1998 Coupe w/ Z51 "jumping" sideways in turns?

[fhturner]

Hello Everyone--

Well, I've been a Corvette owner for about 17 days, 1 hr, 45 minutes now... I've wanted one for years and finally had the chance to buy one. I'm beside myself and having such a great time that I'm pinching myself on a daily basis! Hope I don't wake up to find it was all just a dream...

Anyway, I do have some questions about things that I've noticed so far on my 1998 Coupe w/ 6spd (guess that'd be "M6", huh?) and Z51 suspension. I'll start off with this one about the car's handling in the corners: While it turns like it's on rails in both wet & dry, I have noticed that if I catch a bump while turning, the car will seem to "jump" or "hop" sideways on me. While I doubt the car will go out of control at this point, it sure feels like it will and is very disconcerting. I'm not sure how else to describe it-- just seems like the whole thing loses grip for a split-second and literally moves sideways slightly. When the "jump" is over, I have full control and the steering is just as responsive as ever.

The previous owner's records indicate on one service visit @ 71000 miles "NEEDS REAR SHOCKS PARTS $310 LABOR $97.50". From what he told me, he did not have this done. I'm wondering if worn out rear shocks could be the cause of this jumping behavior I'm experiencing. The car now has just over 78K miles on it, and has fairly new Firehawk run-flats @ 30psi cold.

Any thoughts on this? Could the shocks be the problem? Are worn out shocks to be expected at this mileage (pretty conservative driving over the life of the car)? If so, is the above amount about what I should expect to pay for them? Should I have a local dealer perform this service, or are there less expensive, yet acceptable alternatives? Sorry for the long post, but I'd greatly appreciate any info that you savvy guys & gals could pass along!

Thanks!
Fred

 

[Pinstripe]

What you are experiencing is probably quite normal and can be attributed to several things.

If you have the stock Goodyear EMT's they have a tendency to behave as you describe in a corner/bump situation due to the extremely stiff sidewalls.

The transverse fiberglass leafspring doesn't help either. Some have switched to coil over shocks and most of this tends to go away. Combined with non runflats it can be just about eliminated entirely.

It has happened to me in my 02 Coupe with Z-51 as well and can be quite disconcerting.

 

[fhturner]

Thanks for the quick reply, Randy!

Do you think my situation might be a little different, since I'm running on the Firehawk run-flats? From what I've read, they seem to ride better than the Goodyears-- I don't think their sidewalls are quite as stiff.

And do you think, then, that the shocks are not part of the problem? If not, should I be looking to replace them soon anyway? Any comment on pricing for those? Can you further explain the "coil over shock" switch that you mention (I'm a bit of a dummy on some of this technical stuff!), and how much that typically costs for parts/labor?

Thanks again for your reply. If any others would like to weigh in, too, I'd be most appreciative.

Thanks!
Fred

P.S. Let me really show my ignorance here and ask if there's any way to verify or get a list of options/features that one's Vette was configured with? I don't have the original sticker, and I'd just like to know. I can tell about most things (e.g. dual-zone AC is pretty obvious...), but a listing or something like that would be nice.

 

[c4c5specialist]

Hi there,
I would suggest an alignment check of the vehicle.
Hopping is usually a sign of worn shocks, incorrect tire pressure, incorrect alignment settings, worn tie rods or broken springs.
I would have all these checked before proceeding.
Allthebest, c4c5

 

[johnl]

Look at the inside of the cover of the left most storage compartment in the back. (The small one). On my 97 there is the sequence number and the build codes from the factory.
With these numbers you can look up exactly what was put on the car from the factory. I know they changed this location (of this info) on later models, but have a look. With these numbers we can go from there. I know at www.corvetteregistry.com there was a listing of what these codes translated into. (It may be listed here as well but I haven’t done a search yet). See if the info is there and then we can look up all the poop.

 

[fhturner]

I would suggest an alignment check of the vehicle.
Hopping is usually a sign of worn shocks, incorrect tire pressure, incorrect alignment settings, worn tie rods or broken springs.

Well, call me an idiot, but it appears that my Vette does NOT have the Z51 option-- I find no "Z51" in the RPO codes, only "FE1". Perhaps the previous owner was misled or just confused (or misleading _me_, but I doubt that). I'm guessing that my initial leaning toward the shocks being the problem is probably going to be correct. Tire pressure is correct. The vehicle doesn't wander, so I don't think alignment is the problem. This seems to be more in the rear, so I doubt tie rods. And I think I'd know from general ride "crappiness" if a spring was broken (or would I?). Anyway, this seems to return me back to the shocks.

So, some Q's about that (please forgive my ignorance-- I am learning much but have much to learn!):

1. What type and brand/model are the factory shocks and what are their specs?
2. Is the ~$400 price I mentioned previously about what I should expect to pay?
2a. Take it to a dealer, or any ol' place will do?
3. Should I consider other shocks brands, models, specs, etc.?
4. Under average driving, how long do the Vette's shocks tend to last?
5. What about the front shocks?

Thanks for all of the help so far, and for any other help in advance!

Fred

 

[johnl]

I ran the stockers until they were bottoming out on dips on the highway. Somewhere around 65,000 or 80,000mi.
When I replaced then I drove a couple of C5's different options. Coilovers and hoskitch sway bars etc. These setups were great for the balls to the wall driving out at Thunder hill, but not really an option for me due to the expense and the fact that I use mine for a 200mi/day commuter. I finally settled on Bilstein shocks.
The choices here are HD (Heavy Duty) or Sport. HD being stiffer than OEM and the Sport being harder still. I went with the Sport since I do occasionally do make it out to the track.
You might keep in mind also, no one rides with me. (Except for my 5 yr old).
I have been told when a co worker who rode with me to lunch that it was less comfortable than another coworkers C5 with whom she had also rode to lunch. She mentioned it was almost too stiff. If you have a co-pilot or someone who rides shotgun a lot the HD may be the way to go.
I ordered them online. You can find them at most of the performance suppliers (near $400.00). I changed them myself. It took about 3 1/2 to 4 hours, and most of this time was getting it up and down off the jack stands.
There is a write up somewhere online and I’ll look it up for ya if you want to go this route. I like these. (I think, when loaded up at speed going around a curve I could run over a dime and tell you if it was heads or tails.)
Good luck.
J

Edit: I forgot to mention, the Bilstein manafactures warranty said, "Good for the life of the car". With my commute I will test them on this.

 

[fhturner]

Thanks to everyone for all of the info! I really appreciate it. I think I'll look into those Bilstein shocks, johnl-- thanks for the advice. Just wanted to follow up on a couple of the questions that I posed before.

1. Can anyone tell me the specs I need to know for ordering rear shocks? How about the brand that comes stock (just curious)?

2a. If I don't feel comfortable doing it myself, should I take it to a dealer or just any place that seems somewhat competent?

3. Are there any other brands that I should consider besides the stock or Bilstein brands?

5. Should I worry about the front shocks? Haven't really noticed a problem there, but since I'll be replacing the rears...

And a new Q:
Where is the best place to look for getting started doing some of these things myself? I have no mechanic/service background, so I wouldn't want to get real fancy. But, are there any links/pages that'll tell me the basics, How-Tos, and Dos and Don'ts for working on a Vette?

 

[EHS]

If your planning on working on the car yourself, get a set of the service manuals for your year. They include details on shock replacement, and you can decide for yourself whether you are up to it.

Everyone likes Bilsteins, and you can get these at any number of places.

Here are links for the specs:

http://www.bilstein.com/

http://www.eshocks.com/

Konis are also good, I like the new Edelbrock IAS.

Bilstein Sports or Heavy Dutys run $75 each, Edelbrock IAS are $105/$116 f/r.

Monroes by comparison will be much cheaper.

Generally with shocks, you get what you pay for.

At 80,000 miles, the stock shocks are probably shot. As c4c5specialist indicated, while you are under the car, also check the other items.

 

[atmmac]

You Should be fine taking the car to a competent mechanic i personally find dealers to be a ripoff. If you have a mechanic that you usually bring your cars too bring it to them there bound to be more honest and appreciate your business. As long as it doesnt involve a computer problem i would take it to your normal repair guy. Its your xchoice but thats what i do. If your anywhere near massachusetts on the southb shore check out the Auto Hospital in Hanover they do a good job there i trust them with both of my cars.

 

[DRTH VTR]

bump steer

When I take a corner hard under power, the back end can hop out a little bit when I hit certain road irregularities. I don't think this is necessarily abnormal. I think this is called 'bump steer'

 

[VAmagred01]

I've read this in many magazines about the F45 but never the Z51. So, if you do indeed have the standard FE1, then it might be normal to the suspension being that it's softer than the Z51 (similar to the F45). I actually recall the August 1997 issue of Car and Driver running into this same situation with their '98 tester (F45 equipped). Other than that, you might want to do as mentioned by the experts here.

 

[fhturner]

Wow-- funny how a thread can sit domant for a little while and then experience a flurry of activity! To update everyone, I decided on the Bilstein Sports and just had them installed on Friday. Unfortunately, the installation was not trouble free:

Trouble with Bilstein shock installation

I hope to get the Vette back tomorrow, as the CV boots were not in stock and wouldn't be in until then. So, another day without my baby! :\

Re: Bump Steer-- DRTH VDR, I guess some amount of sideways movement in turns is inevitable during cornering if one encounters a rough surface. However, if these new Bilsteins don't significantly improve the "sure-footedness" of my Vette, I'll be fairly disappointed. I think any "bump steer" that I've been experiencing has been severely amplified by my blown shocks. I should feel like my Vette can handle corners at much higher speeds than my Bronco, wouldn't you agree? Up to this point, I haven't really felt that. So, my fingers are crossed that the Bilsteins will do the trick!

BTW, I got my Bilsteins at eShocks.com for $299/set with free shipping (over $200). Installation was about $125, plus another $100 for 4-wheel alignment. And yes, the original rear shocks were completely gone when they came off, and probably were when I got the vehicle at about 76,600 miles.

VAmagred01-- As I was typing this I saw your post. I understand what you're saying, but I would think that the Z51 being stiffer would seem to make it hop more in a situation like that. In any case, I do indeed have the base FE1 suspension, and I will wait to see how everything goes when I put these new shocks through their paces. Until I get a chance to do that, all bets are off! I imagine it will be a significantly different ride experience with shock absorbers that actually absorb shocks!

Thanks for all the input and info, guys! I'll let you know how things go with the new Bilsteins.

Fred

 

[VAmagred01]

One would think that the stiffer of the 3 suspensions would hop more than the others but for some reason it's just the opposite. Car and Driver wondered if the rear shocks were getting proper messaging from the computer. Mine hops on some expansion joints too (equipped w/ F45) in all settings (i.e. Tour/Sport/Perf.). I had read the article prior to buying my car so I was aware of the possibilty. It's very disconcerting, though, if you're driving aggressively (not that I do that sort of thing:L ).

Good luck on your new shocks! Hope all works out well.

-Kenny

 

[johnl]

I had a problem with the "stiffer of the 3 suspensions would hop more than the others" idea also.
When I went to a racecar driving school a while back they had a video talking about just that subject. There were some "shock cams" and diagrams and all, but the point they were trying to convey was. Stiffer shocks are actually pushing down on the road harder.
Watch the next NASCAR race and see when someone says the car is too tight, (pushing or not turning) they sometimes will remove a wedge, (a big piece of rubber weged into in the spring). This effectively makes the shock less stiff, and it loosens up the rear end and the car can turn better. The “less stiff” shock does not push down as hard and the rear can come around and help the car turn.
It’s hard to grasp but stiffer actually pushes the tire down harder.

J

 

[fhturner]

Thought I'd give everyone an epilogue on this "adventures with shocks" story...

Well, this past Thursday, I finally got my baby back (ribs?), with new CV boots and parking brake mechanism, along with the Bilstein Sports I had installed the previous Friday (when the CV boot damage was done). Actually, I had to re-return to the shop after picking it up Thursday, because the "ticking" noise I had heard initially after the shock installation was still there. That turned out to be the left rear shock, which was not tightened all the way. After another small delay, I was on my way.

So, after getting used to the "stiff as hell" Bilsteins, I set out to test what I hoped would be my Vette's newfound "surefootedness". I searched for rough and bumpy corners, which had given me trouble previously. With the old, worn out shocks, it could get very dicey when hitting a bump going around a turn at moderate speed, as the whole car seemed to jump sideways. I'm happy to report that there are no such problems now that I have the new shocks! In fact, while bumps are definitely noticeable as far as ride smoothness goes, they are now a non-issue when it comes to cornering. I'm glued to the road, baby!

So, the end result of all this is that, since I don't actually have the Z51 suspension, the stiffness of that suspension obviously could not have been the cause of my problems. The cause was definitely the factory shocks being worn out after ~76000 miles.

I'm still trying to get used to the rougher ride of the Bilsteins, but I definitely am liking the new grip that I have in the turns. Now I'll be turning my attention to the small rattles that have been uncovered by the tighter ride!

Thanks to everyone for your input and help in this matter! Just from this one issue alone, I've learned an enormous amount about my Vette, much of it from these forums. If I think of anything else, I'll be sure to mention it here. Any further comments are welcome as well.

Thanks!
Fred

 

[VAmagred01]

Congrats! Glad to hear it.

These cars are a blast! Definitely enjoy it!