The secret to aligning a Corvette is to preload it.

 

have all your wheels/tires RoadForce Balanced.

its your only solution!

 

Yes, this is what I am going to have redone on my car. I can see that the factory spec for the base front wheels Toe-In is almost straight, i.e. 00 05'. At this geometry, there is very little wheel "wedge-in" action which could allow the wheels to go into induced "wobble" at certain resonance left-right. The factory spec allows +00 25' increase of the base Toe-In, up to the max of 00 30'. As I cannot remember to what Toe-In my wheels were set the last time, I am going to try with Toe-In closer to the max, 00 20' or 00 25'. Perhaps this will solve the vibration.

 

***Update***

Got the car in the air and had a good look at everything this morning. I did find a few questionable items that I will list below, but ended up switching ttires front to back and the vibration is pretty much gone. I do feel it faintly in the right rear (tire was previously on the right front), but it is minimal. I plan on having the tires road force balanced anyway as well as an alignment. Interesting notes on the alignment above. I always ask the shop to go to the factory recommended max on caster (cars always track better with max positive caster), and will also ask them to go near max on the toe in, thank you.

Rear Suspension - No play in the wheel bearings, axle shafts, sway bar, or lower shock mount bushing. The foam spring isolator is starting to fall apart so I assume the upper shock mounts are not far behind. Ordered rear upper shock mount foams and spring isolator foam.

Front Suspension - No play in wheel bearings or ball joints, but the front right sway bar link is bad and both outer tie rods has some play. Also, upper shock mount foams are deteriorating badly. Have ordered upper shock mounts, sway bar bushings, sway bar links, and outer tie rods.

Driveline - Both Jurid couplings look good and I could not feel any play. Center bearing carrier on the driveshaft also looks good. Motor mounts dont have much (if any) play, but the trans mount has a little. Might be normal as the rubber looks good and it is not broken. Will leave all of these parts for now, I see no need to replace.

At this point I am OK with how the car drives and I assume replacing these parts along with a road force balance and good alignment will only make it better. Just had the car out for a couple of hours (70 miles or so) and it's just an awesome car. Was only on the highway for 10-15 miles and for the most part the car is vibration free. I'll take it to work tomorrow and that will be the real test (40 miles all highway each way).

Parts I'm going to replace before the alignment are - front & rear swaybar bushings & links, outer tie rods, front & rear upper shocks mounts, front & rear brake pads (will re-surface original Brembo rotors). I will update after everything else is done to see if there's more improvment. I'll also update tomorrow after my ride to and from work to see if the vibration is really gone/minimal with just moving the tires front to back.

Thank you to everyone who has contributed, great guys on this forum.

 

Is there somewhere on this site or anywhere else that lists torque values for X308 common fastners? Want to make sure I put everything back together properly once I start working on it. A service manual would be even better, where is a good place to get one for these cars?

 

Right at the top of this forum in the Stickies, I believe the JTIS21 has updated install instructions for Win10.

 

I attach pages from the service manual showing the suspension torques.

 

Thank you, much appreciated. Is there somewhere I can get the entire PDF? For some reason I can't download and install the JTIS21 in the Sticky. I don't mind paying for a PDF manual if it's available.

The only thing I dont see listed in the front is the 5 shock mount plate bolts to the body. Any idea on that one?

 

If you have a way to send me a link to your Dropbox or something, I can upload the Service Manual (70 MB) and the Parts Catalogue (60 MB). Alternatively, I can brake the files into few parts down to the size that can be attached to email. PM me about this.

The shock top mount bolts are M8 for which the standard torque is 24 NM.for Grade 8.8 (stamped on the bolt head). You can use this standard chart for tightening bolts, just make sure you are looking at the value corresponding to the bolt grade.

 

Well, I spoke too soon. Drive the car to work today and it's the same (if not worse) than before. I guess I had it on an exceptionally smooth highway surface for too short of time yesterday or jsut got lucky. Parts are on the way and will get everything installed as soon as I can. If no change after that then it will be a road force balance & alignment. If it's still no good then I'll be back asking for more suggestions...

 

Go and get the toad force balancing TODAY before you replace anything. Make one change at a time. When u get the road force balance ask them to show you what the balance is BEFORE and AFTER.

Any roadforce above 25 can be felt. If your before is over 25, youll see results. And make sure the post numbers are below 25.

mine were horrendous. I had 4 bent rims!!! New rims and its smooth as silk!

 

Performance tires will enhance any faults in your suspension....specially the wider you get, your geometry is intensified. I had my tires road force balanced 4 times, had the wheels spun for true and the alignment couldn't have been more on the 3 times I had it done. The road force balancing helped immensely on the 4th episode, the 1st 3 were done at the purchase shop, the 4th at a sister shop. So I chalked that up to either a unqualified tech or not properly dialed in machine? I even thought I had a bad belt, but after rotation, the results were the same.

Now for the link I provided, that propshaft bearing has a load on it, which I show the wear from that in the pics. I also want you to be aware of the jurid couplings, again where I show in the pics, that you can't see the wear unless they are taken out and see the stress points. If there original, your talking 17+ yrs old and its a high torqued item. But if the PO had done some backyard mechanics, perhaps this (or at least part) of it is your issue... https://www.jaguarforums.com/forum/x...pshaft-207717/
When removing the bolts & nuts, they are supposed to be marked for replacement back where they came from for balance. The direction of the jurid coupling is important also.

I'm hoping your issue is just tie rod ends and an alignment, but reviewing that thread.., if you haven't already, ..couldn't hurt.

 

Interesting thread, thank you. If the road force balancing and other worn part replacement do not solve the issue the shaft will be my next culprit. I did not realize you could not tell wear in the couplings when mounted, but they do look like they've never been removed and most likely original. If it were the driveline, wouldnt the vibration change (for better or worse) when letting of the throttle or putting the car in neutral when it starts? Every rear end or driveshaft issue I've ever had will at least change when load is applied or removed.

Going to find a shop to do the road force balancing first and go from there. My biggest fear is finding a shop that does it but having an unqualified or uncaring tech do the work. My understanding is that si the process must be done properly for it to be of any benefit.

 

Highhorse has a good point. Not all techs know what theyre doing and some dont care. I had a shake in my brand new hellcat from the day I bought it. Brought it back to the dealer 4 times while they balanced and rebalanced, swapped tires and balanced twice more.

took it to another shop and PRESTO! They got it down to 21lbs and cleared up the shake. The tire guy at the dealer said their machine myst have been out of cal! Lmao

 

That's exactly what I'm afraid of, spending the time/money to have it done and having them half-*** it and be in the same spot I'm in not truly knowing if the tires are properly balanced. I like to do everything myself because so many people take short cuts nowadays.

On another note, I drove the car home from work today and it was absolutely terrible, much worse than it was before I swapped wheels front to back. I couldnt wait to get out of the car to be honest, so frustrating. That leads me to believe that it has to do with the wheels or tires. I wonder if one of the BBS wheels is slightly bent causing this issue and the first shop that balanced the tires either did not notice or did not tell me. I asked the guy who did it if everything looked good and he said, "They all zeroed out fine" so I took that as everything being good. I really hope one of the wheels is not bent, doubt I'd be able to find a replacement for a decent price. There is a really good alignment shop by me that does chassis work and alignments for a lot of local racers, migjht stop by there tomorrow and see if they'll take a good look at everything. I dont think they have a road force balancer, but at this point I'd rather have someone that knows what they're doing look at the wheels/tires and let me know if they see an issue. They do fix alloy wheels so maybe if there is a slight bend they can repair rather than me having to replace.

Anyway, thanks again to everyone for their opinions and advice. I'll be sure to report back as I hopefully get this figured out. I'm determined at this point.

 

Part of the road force balance is measuring the rim and wheel runout. Thats how they found the bent jag wheels although you could actually see it when they spun the wheel. It was bad. See blowup pic below.
Also, theres no need to worry if the tech did it right if you see the results on the screen. The blowup pic below shows the final result was 25lbs.

This tab show the wheel and rim runout

This is the result- 25 lbs. anything higher and youll feel it

 

I have brand new rims on my car (onto which I put new Continental tyres) and it did not eliminate the vibration. I think the only way is good wheel balancing (RFB) and experimenting with the Toe-In. Or perhaps other brand tyres would perform better. I noticed that Continental tyres are considerably lighter then other brands of the same size. This should actually reduce the possibility of vibration but who knows; the Continentals also have rather soft side walls so this could have something to do with the vibration.

 

In the case of my hellcat, it had 2 brand new 200mph rated pirellis tires that were bad from the factory that they warrantied the tires out for me. I had been back and forth to the dealer numerous times trying to fix it. Same symptoms- a vibration over 70 mph.

I found out all tire manufacturers warranty tires for 12 months down to a certain tread depth. The tires were faulty and after checking online. Google search for your brand and vibration over 65 and see what comes up

 

I know that Continental DSWs have balance & flat spot issues, I have read quite a few threads on other forums about it. I put them on a Mustang about 5 years ago and since new could never get them right, apparently they have very soft sidewalls. Couple that with a 5000lb Jaguar and you have problems...I never would have put them on the car, they were on there when I got it.

Stopping by the chassis shop this morning to see if they either have a road force balancer or know someone who does. Really hoping that's the issue here...

 

I highly recommend to NOT install Goodyear Eagles. What a horrible tire, poor traction (especially on wet roads) for a so called performance tire and balance out of the factory was bad. All the counter weights on them vs the Michelin's is worlds different. I only had something like 10k on those when I dump trucked them.