Rear suspension: Excessive toe change

Sooooo...

Handling on the Racecar has been dicey for the last several events. Dis-assembly and manipulation of the rear suspension has shown that the car has +/- 2 degrees of Toe variation. Tracking down the cause shows that the A-arm pivot bolt allows the hub carrier to rotate and cause most of the variation.

Car us using GT6 hub carriers. Rear suspension is 60's style 4 link with a reversed lower A arm. The bore in the hub carrier is .500"+. Current bolt is a standard grade 8 with a diameter of .494". Bore length is approx. 3.75". A-arm pivot bores are reamed to .499"

I have ordered an AN-spec bolt. The diameter on these bolts is nominal .497". The new bolt should get rid of (most) of the variation. Plan B is to use Loctite sleeve retainer between the bolt and hub carrier. (Yes, it may be a B**** to disassemble, but that doesn't happen very often.)

Plan C is to drill and ream the A-arm and hub carrier for a tight fit to a 9/16 bolt.

Has anyone else seen this sort of problem? How did you fix it?

TIA,

Rog

Getting rid of the slop is a good start. .002-.003 won't cause a problem if the bolts are torqued well.

'1960's style 4 link'. Can you post a pic of the setup, viewed from the bottom?

Are you using the stock GT6 toe link at the stock angle? If so, they are way too short and that can cause a lot of rear toe change.

I prefer two parallel lower links to a reversed A arm, precisely to avoid that situation.
The effective wheelbase will change slightly with suspension travel, but you can eliminate toe changes (if that's what you want!).
Works well when you have limited length trailing links (as in Spitfire/GT6).
OTOH, by making the chassis pickup points of the two links different, you can implement controlled toe changes (in either direction). This may be useful to fine tune the handling.

Carter

Guys,

Thanks for the inputs. Photos below:

To Curmudgeon: Photo of left rear suspension shows arm position. Lower toe link is (essentially) production GT6. Link is parallel to the ground at stock RH. This suspension was installed and dialed in about 10 years ago and has worked great for 7+ years. (And "great" is in the context of removing the stock Long-short-arm GT6 suspension.)

to Erohsic: I believe that I looked at the "two parallel lower links" design and went with the reversed A-arm because it required less frame rework to install.

Photos are not appearing in the Preview, and I suspect I get to do this again, but the photos show the left rear suspension with no coilover at approximately actual RH. Other photos show the inner mount for the Top radius rod, and the outer mount for the top radius rod.

Thanks again,

Rog