Failed Shock Mount

[Jim Craik]

Other than the small spacer and how the sway bar end is designed, I'm not sure what the difference is between these two desigens.

I have replaced the missing exaust bolt.

 

[Seymour Snerd]

Other than the small spacer and how the sway bar end is designed, I'm not sure what the difference is between these two desigens.

I'm not sure of anything (except that yours failed). But in a situation like this the difference between the current SPF design and a "correct" one would be visually minor and not necessarily visible in a single photograph. I see enough difference not to be able to conclude anything.

What matters is that yours failed, and it's safety-related. So unless somebody can prove that your case is some kind of fluke, that means all of our cars have a safety-related "issue". I don't need to see more failures to be concerned and to want to take corrective action. I can take the hint....

 

[Jim Craik]

Absolutly, Alan,

I strongly recoment that the rear shock mount on all SPF cars be inspected and reinforced.

In a perfict world the manufaturer would send out a kit with the correctly shapped plates and longer bolts, but this is not a perfect world!

So I imagine we will have to do this ourselfs.

I still maintain a lot of this is expectations when it comes to GT40s'..........

It you are expecting a modern super car, you will be disapointed.

But if you are expecting a 1960s' British race car, and all that comes with that, then I think is a very good one

 

[Terry Oxandale]

This is one of those rare, but important examples of why my chassis weighs 30% more than it needed to. I am so paranoid about a failure on a critical component while on the public roads.

 

[Seymour Snerd]

One more thought for anyone contemplating a fix for this: any rearward sloping of the anti-roll bar would contribute to the twisting action. More precisely, if the anti-roll bar arms are anything but at a right angle to the vertical links, they exert some non-vertical on the pivots.

This is conceptually simple to fix with a change to the vertical link length. In reality I think SPF GT40 rear rear-antiroll bars by design slope about 30 degrees, so if twisting is the problem here, that's just making it worse, or could even be the root cause. See the SPF on the left vs. P1015 on the right:

 

[DaveM]

One more thought for anyone contemplating a fix for this: any rearward sloping of the anti-roll bar would contribute to the twisting action. More precisely, if the anti-roll bar arms are anything but at a right angle to the vertical links, they exert some non-vertical on the pivots.

This is conceptually simple to fix with a change to the vertical link length. In reality I think SPF GT40 rear rear-antiroll bars by design slope about 30 degrees, so if twisting is the problem here, that's just making it worse, or could even be the root cause. See the SPF on the left vs. P1015 on the right:

View attachment 54758 View attachment 54759

You read my mind Alan. I fabricated 3" longer vertical links to give correct geometry to the sway bar. This gives a lot more useful adjustment and as you say possibly less twisting of the pivot point? Any mechanical engineers want to chime in?

 

[Rick Muck- Mark IV]

Looking through some reference material here I see several of the MK IIs had the SPF type of sway bar mounting. As SPF (Hi Tech) used a MK II as the sample for the tooling of the chassis it explains how that design was selected.

I wil talk with the factory soon and review this with them. Perhaps a reinforcement kit might be in order but no promises yet.

I will keep everyone informed.

 

[Mike Drew]

FWIW, here's how the sway bars were mounted properly:

This is P/1080, a late Gulf-spec car. I deliberately shot closeup photos of the sway bar mounting because I was highly dubious of the SPF scheme, which seemed decidedly amateurish in comparison, and in the someday-faraway-future when I do finally get my GT40, I was going to have my car converted to follow the factory specification before it ever turned a wheel on the road.

Note that there is a sturdy and reinforced inverted U-shaped chingus which is captured by the shock mounting bolt; the sway bar is then contained in sturdy aluminum blocks which are bolted to said chingus.

 

[Jim Craik]

Mike,

As I understand it this is a photo of P1031, a MKII Le Mans car.



Although a few cars appear to have the SPF style of sway bar mount, by far the most common mounts are as you have shown.

I want to add, that I have now pulled apart both sides of P2264 and the left side shock mount (not the one that failed) shows the start of similar cracks!

I stongly suggest that all SPF GT40 owners check the shock mounts for this.

 

[Jim Craik]

This photo shows the areas where the cracks started.


The left side shock mount (not the one that failed) shows small cracks forming right were the red arrows point.

Rick, I have waited to hear back from your contacting the factory, what do they have to say?

I would think they would be very interestred in this failure, as I have not "tracked" this car, nothing but alot of "relatively" calm street driveing!

 

[Kirby Schrader]

I found this all very interesting... and will, of course, see what mine look like.

However, I would think this 'small fix' could become very expensive for some of us. Well, me for sure.

I actually had new pieces made to support the sway bar so it would sit lower. Why? Because said sway bar was rubbing on my very expensive stainless steel exhaust system. One could argue the headers were made 'incorrectly', but that's neither here nor there. They exist.

So, to implement the fix portrayed below, I would either need to replace my exhaust system or the sway bar. Obviously, the sway bar would be cheaper! :laugh:

However, I feel the longer link arm to raise the sway bar arms to the horizontal position (as suggested to me by the very worthy Mike Trusty) takes away a lot of twisting moment that the angled arms create.

I shall continue to monitor for cracks (would hate to be at TWS and have that happen).
Kirby

FWIW, here's how the sway bars were mounted properly:

This is P/1080, a late Gulf-spec car. I deliberately shot closeup photos of the sway bar mounting because I was highly dubious of the SPF scheme, which seemed decidedly amateurish in comparison, and in the someday-faraway-future when I do finally get my GT40, I was going to have my car converted to follow the factory specification before it ever turned a wheel on the road.

Note that there is a sturdy and reinforced inverted U-shaped chingus which is captured by the shock mounting bolt; the sway bar is then contained in sturdy aluminum blocks which are bolted to said chingus.

 

[Terry Oxandale]

FWIW, here's how the sway bars were mounted properly:

This is P/1080, a late Gulf-spec car. I deliberately shot closeup photos of the sway bar mounting because I was highly dubious of the SPF scheme, which seemed decidedly amateurish in comparison, and in the someday-faraway-future when I do finally get my GT40, I was going to have my car converted to follow the factory specification before it ever turned a wheel on the road.

Note that there is a sturdy and reinforced inverted U-shaped chingus which is captured by the shock mounting bolt; the sway bar is then contained in sturdy aluminum blocks which are bolted to said chingus.

I agree. Cantilevered bar mounts don't seem to make a lot of sense.

 

[Seymour Snerd]

So, to implement the fix portrayed below, I would either need to replace my exhaust system or the sway bar. Obviously, the sway bar would be cheaper! :laugh:

Kirby -- if you decide to replace your exhaust system I'll take your old one off your hands.

Seriously though, I suspect we could bend our existing sway bars to make enough of a "U" to go over or under our exhaust systems. I have one of those high leverage bar benders designed for just that purpose.



Right now I'm in the curious position of not being able to mount my rear sway bar anyway, because I have a 351 roller with FE engine and the bar wants to go through the transaxle mounts. So I've simply removed it and will wait to see what develops from the factory and our various after-market friends.

In the long run what I'm hoping for is a P1032-style Mk II mount (see picture in my earlier post ) rather than the Mk I style Mike Drew shows. Hopefully both will be developed.

 

[Seymour Snerd]

Although a few cars appear to have the SPF style of sway bar mount, by far the most common mounts are as you have shown.

There are at least three styles, all of which are shown somehwere in this thread.

Most of the Mk II pictures I've seen have the type of P1032, in my earlier post, which is another of the "on top" mountings but elevated a few inches and to the rear about 1 inch. See below.

View attachment 54712

 

[Mike]

Are there any other documented failures other that the original authors car? Thanks

 

[Seymour Snerd]

...I have not "tracked" this car, nothing but alot of "relatively" calm street driveing!

The key phrase being "a lot of". If this is a fatigue failure it's the number of bump cycles that matters, and in that respect a race car leads a pretty easy life. An hour on typical California broken pavement at street speeds is probably worse than an hour on a track. At typical street speeds and 28,000 miles you probaby have nearly a thousand hours on that thing. Congratulations!

Does anyone else have odometer mileage in that vicinity?

 

[Rick Muck- Mark IV]

Jim,

Did you get my PM?

Rick

 

[Mike Drew]

Guys--just FYI, check out the solution that Chris has employed on his genuine GT40 P/1079. This is a far-from-original car (in that it was totally destroyed at Le Mans in 1968, and then comprehensively rebuilt years later and presumably improved somewhat along the way). Still, it shows some innovation in the sway bar mounting system.

I still prefer the original scheme (that is, presuming it's original?) as seen in my photo of P/1080 above....

 

[Jim Glickenhaus]

Hard track use can put great stress on a lot of things. After our 24 at The Ring our left side shock mounts and other pieces were coming out of the chassis (P 4/5 C). We're making a lot of downforce (2800 lbs at 130 mph) and pulling 2.8 G's in medium turns but beefing up chassis is often a very good idea and we will be beefing up ours.

Best

 

[Seymour Snerd]

Guys--just FYI, check out the solution that Chris has employed on his genuine GT40 P/1079.

Mike --

I can't make out how the aluminum block is mounted to the frame. Do you know? The only obvious method is that the four allen screws are through-bolts.