Standard GTD front ball joints specs?

Howard Jones

I am in the process of building an all-rod-end suspension for my old GTD. I have finished the entire rear and am now working on building a set front lower A-arms to incorporate rod ends. I did the top one several years ago to allow for easy camber and caster adjustment. I am in the planning stage, and it occurs to me to investigate the possibility of using a simple screw-in ball joint and weld-in cup at the bottom. This makes the design of the a-arm a little simpler and a bit lighter, However, I am having a bit of trouble working out the existing ball joint taper spec. so I can find an appropriate ball joint.

large end = .892"
small end = .807"
lenght of taper = .75"

This works out to approx. 3.2 inches per foot or 3.24 degrees

Everything I have read on ball joints says they are nearly all 7 degrees taper with the remaining, mostly 10 degrees. I have used a couple of taper calculators as well as my own trig calculation, and I still come up with approx 2.5 degrees of taper angle. WTF!!! Do you double the single-side angle? This would still be a lot less than 7 degrees but at least it would be in the ballpark.

I would rather keep the Granada spindles in order to not completely redesign the whole front of the car around the new ones. I have stopped tracking this car and it has become a Sunday morning toll road blaster so I have kept the uprights/spindles and just designed suspension links for them.

Does anybody know the taper angle for the original Granada spindle and ball joint? Is it possible that they are that much different than everything else? Or more likely I am completely off base with my calculations. Need some old guy's help with this. I could just use the old ball joints I guess but I would really like to have explored the options. Is there a different ball joint I can use that isn't so big and doesn't weigh enough to fit a Panser? I don't intend to do this again.

I have the original Granada spindles, wishbones, and lower ball joints. Same as these.


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Mike Pass

By my calculation using your data
The difference in diameter end to end is 0.892 - 0.807 = 0.085
Over 1" Sine of angle is 0.085/1.0 = 0.085
arcsine of 0.085 is 4.87 degrees

However this may help.

I really don't see any issue with the usual bottom ball joints. The entire weight of the front of the car is taken by these joints. The weight of the joint is insignificant compared to the attached unsprung weight of the hubs, discs, calipers , wheels and tyres. A GT40 front end is lighter than a Granada Mk2 so the bottom ball joint is well up to the task.
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Howard Jones

With a rethink of the math and the taper length correction, I am coming up with .085/.75=.113. then (arcsine) (.113 ) = 6.48 degrees or so. So given measurement error I think the taper angle of these balljoints is more than likely 7 degrees since that seems to be standard. The "balljoint taper" must be usually stated as a total as the taper calculator above comes up with right at 1/2 of the "total taper spec".

Thanks for the math remediation Mike, you got me to focus, it's been a long time since I was doing trig...........

So I think I can just use the original ball joints to keep the source of the parts as original for the next guy.......I won't live forever and somebody else will need to take care of the old girl someday.

Oh and 2.5 D is the 2.5-liter diesel version. Nothing to do with the balljoint specs.
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