Lorax

Looks like I'll have to JB weld mine now.



Anyway, how hard could it be to fabricate a new steel trailing arm anyway? No harder than a front control arm right? I would like to do that as well as get rid of the whole torsion tube assy, does anyone other than kokeln sell a revamped unit?

porshhhh951

ah so im confused. This isn't a local shop. My bad.

Chads996

I knew Jay would come through for you. Good stuff. My coilovers just shipped.

C.

porshhhh951

link to website?

Chads996

www.ground-control-store.com

flosho

Jay any ETA on the steel arm version? I've emailed a few times but gotten no response.

Duke

I was thinking about the trailing arms the other day and while one would like to see a double shear bolt there Porsche believed the setup to be good enough when designing the suspension of the 964.
The 964 has rear coilovers with NO t-bars and the trailing arms looks very much like ours.
Why not investigate within the 964 crowd if their arms are subject to failure, or if they do any upgrades to make it work. And the 964 has a lot of rear weight to carry!
The mount doesn't seem any beefier than ours.

Picture courtesy of a rennlist member:

mj951

Duke, thats an interesting comparision. I have been planning a TB delete and suspension upgrade for my winter project but have some reservations after following this thread, my car is a weekend/de '89 turbo.

Below is an image of the 964 rear suspension, one obvious difference is that the control arm and trailing arm swap locations between the 964/944. On the 964, the control arm is more inline with the rotation axis as the suspension travels and on the 944 the trailing arm is more inline with the suspension travel. I am not sure if this matters as when fitted with coilovers these components are not supporting the weight of the car, they are simply allowing for rotation. I did find that the 964 lower strut mount is torqued to 139 ft/lbs so the discusion above regarding torque on the 944 lower shock mount sounds correct.

I suspect reducing as much lateral movement as possible when changing over to coilovers on the 944 helps keep the lower mount within its designed limit of travel. The polybronze spring plate bearing and spherical bearings at the inner control arm mount will be part of my project if I decide to do this swap. The Koklen torsion tube delete is also another nice upgrade though very expensive. I have seen a few custom conversions of the end of the torsion tube allowing for a spherical bearing rather than the polybronze bushing, but addition work involved and I'm not crazy about modifying the end of the torsion tube to that extent.

I would like to keep this discussion going, can one go to full coilovers on the rear of the 944 and be confident on the street that the suspension will not fail?

Van

Technically, no.

Failures happen for all sorts of reasons. Front ball joints fail on the street - although they fail more on the track...

That's just the nature of the beast - a coil over conversion is using the suspension arm in a different way than Porsche intended.

MM951

17hrs later I have 2 new lower mounts and a bunch of ground control stickers. can't beat that service

Duke

That's a statement I'm trying to avoid here. It's too simple to state that as a cause of failure. Hence my comparison to the 964 trailing arm. If the design itself is at risk I'm confident the 964 trailing arms would have turned out different.

Of the 944 rear coilover bolts that have failed - we should investigate what bolt arrangement they have. I wonder if there is records of any broken bolts when using a stock bolt with a Bilstein offset mount?
The broken bolts that I have seen are using spacers or a different solution than the stock bolt.

Some parts fail, even though they're being used as intended by the factory.

Jeremy Himsel

Agreed. With the exception of one, every one that I've seen was using a diffent bolt. The one I saw using the stock bolt had a 900lb spring and no t-bars. This car broke the threaded tab from the trailing arm. The upper mount had some stress cracks as well.

mj951

Van, I'm not looking for a sure thing as that does not exist and there will always be risk when modifying a car from stock or running a stock car on the track. That being said, understanding the causes or at least the specifications surrounding a failure, stock or aftermarket, can help us all make informed descitions. I have done plenty of searching and recognize most of the changes people are making on the front and rear suspensions of the 944 but a complete understanding as Duke is suggesting as to what failures have occurred and the specs of the components would be useful. For example it's well understood that lowering the ride height to a point where the front control arm is no longer parallel to the ground has equated to a higher number of ball joint failures than when running control arms parallel to the ground.

I don't know if a pole would be of use but maybe thoughs who are familier with rear and front end suspension failures could post up the specifications of the suspension modifications and the particulars of the failure. If we gather enough information we may learn something. Actually a pole may work as we should also understand the number of cars that have made modifications without any failures to date. Just thinking out loud hear, maybe others have come to some conclusion/comfort with the modifications they are making and I'm just getting caught up.

Mike, this is not meant to bash any of the manufactures out there, simply trying to become informed. I'm glad to see you'll be back on the road in no time. It sounds like you got lucky, had you been pushing the car through a corner when the bolt failed it would have gotten ugly quick.

MM951

Hey guys, while under the car trying to get the broken stud out I noticed something funny about the coilover..

The spring isn't seated on the hat properly and it may just be my imagination, but it seems like the snap ring isn't being consistenly covered the hat (that is what they are called right?) - will this be a problem or when it is loaded will it correct itself?






other side:



again, I am still pleased with the coilovers (and will be buying more stuff from them) and GC seems to stand behind their products.... I'm just worried about the shock. what do you guys think?

Lorax

I can't see from the pics, but the snap ring needs to be all the way in it's groove, and the opening facing the opposite direction of the opening in the hat.