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Old 12-04-2013, 09:44 AM   #1
VThokies
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Default How to lower the C7?

For those that have done this on their own, can you provide some basic instructions on lowering with the factory bolts?

I tried adjusting mine last night. Pulled the front wheels off and could get to the head of the 10mm adjusting bolt, but it would only turn about half a turn before getting real tight. The wrench did not feel like it had a very good fit on the bolt, so I was concerned about bearing down on it until I learned a little more here first. Should the car be jacked up or sitting on the suspension? Or does it matter?

Any insight would be appreciated, Thanks.
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Old 12-04-2013, 10:10 AM   #2
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Everyone says it's the same process as the C6 (I am waiting on my car to be built). Should be able to find write ups on it easily, but here are 2 videos.



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Old 12-04-2013, 10:38 AM   #3
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Thank you. That is very simple.
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Old 12-04-2013, 10:39 AM   #4
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You must use a bottle jack as the video shows to get the weight off the bushing/lowering bolt. Then it will turn with little effort. It's easy just as the video shows. No need to remove the wheels but I did drive each corner onto a ramp for more working space and turned the front wheels. I accessed both front and rear from behind the wheel. Use a ratching box end wrench for easier access to the bolt. Took about one hour for all four corners. I got 3/4" in front and 5/8" in back. Makes a big difference in the look.

You will be partially under the car and the spring will have much stored energy... BE SAFE!

Last edited by 66dreams; 12-04-2013 at 10:47 AM.
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Old 12-04-2013, 10:43 AM   #5
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You can also use a floor jack and jackstand. Jack up the corner you want to adjust using a jacking puck. I then used a jackstand and a piece of rubber cushion. Put the jackstand under the leaf spring, and slowly let the floor jack down so that the weight of the car is pressing up on the spring. This allows the ride hieght screw to be turned.

I didn't have a bottle jack, so this is what I used.
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Old 12-04-2013, 10:53 AM   #6
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I don't understand why people are so into lowering their car. The maintenance manual has ride height dimensions that should be followed. This dimension provides for proper suspension travel and in turn effects the car's handling. Most here worry about performance, yet compromise it for car's looks? Scraping on slight road imperfections/dips doesn't enhance my motoring experience. My car will remain at the ride height as stated in the manufactures maintenance instructions.
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Old 12-04-2013, 10:57 AM   #7
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Quote:
Originally Posted by Larry/car View Post
My car will remain at the ride height as stated in the manufactures maintenance instructions.
That's your choice, and you're clearly free to choose it.

There's also a reason that the plastic air dam pieces are cheap and replaceable. Even at stock height they scrape on many things around here, causing no damage elsewhere.
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Old 12-04-2013, 10:58 AM   #8
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Quote:
Originally Posted by Larry/car View Post
I don't understand why people are so into lowering their car. The maintenance manual has ride height dimensions that should be followed. This dimension provides for proper suspension travel and in turn effects the car's handling. Most here worry about performance, yet compromise it for car's looks? Scraping on slight road imperfections/dips doesn't enhance my motoring experience. My car will remain at the ride height as stated in the manufactures maintenance instructions.
Good for you.
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Old 12-04-2013, 11:08 AM   #9
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Our C7's handling was greatly improved after lowering on the factory bolts. Virtually all body roll was eliminated. For the OP, just make sure to get a good alignment done on the car afterwards. Most vehicles are out of alignment by the time they reach the dealerships anyway, but angles may also change with the drop, and an alignment is much cheaper than replacing tires earlier than expected!
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Old 12-04-2013, 12:33 PM   #10
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Not sure if the videos show it (I can't access You Tube through my work laptop while on the company network), but when you're jacking on the leaf spring, make sure to put a towel, rag, or something between the jack and the spring. You need to make sure that you don't nick the leaf spring because damaging the epoxy surface can cause moisture to wick into the fiberglass and cause delamination.
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Old 12-04-2013, 12:38 PM   #11
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Quote:
Originally Posted by Larry/car View Post
I don't understand why people are so into lowering their car. The maintenance manual has ride height dimensions that should be followed. This dimension provides for proper suspension travel and in turn effects the car's handling. Most here worry about performance, yet compromise it for car's looks? Scraping on slight road imperfections/dips doesn't enhance my motoring experience. My car will remain at the ride height as stated in the manufactures maintenance instructions.
It's my understanding that as long as the stock bolts are used the car stays within specs anticipated by GM.

Last edited by 4-Sho; 12-04-2013 at 01:23 PM.
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Old 12-04-2013, 12:50 PM   #12
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Did any of you simply have the dealer do it for you prior to you taking possession? Would seem like the easy thing to do considering that you would need the car to get alignment as well no?
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Old 12-04-2013, 12:53 PM   #13
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[QUOTE=David@Vengeance;1585589870]Our C7's handling was greatly improved after lowering on the factory bolts. Virtually all body roll was eliminated.

Has handling actually improved or are you feeling the reduced suspension travel actually masking the fact that handling has actually degraded somewhat. Has anyone actually performed a before and after capability check on max lateral G force capable after lowering. Also how does the lowered suspension affect stopping distance, acceleration, active handling etc. Maybe it is my aviation maintenance background, in aviation you don't just randomly make changes. Engineering made a determination as to best settings for a good compromise in handling insuring max safety. We need engineering to voice concerns. I'll add one other concern, if in a fatal accident and lawyers discover that the suspension was adjusted at random, what kind of legal outcome will that be? Lawyers look for out of the box items to support their case. Is there a statement in the maintenance manual stating the car remains within specifications if lowering with stock bolts?

Last edited by Larry/car; 12-04-2013 at 12:59 PM.
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Old 12-04-2013, 12:59 PM   #14
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I'm still waiting for delivery so I can't say with complete certainty, but from what I have read there are two conflicting versions of how to lower the rear. One is as shown in this thread, and the other is that because the spring sits below the control arm the adjusting screw is turned in a clockwise direction, extending the bolt toward the spring and causing the suspension to go higher into the body. In effect, the rear is lowered. If so, there is a design change in the rear suspension from C6 to C7. Maybe someone with first hand experience can address this issue and set the record straight. There's no difference in how to make the front suspension adjustment.
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Old 12-04-2013, 01:10 PM   #15
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[QUOTE=Larry/car;1585590736]
Quote:
Originally Posted by David@Vengeance View Post
Our C7's handling was greatly improved after lowering on the factory bolts. Virtually all body roll was eliminated.

Has handling actually improved or are you feeling the reduced suspension travel actually masking the fact that handling has actually degraded somewhat. Has anyone actually performed a before and after capability check on max lateral G force capable after lowering. Also how does the lowered suspension affect stopping distance, acceleration, active handling etc. Maybe it is my aviation maintenance background, in aviation you don't just randomly make changes. Engineering made a determination as to best settings for a good compromise in handling insuring max safety. We need engineering to voice concerns. I'll add one other concern, if in a fatal accident and lawyers discover that the suspension was adjusted at random, what kind of legal outcome will that be? Lawyers look for out of the box items to support their case. Is there a statement in the maintenance manual stating the car remains within specifications if lowering with stock bolts?
I completely understand where you are coming from, and you bring up some good points, but the biggest statement to everything you have stated is that GM designed the suspension to have adjustable ride height. If it wasn't meant to be adjusted, then they wouldn't have engineered it that way.
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Old 12-04-2013, 02:30 PM   #16
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The lowering bolts are a spring pre-load adjustment.

That means that the suspension gets softer when the car is lowered and stiffer when the car is raised. So that's actually a load carrying adjustment.

Race cars use spring pre-load for fine tuning of corner weighting or for oval-track wedge adjustments.

The race car might be both too high and too stiff but often the suspension needs to be stiffer when lowered to avoid bottoming.

And so this is why coilovers are popular. Some coilovers are simply a shorter shock body than OEM or Replacement and then have spring pre-load adjustments while other coilovers have a shock body length adjustment and a spring pre-load adjustment. Also, catalogs of springs for coilovers can be found as straight or tapered, inner diameter, rate, and length
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Last edited by B Stead; 12-04-2013 at 02:40 PM.
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Old 12-04-2013, 03:28 PM   #17
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Quote:
Originally Posted by B Stead View Post
The lowering bolts are a spring pre-load adjustment.

That means that the suspension gets softer when the car is lowered and stiffer when the car is raised. So that's actually a load carrying adjustment.

Race cars use spring pre-load for fine tuning of corner weighting or for oval-track wedge adjustments.

The race car might be both too high and too stiff but often the suspension needs to be stiffer when lowered to avoid bottoming.
If I understand correctly this means lowering the car on the stock bolts will have an impact on handling? My biggest concern would be an increase in over or under steer. Are all C7's set to the same ride height at the factory or have there been variations?
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Old 12-04-2013, 03:30 PM   #18
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Quote:
Originally Posted by Larry/car View Post

Has handling actually improved or are you feeling the reduced suspension travel actually masking the fact that handling has actually degraded somewhat. Has anyone actually performed a before and after capability check on max lateral G force capable after lowering. Also how does the lowered suspension affect stopping distance, acceleration, active handling etc. Maybe it is my aviation maintenance background, in aviation you don't just randomly make changes. Engineering made a determination as to best settings for a good compromise in handling insuring max safety. We need engineering to voice concerns. I'll add one other concern, if in a fatal accident and lawyers discover that the suspension was adjusted at random, what kind of legal outcome will that be? Lawyers look for out of the box items to support their case. Is there a statement in the maintenance manual stating the car remains within specifications if lowering with stock bolts?
Please...we are talking about lowering the car because it looks better...not running Lemans race. The amount of travel lost in the shocks from lowering on stock bolts is not significant enough to make a damn bit of noticeable difference whether it be negative or positive.

Last edited by LFZ; 12-04-2013 at 03:36 PM.
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Old 12-04-2013, 03:34 PM   #19
Hot Rod Todd
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GM might have a ride height specificaiton, but obviously they have trouble following it. Some cars look normal, while others look like they are way too high. Some people are looking to slam their cars to make them look cool, while others like me just want it to look more normal and not be the highest Corvette in the parking lot.

I noticed different ride heights in C6's, but it does not seem to vary as much as it does on the C7.
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Old 12-04-2013, 04:04 PM   #20
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Quote:
Originally Posted by blaine View Post
If I understand correctly this means lowering the car on the stock bolts will have an impact on handling? My biggest concern would be an increase in over or under steer. Are all C7's set to the same ride height at the factory or have there been variations?
The lowered car is a lower center of gravity. Then the lower center of gravity is less load transfer. But now the car can go faster in a curve and that tends to replace the previous amount of load transfer. In other words the previous amount of load transfer now tends to occur at higher G-forces. At lower speeds the car will just feel less stressed in a curve.

The softer suspension will be less traction on the turn-in without a change in peak traction at mid-corner. That turn-in traction can even be felt with moderate accelerating from a stop while turning. The softer suspension will be a slower responding car but it is possible for the car to be too much and that also related to tires.

If the front suspension is softened more than the rear then that is an increase in oversteer. If the rear suspension is softened more than the front then that is an increase in understeer.

The factory probably corner weights each car (with the spring pre-load) to make up for chassis and suspension imperfections and that while attempting ride height and rake
.

Last edited by B Stead; 12-04-2013 at 04:28 PM.
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Old 12-04-2013, 04:04 PM
 
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