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I had the same experience going from a steel spring to 355# composite. I had Bilstein HD shocks front and rear and with the steel spring the HD's were perfect. But with the composite those same HD shocks were very mushy. It bottomed out a few times on my test drive and goosing it in turns made the rear wobble and squirm. I switched to the Bilstein Sports on the rear only and that fixed it 100%. No bottoming out and a stable feeling no matter what driving I did.
looks like I've been thrown in this discussion too. purchased a restomod from a fellow and he put on a a trw 602-103 spring, 340#
also has bilsteins front and rear but i haven't checked exactly what models
tires are 245/45/18 front and 255/45/18 rear
i noticed the 4" higher rear when trying to get this thing on quickjacks, the front sits at about 26.5 and the rear at 30.5, so i need to drop the rear by 4 inches to match the front
i got some 10.5" extended c4 bolts i haven't installed yet, but my plan is to install them, get the nuts to 9" and check the ride height. IF i can get to 28" in the rear i'll be happy with that, and cut off the rest of the bolt
looks like I've been thrown in this discussion too. purchased a restomod from a fellow and he put on a a trw 602-103 spring, 340#
also has bilsteins front and rear but i haven't checked exactly what models
tires are 245/45/18 front and 255/45/18 rear
i noticed the 4" higher rear when trying to get this thing on quickjacks, the front sits at about 26.5 and the rear at 30.5, so i need to drop the rear by 4 inches to match the front
i got some 10.5" extended c4 bolts i haven't installed yet, but my plan is to install them, get the nuts to 9" and check the ride height. IF i can get to 28" in the rear i'll be happy with that, and cut off the rest of the bolt
With 18" wheels you have a lot more room to work with longer bolts. I'd still throw that TRW spring in the bin and get a low-arch spring from Van Steel, but you may be able to get the result you want without putting the tires in danger from being cut by the spring/bolt ends.
i'll be keeping the bolts within the rim diameter, but there's less tire deformation when you have way less sidewall than the 15s, so i'm less concerned about it.
i mean, a low arch spring sounds great but from what i hear the trw spring works well aside from this one issue, and it's $489 i can spend on other things in the car, heh
there's also the matter of my front being shockingly low, 26.5 when other folks are like 27.5 or 28. Normally i'm all for low but past a certain point rough roads get really impractical. I may need to get better front springs (i don't know exactly what springs the PO used)
Last edited by jokeitch; Jun 22, 2020 at 02:44 AM.
On the rear it is a one to ratio. 1 inch longer bolt gives you one inch drop. Just make sure the end of the spring stays within the rim. The sidewalls move an amazing amount in cornering and can cause a blowout if the spring is too close. I have seen the sidewalls move over 2 inches sideways in a a video!
On the front that is so low the PO must have cut the springs.
Last edited by leigh1322; Jun 22, 2020 at 09:45 AM.
the entire bolt is far too long, but if i chop just below the nut, it should be ok
again the distance from the top of the bolt to the bottom of the locknut is 9"
however i didn't get much drop. This is right after putting the car down, but after pushing on the rear a bunch of times to settle it out, it only got to 30 inches flat, so i lost MAYBE an inch of height by doing this
should i expect to lose another 2 inches at least by driving the car around? or is this how low it's going to get
by the way the rear shocks are quite bouncy unfortunately, it's Bilstein B6 performance series front and rear, but maybe i need something stiffer in the back
If you cut an inch off the bolt and remove a good portion of the threads, what happens when you need to remove the spring or replace the bushings.
Will you have enough thread left on the bolt to relax the spring to safely remove the bolt?
Is the nut lower than the bottom lip of the wheel?
What happens if you have a flat or blowout at 65 mph?
Why not replace that TRW spring with a Van Steel and use a 6.5” or 8” bolt, or would a 12” bolt would get you to the proper ride height?
not in a position to drop $500 on a vansteel spring unfortunately, and if i do any suspension changes i'm going with the vansteel coilovers set instead of the leaf spring
when replacing the spring the process is to use a jack to push the spring up a bit so you can take the nut off, so that should be fine, if anything i'll be easier
the nut is just inside the rim of the wheel so if there's a blowout, it won't dig into the ground
theoretically it is a 1;1 ratio drop. you would think you lower both spring ends 1 inch the whole car will follow. but it seems to be more 2 inch of bolt length gives 1 inch of drop.
No it's not. The trailing arm is suspended from two points; front (TA bushing) and rear (spring). You're only moving the rear suspension point up. The drop at the hub will be at whatever ratio the hub is located between front and rear suspension points. Eyeballing it's about 2/3 towards the rear point.
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Agree on the drop not being 1:1...I was getting about 50% on the wheel to body change for a bolt length change. Might want to keep the nut from working out somehow. Lock nut or drill a hole at the end of the bolt to put a C. pin in like the stock version.
i'll be keeping the bolts within the rim diameter, but there's less tire deformation when you have way less sidewall than the 15s, so i'm less concerned about it.
i mean, a low arch spring sounds great but from what i hear the trw spring works well aside from this one issue, and it's $489 i can spend on other things in the car, heh
there's also the matter of my front being shockingly low, 26.5 when other folks are like 27.5 or 28. Normally i'm all for low but past a certain point rough roads get really impractical. I may need to get better front springs (i don't know exactly what springs the PO used)
If you raise the front a inch(new springs or a spacer that goes under your current spring) the back will come down. I know it doesn't make sense but it worked on my car when I had the front too low.
The two trailing arm measurements are 16.8 and 20.0 inches. So for a 1" spring bolt drop you should get a 0.85" car drop.
Another thing, if all you did was "sit it down" off the jacks it will sit really high due to the camber changes. All you need to do is roll the car back and forth a few feet and the sideways tire scrub should go away and the car will settle back down.
Third thing if you had compressed spring cup bushings and put in new ones that actually can raise the car. Not sure how much but could easily be an inch I bet. Poly ones might never squish but the rubber ones should lower some after a few hundred miles. What kind did you put in? As I look at post 184 & 191 they look much thicker in the more recent post.
ah, i haven't tried rolling it back and forth yet, need to do that
i replaced the bushings (and the washers, and the retaining nuts) with the ones that came with the bolt kit https://www.corvettemods.com/C4-Corv...le_p_6690.html
since the new bushings seemed identical to the ones i was replacing but the ones i replaced were somewhat squished by now
