Rear Lowering Bolts

[RussMcB]

Is there anything special about these? Can I simply order the correct size and strength from a fastener vendor?

Does anyone know the length of the bolts offered in the aftermarket kits?

They say they'll lower the car .5" - 1". Does that mean they are 1" longer than the stock bolts?

Thanks in advance.

[Gunny]

Russ,

I lowered a '94 LT1 that I owned several years ago ... lowered the front by shaving the spacers off the spring then replacing with shims and the back using the bolts. Front is several degrees more difficult than the front but seemed worthwhile to me at the time.

Get grade 8 bolts/nuts from a reliable source ... this is from memory but I think I got 2" longer bolts and it seems like the nut was either a nyloc or all metal locking nut. I decided to add one more safety feature ... I cross drilled the end of the bolt and added a cotter pin. Sometime afterward I discovered the nuts had worked a little loose and the cotter pin kept them from going all the way off, so I recommend you consider using the cotter pins (or similar). I think some C4 owners used double nuts, but I believe the cotter pins to be a better solution.

If you lower the rear very much you may want to lower the front ... pm or email me if you're interested in pursuing this as I think I have a spare set of shims that I was planning to use on my 90Z (have since decided that I don't want to lower her).

I've not done it, much less owned or even driven one, but have you considered coil overs? that seems like a good way to go (didn't say cheap, just a possibility, tho).

On a different note ... the track you frequent ... is it west of Dawsonville? name? link? thanks.

[32valvesftw]

As the owner of a lowered 91Z I would advise you to think about the roads where you live. Mine is a little tricky to drive around town as I have to plan the route to avoid speed bumps, pot holes, manhole covers, etc....

[Karl]

Is there anything special about these? Can I simply order the correct size and strength from a fastener vendor?

Does anyone know the length of the bolts offered in the aftermarket kits?

They say they'll lower the car .5" - 1". Does that mean they are 1" longer than the stock bolts?

Thanks in advance.


10" for the mad kit.

[Karl]

I had 11" bolts from fastenall or some other bolt mfg before going to coil overs.

[RussMcB]

Thanks, guys. Great responses.

My car looks too high in the back. That's my main reason for lowering. Maybe it will improve handling, but I'm at-the-limit so infrequently I doubt I'd notice.

I think I'll leave the front as is. It looks fine, and I'm running 11" wheel widths in front so don't have a lot of clearance.

I'm buying a new (to me) race car soon, so I'll only be taking the ZR-1 to the track occasionally. Otherwise the coil overs would be worth considering.

Gunny, next month (March 13) I'll be at Atlanta Motorsports Park in Dawsonville, GA (home of Awesome Bill Elliot :-). It is a really fun track. Check it out: http://atlantamotorsportspark.com/about/circuits

[RussMcB]

Follow up:

Well, looking for a pair of generic bolts instead of buying the kit from a Corvette vendor was a waste of time. Not an easy size to find. After a bit of internet searching I found the bolt available from Fastenal for $35 each! :-)

I suppose they're out there, but I'll just buy the kit and forget it.

[randy ransome]

I bought 2, 12 inch, from my local Fastenal about a month ago for $16.39 tax and all.





:fahne:

[RussMcB]

I bought 2, 12 inch, from my local Fastenal about a month ago for $16.39 tax and all.Interesting. Do you still have the PN maybe?

Here's the only 9/16" 10" bolt I found on their site:
https://www.fastenal.com/products/details/14283?term=14283

[randy ransome]

The top Part No. is the Bolt. The bottom No. is the nut.

http://i576.photobucket.com/albums/ss210/randyransome/Screen%20Shot%202016-02-28%20at%208.31.01%20AM_zpsl3d00x9t.png (http://s576.photobucket.com/user/randyransome/media/Screen%20Shot%202016-02-28%20at%208.31.01%20AM_zpsl3d00x9t.png.html)





:proud:

[WVZR-1]

The top Part No. is the Bolt. The bottom No. is the nut.

http://i576.photobucket.com/albums/ss210/randyransome/Screen%20Shot%202016-02-28%20at%208.31.01%20AM_zpsl3d00x9t.png (http://s576.photobucket.com/user/randyransome/media/Screen%20Shot%202016-02-28%20at%208.31.01%20AM_zpsl3d00x9t.png.html)







I believe that what you bought were 5/8 and NOT 9/16 and based on the fact that the OE bolts are really M14-2 X 225 the 5/8 are maybe a stretch and to be considered a "no fit". I've never tried a 5/8 but I have 9/16 and I'd think (it's been many years) that the 5/8 won't work. 5/8 would explain maybe the lesser cost also.

Maybe someone has a new bushing and they can confirm the diameter of the bore. I don't have one new or used.

[randy ransome]

I believe that what you bought were 5/8 and NOT 9/16 and based on the fact that the OE bolts are really M14-2 X 225 the 5/8 are maybe a stretch and to be considered a "no fit". I've never tried a 5/8 but I have 9/16 and I'd think (it's been many years) that the 5/8 won't work. 5/8 would explain maybe the lesser cost also.

Maybe someone has a new bushing and they can confirm the diameter of the bore. I don't have one new or used.

Yes they are 5/8 but I got them to fit without much trouble.
5/8 has got to be stronger than 9/16.
Mine work fine.



:USFlag:

[WVZR-1]

Yes they are 5/8 but I got them to fit without much trouble.
5/8 has got to be stronger than 9/16.
Mine work fine.


"without much trouble" - tells me NO FIT - also I believe the first/only time I've seen a "USS/coarse" substitution - I don't get it

[randy ransome]

"without much trouble" - tells me NO FIT - also I believe the first/only time I've seen a "USS/coarse" substitution - I don't get it

I was only trying to give you the information on the bolts I used.

You do what you want with that info.

:USFlag:

[IMZZ]

I tried the Fastenal route too and they could not find a bolt that size. They took my number and called me back when they found it and quoted me about $35 a bolt.

I ordered the kit from a Corvette shop and they just notified me that they are out of stock.:(

Anybody else just lower the rear. I don't want to go too low and drag on everything but the rear fender gap is just too wide.

[Mystic ZR-1]

Wouldn't lowering just the rear screw up the
balance/handling of the car?

[RussMcB]

Good responses. It's good to know the original size is 14mm, and that 5/8" and 9/16" are options.

I went ahead and ordered from a Corvette vendor. I never found a significantly less expensive alternative. Even the Fastenal PN above appeared as $15 apiece on their web site. I'm sure a more reasonable price is out there, just not worth the effort to find it.

Now I'm thinking about the next steps ...

I like Gunny's idea about the cotter pin. Good safety measure. I'm also leaning towards jam nuts. I *think* that will give a little more adjustability. Maybe even help with cross weights? I'm hoping to find that out in a week or two.

Wouldn't lowering just the rear screw up the
balance/handling of the car?I haven't come across any posts saying it screws up geometry or roll centers. Just not to go too far because the bump stops are abrupt.

[RussMcB]

I tried the Fastenal route too and they could not find a bolt that size. They took my number and called me back when they found it and quoted me about $35 a bolt.

I ordered the kit from a Corvette shop and they just notified me that they are out of stock.:(

Anybody else just lower the rear. I don't want to go too low and drag on everything but the rear fender gap is just too wide.Ken, I ordered from these guys (and they say they are in stock):

http://www.vbandp.com/component/virtuemart/?page=shop.browse&category_id=114&Itemid=1

I'm planning to lower only my rear. Like yours, mine is too high compared to the front. Front seems perfect, rear has big gaps between the Goodyears and fender lips. Might be because I'm not running a spare tire or original heavy exhaust (but it was too high even before I made those changes).

[IMZZ]

Ken, I ordered from these guys (and they say they are in stock)

Thanks for the info. I had already ordered them from the other place so I guess I'll just wait for them.

[Hib Halverson]

With respect to rear trim height, the first thing to do is get under the car and inspect the rear spring mount.

There may be metal "shims" either above or below the rear spring. To have the lowest ride height with the most suspension travel, the first thing to do is make sure all the shims which are there are below the rear spring. You don't want any above the spring and you don't want a mix of shims above and below. You want them all below the spring. Do not remove the shims. Just make sure they're all on the bottom.

As for rear spring bolts, keep in mind that long, grade-8 bolts from generic bolt suppliers (Fastenal, Granger and etc) may lack one important feature that some of the C4-specific lowering kits sold by Zip Products and other Vette parts vendors have and that is the bolt being threaded for a uncommonly long distance. Having 3 or 4 inches of threading on the bolt gives you trim height adjustabillity which you can't get with a bolt having an inch or an inch-and-a-half of thread.

With C4, suspension travel is limited to begin with on those cars. For street use, a little lowering can be desireable but a lot of lowering is going to make for two problems 1) lack of rear ground clearance and 2) lack of adequate suspension travel at the rear.

Finally, I have found with "Barney," my '95, that having proper adjustable rear spring bolts is really nice when the car is loaded up to the max with two people and cargo for a long road trip. For many years my standard procedure before the Wife and I load up for a long trip is to use the spring bolts' adjustability to raise the rear of the car half an inch or so. Once we, all our gear and a fuill tank of fuel are in the car, it will sit level. Not only does that insure adequate suspension travel at the rear (and the ride comfort which comes with that) during the trip but, if the trip involves night driving, it's preserves headlight aim.