familyman's C7

Does anyone know what the thread pitch is on the factory lowering bolts? Knowing this seems like it would eliminate the guess work of how far I am lowering the car.

haljensen

Will still be some math involved since the bolts aren't at the end of the spring. The bolt is at the near the middle of the wheel arc, not at the end of the arc. It's not like the old 2" lowering blocks gave you 2" of lowered height.

You'll need to measure from the pivot point of the spring to the bolt, then from the pivot of the spring to the bushing at the wheel, then calculate how much xx movement of the bolt will give at the wheel.

timd38

Sorry, I don't understand what the thread pitch has to do with it.

haljensen

He's probably thinking that if 1 turn = 1/10 of an inch then 10 turns = an inch.


Like 1/4 X 20 = 20 turns per inch?

timd38

Good luck with all the calculations. All I know is that you can drop the front more than the rears and most lowering bolts are junk.

M8 1.5 is what I think they are.

familyman's C7

Yes, that is what I was thinking. I was wrong though, thanks for the explanation.

Just Enough

I think the thread is a 14x2 which would be about .078 per turn (2/25.4=.079). With the placement of the adjuster on the lower a-arm at about 80-90% of the swing distance you would get about .09-.100 inches of wheel movement per turn once the car has been driven and the pad settles. Hope that helps

familyman's C7

Thanks for the further explanation. I'm looking to drop it about 1" so 10 turns should do it +/-.

haljensen

Just remember to turn both sides the same number of turns to keep the corner balance correct. Get an alignment after the lowering.

timd38

Not sure if you have an inch or not on the rears. The fronts should be ok.

BEZ06

Take a look at the Service Manual for that info:




You can see that the Service Manual says one turn of the bolt will give you 2mm or 0.079 inches of height change.

The Z height discussed above is the front of the car, but the adjustment of the D height in the rear has the same 2mm per turn spec.

Therefore, 3 turns is slightly less than 1/4 inch, and 4 turns is about 5/16 inch.

Like Just Enough said in his post above, you may get a little more movement if you measure out at the fender.

Forum member Gearhead Jim says in an old post in another thread: "1 turn of the bolt = about 1/4" change out at the fender lip, initially.
After a week and 500 miles of driving, the change had decreased to about 1/8". Do an alignment at this time."

He makes a good recommendation to get it aligned after you change ride height.

Bob

riverrat68

Is it clockwise to raise and counter clockwise to lower? I think the previous owner lowered mine. I want to raise it back to stock height.

Gearhead Jim

After measuring mine several times and then adjusting and measuring several times again, I found that one turn of the bolt will lower the fender (measured at the top of the wheel well arch) about 1/8", after the car has settled. You may need to drive several hundred miles for the settling to finish, then get an alignment (a whole 'nuther set of numbers!)

One inch is a lot of lowering on the stock bolts, and you want to maintain approximately the front-rear relationship for aero reasons.

Many trackheads say that lowering a little is helpful, lowering a lot isn't.

riverrat68

I think whomever lowered mine, lowered it too much. I think I read to raise it, turn bolt clockwise.....I removed the wheel, but I cannot turn the bolt. It is able to go counter clockwise about a quarter of a turn, I can turn it back. but that is all It will go. Am I doing it wrong?
Jer

BEZ06

Did you take pressure off the pad of the bolt before trying to turn it??

The bolt screws in up through the leafspring, and the rubber pad bonded onto the head of the bolt sits on a web of the lower A-arm:




In order to turn the bolt you need to lift the leafspring so the rubber pad is up off the A-arm, then it should turn easily.

In the picture above, after raising the car by jacking up on the frame, I used a bottle jack to raise the leafspring to relieve the pressure from the bolt.

Bob

riverrat68

Thenk you. I did not relieve the pressure. I was thinking of that , but talked myself out of it. Do you know of a video out there that show the whole process? I don't have a bottle jake right now, but I will by 10am on Monday.
Thanks and Happy Easter.
Jerry
River Ratt

panthermfg1 A

No.
20 represents the #of threads per inch so take 1.0” divide by 20 = .050 thousands of an inch so one complete turn of bolt would either raise or lower bolt by .050 of an inch ask any machinist

torquetube

And 0.050"/turn x 20 turns = 1 inch. Which is what he said.

A single-start 20TPI bolt like an ordinary UNC ¼-20 takes 20 complete turns to move an inch.

Let's not resurrect an old thread to correct somebody who wasn't wrong in the first place.

touring2

and there is a GM tool to lift the spring. it's about 40 bucks on fleabay. I am using mine right now KENT MOORE TOOL J-42743 CORVETTE TRIM HEIGHT ADJUSTMENT TOOL