Cause of squirrelly feel on hard acceleration?

[VetteMed]

I've noticed recently that my Z seems to be a little squirrelly on hard acceleration, almost "darty", which is rather disconcerting when the speed gets up there. It's almost like the car wants to go in random directions, and it takes effort to keep it pointed straight.

The only thing still original in the front end, is the steering rack, so I'm a little suspicious that maybe there's some slop in that... though I guess it's possible one of my other front end components has worn prematurely, with only about 10k miles since rebuilt.

Any thoughts on what might cause that loosy-goosy feeling on hard acceleration?

Thanks
Andrew

[Kevin]

do you have c-beam plates?

[VetteMed]

Yup, sure do. torqued to spec, as of not too many weeks ago.

[gbrtng]

Sounds like it's time for a 4-wheel alignment including thrust angle using the factory specifications as a starting point.

[PhillipsLT5]

http://www.vbandp.com/index.php?option=com_docman&Itemid=148

[VetteMed]

Yeah, I was wondering about that... I had a Euro import shop do the alignment last year, it's never been quite right (little pull to the right), but I was ignoring it. Perhaps it's time to take it back for a re-do.

Unfortunately this is the shop that came most highly recommended in this area. Maybe it's worth a trip to Corvette Masters about an hour and a half from here. Not sure if they do alignments though.

[PhillipsLT5]

VBP #s need to be cut in 1/2 for each side, see instructions

[VetteMed]

VBP #s need to be cut in 1/2 for each side, see instructions

Just the toe gets cut in half, right?

[scottfab]

Yup, sure do. torqued to spec, as of not too many weeks ago.

Is it worse with the top out?
Does it do it on completely flat ground?
I found a marked improvement in this darting around when I
replaced the lower a-arm bushings.
It's still not zero but much better.

[rhipsher]

Mine felt like that until I rebushinged the entire car with poly. Brand new inner/outter tie rods. And rebushing the steering rack. All my problems were gone instantly. I do all of my own work because I do a better job than any shop. The only thing I use a shop for is to mount and balance my tires and do a road force alignment. Thats it.

[VetteMed]

Entire suspension has been redone with poly bushings, and Banski rod ends in the rear.

[scottfab]

Mine felt like that until I rebushinged the entire car with poly. Brand new inner/outter tie rods. And rebushing the steering rack. All my problems were gone instantly. I do all of my own work because I do a better job than any shop. The only thing I use a shop for is to mount and balance my tires and do a road force alignment. Thats it.

Ya know I'd bet most of us do our own work but that's just a guess. Oh boy time for another "poll" to find out.

I've done everything from rebuild the ZF6 to fixing the electronics in the door chime. And I published "How to" pictorials on the ZR-1 Net Registry page for many of these. The only time mine has seen a shop was to verify the alignment I did using a square and a tape measure :p. Even with tire replacement I just take the wheels down. No sense in traumatizing the car by letting it see the inside of a shop. :-D

I need to go check my steering rack in the next few days. Could it be ???? hmmmm

Another thing that leads to twitchy steering is out of spec toe in. If it's too close to zero...... not good.

[tomtom72]

Disclaimer: I've never done an alignment using the string method. I've never rebuilt any of the suspension myself.

With that said Andrew I'm thinking
1.) just on hard acceleration? Not just going very fast down the road, as in steady state velocity?
I think it's the Camber settings if they're at zero(?) you get very quick steering, but ya have to pay attention & stay on top of the steering. I think?

2.) Too much weight transfer under hard acceleration due to too much rear end squat? I don't really know what to do about that as it's supposed to be 'designed' in to our rear suspension. Maybe too much HP? I'm just throwing this out there as I pulled this out from you know where.:o

3.) check the rack for too much free play. My backyard method would be to center the wheels, and then move the steering wheel and see how long it takes the tire to react. I would think you would get a sense if it took too much steering wheel movement to get tire movement? What about the rack mount points?

4.) the thrust angle thing along with the rest of the alignment specs would be on my list also. I had a 'pulls right slightly' going on after my last alignment but it turned out to be the rear toe! I had no trouble with straight line stability, at constant velocity or under acceleration, just that slight pull to the right.

5.) You rebuilt the suspension so is it possible something failed ( due to a defect ) in the front end? Like maybe just at one side of the car? Like an end link or bushings?

6.) bad shocks? Like the rears compress too easily & unload the front too much? Hey, how important is our front spoiler to stability?

:o okay I think I'm out in left field now so I'll be still. :o

:cheers:
Tom

[VetteMed]

Disclaimer: I've never done an alignment using the string method. I've never rebuilt any of the suspension myself.

With that said Andrew I'm thinking
1.) just on hard acceleration? Not just going very fast down the road, as in steady state velocity?
I think it's the Camber settings if they're at zero(?) you get very quick steering, but ya have to pay attention & stay on top of the steering. I think?

2.) Too much weight transfer under hard acceleration due to too much rear end squat? I don't really know what to do about that as it's supposed to be 'designed' in to our rear suspension. Maybe too much HP? I'm just throwing this out there as I pulled this out from you know where.:o

3.) check the rack for too much free play. My backyard method would be to center the wheels, and then move the steering wheel and see how long it takes the tire to react. I would think you would get a sense if it took too much steering wheel movement to get tire movement? What about the rack mount points?

4.) the thrust angle thing along with the rest of the alignment specs would be on my list also. I had a 'pulls right slightly' going on after my last alignment but it turned out to be the rear toe! I had no trouble with straight line stability, at constant velocity or under acceleration, just that slight pull to the right.

5.) You rebuilt the suspension so is it possible something failed ( due to a defect ) in the front end? Like maybe just at one side of the car? Like an end link or bushings?

6.) bad shocks? Like the rears compress too easily & unload the front too much? Hey, how important is our front spoiler to stability?

:o okay I think I'm out in left field now so I'll be still. :o

:cheers:
Tom

Tom, all good things to consider.

At constant speed, the steering feels stable, with that slight pull to the right. Not darty at constant high speed for the most part, just while accelerating.

Shocks were rebuilt by Bilstein a few years ago, perhaps 30k miles on them (PO sent them out). Not that this is a guarantee of anything! I don't feel the floaty bouncy feel that I felt in my other Z when the shocks needed to be redone.

Steering rack, and steering rack mount bushings, are all original, and I'm a bit suspicious about that being an issue.

A defective front end component is certainly possible. On my old GMC truck, I had a new tie rod fail 5k miles after rebuild of the whole front end.

Thanks,
Andrew

[scottfab]

If the car wants to walk to the left under WOT that is "torque steer".
Basically the twist of the body from high torque. It's a fairly well understood problem with the C4 frame. Lots of thread on it recently under the Killebrew fix, the factory cross brace, R-D racing cross brace and I am sure others.
That's different from "twitchy" steering.
It can make you look like you've been drinking if you have twitchy steering on a rutted road. :cry:

[PhillipsLT5]

I think it is toe, camber & caster all cut in 1/2
That is how I did mine with me sitting in the car
You can contact VBP to be sure

[VetteMed]

I think it is toe, camber & caster all cut in 1/2
That is how I did mine with me sitting in the car
You can contact VBP to be sure

I think just the toe gets cut in half - it's listed as "total toe", half on each side.

Camber and caster are unrelated from side to side, and so are set as written.

[PhillipsLT5]

I just got off the phone with them, it applys to toe, camber & caster, cut all in 1/2

[VetteMed]

I just got off the phone with them, it applys to toe, camber & caster, cut all in 1/2

I don't understand... That means they only want 2.5-3.5 degrees of caster? Why would that be halved?

[rhipsher]

Entire suspension has been redone with poly bushings, and Banski rod ends in the rear. Ball joints to? Batwing bushings also? Just trying to narrow it down. If every things been done then I would have to say alignment time.

[batchman]

From the sound of it (ie at higher speeds) your problem is front end rather than usual wonky rear grip.

For front stability you want *more* caster, will increase steering effort and centering. If you have a matched pair side-to-side of shims on the rear-most end of the upper arms, pull 'em both.

For front stability you want more toe-in, easy to do yourself and tune out your pull at the same time. Use small increments (like 1/8 turn).

One thing to look at that happened to my car - the rag joint loosened up on the rack end. Those joints suck anyway, tonight I'm going to try grafting in the "hockey puck" style from a regular C4. I am just afraid they went to the canvas one due to angle as it's a lot further down than the normal one...
(sorry 'cuz that sounds like a hijack)

I've never used the Banski arms (not allowed in my rules) but sometimes when you take compliance out of one joint you increase the stress on another to the point where it moves more than otherwise would. So I guess I wouldn't rule out a bushing in the rear somewhere. In fact the more I think about it the rear is a good candidate as the steering rack and bushings etc would be more wonky under cornering load than while accelerating.

Best,
- Jeff

[VetteMed]

Ball joints to? Batwing bushings also? Just trying to narrow it down. If every things been done then I would have to say alignment time.

Yep, all ball joints were new last year, batwing bushings new poly last year.