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VBP Dual Mount Rear Spring or 420# Spring: Opinions?


Well-known member
Dec 30, 2002
Dallas County, Texas
'75 Modified Red Ragtop: "LEFTLN"
Monday, before close of business, I intend to order one or the other of these from VBP.

I was on a short trip when the starboard rear spring hanger decided a 1/2" something less than Grade 8 bolt was not going to see a full thirty years of service. (It had a weird "5" on it and FIVE hash marks, rather than three (or six for a Grade 8) in normal marking proceedures - maybe it was a Grade SEVEN?)

I wasn't in a safe place to stop and thought it was a flat, despite the lack of influence on handling, so I drove it about three blocks before shutting it down. Oddly it handled fine, despite the annoying dragging sound. :)

Once it was towed to the hacienda, I went to a local hardware store and replaced the broken 1/2" bolt with a 3/4" Grade 8 and used a donor poly bushing supposedly destined for a leaf spring mount on an old mopar for the bottom cushion. This took "slight" modifications to the bolt head to make it drop in the end of the trailing arm. Before I finished reinstallation, I cleaned up the outside of the spring, which had been exposed to "road machining."

While I was doing so the edge of the spring snapped off - not quite halfway through the mounting hole.

Undeterred, I cleaned up and ground the end of the spring, cleaned up and ground two 5/32" Grade 8 washers and welded them to the spring around the hole, above and below. I had little hope this would work, expecting it to create a brittle zone in the spring not far from the weld zone, or so detemper the end that it would simply bend. Since I got enough penetration I didn't really expect the washers to not stay attached, although that was a third potential failure mode.

I positioned tons of metal clamps all over the spring, in greatly decreasing numbers the nearer the weld, to serve as heat sinks. I was carefull to quickly removed the heat sink clamps and let it air cool as long as it wanted (without water, etc.) so it would tend to annealing rather than embrittling.

Something went right, because after all this, the thing has held, showing no deformation and no sign of cracking after a few dozen miles of the worst bumps I could find.

Now I need to get a decent replacement for this frankensteinian affair (although I think I'll KEEP the 3/4" bolts for hangers....)

I am having the exhausts rerouted to go directly under the center of the spring to minimize heating of the fiber spring going on there, as well as installing a heat shield of some kind.

I had already intended to shortly replace the 7 leaf thing there with the biggest spring I can find...the 420# fiber one. It needed some more spring to - the one on there was just too weak.

Now, should I just put the 420# thing on there or swap to the dual mount system? Only about $125 seperates the two. I understand there are a few holes to be drilled in the rear frame thingy there, but otherwise this is a drop in.

This car is aimed at being a maximum effort for performance. I already has a decent suspension (VBP transverse front end with tubular aframes and the largest front and rear sway bars they make.) It's firm and harsh, already showing over .6g lateral on a meter, still with 15" tires. I don't mind it harsh.

Rear shocks I should change to? (Currently new KYB's.....)

Anybody have experience in both? Either?


i am running the complete VB&P perf plus system. basically the same as what you have if you go with the dual mount spring. i would highly reccommend that you go dual mount! you need to drill a few holes in the differential crossmember for the spring mounts, but it is a piece of cake. the dual mount does a couple of things for you. first it acts like a sway bar, second reduces harmonics from side to side, third drops a lot of weight from the car and finally and most importantly gives you the ability to change ride height and spring rate independantly. it has been a few years, but i spoke with Brian, a tech at VB&P. he hooked me up with a sweet combo. the spring rates are quite a bit less than what i wanted, but they work just like he said they would. i have no complaints at all! rear rate was 320 and front was 460ish. i can't remember the exact on the front, and my paperwork is 1000 miles and two weeks away. every local Corvette guru i give a ride to compliments how nice the ride is and how great it corners. give the techs a call, they friendly and very helpfull. the Bilstien shocks came with my kit, they are valved perfectly for the spring. Brian

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