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Some careful measuring, multiple times, showed that replacing my Z51 shocks with base shocks; lowered the car 5/16" in the front and 4/16" in the back. That's typical, apparently due to reduced gas pressure in non-Z51 shocks.
I could have the car raised back up by that amount and it would be "close enough", but...
Considering how much the alignments varied when coming out of the factory, the correctness of the original trim height is also questionable. I'd like to get the height set according to the specs in the Service Manual, but it ain't easy. You can't just measure fender height or something like that, because there are other production tolerances involved.
The official method involves installing the "J 42854 Trim Height Measuring Gage" on part of the suspension, then measuring the gap between the gage and some other part.
My dealer doesn't have the J 42854 and obviously has no experience in using it. Does anyone know of a dealer in the Chicago area who actually has this gage and knows how to use it?
Or is there another, easier, way of measuring to get the same specs?
Fagitaboudit!!! That stupid tool is nothing more than a very expensive measuring device - nothing more than a sort of caliper device. You don't need it to take measurements.
The front ride height measurement is the "Z Height", and the rear measurement is the "D Height".
The measurements of those distances is from the bottom of the lowest part of the ball joint to the center of the mounting bolt on the front side of the lower control arm. Below are the specs from my 2010 manual, which are actually about 2mm higher in the front, and 7mm lower in the rear than my 2006 manual - so they've reduced the rake a bit over the years.
The Z height specs are:
Base and F55: 48 mm (tolerance: +/- 6.4 mm)
Z51: 47 mm (tolerance: +/- 6.4 mm)
Z06 and ZR1: 43 mm (tolerance: +/- 6.4 mm)
The D height specs are:
Base and F55: 115 mm (tolerance: +/- 6.4 mm)
Z51: 114 mm (tolerance: +/- 6.4 mm)
Z06 and ZR1: 102 mm (tolerance: +/- 6.4 mm)
The tech setting the height is supposed to bounce the suspension up and down a couple times and take the measurement - do that several times and take the average to see if it's within the spec.
So.....there's absolutely no need for some dumb tool - just use a ruler or tape measure.
And.....as I mentioned above, the specs have changed quite a bit over he years and there's a 1/4 inch tolerance, so the actual trim height is not something to get real worried about. I say just set it to what looks good to you and works with the speed bumps, driveway dips, and general road conditions you have to deal with.
Many race cars are lowered quite a bit to get the CG low and the owners are more concerned about corner weighting the car correctly than rake - they'll use aero components to get the stability they want.
dont over complicate something so simple.
just measure the four corners. get it to sit where YOU want it to then have it aligned.
if gm cant get the cars out their door set to their specs then they obvisouly arent that important. to many of you guys think vette are some special ultra high level science mobile. its just a car same as a cobalt or camaro just a lil faster.
dont stress trying to get it dialed in to the .001'' just adjust the ride height to where it makes you happy and suits your needs. a 'good' alignment shop can set it up so everything will be perfect.
i lowered mine all the way in the front on stock bolts and bottomed out in rear on lowering bolts. then put it on weight scales messed with it a lil to get weight balance where i wanted it. then alignment shop. tires are wearing perfectly handles better than stock, rides great, looks better.
...
I say just set it to what looks good to you and works with the speed bumps, driveway dips, and general road conditions you have to deal with.
...
Geez, if I set it that way then I'll be three feet in the air like a monster truck.
Seriously, that's a big help. Thanks.
Some time soon I'll get it up in the air and see if I actually have the ability to take measurements that way.
My 2009 specs are the same as your 2010, it's interesting that they changed (the rake) over the years. Appearance, obstacle clearance, suspension travel, aero,...???
Yeah, it's curious that they have changed the specs - it's not much, but it raises the front and lowers the rear so the rake is changed a pretty good amount.
I don't know why they did it, but I bet it's for the same reason most of us lower the car - for cosmetic purposes. My 2005 Coupe really looked stooopid until I lowered it - the azz end was sticking so far up in the air it looked totally ridiculous.
Here's info from my 2006 Service Manual and you can compare it to the specs from the 2010 SM in my previous post:
The Z height specs are:
Base and F55: 46 mm (tolerance: 39.6-52.4 mm)
Z51: 45 mm (tolerance: 38.6-51.4 mm)
Z06: 41 mm (tolerance: 35.6-47.4 mm)
The D height specs are:
Base and F55: 122 mm (tolerance: 115.6-128.4 mm)
Z51: 121 mm (tolerance: 114.6-127.4 mm)
Z06: 109 mm (tolerance: 102.6-115.4 mm)
BTW, for anyone wanting to raise/lower the car, the SM says that one turn of the height adjusting bolts is equal to 2mm (.079 inches) of trim height, so 3 turns equals just under 1/4 inch.
Today we had the car up on a rack and I considered checking the front trim height, planning to use just a level and ruler(s).
The drawing on page 16-72 of my Serivice Manual makes it look like you can just lay the level on the bottom of the ball joint and aim it toward the control arm bolt, then measure. But the bottom of the lower arm is curved and hangs down below the ball joint, that looks like it blocks the level.
I had other things to do and didn't investigate any further.
If we angle the level forward so it ends up under the front of the control arm bolt, will that miss the curved portion of the arm near the ball joint?
Today we had the car up on a rack and I considered checking the front trim height, planning to use just a level and ruler(s).
The drawing on page 16-72 of my Serivice Manual makes it look like you can just lay the level on the bottom of the ball joint and aim it toward the control arm bolt, then measure. But the bottom of the lower arm is curved and hangs down below the ball joint, that looks like it blocks the level.
I had other things to do and didn't investigate any further.
If we angle the level forward so it ends up under the front of the control arm bolt, will that miss the curved portion of the arm near the ball joint?
Or is there another secret?
My son & I discovered the same as you. We tried to measure but the indentation causes measuring problems. The chart in the manual reflects the distance from the control arm bolt which is "indented". The special tool fits in the "indentations", has a level built in and the other end attaches to the upper part of the control arm bolt on the other end. The tool has little tics that are mm and thus you get a reasonably accurate trim adjustment height.
EDIT: The ~$250 list price was way more than I was willing to pay for this tool. But when your link showed me one for $37, brand new in the box from a reputable seller, I ordered it today.
I'll post the results in a couple of weeks after trying it.
Last edited by Gearhead Jim; 08-13-2011 at 09:03 PM.
EDIT: The ~$250 list price was way more than I was willing to pay for this tool. But when your link showed me one for $37, brand new in the box from a reputable seller, I ordered it today.
I'll post the results in a couple of weeks after trying it.
EDIT: The ~$250 list price was way more than I was willing to pay for this tool. But when your link showed me one for $37, brand new in the box from a reputable seller, I ordered it today.
I'll post the results in a couple of weeks after trying it.
Originally Posted by Buzartiano
Old thread but did the tool work?
Shame on me for not updating my post.
The tool "works", but...
The car must be up in the air on a level alignment rack.
It took two of us to use it properly, one holding and one measuring.
Part of the tool fits onto a bolt on the front suspension, and it fits on kinda crooked. It appears that's the only way to do it, so I guess it's ok.
Since this thread was started, GM finally came out with some official measurements using the wheel well lips on the fenders. Unless the car has been crashed and repaired, I think the fender measurements are just as good as the under-body measurement using the tool.
As previously mentioned, GM changed the trim height numbers over the years and later cars are supposed to have different front-rear "rake" than the early ones. I'm using the P-height and R-height numbers from the 2010 chart below, seems to work well. Measurements are based on full tank of gas but no people or luggage. Presumed to be with new tires, so every 1/32" of tire wear will lower your numbers by that amount.
Lift the car and jack the wheels slightly so the adjustment bolts are not under load. If the bolts are stuck, spray them with PB Blaster and tap gently a few times. If they don't come loose, re-spray and drive the car for a couple of days, try again.
BEZ06 pointed out that it takes about 3 turns of the bolt to change the trim height by 1/4", BUT...
The bolts and trim height are well inside of the fender lips, so each turn of the bolt will raise/lower the fender lip by about 1/8". After doing the adjustment, the car will be way up in the air like a monster truck, but will settle down to the 1/8" per turn value after being driven a couple of hundred miles. Once you get it right, time for an alignment.
Last edited by Gearhead Jim; 06-09-2016 at 08:41 PM.
Thanks for the update. I've only measured my front fender arch but it's at 25 & 1/16" which is over 2" lower than the chart. No wonder I can't drive over a crack in the pavement.
My 08 with Z51 option sits exactly 1" lower both front and rear than the measurements listed in the chart. I am the second owner so I don't know if my car has been lowered or not, but I like the way it looks at it's present height.
Here is another way.....
Get a paint stick cut two short pieces. Go to the correct point on frame. Slide them until they r touching the frame and floor. Slide out measure.
End of story.
Robin
Do you have numbers for what the measurements should be? AFAIK, GM does not publish any specs for that, some racing teams do but their numbers may not applicable for a street-driven car.
Thanks for the update. I've only measured my front fender arch but it's at 25 & 1/16" which is over 2" lower than the chart. No wonder I can't drive over a crack in the pavement.
I had a similar problem. When I checked it with a tape measure, it was pretty low. Car scraped on normal roads. Had a "Good" dealer set it at the spec posted and all is will.
03-06-2015, 03:32 PM
Measuring Ride Height ("Trim Height")
