If you run into clearance issues with the longer bolts......you can always install them upside down to gain an inch or better of clearance around the rim area.
I think removing a spacer and going to a 10" bolt cut to 9" flipped upside down would save the situation. It wouldn't hurt anything......but I would get the alignment checked afterward.
I think you could get an inch and a half doing this........just a thought. Is it the right way? Not really.......but I can't see what it would hurt

Jebby

 

Interesting. @Jebbysan, removing a spacer... do you mean the rubber bushing? The nut would rest on the washer and that would rest directly on metal
of trailing arm ?

I have asked Zip to take their product back. If they don’t, I suppose I will try longer bolts in the meantime to see if that he an affect on the vibration. Apparently some here have been living, even quite well, with TRW spring and longer bolts.

 

No......the spacer in the center that mounts the spring. Flipping the bolt will give a little clearance at the bottom as a bolt head is not as big as a nut/thread.

Jebby

 

Hopefully this setup will solve your problems.

I too had the TRW spring back in the day, thus why I mentioned it. With that setup, I had the same issue and ended up returning and ordering a Vette Brakes spring.

 

Wow there is a lot of bad information here but some good. First off let's clear up the TRW spring. There is no TRW spring, they do not make them anymore and when they did, it was the one you wanted. They were great springs when they were available and every one selling Corvette parts used them. I for one was not a huge fan of the VB&P Spring. We sold them, but I preferred the TRW. Muskegon makes the spring now that everyone is calling a TRW spring because it mimics the shape of the TRW spring. TRW is a tier 1 manufacture and the reason that spring was made was because of the 81 Corvette went to a fiberglass spring, that fiberglass spring. So lets address the "bad" fiberglass vs steel because that explanation was way wrong. When a steel spring breaks, it drops you on the ground period. When a fiberglass one breaks, sometimes it will and most of the time it will not. They were designed and the better replacement for the steel and it is why they were used as the front and rear springs in the C4. Yes there may be a current team running a steel spring, but they are running on 50+ year old technology and not better.
So here is the issue you are having, for one did you change your front springs? I will assume no, because that is usually part of the issue. So the front springs have sagged a little, they look better when they do, but they have sagged. Now you install a new spring in the rear and maybe even a different weight spring. GM used different size outer bolts depending on what spring the car had. You will have to do the same, that is what will control your ride height. You are also running a 60 series tire which is shorter than the original F70-15 so you now have more room in between the fender and tire, another issue but it is not created by the spring or the suspension. Half shafts. So if you run a longer bolt in the back, it will lower your car and eliminate the space between the flare and the tire. It will also level out your halfshafts. It will fix all of the issue because that is what the problem is. If you want to send the spring back to us that is fine, there is nothing wrong with it but we are not going to pick up the shipping bill for it, that would be on you since there is actually nothing wrong with the spring.
You can use the Vansteel spring, they are now having their own spring made and there is absolutely nothing wrong with it. I actually like it and I have used many of them. I know Dan and Paul very well along with Dan's father Arnie, they will not lead you down the wrong path if you want to go that route either. Is there an advantage to their spring vs the one you have now? No I don't see one unless you want to run a trimmed spring and they do offer that. I just had to put one of the Van Steel springs in a 71 because it was running a 275 back tire and the spring was too wide. That is odd about the 5/8 bolts on the cover, they were 9/16 until 78 when they went to 7/16. If you have any issue please feel free to email as I do not monitor the forum, only the alerts. jabbott@zip-corvette.com
Thank You
Justin

 

Brilliant ! You have mail, @J.Abbott

I appreciate you standing behind the product. I would rather have the issue solved than sending it back.

My front springs are new from Zip: SU-660 and are supposed to restore the original ride height yet be stiffer than stock.

My tires are actually 70s series 225/70R15. These are pretty close to the originals in diameter.

The 5/8 differential, I have not figured out

I measured my end bolts as carefully as I could. I think the are 8 or 8.5-inches.

So the solution is longer bolts...

 

Just to be sure about my differential...

Can a kind soul please measure this dimension ?



With my 5/8 bolts, I want to make sure my carrier is not oversized and throwing everything off.

 

I'm still mad at you guys for selling me a incorrect vacuum diagram. I wasted days trying to get my system to work correctly.

 

On my 1968 3.08/M20 car this is approximately 5 inches.

 

The solution is not longer bolts. A work-around is longer bolts. Did GM ever use 10" bolts from the factory? I'd love to be proven wrong, so I'm asking. Please reference a GM part number if they did.

I'm glad to see Zip stand by their product. I've had nothing but great customer experiences with them. Perhaps this spring is correct if you fix the front springs and go for the lifted 4x4 look with your Vette. But if they can exchange this TRW-style Muskegon spring for a low-arch VanSteel spring, I think you will be happier.

 

The PO installed a fiberglass rear spring in my 71 coupe resulting in the rear sitting high. I swapped the spacers and went to 8 inch bolts but to me it still sat high. Will go to a taller tire at some point but the fact that there are no rear mufflers (side pipes) and no spare probably is not helping.

 

After reviewing all the great information that came from your post string and looking at my car again, I think I am just going to leave the stance of my car alone. If anybody asks I will tell them it is designed that way to improve the torque transfer from the wheels to the pavement during 1st gear burn outs. Best of luck in your quest!


Side view with 1.5 inch rear higher.

 

 

Soooo, after a little back and forth by e-mail with Zip, and checking my finances, I decided to go (for now) with 10-inch bolts.

I have figured out that the bolts on my ride are 8-inch. Ten inches should be more than enough to bring the rear down to what I would deem the correct ride height: half shafts parallel to the ground. For me this is critical because I am chasing down a driveline vibration here and this is one base I need to cover.

I am, of course, concerned that the link bolts will be extend a little low, but as some people here have managed for years and thousands of miles, I may be able to live with that for a while. I like the idea of flipping the bolts upside-down. Likely, I will have to trim then one way or another.

The 10-inch bolts are ordered.

#staytuned

 

You can’t flip the bolts. There is no clearance inside the trailing arms for any excess bolt length, especially if you have sway bar brackets. Just put them in the normal way, set your ride height, and trim with a cutoff wheel as necessary.

 

The reason why GM didn't offer a 10" bolt was because GM never used a short tire and all the new Corvettes looked like 4x4's. The arch of the spring also depends on the spring rate of the spring. If you look at the GM original springs a 9 leak has more arch than a 7 leaf and a 5 leaf Daytona is pretty much flat. 10" is absolutely the way to go and he may have to trim them a little, no harm in that at all.

 

?? who sold you the incorrect one. We have been selling the same one for decades with no issues. Did you try and call anyone instead of spending days figuring something out?

 

After install you might want to check your parking brake cable adjustment....mine was off when I tried the longer bolts.

 

I've done it......there is a hole on the top of the box.....bolt goes through it......plenty of room for the nut.
I do not do it unless rim clearance is an issue because it is a pain to assemble and disassemble......but it is a safe way to gain a half inch when half inches count!
This year I will probably flip the ones on my front monoleaf......they do not hang down much, but they do more than I like.

Jebby

 

However, that hole is covered when you have factory sway bar mounts. Have to the spring bolt, then install the sway bar mounts. Usually the head of the bolt is right up against the nut plate inside the trailing arm.

Also, I would be concerned with the shank of the bolt moving around and hitting the side of the hole.