2000 ACR rear wheel hop in aggressive turns...

[Jeff-00-ACR]

Hi All, been a while.

I've got a 2000 Viper ACR, all stock, stock full soft shock settings. Haven't been out to autocross in a couple years, but want to get back.

Problem: Last few times I did autocross, I noticed during aggressive turns the rear would hop. I also notice during a quick aggressive turn in a parking lot, had the same hop. It actually hurt my autocross times because I have to back out of the throttle when I feel this hop. I have a forward looking onboard camera that really shows the problem.

Any ideas? My guess is suspension issue. Maybe the ACR shocks need to be at a different adjustment other than full soft. I usually run about 30 pounds air front and back during autocrosses. Stock Pilots.

Any thoughts would be greatly appreciated.

 

[ROCKET62]

Have you changed the fluid lately and if so was the friction modifier added?

 

[Jeff-00-ACR]

Sorry to sound like a 'know nothing', but what fluid. And no I've changed nothing. It's had it's normal maintenance at Dodge, but doubtfull if any suspension maintenace was done in those servicings. Normal servicing fluids I'm sure.

It has about 25000 miles. And I don't recall having the rear wheel hop when the car was newer. I've autocrossed it since I bought it. And it seems like only the last 3 or 4 times I've autocrossed it I've felt some hop. Probably in the last 8000-12000 miles.

 

[Chuck 98 RT/10]

He's talking about rear differential fluid with the 4 oz friction modifier. And unless you watched somebody do it I would trust that it had been done. Also make sure they use rear end fluid and not the lighter weight tranny fluid.

 

[Tom F&L GoR]

The friction modifier everyone is referring to lets the clutch system in the differential slip smoothly; It has to slip some in order to let one wheel rotate at a different speed than another, as it would in a shorter radius turn. Without slipping the wheels would hop, just like a 4WD system would (and an AWD system wouldn't.)

To make it worse, the differential lock up mechanism tries to lock up more under power, so a turn into the parking lot space may be fine, but the same path at an AX may chatter.

I don't have the dealer service schedule in front of me, but it's possible the differential fluid hasn't come up for service at 25,000 miles. There's no harm in adding more. It's a little plastic bottle with a spout you squirt into the fill plug on the passenger side of the differential.

 

[Chuck 98 RT/10]

I believe diff service is 15K.

 

[Jeff-00-ACR]

Thanks to everyone for your valuable input. I was planning on taking it in for an AC charge, so I'll also have them service the rear and use rear differential fluid with the 4 oz friction modifier.

Thanks again,
Jeff

 

[GTS Jeff]

You might wan't to have your shocks serviced too, Koni recomends that the 2812's get rebuilt about every 15k miles. I just recentely bought a complete set of 2812's and the fronts had less miles then your car and they looked fine, but when I sent them in for a rebuild I found out they weren't. The price on getting them rebuilt is pretty reasonable too.

 

[Jeff-00-ACR]

Thanks GTS_Jeff, I'll go ahead and check the shocks too. Where do you suggest getting this service done?

btw, your name, vca registration date, and # of posts are irily similar to mine.... scarry....

 

[GTS Jeff]

There are only three places to have it done, check the link below.
http://www.koniracing.com/shopservices.html

hope this helps

 

[Jeff-00-ACR]

Possibly when I had it serviced around 15k miles, they changed the rear fluid, but didn't use the right stuff. Because I noticed it suddenly at an autocross about 10k miles ago, and it hadn't done it previously.