I went out for a Test and Tune yesterday at Toronto Motorsports Park. The track surface is pretty course, but dusty. Short straights and tight corners kept speeds down to mostly second gear with a few bursts up to redline in 3rd. Anyways after 15 years of racing my car it did something different. It is an FC NA car with poly all around and some rod ends. Aluminum engine mounts and poly transmission mount.

In a couple of the corners, when the car was loaded up on the back tires (Toyo RA1's, 225x50x15) and I was hard on it in second gear, about 8,500 rpm, I was getting a shudder out of the back end. If I didn't know better, I would say it was like tire shake that we used to get drag racing leaf spring cars. A couple of times I let the car slide a bit while it was doing this and when I came around the next lap, I could see the slide marks with a tire patter in it. I am running Koni yellows with race damping in the rear. I adjusted them from a softer setting to almost full firm and the effect was reduced.

What was going on? I never have run my car at such a small track before, but it has never done this at larger tracks. Can you get wheel tramp with an FC suspension?

Eric

 

I just got a few really good clues from an engineering forum. Makes sense and I am going to try them.

If anybody else has ideas, please let me know.

Eric

 

What was the advice you got from the engineering forum?

 

My rear diff bushings were deflecting and allowing diff wrap up. Usually only happens in the rain, but the 2004 build date RA1's were sooo hard that they were giving me the same effect. Need to put the stickies back on and replace the diff bushings with poly. Simple really.

Eric

 

flip the rear diff mount crowns over, and voila- solid mounts.