It seems like if am going straight, push in the clutch and coast, and lets say a minute later I downshift to 3rd gear from 4th to do some very, very mild engine braking, it will feel like the rear end of the car is pulls to one side or the other. If I upshift under hard power it doesn'tseem to do it. If I upshift under more moderate, cruising conditions, it feels like it wants to try and turn a little. Sort of like it's trying to snake around. For lack of a better way to put it, it actually feels like the rear end is pivoting around the pumpkin to track left or right. A mild correction later and it's no longer there.

If I let off the gas and coast in gear, and then get back on it, it will do it a little, but very mildly. It seems like mild shock loads cause this behavior up to a point where it just gets absorbed by all the other commotion under WOT acceleration. This is the only car I've ever driven that has a posi, and I imagine that with an automatic you wouldn't notice or feel this very much given the kind of jolts it needs to do it.

And to be clear, this all started once I put my posi 9-bolt in the car. It also got tubular poly/poly rear LCA's at the same time. Could be either of them, I dont know.

Does a posi have a sort of mild inherent twitchiness to it when run with a manual that will suddenly slam power through it, or resistance? Or should I be looking for wallowed out LCA holes and panhard rod mounts?


For the record:
Tubular poly/poly lower control arms
Koni rear shocks
Posi rear

Through the course of time, the springs got cut, isolators got removed, panhard bar got replaced with a poly/rod end tubular panhard bar, and none of those had any effect on it.

 

Is the panhard adjustible? Maybe confirm the rear is centered since the springs have been cut/lowered.

 

Is this on asphalt road? or a crowned road? as minor it is it may be groove wander.

 

Would groove wander be that much more pronounced during just situations where there are shock loads on the differential?

The behavior seems to act like what people describe "2-way" posis as being, but those are apparently a specific type of clutch type posis, not cone type.

But yes this is driving around on street roads.

 

i started to feel sensations like this after going to poly bushings, that combined with the squeaks, vibes, and other harshness have turned my mind to going back to rubber since my car is only a driver.....

to me my car feels like more of a chore to drive since the poly got put in...

 

Poly is really a poor choice for controlling articulating motion. Myself and a few others have been trying to preach this here for a while now with only mild success. The problem is you will get 100 guys who don't drive their car hard but think they do, saying the poly is working well for them.

I don't really think the poly bushings are the OP's problem though. Not much articulation going on during his experiments.

 

Hey infernal, do you still have the original lower control arms that you could slap on to test?

If not maybe a local thirdgenner would be willing to lend a set. Heck if that falls through, I'd be willing to loan my Spohn del-sphere LCA's to you. I would need them back by mid March though.

 

Im starting to think this is what it is after all...

I got my LCA's for almost pocket change, maybe it's time to step up and get some nice spherical bushing LCA's. I've been wanting to for a while anyway... there's just always another project in the way.

I've always known poly/poly wasn't ideal, but I've spent more on cd's than those LCA's so I didnt think it was a bad deal. Probably helps at the drag strip but I'm more interested in the twisties anyway. They'll be gone as soon as I can afford it.

I just dont see what else it could be unless it's just how the 9-bolt posi acts.

 

Strangely enough, turned out to by my idler arm. It had a lot of slop in it, and i suppose every time it got loaded/unloaded it would settle differently and the car would track funny. Drives straight as an arrow now. Maybe that helps someone, maybe it doesn't, but the problem is solved.

 

i forgot all about this thread, but i have fixed my twitchy issue also, it turned out to be the lower ball joints were trashed, i bought a rockauto house brand and in 7k miles they were toast in a daily driver. when i removed them i found they were very sloppy and gritty when moved by hand. I replaced them with MOOG this time around.

Lesson learned.