Rear Monospring Advice

68/70Vette

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Torrance, Ca.USA
I need to buy a mono spring for my 1970. The choices, as I understand it, are to buy a VBandP mono spring or to buy their dual mount mono spring. The dual mound allows some height adjustment and allows you to run without rear anti-sway bar. This is for a BB engine. It'll be about 502 cubic inches and I'm sorta planning for 600 Hp. I have Tom's tuned differential case and 1350 u joints and the 30/32 spline half axles (spindles). Also have Toms offset trailing arms and struts.

Opinions? Just buy a monospring at 360 pound inches or 420 pound inches? For the dual mount, its a few hundreds of dollars more. Is it an advantageous product to have? I looks like you can adjust stiffness and ride height with it. Any comments from people who have bought one?

(PS, the dual mount functions as a sway bar. Not really too interested in that. I want my car to have understeer, since I'll be driving it on the freeway (not motocross) and I want to avoid off-torque oversteer. )

Thanks
 
look at my "rear suspension overhaul" thread, that dual mount spring is really sweet.... I only put a few miles on it but it's a huge improvement over the 7-leaf that was in there before....

214f8cbd5a67500.jpg
 
look at my "rear suspension overhaul" thread, that dual mount spring is really sweet.... I only put a few miles on it but it's a huge improvement over the 7-leaf that was in there before....

214f8cbd5a67500.jpg

In '95 I put the VBP single mount 360 lbs spring in the back, with the Bilstein switchover some years ago, I find it GREAT!!!.....

now is the spring itself different?? if so, I not bother, but if some cheep hardware changes can get me home with some ride/handling inprovements, it maybe go on the list.....

anyone with a A-B direct comparison with modern enough tires/wheels??

:confused::gurney:
 
I noted that the dual mount spring does not mount to the diff cover. When the transverse spring was mounted to the diff cover, then approximately 1500 pound of force was pressing the differential up into the differential crossmember. With the dual mount, the diff is now "hanging" from the crossmember by 4 bolts. With a big torque load, differential tends to rotate with the nose of the differential deflecting upwards. With a conventionally mounted spring, this upward rotation is inhibited by the 1500 pounds of clamping force by the spring. With the dual mount, the only thing inhibiting the upward rotation is the differential nose bushing that presses against the frame crossmember. Question: does the dual mount leave the differential in a weaker condition since the body weight is no longer pushing upward on the cover?

Have people been running the dual mounts at the drag strips with no issues????
Thanks
 
One thing is for sure. Breaking a diffy cover is pretty much impossible.:)
 
One thing is for sure. Breaking a diffy cover is pretty much impossible.:)

With the dual mount composite spring, the differential cover is not experiencing any significant forces. It's just hanging from the crossmember. When torque hits the diff, it's going to rotate upwards, with only the most rubber bushing to inhibit it's rotation.

With the stock transverse steel spring, or the composite transverse mono spring, the differential cover is seeing the entire weight of the back of the car; 1600 lbs. This is a clamping force that will tend to inhibit rotation of the differential when it sees a torque load. With the dual mount VBP mono spring, there's no 1600 pounds of upward force on the diff cover, there's 0 pounds.

With all respect to your statement: I have a Toms Differential/Muskegon Brake differential cover. Both their names are cast in the cover. They cover is "beefier" than the stock covers, because the stock covers were cracking...breaking a stock cover is nowhere near to being impossible... it's very possible according to Toms and Muskegon. I've also have definitely seen photos on other forums where people have posted photos where their stock covers cracked.
I think also that people that build differentials have found the odd occasional factory differential case that is not acceptable for upgrading.
 
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wow, this is a very interessting thought.... have to admit I never thought about the weight of the rear of the car possibly adding strength to the diff....

so you think the engine torque might actually rip the diff off the crossmember ?? there are only four bolts so that's not much.....

how about a support structure bolted to the diff and welded to the crossmember (like a frame) .... that shold do the job....
 
There should be some pictures of my dual-mount hanging around here, too.

look at my "rear suspension overhaul" thread, that dual mount spring is really sweet.... I only put a few miles on it but it's a huge improvement over the 7-leaf that was in there before....

214f8cbd5a67500.jpg

In '95 I put the VBP single mount 360 lbs spring in the back, with the Bilstein switchover some years ago, I find it GREAT!!!.....

now is the spring itself different?? if so, I not bother, but if some cheep hardware changes can get me home with some ride/handling inprovements, it maybe go on the list.....

anyone with a A-B direct comparison with modern enough tires/wheels??

:confused::gurney:

I think the dual-mount spring is different, but I haven't looked at them side-by-side for a while.

I noted that the dual mount spring does not mount to the diff cover. When the transverse spring was mounted to the diff cover, then approximately 1500 pound of force was pressing the differential up into the differential crossmember. With the dual mount, the diff is now "hanging" from the crossmember by 4 bolts. With a big torque load, differential tends to rotate with the nose of the differential deflecting upwards. With a conventionally mounted spring, this upward rotation is inhibited by the 1500 pounds of clamping force by the spring. With the dual mount, the only thing inhibiting the upward rotation is the differential nose bushing that presses against the frame crossmember. Question: does the dual mount leave the differential in a weaker condition since the body weight is no longer pushing upward on the cover?

Have people been running the dual mounts at the drag strips with no issues????
Thanks

The differential cover usually breaks at the spring mounts, not the crossmember mount (at least in the broken ones I've seen). I have solid mounts in the crossmember (not a reinforcement plate), and a poly bushing on the nose bracket. The diff doesn't seem to mind at all, nor move any more than usual. It's hanging, but it's hanging by four large bolts running into a heavy, webbed piece of cast iron.
 
This fits into the same discussion as the traction bar which is meant to keep the diff from moving under heavy torque. Maybe some kind of torque bar system would help in the dual spring set-up.
 
I just thought of this, but my dual mount was well-used when I got it from a race car that was being parted out. VB&P has been selling them for a long time, if they've run into any issues with the differential mount, they'll know about them and what to do as a corrective measure.
 
I just thought of this, but my dual mount was well-used when I got it from a race car that was being parted out. VB&P has been selling them for a long time, if they've run into any issues with the differential mount, they'll know about them and what to do as a corrective measure.

If you've a dual mount from a race car, that's a good evidence that they're suited for rugged use. Thanks

Looks like to mount it you've got to drill some holes into the crossmember for the attach brackets. This is most likely an easy job for a hand held electric drill. Anyone recommend welding the brackets after bolting them in?
 
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the dual mount spring design came up in the late 80's ???

what racecar used this aftermarket dual mount setup??? VPP was founded when ???

I think it's a good idea to look into additional diff support with the dual mount spring setup...

think of it this way : IF the cross member bolts gave away, the spring would support the diff and keep it from rotating... with the dual mount it seems possible to rip the diff off the crossmember....

scary thought....
 
I not following the "clamping force" idea. The clamping force between the crossmember and the diff is probably 10's of thousands of pounds so another 1500 is not a big deal. Also, the load path for the dual mount and the stock spring is the same into the crossmember/frame interface.
 
the dual mount spring design came up in the late 80's ???

I think it actually dates back to the late 70s or early 80s.

what racecar used this aftermarket dual mount setup???

Somebody's Corvette racecar, I bought the spring and crossmember when the car was being parted out on eBay. It had a lot of wear, VB&P's customer service was awesome. The spring itself was fine, but they set me up with replacements for the badly worn metal bushing cups/plates and the mounting blocks, parts they don't normally sell separately.

VPP was founded when ???

VB&P was founded in 1977, as their website says.

I think it's a good idea to look into additional diff support with the dual mount spring setup...

Why? The majority of broken differential covers I've seen are broken at the spring mount, not the crossmember mount. That would seem to indicate that the spring is causing more stress on the differential than the fact that the differential is hanging from the crossmember. I really doubt that anything beyond one of the HD covers would be necessary.

think of it this way : IF the cross member bolts gave away, the spring would support the diff and keep it from rotating... with the dual mount it seems possible to rip the diff off the crossmember....

scary thought....

I'm pretty sure if that happens you'll have far bigger problems than some potential differential rotation. For one thing, I've never seen the differential mount bolts break, nor have I ever seen the crossmember bolts break. Worst case, if it falls, it's going to drop less than 2" before the spring catches it - and the tongue mount is still going to be there.
 
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VBP has had their share of problems since a head honcho there left, I think her name was Shirley, but I could be rong on that, anyway, she gone maybe a dozen years now, she had another good reason for a move north, like hubby transferred/family/whatever, unrelated to VBP.....at any rate VBP has suffered greatly in the PR/CR/Marketing since losing her....

I have noticed it even in the minor dealings with them since then....when the initial build of my car was going on, that chick straightened out a couple minor issues with no sweat....and quickly too....

I don't remember the last purchase....been too long, but when buying the Bilstein shocks, it was kind of a mess.....eventually fixed....

PR/CR is a very critical hot spot, and if you have the RONG person in charge, it's a super quick way to go outta business....

Ralph Eckler sold to xyz group, and they ran it into the ground, so Ralph bought it back again, I"m TOLD.....but somehow it's not the same still.....

maybe it's the general economy....

:gurney::pprrtt::confused:
 
VBP has had their share of problems since a head honcho there left, I think her name was Shirley................

I have noticed it even in the minor dealings with them since then....when the initial build of my car was going on, that chick straightened out a couple minor issues with no sweat....and quickly too....

Pattie. I still have her personal email.;)
 
I have had all three rear springs (7-leaf, centermount 360 mono, and dual mount mono). The centermount made a huge difference in ride quality over the 7-leaf, much smoother. The dual mount made just as big an improvement over the centermount, very firm ride but not harsh at all. I have my dual mount set at the center position on the adjustment and have not played with it as of yet. As far as the clamping pressure on the diff cover, I would think even though the spring is pushing up it is not contained front to back. If you apply rotational force to the diff it will still move. I would suggest solid front diff mount or traction bar to limit rotational force. I would recommend the dual mount. Just my opinion
 
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