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More on TCP R&P Wheel Shimmy Issue

C

Chris Kennedy

Member
Hi:

I started this post several weeks ago and promised I would get back with some updates. First, here are the alignment specs:

1. Caster: 3.2 positive (L) 3.5 positive (R) (a bit less positive than I originally thought, but great for directional stability).
2. Camber: .8 positive (L) .9 postive (R)
3. Toe: .2 (L) and (R)

I checked the rotors, and they are fine, and all ball joints, tie rods, wheel bearings are fine, too. Car runs 225 60 15 tires on Torque Thrust Ds, all road force balanced, have rotated everything nevertheless, no change. There also appear to be no traditional bumpsteer issues, and I drive this car a lot in the real world (app 12K miles a year). I am also checking with Flaming River, a competitor of TCP, to see if this part of some larger issue with these R&P conversions in general. TCP really had nothing to suggest. The shimmy also seems to be influenced by road surface, although I have not seen a pattern as to which surface does what. One thing I am also checking with Flaming River about is their shock-absorbing u-joint. I am wondering whether part of the problem is simply harmonic vibrations in the system, itself, that don't result from any particular imbalances. Thoughts are welcome!

/s/ Chris Kennedy
 
Positive camber? Really??? You should be running about .5 neg camber. Toe should be around 1/8" in. The caster sounds fine.
 
"silverblueBP" said:
Positive camber? Really??? You should be running about .5 neg camber. Toe should be around 1/8" in. The caster sounds fine.
Click to expand...

Mark , good observation !!
You have to check your camber again. :confu
 
Re Camber: Yeah, I'd prefer some negative camber, too, but we're talking about 1965, and these cars ran a bit positive. That's something I am thinking about dealing with later, but it's not a shimmy issue.

Thanks,
/s/ Chris
 
They ran pos camber back when the tires were skinny and bias ply. Modern radials need a little neg camber. Why so much toe in? Seems that it might be scrubbing the tires.
 
I have no experience with the R&P, but...

Could that much toe in along with positive camber cause the shimmy? Picture 2 tires toe'd in too much and tilting with pos camber and visualize what would happen as they travel forward. It could be scrubbing the tires enough to create a shimmy.

Can you mount a camera to get video of the tires or front suspension at speed?

Are all the parts up front new?
 
"Chris Kennedy" said:
Thanks for your thoughts----I have been doing some additional research, and excessive toe in may be an issue.

/s/ Chris
Click to expand...

I think I'd run no more than .12 toe on each side.

That positive camber ain't doing you no favors either. If there's no way to lose some of the camber at least dial down the toe.
 
Thanks for the advice and insight. There doesn't appear to be any toe scrub tire wear pattern. Something to bear in mind is that my primary concern at this point is the wheel shimmy. I would like to get that issue identified, first, and if it is alignment then we'll take care of that, yet the consensus to this point seems to be that it is not an alignment issue. If not, the car tracks beautifully and handles well as is , which I largely attribute to all the work on positive caster which was really tough to get, so I am reluctant to tinker too much (but the toe should be fairly easy to dial back). The camber situation is the subject of some other thoughts, but as is works fine until the real solution comes along. I drive this car a couple of hundred miles a week in the real world, and a virtue to me is being able to drive an old car like this comfortably as if it were contemporary car (e.g., to the store, in the rain, in traffic on the freeway, etc.) and not tinkering with major things continuously. That was the goal of the conversion work I did and, other than this shimmy, it was successful. I did email daze cars last night to see what their take is.

Cheers,
/s/ Chris
 
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