12 Bolt in a Nova help...

[bs46488]

I just got my 1970 Nova LS swap project on the road. I have about 200 shake down miles on the car.

The previous owner put the 12 Bolt with 4 leaf Z28 springs into the Nova and had new 3.42 gears installed in 2011. It has been a project since that time and has been sitting/moving back and forth in my garage.

I replaced the outer axle seals because of a leak and put in fresh conventional 80w90 gear oil and a bottle of additive. About a 100 miles ago I added a 2nd bottle of GM additive.

The rear end has a horrible jerking/clunking noise. The noise is extremely loud and you can feel it in the car at low parking lot speeds. Going straight down the road no issue, but as soon as you hit the gradual turn on the exit ramp it hits hard and feels like the axle will continue to go straight. When driving around a corner the axle feels like it shifts positions. My dad watched me drive the car at low speed circles and he can see the outer axle/wheel hub physically jerk front to back.

I can't find any loose suspension parts. Everything is torqued to spec. No noticeable wear items in the rear.

Any suggestions on what to try next?

[raustinss]

what carrier is in it .... is it a locker ?

[bs46488]

As far as I can tell it is the factory GM positrac carrier

[bs46488]

Well after driving around with 2 bottles of additive in the car the noise has improved but is still present.

I decided to drain and take the cover off. I don't see any issues or broken pieces.

Do I just refill and keep driving?

https://static1.pt-content.com/images/pt/2021/04/AicOKKtl-1.jpg

[Canadianwraith]

I would be checking backlash myself. Something is obviously wrong

[raustinss]

Totally forgot to respond , I would have asked about additive , now that we crossed that one I agree with canadainwraith. Id check the gear backlash if this is beyond you , set something up with the local performance shop or even local gm dealer .

[Lonnies Performance]

Typically excess backlash will be felt during on/off throttle transitions, but turning will have little to do with it.

Often worn clutches can exhibit erratic behavior, but mostly it is due to the wrong fluid.
You are feeling the clutches sticking/releasing, which if often felt & sometimes heard. Yes you can actually see it break free.
I would try a new bottle of additive & some 85w140 non-synthetic fluid... I've never had problems with Lucas or Valvoline.
Many times after a fluid change, it takes a bunch of figure 8's in an empty parking lot to work the fluid in.

You can also check the preload springs as there was a high pressure version offered that had better lock-up but also more tendency to jerk & chatter.
They were color coded differently, but I honestly forget the color after all these years. The springs are relatively cheap, but a pain to install.