VPB Dual Mount Rear Spring

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Sky65

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Aug 27, 2008
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Maryland
I am using a VBP dual mount rear spring on my 65. For some reason I can't seem to get the rear ride height up where I want it. As I tighten the spring end bolts it just seems to bend the spring. VBP says get a stiffer spring but when I put the current spring on the stiffest setting the car rides too hard and the ride height still will not raise where I want it. I can jack the the car on the strut rod inner bracket and the car goes up and ride height changes. I have offset rear control arms with poly bushings and strut rods with heim joint ends .Thoughts?

Thanks
Tom
 
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The only thing I can think of is that when you change the ride height the track width changes slightly also. So the tires may be keeping it at a fixed height. Try adjusting and roliing the car or put a couple of layers of garbage bags under the tires (the tires wil slip on them).
 
Thanks. I noticed after I moved the car it went up slightly. I was wondering if the poly bushing was the problem. As the trailing arm goes up and down the bushing twists doesn't it? I wonder if the pressure of the spring alone, without the weight of the car bouncing, is not strong enough to twist the bushing and let the TA go down and increase ride height?
 
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You've just hit on why I don't like poly or rubber for that trailing arm bushing, without a major redesign of the rest of the rear suspension. I installed spherical bearings in my T/As. If there was a top locating link, and the half shafts had the ability to adjust length (either with a sliding splined section or CV joints), then the twisting of that bushing would be minimized.

All of that said, I used to deal with alignment specs every day. I can't think of a ride height adjustment on any car that didn't say something like "drive the car around the block and re-check height."
 
First off: I have been bitching about poly for a few years now, ever since I noticed how this crap crumbles over time.....
Now funny: my poly trailing arm bushings were actually in pretty good shape after 8 years, maybe 6000 miles (guesstimate) .....
Funny fact is: the trailing arm bushing is the one location where poly is not appropriate at all, however in my case, the poly did fine....

Consider a JohnnyJoint for the front trailing arm ......

I also have the dual mount spring: no complaints whatsoever, ride height is easily adjustable.....
 
MYBAD79 said:
First off: I have been bitching about poly for a few years now, ever since I noticed how this crap crumbles over time.....
Now funny: my poly trailing arm bushings were actually in pretty good shape after 8 years, maybe 6000 miles (guesstimate) .....
Funny fact is: the trailing arm bushing is the one location where poly is not appropriate at all, however in my case, the poly did fine....

Consider a JohnnyJoint for the front trailing arm ......

I also have the dual mount spring: no complaints whatsoever, ride height is easily adjustable.....
Click to expand...
Thanks. Do you know what the spring rate is on your spring? What setting are you using?

Tom
 
Sam Cogley said:
MYBAD79 said:
First off: I have been bitching about poly for a few years now, ever since I noticed how this crap crumbles over time.....
Click to expand...

I have yet to have a poly bushing crumble on any car I've owned, even after a lot of miles on some of them.
Click to expand...

My Energy Suspension bushings seem to be fine, had that brand on my Z28 as well..... It seems to be a problem with low quality poly from some of the vendors....

You've seen the photos I've posted, right? Just want to make sure you know I'm not making this up..... My body mounts crumbled like termite infested dry rotted wood..... Even the strut rod bushings crumbled to dust..... I think these were both from MidAmerica .....
 
Sky65 said:
MYBAD79 said:
First off: I have been bitching about poly for a few years now, ever since I noticed how this crap crumbles over time.....
Now funny: my poly trailing arm bushings were actually in pretty good shape after 8 years, maybe 6000 miles (guesstimate) .....
Funny fact is: the trailing arm bushing is the one location where poly is not appropriate at all, however in my case, the poly did fine....

Consider a JohnnyJoint for the front trailing arm ......

I also have the dual mount spring: no complaints whatsoever, ride height is easily adjustable.....
Click to expand...
Thanks. Do you know what the spring rate is on your spring? What setting are you using?


Tom
Click to expand...

Second to stiffest setting..... I am really happy with the setup, in fact, so happy that I bought the front dual mount fiberglass spring as well....

See my "Johnny Joint" thread..... It's not a easy install but if you choose to go that route I can cut/weld if you pay shipping the arms back/forth..... Then again, a local shop probably charges less than USPS for shipping.... :smash:
 
MYBAD79 said:
Sky65 said:
MYBAD79 said:
First off: I have been bitching about poly for a few years now, ever since I noticed how this crap crumbles over time.....
Now funny: my poly trailing arm bushings were actually in pretty good shape after 8 years, maybe 6000 miles (guesstimate) .....
Funny fact is: the trailing arm bushing is the one location where poly is not appropriate at all, however in my case, the poly did fine....

Consider a JohnnyJoint for the front trailing arm ......

I also have the dual mount spring: no complaints whatsoever, ride height is easily adjustable.....
Click to expand...
Thanks. Do you know what the spring rate is on your spring? What setting are you using?


Tom
Click to expand...

Second to stiffest setting..... I am really happy with the setup, in fact, so happy that I bought the front dual mount fiberglass spring as well....

See my "Johnny Joint" thread..... It's not a easy install but if you choose to go that route I can cut/weld if you pay shipping the arms back/forth..... Then again, a local shop probably charges less than USPS for shipping.... :smash:
Click to expand...
That's where I am. 2nd to stiffest.
I can't find the thread. Mind posting a link?
Thanks
Tom
 
Just saw this thread.

Yes, you have to jounce the suspension while moving to see how adjusting the bolts changed the stance. I go drive around the neighborhood, bouncing over the alley entries, forward & reverse, and turning left and right to 'exercise' the suspension and then back into the garage to check the height. Got to have a fairly level surface too or you'll not get a true measurement.

The ratings on a dual mount, from the softest (farthest inboard) bolt settings to the stiffest (farthest outboard) are about 325, 350, 375, and 400 pounds, assuming you mounted the brackets per VBP specs. I too have mine on second from stiffest.

Another thing to keep in mind with a dual mount spring is that there is no centering location. You have to measure it and adjust it side to side to center it to keep the spring rate even on both wheels.

I found mine was off by almost 3/4"! I have always had one bolt with more 'reveal' below the spring than the other, when I centered the spring it helped even it up. I still have one bolt sticking down about 1/2" farther than the other though. Everything else I can think of to check measures out equal, so I don't know why.
 
Thanks for thee replies. I guess I need to clarify what my issue is. I drive the car all the time. Literately daily. For that I use the next to stiffest setting on the spring. I have also done the HRPT for four years now and long hauled each one. We load the car down for two weeks on the road and I for that I use the stiffest setting. Problem is my rear tires just catch the small fender flares on compression so I dropped the bump stops about 1 1/2" to keep the tires from hitting. So I have very little suspension travel. If I can get the rear up a little higher I will gain suspension travel. The damn thing just doesn't want to go up any higher than it is using the spring end bolts. I'm afraid I will break the spring if I crank down on it any more. Yes I know getting the right offset wheels is the proper thing to do but until I rebuild the diff, worn stub axles, I don't know what offset I need. As far as spring rate it depends on what spring rate you start with. Mine is marked 247#. But obviously depending on mounting position the effective rate changes. Gary at VBP told me mine was a middle of the road rate. I could go stiffer, and may because I only use the two stiffest settings, but even in the current stiffest setting I can't get the rear up where I want it and the ride is too harsh without the car loaded with my crap and full tank of gas.

Thanks
Tom
 
If you have threads left then you can adjust it..... You must have some serious binding on your trailing arm if you crank up that bolt on the spring and ride height doesn't change....
Think about it this way: all you're doing is changing the relative position of the spring end to the trailing arm. Let's say the bolt is 8" from head to the nut and your ride height is 26" ..... The weight of the rear of the car remains the same so with no other changes like spring-rate you should see 27" ride height if you crank that nut up 1" so that you have 7" from head to nut.....

Check if your trailing arm is hitting the frame (at the front trailing arm pocket) .....
 
I agree. Changing the bolt length should have no bearing on the pre-load tension of the spring. All it does is change the distance between the spring and trailing arm.

Sounds like you have a binding problem somewhere. Shocks maybe? Or sway bar? Or as Karsten mentioned, perhaps something in the trailing arm pockets. Hard to say....You might want to unhook the shocks & spring (and sway bar if you're running one) and work the TA to see what it does.

As far as wheel offset, "in my experience" you don't want any less than 4" backspace for an 8" wide wheel with stock fenders. I tried 3 3/4" BS (4 1/4" outboard of wheel centerline) and it just did not work. My tires hit the fender lips. I too tried lowering the bump stops and jacking up the spring rate. That only made it drive like it was almost without rear suspension and in fact really screwed up the handling because it was so rigid. Not to mention unpleasant. The only cure was to get the correct wheels to clear the fenders.

http://vettemod.com/forum/showthread.php?t=10212 (page 2)
 
I agree there must be some binding somewhere. If I jack the rear of the car the body goes up and the wheels stay on the ground. So it is not completely bound up but enough to restrict motion. If I bounce the car the suspension works. I am running 17X9 5" BS wheels on the rear with 275/50 Nittos. I don't know how to calculate wheel BS because there is so much yoke end play the wheels have allot of in and out slop. When I get the rear rebuilt I will replace the stub axles and then I can get a true measurement. I'm looking for a temporary fix. Maybe I am being to cautious. I still have threads to go on the bolts. Thoughts?
Thanks


2hpt387.jpg

ablf88.jpg
 
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At this point I am not sure what, but something is wrong there !

With the nut run up that high your Vette should have that 4x4 look.....

Look at this pic below, that's the bolt that came with the VBP kit, threads under the nut is about 1"

214f8cbd5a67500.jpg
 
Is hard to say from the pictures but it looks like the spring supports are too close together.
 
Here are some pictures of my dual mount install: RearSusp2sm.jpg

RearSusp1sm.jpg

The spring is a bit stiffer than the standard dual-mount, it came off of a race car.
 
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