Hey guys, I need some help with some suspension issues I have been having. I have a c5 with an upgraded base model suspension (non magnetic ride). I have replaced the original shocks (now bilsteins sports), the springs replaced (now 2002 z06 leaf springs), the original plastic end links (now metal end links), lowering bolts (max down), and the sway bars are (now 2002 z06). finally, the tires 19 by 325. The problem is, the car is very unstable at speeds 60 and above. The car feels as if it does not have any sort of sway bars/stabilization, at all. I am curious if anyone else has had a similar setup and what it was. I am am not sure if my lowering bolts are are the problem or what.

any suggestions are welcome.

 

Have you had a 4wheel alignment? There are some different specs over stock that some people prefer. Do a search or maybe someone familiar will post them for you. Make sure you tell the alignment shop you prefer to keep it lowered, because tire pressure and ride height are supposed to be the 1st things checked when aligning a car.

 

I have not had an alignment. That probably wouldn't be a bad idea at all.

 

If anyone knows what the specs are when the car is lowered all the way, I would appreciate it.or a link to where I can find them.

 

http://forums.corvetteforum.com/auto...e-learned.html

Second post, lots of good info, and links to performance alignments.

 

Google "pfadt corvette alignment specs" and their recommendations page pops up. Decide how you use the car because the further you go down the page the quicker the tires will wear. If you drive straight line a lot then keeping the camber low helps the tires wear evenly. Also, make sure the shop keeps the camber and toe as equally side to side as possible.

As an example of why the stock ranges are no good - it allow both rear wheels to to point to the left or right which would make the car rear steer.

 

You have made a boatload of changes and any number of things, either maintenance or setup could be the issue.

First, look at your front sway bar and make sure it isn't broken or disconnected. If the front bar isn't working (these bars can crack and break in the area under the bushings) the car will feel sloppy (because the from roll stiffness is lower) and it will be "loose", because the front/rear roll stiffness distribution is out of whack. Looks at the bolts and the brackets and make sure everything is in order, and it isn't a bad idea to inspect the bar by removing the brackets and looking carefully at it.

You noted that you have lowered the car and are max down. On what bolts? Does the car still have the proper rake (1/4 to 1/2 inch higher in the back as measured at the jacking points). If you do not have proper rake the car will lift in the back and be unstable at speed, although 60 mph seems a bit slow for that to start happening.

Many are saying that it could be an alignment issue and that is what it most likely is.

What often happens is that the rear shocks bottom out (because you have no rear suspension travel with the car set that low) and then the shock acts like a wedge and pushes out on the bottom of the rear upright. This causes the rear alignment adjusters to slip because the forces are huge. The rear toe changes and the car drives strange. This is a very common occurrence on cars that are excessively lowered. If you want to keep it that low you will likely get very friendly with your favorite alignment shop and tire dealer.

 

Yeah, the car was lowered when I bought it. I really hated how bad the car drove, so I tried to upgrade all the suspension part's that I could. The springs and sway bars are used and came off a couple z06. I didn't see any cracks, but didn't really think to look for them, either; I will check on that. The shocks and end links are the only thing that I bought new. I am not sure exactly how low the car sits, though, I did measure it when I put all the new parts on. I am pretty sure that I can not fit two fingers in between the fender well and rear tire. The lowering bolts are not factory; they are some aftermarket bolt. I am not sure what the tire pressure in the front or back should be. I find that the large tires ride better at high pressures 40 in front and 35 back. Again, the car needs an alignment, badly.

 

The tire pressure for all four tires should be 30 psi. You need to let some air out or you will be blowing through tires and will experience a horrible ride.

 

yeah, the ride quality suck really bad a 35 Nd 40.

 

You need to raise the car on the spring bolts if the car ride is too rough. Lowering with aftermarket bolts leaves very little suspension travel so the car rides rough because it's bottoming on the bump stops all the time.

 

I tried to see if I could raise the car today with the bolts that are currently on the car, but that didn't go as anticipated; the bolts are just too long. I tried backing the nut on top of the bolt off and closer to the top of the bolt's threads, but that resulted in the car resting even more on the tire. Now, this is where I am wandering if anyone had tried putting washers on on an aftermarket set of lowering bolts to raise the car back up. If so, did it work w/o issues?

 

You must be asking about the rear bolts. There is no reason you couldn't use washers. Best would be to buy shorter bolts.

 

Yes, i did mean the rear. I assumed everyone just read minds, lol. I'm a little absent minded. I went to the local hardware store and they did not have a grade-8 bolt that matched the bolt's profile. The bolt is 7" long and I wanted to find a bolt that was 6". Unfortunately, they not only didn't have a 6", they didn't have the right thread count or profile. I have heard that you can't get the stockers unless you buy the whole spring setup. That would be a little pricey for a couple of bolts, if true.

 

You can only get front adjusters with the springs. I think the rears could be bought by themselves.

 

Yes, i did mean the rear. I assumed everyone just read minds, lol. I'm a little absent minded. I went to the local hardware store and they did not have a grade-8 bolt that matched the bolt's profile. The bolt is 7" long and I wanted to find a bolt that was 6". Unfortunately, they not only didn't have a 6", they didn't have the right thread count or profile. I have heard that you can't get the stockers unless you buy the whole spring setup. That would be a little pricey for a couple of bolts, if true.

 

Unless it's some kind of super hardware store you probably aren't going to find what you need at a typical Ace store. You can go to McMaster Carr and get what you want in a day or two. Order the bolts and matching nuts and washers as a unit.

Grade 8 bolts are strong, but they are also brittle. AN bolts are actually better, if you use a CRES bolt that would be fine too, but you are going to have to go to a proper aircraft bolting house to get those.

 

Well, I managed to get the washers for the rear and install them. I also removed and greased the front and rear sway bar bushings; glad I did because they were very dry. After letting the car sit over night and a quick highway drive, the car settled a lot. I went from being able to fit 3 fingers in between the rear tires last night, to barley 2 today. Even with the drop, the car is still higher than it was. I am going to remeasure the car again this afternoon at the front and rear jacking points to see if it remained at the necessary rake point.

 

Well, with all the hack job suspension settings that the car has been exposed to by the past owners;

I would carefully examine every part of the front and rear suspension for damage or wear.

Check the following before you do any sort of alignment.

- Figure your desired ride height and set it! Ride height and rake has a MAJOR effect on alignment. If you get an alignment and you change Ride height and Rake angle, you will need another alignment.

- Check front and rear wheel hub bearings for slop/lost motion. If any of the wheel hubs have any bearing slop, I would replace the set on that position 2 front, 2 rear.

- Steering rack mounting bushings. With the car on the ground, engine running, have someone move the steering wheel left and right 1/2 turn. See if the steering rack has excessive movement in the mounting bushings. Check the steering rack tie rods and see if there is any lost motion in the connection inside the steering rack or at the joint end.

I have CCW 19" 505a wheels with much wider Toyo Proxis tires.

My best wear/performance tire pressure settings COLD are:
28 Rear / 30 Front.

MAKE SURE that you are not bottoming out the shock on the shock bumper! That will seriously hinder suspension performance and handling!



Bill

 

Hey thanks, I appreciate all the extra info. I am curious on a couple of the things that you proposed. Is there a good test for the Wheel hub bearing?
Also, I have had several people suggest testing out how much the shocks travel, but I have not found a good test. Do you have or know where I can find a good test to test the shocks. As low as the car was, I came to determination that the car just didn't have any, lol. Even the little bit the car has been raised, the ride has improved a lot.