzzling one since the part had relatively little time on it and apparently hadn't been bashed into anything.[/quote]
I have not touched the car yet but once we pull out the pin I'll take some pics, post, and analyze.
One offsetting matter that should actually decrease the odds of failure is the weight. Our race cars are not tossing around 3200 pounds of weight but rather 2,500-2,600 pounds. Much lighter configurations that inherently reduce loads across the board. Nevertheless, as the discussion has continued to point out, it is obvious that the additional forces generated by the geometry issues and g's generated by grip in our race setups are higher than the respective offsetting force saved via the weight reductions.
I do disagree on the subject of the upgrades ultimately leading to something else failing. In my opinion, if the A-arm's two inner poins, ball joint Pin, steering tie rods, and hub are all upgraded such that they can withstand the forces generated by full race grip steering angles, braking, and the ocassional curb bump and "lip ride", then nothing outside of the wheel should fail unless there is a hit, which takes the discussion to a diferent level..
It seems like well enginerered parts in the correct setup should do the trick. In all our cases, it appears that one way or another, either by a missing "best of best" part or previous hits, or more tha a few seasons (fatigue) we have seen the failures. In my case I believe it was a smaller than needed pin diameter. Period. No hits or fatigue to blame. A design and engineering issue that should have been discovered and addressed before offering the Pin to the market with the high end A-arm from Kokeln. I believe that if I would have had the larger Pin, the failure would have not occurred. And as we are finding out, we may not know of a failure using the RE or Kokeln arms with the larger pins and aftermarket hubs. I may be barking up the wrong tree but in my case, Kokeln should have never produced the smaller Pin and/or upon discovering of the ensuing failures, rather than just producing a larger Pin and placing for sale casually, they should have contated all previous purchaser of the smaller Pins for action to replace. Maybe they did. I don't really know.
Ultimatey, it may be that the RE geometry-adjusting A-arm, with the larger pin, and the race spec hub should do the job and hold. Replacing the pin sasonally or after a hit, and replacing the hub maybe after 2 or 3 season, should keep the suspension system battle ready with no failures. But then again, I am not certain.
A-Arm Pin Failures on track - PorscheDude - 09-04-2008
Does anyone have a data logger?
I am curious as to the lateral g's you huts are seeing on the track.
A-Arm Pin Failures on track - Torbjorn968 - 09-05-2008
[quote name='smokiemon968' post='58946' date='Sep 4 2008, 06:30 PM']Does anyone have a data logger?
I am curious as to the lateral g's you huts are seeing on the track.[/quote]
I have 1.35 Gs recorded in flat cornering with Michelin Cups and Yokohama 032. 1,45 G in corners with a mild inner slant (what ever that is called in English?). The best lap times are a couple of seconds off the best Club Racing times so max possible Gs should not be much more. This is recorded using a Drift Box.
A question to you all: how and where does the original A arms fail?
A-Arm Pin Failures on track - PorscheDude - 09-05-2008
I believe it is the same pin that fails on the stock arms.
A-Arm Pin Failures on track - Torbjorn968 - 09-05-2008
[quote name='smokiemon968' post='59005' date='Sep 5 2008, 01:19 PM']I believe it is the same pin that fails on the stock arms.[/quote]
Yes, but are the arms themselves a potential structural problem or just the pins?
T
A-Arm Pin Failures on track - PorscheDude - 09-05-2008
As far as I have read, just the pin.
A-Arm Pin Failures on track - wonko - 09-05-2008
If it were just the pin, why would you not just replace the stock pin with some beefier one? There would be no need to replace the whole A-Arm assembly. Also, why would one go to heavier steel vs the stock cast aluminum? I have been led to understand it was the actual arms that failed, not the pins.
I don't claim to have first hand knowledge, but if that is incorrect, then there is a whole market for beefier a-arms that are completely unnecessary.
John
A-Arm Pin Failures on track - wonko - 09-05-2008
Ok. On researching it, it appears that it may be the ball joint that actually fails. A-arm failures were significant enough in IMSA competition that they require all 944/968 cars to upgrade to the Fabcar arms.
In the 924/944/968 FAQ This document from PCNA seems relevant, though it doesn't answer the question completely. It does address several of the previous geometry comments previously posted though.
John
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..
A-Arm Pin Failures on track - flash - 09-05-2008
lookie there - number one - suspension geometry problems when lowered too far
i understand number two as well - that's a cracking issue at the hole if things go wrong, because of the oem link they used
good find
A-Arm Pin Failures on track - Torbjorn968 - 09-06-2008
[quote name='flash' post='59071' date='Sep 6 2008, 01:55 AM']lookie there - number one - suspension geometry problems when lowered too far
i understand number two as well - that's a cracking issue at the hole if things go wrong, because of the oem link they used
good find[/quote]
Time to get the car up on a lift and have a look at angles and binding then!
Flash: I do not understand no 2. How would stiff swaybars worsen things? Due to lifting the innerwheel and thus in effect further lowering the car during cornering?
//TL