eniac

Stock Alum. arms will handle 400lb springs just fine. For added security you would want to install longer pins. I have an extra set waiting for just that.

odb812

anyone have a source for these longer pins that work with the factory control arms

eniac

Rennbay

Oddjob

Be a little careful jumping on the band wagon with these longer pins. There are some design concerns with extending the pins. From a mechanical perspective, it increases the lever arm, increasing the stresses at the base of the pin and the control arm stocket.

There has been quite a bit of discussion on this in the past, with some reputable/knowledgeable individual(s) advising against the idea.

I am not advocating for or against, because I have not used them myself, but as a mechanical engineer, I do believe there is some merit to the concerns. So my only recommendation is to do some searches on the 944, the 951, and the Racing forums and review some of the comments regarding longer pins, and many of the rebuild kit issues - then make your own decision on what concerns you are willing to dismiss and which risks you are willing to take with respect to control arms and balljoints, depending on how you use/drive your car and your available finances.

eniac

Also note these longer pins should only be used on lowered cars.

Oddjob

This is one thread in particular:

https://rennlist.com/forums/showthre...ferrerid=15894

odb812

wow, quick response and good info. so are these problems consistent with the aftermarket control arms with varying pin lengths like the racer's edge units for example?

Oddjob

Unknown. I think Chris Cervelli's comments/experience were with custom made long pins for Fabcar arms, but Im not positive about that. And this was with race cars, not street cars.

I dont personally dont know of any RE arms in use with longer pins, and only personally know of one car that has the standard pin RE arms. The RE units are still pretty new to the market place. Karl Poeltl does his own FEA on his designs, so Im assuming he may have some analysis and data on the balljoint stresses with standard length and long pins. If you are considering going with RE arms, it would be a worthwhile discussion to ask Karl about the longer pins, and see what he says about potential higher stress loading.

Matthew DiRenzo

NO mystery to this at all... if you make a longer pin with the standard groove and pinch bolt design, yeah, that's a bit dodgy. The solution is to create a threaded pin that tensions the entire joint, along with a conical spacing collar concentric with or machined as part of the threaded pin (I'd opt for the former to reduce complexity). You've now eliminated any possibility of an unwanted bending load and created a much stronger joint. Make the pin out of something serious and give it a reasonable heat treat. Increase the diameter of the pin if you want (within reason). Eliminate the ball joint and use a 3/4" rod end with appropriate shank diameter or equivalent spherical bearing. Draw assembly tight with a nut on the bottom. Problem solved as best as possible without a complete redesign... engineering 101, folks. Appropriate levels of expertise assumed w/respect to this process. If you don't know how, find someone who does... failure's not an option on this one.

odb812

Jim,
FEA? I'm in the military, so I am already fluent in one language of acronyms, but between the the internet and engineering/racing acronyms I'm falling behind. Like roflmao. I know that means something is funny, but what exactly it stands for is beyond me.
Anyways, I looked around the racer's edge site and found an answer to the question. This is directly from the site.

The 944 front aluminum control arm has long been know to be a weak point in the car's suspension. Also, when drivers lower their car they throw the suspension geometry “Out of Whack” and thereby lose a lot of the improvement they are hoping to make. Our A-arms are lightweight, much stronger than the original factory arms, and come with spherical bearings at the front inner pickup and also at the outer ball joint location. Our replaceable pins are tensioned in place, like a wheel stud, so you now have a very strong outer spindle pin that can be made longer than the factory original, without risk of failure. Due to this improved mounting system, we can offer pins of various lengths to correct geometry for lowered cars.

So it looks like the problem is solved with these units.
Todd

Matthew, we were posting at the same time, so my comments are not a reflection on what you said. You obviously have more knowledge of these things than I. I was merely commenting on whether this failure is taken into consideration with the racer's edge part.

Matthew DiRenzo

Nope, that's perfect ODB. Looks like someone else already solved the problem exactly as I described (or near enough)... no surprise there, it wasn't particularly difficult. FEA (finite element analysis) is essentially a computer simulation using specific numerical techniques. Complete overkill for such a simple problem.

RKD in OKC

ROFLMAO Rolling On Floor Laughing My Axe Off

odb812

Thanks Matthew and RKD, I'll put those in my acronym dictionary. At least each letter in those acronyms stands for something. You should see some of the bs the Army comes up with.
Thanks for the comments as well Matthew. It really makes me more confident in my planned purchase that someone who knows about conical spacing collar concentrics and shank diameters thinks the principle behind the parts is valid.
Todd

sawood12

I did alot of reading up on this when I was installing my KW and the following is what I summised from all the stuff I read. I believe that the problem with the stock arms is not that they are necessarily weak, but it is when you lower the car the angle of the a-arms flattens out and the ball joint can be forced to over-rotate such that the pin contacts the rim of the a-arm ball-joint socket. This can lead to either a failure of the pin or the end of the A-arm itself as the pin wears into the a-arm socket rim. The longer pin kits get around this by correcting the geometry of the a-arm on a lowered car so that the ball joint is operating in its intended range. Having installed the Rennbay kit on my car following lowering I was (and continue to be) a bit concerned about how long the pin is as it does look too long and slender to my eye. I wish i'd gone for the 19mm dia upgraded pin now. I did post a thread asking other users if they had experienced any problems or even heard of any problems with this kit and the response seemed to be an no so now i'm even more concerned after reading the doubts of some on this particular thread!!

With aftermarket arms like the RE ones I believe they get around this problem whilst keeping the pin shorter, and therefore stronger, as they use a larger dia ball joint that can cater for the required rotation on lowered cars. One thing is for sure - if you lower your car significantly you definitely need to consider what you're going to do with the ball joints as I personally know of someone who has had a failure. Thankfully it happened on a trackday so he just skidded out into the gravel, but if it had happened on the road things would have been very different.

I'm beginning to wish i'd just bitten the bullet and gone for aftermarket arms now.

Skip Wolfe

I am not a big fan of the longer pins in stock arms as well. Here is another thread where it was debated ad nauseam.

https://rennlist.com/forums/showthre...=365392&page=2

Mike - I would recommend the Racers Edge units. Are you thinking of converting to late offset or staying with the early?