I have a weird problem that has me totally stumped:

As I go from decelerating to accelerating, the rear end seems to shift, and I have to correct with steering input to keep from changing lanes. It feels like the rear end is changing alignment as the load shifts from slowing to going. And I'm not talking about hard driving either- just normal cruising. And it did this with the stock 305 too.

Keep in mind that all of the suspension, front end, and all bolts are 100% brand new. It was just aligned. It's got all new poly bushings. Everything is from Spohn. And it has a brand new 9" rear end.

The real puzzler here is that it did this before with all my old suspension and rear end. I thought that the problem would eventually go away as I upgraded parts, but there's nothing left to change now.

I had a theory that the LCA bolt holes were elongated which was allowing the rear to slightly shift back and forth. But I just pulled the bolts out and the holes look perfectly round. There is only a tiny normal amount of play between the bolt and the bracket hole- actually less than there is in the bushing itself.

So, could the chassis just be that loose? I can't believe that to be true. It has zero rust and it is a hard top car. I do not have subframe connectors yet, but I should be able to just drive straight down the road without them.

Any suggestions would be great. Let me know what you think.

thanks in advance.

 

It did this with the old rearend? or just with the 9" ?
if your 9" has a locker in it thats whats doing it.

 

What's the condition of the track bar (Panhard) and track bar brace?

JamesC

 

TTOP350- It did this before with the old suspension and old rear end. The rear does have a Detroit Locker, but how could that make it drive so wiggly?

JamesC- The panhard bar is brand new adjustable Spohn unit with poly bushings and new bolts, but it did this with the old stock bar too. The jam nuts are tight. The track brace is stock, straight, and bolted in tightly.

Thanks for the tips. This is really strange, huh?

 

Condition of the shock towers (just shooting in the dark here)?

JamesC

 

The rear shock towers seem fine. They are not rusty. Shocks are new and mounted tightly.

But what about the front struts? Don't they mount into a rubber bushing at the tower? What if that is worn out? When I installed them, I did notice that the strut would move up and down in the bushing a bit, but I assumed that was normal.

BTW. I just noticed you're a fellow Kansan. Been hot enough for you lately?

 

The strut mounts do have some rubber, which will not only deflect but also deteriorate with age. How that might effect your issue, I'm uncertain. Many members, to include me, have gone to Spohn (or other after market manufacturers), who offers a spherical bearing in his version. Very nice.

Yeah, Lawrence. The heat has been insufferable! It was finally cool enough today that I actually climbed out of the La-Z-Boy and threw in a new cap, rotor, wires, and plugs in my Jeep.

JamesC

 

That would be my first guess.

I had one of my panhard bolts come ever so slightly loose, it had about 1/16th of an inch in side to side play.

It felt like the rear end was going to fall off from that tiny amount of play. I've since replaced the bolts and locktite'd them.

 

Yeah, this does sound like something the panhard bar could cause. I'll re-check the torque.

Also, I wondered if having an adjustable panhard bar meant that it would slightly twist as the pinion angle changes. I do have my adjustable torque arm set at -1.5 or -2 degrees. As I transition from decel to accel, that angle goes up and down. If I didn't have the panhard adjuster jam nuts tight enough, it could unscrew itself back and forth and change the length of the bar. But it just doesn't seem like you could feel such a small adjustment as that.

Maybe I'll get a non-adjustable chrome moly bar and see what happens.

 

Was the car ever in an accident?

 

The detroit locker has spring loaded teeth in it that has play in them. When you stab the throttle it will push the car right or left. Let off the throttle and do it again same thing. You never know which way itll push the car tho.
If it did it with the old rear and clutch or cone style diff you have other probs. Like a loose panhard bar. the factory bolts shouldn't let it move too much tho..
Do a quick google search for the locker. you can see the guts 2gether and exploded veiws. you'll see the play between the teeth..

http://www.stockcarscience.com/blog/.../differentials

 

Sailor- No accidents. The car is one of the most straight and solid ones I've seen, and I hope to keep it that way! There's a big S curve near my house. As I'm driving around it and tip back into the throttle half way around, the car lurches toward the oncoming lane. I'm afraid I'm going to wreck this thing if I ever start driving hard, so that's what is prompting this question.

TTop350- Nice link and good info. And that makes sense. But if a locker can upset a car that much, then that makes me not like it anymore. But I really have no other option for a heavy duty drag car. I wonder if a spool would be worse or at least more consistent? What diff do you use?

 

Detroit locker.

When I had a powertrax the car did the same thing.