SWCDuke

... have a friend with a low mileage, very original L-71 Coupe. On a test drive I noticed that the car was unstable with a sharp left flick of the wheel, but okay to the right. An alignment check showed that the left side has toe-in, but toe-out on the right, which explains the instability (tendency to oversteer).

With such low mileage I expect the shim stack is OE, but we want to swap shims side to side on the RH side to achieve about the same toe-on as on the left side.

To do this I need an accurate measurement for the distance between the center of the pivot bolt hole and the rear spindle axis. On the car I measured about 17", but if anyone has a loose trailing arm, I'd appreciate if you could measure this distance within about 1/16th inch and report.

Duke

Ol Blue

Duke
The original trailing arm I took off of my 63 measures 17 7/16" from center to center hole .
Gary

SWCDuke

Thank-you! My preliminary calculations indicate that we need to swap 3/32" of shims from the inside to the outside of the right trailing arm. The current toe is, left .0424" toe-in, a little over 1/32, and the right side is .0236 toe-OUT, a little less than 1/32", which is why the car wants to oversteer with a sharp left flick of the steering wheel. These cars are really sensitive to static rear toe, and any amount of toe-out will cause handling instability.

Fortunately we can achieve the new settings by simply swapping existing shims. No new shims are needed.

The current shim stack in inches on the right trailing arm are inside...outside:

1/32, 1/4 ... 1/4, 1/32, 1/32, 1/8... total 9/32 inside, 14/32 outside

The new calculated shim stack is:

1/8, 1/32, 1/32 ... 1/4, 1/32, 1/4... total 6/32 inside 17/32 outside.

This should bring right side rear toe into the range of 1/32 to 2/32 toe-in, very close to the left side value.

The owner has a four post lift and we will use a long screw jack to relieve the spring load on the trailing arm while leaving it at normal ride height, then remove the bolt, reconfigure the shims, and reinstall and torque the bolt. I'm going to try to convince the owner to renew the spring link cushions, too. They're original and well compressed, but surprisingly, not cracked at all.

Duke

Powershift

Original shims were carbon steel...........so the thinner ones may be corroded too badly to reuse. Suggest having some SS replacements available

Larry

SWCDuke

This L-71 coupe only has 15K original miles, which is supported by service documentation over the years that the current odometer reading is true actual mileage. The undercarriage doesn't even have any surface rust including the rear toe shims. Of course, we'll inspect the shims, and I'd be willing to make an even odds bet that the insides near the pivot bolt will still look like fresh, shiny steel.

I could believe it's never been driven on wet road, but don't know for sure. The owner also wants to maintain originality. He's fighting me on replacing the spring link cushions because they are original. My argument is that they are still available from GM and are basically a wear part that needs to be replaced periodically, and at 52 years old, it's time to do so despite the low mileage.

Beyond the above I concur with your recommendation to replace the shims either with SS or plain steel if anything beyond minor surface corrosion is observed. SS may be overkill given the type of service a restored or low mileage original sees nowadays and will result in a deduction in NCRS judging if that's an issue.

BTW, this car received a Duntov Award at last year's NCRS National Convention in Las Vegas, but the handling instability makes it basically unsafe to drive and needs to be corrected. It reminds me of the Renault Caravelle that a GF owned back in the mid-sixties. The rear always steered in the opposite direction of the front, even in normal driving and it you pushed it, it was downright unstable... the weirdest driving car I've ever driven. IIRC it was basically a fancy two-door convertible body on a Dauphine floor pan, swing axles included, and was the Renault equivalent of the VW Karman Gina.

If you were around back then you may remember Renault's advertising slogan - "Fifty million Frenchman can't be wrong". Yeah, right! Ask the Germans! It's no wonder they dropped out the US market after a few years, only to return in the seventies with the "5" and Alliance that were equally unreliable seeping piles of sh...t, and they haven't been back since.

Duke

Powershift

Duke:

CS shims are still available somewhere, but not sure where anymore. Perhaps Bairs or Paragon. Just about everything else sold is now SS. I guess they could also be made at home.........especially the 1/32 or 1/16 thickness.

Yes, I remember the Renault Caravelle.

I recently had my 1967 4 wheel alignment done. I too have a shim to move on the driver's side rear, but fortunately both rear ties have toe-in. Just one has more than desired.

DR REBUILD has excellent rubber cushions, but GM replacements should be as good.

Larry