VB&P suspension - after the install

[cascotty]

Scott,
I have the "Grand touring package" on the 81, and installed it some 3? years ago or so. It uses 460 coils in front with an 1 1/8" sway, and the 360lb spring and 1" sway in back.(Memory, don't hold me to it) The larger sway in front works pretty good, but as I have learned from Howard and TT and many others, plus my own experience, too stiff a rear sway on these goofy rears tend to cause fishtail. Howard has told me to try a 3/4" rear, and I just may soon.($$$)
As for the dual mount units, yours is the first I have toyed with, and I claim ignorance. TT and some others have way more time tuning one than me. IF we could fly Howard out of the first snow, I know we could tune our cars in a day, but that might cost some more $$. (Although a "Chasis tuning for IN AND OUT tour" might be a good idea)
My GUESS would be with super soft Hoosiers, and flat out racing, the stiffer the better. BUT<, when compromising for "real street" spirited driving with pot holes, swales, and other obstacles like harder street compounds, it's just whatever works with what you have to work with. (Double talk):sweat:
John and I made the same suggestion at the same time. Unless we hear better, I think we are all on the same page.

I think the disconnect the rear sway bar idea is a couple of steps ahead of me. I haven't played in, or near, that realm. Also, I'm no Dan Gurney so I know that I'm fallible when interpretting the feedback the car is giving me, but, I'm not clueless either. Rather I think I need to focus the discussion a little. Let's talk about freeway driving in So. Cal. where there is a sharp transition and more often than not, an inch or two drop across and perpindicular to the lane, if I hit that at 70 to 80 miles an hour, I was feeling a bump and then a sharp hit. The car feels slightly unstable to me when it hits like that, but it doesn't step out, twitch or anything like that, thank god! If both rear wheels are moving up simultanously to soak up the same transition the sway bar has no effect. So I raised the car and gained some suspension travel and the hit goes away. I think okay, I need that much travel but the question is how best to get it. Leave the ride height, lower/trim the rubber bumper blocks or some of both. So far I've got VB&P saying a lot of people trim them and also I should lower the car some. Or, I can go to the stiffest spring setting or swap for a stiffer spring. This makes perfect sense to me. Since the latter suggestion amounts to make the suspension really stiff to compensate for the loss of travel I'm not in favor of that for the street. I'd rather gain a little travel and lower the car some.

Around town hitting potholes or if in my case running over 3" high swales in asphalt caused by stone pines roots on one side of the car doesn't cause the any twitching or other unsettling issues that I've noticed. But this is going around gentle curves at 30-40 miles an hour, so it is not really being pushed to hard either. However, if I had noticed that problem I'd be saying hey maybe I got a problem with sway bars.

 

[cascotty]

You will need to be patient & work with it to dial it in, all our cars & situations are unique. I envy you your wheels & tires, that's on my list of things to come. I know mine are mushmasters.
For whatever it's worth, I run 550# coils & 1 1/8" sway bar up front, but have not done a 4-wheel alignment since I installed them & replaced the t-arms so I have not done any parking lot tuning runs.

Exactly. I'm not planning on doing anything in a rush just one small step at a time. I'll give my impressions of the change, but it is just my honest opinion as to how it feels. It will be here so if anyone else is going to tune this type of suspension in the future they may have some decent ideas on what to do, or not to do. Also, I am open to suggestions/input as I go through it.

 

[kwplot34]

I don't know anything about these new fiber glass springs and VB&P suspension parts,but after reading alot of these post about trying to set them up :flash:
makes me glad that my car came with the Gymkhana suspension,so far it has never given me a reason to swap it over,or change any part of it,and especially after the Ca trip,what a blast that was
Hope you get it figured out Scott before the next trip,i'm looking forward to seeing your car.

 

[MYBAD79]

If anyone else has modded these bump stops, I'd like to know how you did it and how much you elected to take off.

You can buy these bump stops at AutoZone, they're cheap. (in case you cut then too short)

 

[cascotty]

So I went with lowering the rear 28 inches floor to fender. I took all kinds of measurements but in the end I've decided to key in on the measuring the distance from the rubber bump stop to the pad on the TA and to keep it even side to side. I'm at 1 1/4 inches on each side which wound up being 28 floor to fender.

In the front, I lowered it to about 27 1/2 floor to fender.

I went for a drive over some bad freeway and also some bad roads. I didn't feel any of the hit from impacting the bump stop in the rear that I described earlier. It actually felt good overall.

Checking bump stop measure after the drive, in the rear it was a nice equal 1 1/4 on each side, so I'm leaving it there for now. The half shafts are pretty close to being level on each side as it sits now too. Checking the bump stop clearance in the front is more difficult, I just can't get my little 4 inch rule, flashlight and eyeballs lined up. So I wound up using my 1-2-3 block as a fat feeler gage.
On the Drivers side it was a snug fit while on the other it was really loose. I readjusted the Pass. side to lower it down so that it was snug too. I'm at 27 5/16 inches to the fender lip on the Pass. side and 27 7/16 inches on the Drivers side.

Someday I'm going to disconnect the front spring and see what that 1 inch clearance translates to in total vertical wheel movement.

I'm toying with the idea of lowering the front a little bit more. I'm also trying to think of a way to create a tell-tale mark if the bump stop hits the frame or TA. Then decide wether or not I want to cut some down and/or if they can be purchased in a lower size.

By the way, the bolts wound up extending 1 3/4 inches from the nut pretty evenly all the way around.

 

[Wesch]

Hi

What I don't understand is :

I had to tighten the adjusting nut about 2 inches to get 1 inch lift. Clearly this added a lot of pre-load on the spring. Hmm maybe too much?

The weight of the car always stays the same. Why will the car only move 1 " up when you tighten the nuts up 2 " ? No preload can be added or removed from the spring. The load is purely the weight of the car.

Something is binding here.

Rgds. Günther

 

[MYBAD79]

The weight of the car always stays the same. Why will the car only move 1 " up when you tighten the nuts up 2 " ? No preload can be added or removed from the spring. The load is purely the weight of the car.

Something is binding here.

Rgds. Günther

I agree. Running the nut "up" pulls the trailing arm "down", closer to the spring, nothing else... the arc of the spring should be the same no matter if the nut is high or low....

That's why I asked about the arc in reply #4:

Rear spring:
If you run that nut down to where it normally is (1/2" from end of bolt) - is the spring still bent upwards like the second picture shows ? The reason I'm asking is that the load on the spring never changes when you adjust ride height, you only "pull" the trailing arm down, closer to the spring.

 

[big2bird]

I bet if he disconnects the sway bar links, the bind will go away.:idea:

 

[cascotty]

I just loosed up the sway bar bolts and nuts. There are rubber washers on each side of the top and bottom of the bar and top and bottom of the connection to the TA. There was no crush to indicate compression of the rubber. Loosened up the nuts and there was no indication of any bind. I also loosened up the the bolts holding the spring to the dual mounts and noticed no movement. I wondered about the smart strut causing bind but this is in both the front and rear. If you all think of something I should look at or do to test the binding idea let me know.

I measured the sway bars to make sure they are the same as advertised - they are - 1.125 front and .750 rear.

After Sundays drive, it still feels much improved. I think I can make a significant difference in what is still a rough ride with air pressure. I read what I could find on tire pressures for C4's and C5's which would be similar to my tires and they are between 30 psi and 35 psi. So I'm thinking I will drop 2 psi out of the tires to 31 PSI cold.

I also want to try dropping the rear spring rate setting one notch ( it is at the next to stiffest setting now). There is work being done on a freeway onramp that I use which has a big drop near the end of the ramp, and the rebound off of that bounced my head of the roof (about a 2 inch gap). But I did not feel it bottoming out. Maybe it is becoming clear in this thread that the roads in my town are pretty crappy. In particular the above is an extreme road condition, and it tosses my CTS too.

 

[big2bird]

Scott. Try removing the sway bar links altogether.

 

[Twin_Turbo]

Whenever adjusting the suspension you indeed need to remove the sway bar links so you don't end up preloading the bar.

 

[RossLato]

you have your spring end bolts on in reverse, supposedly you cannot remove them now to reverse them w/out disconnecting the Aarm from the spindle.

 

[cascotty]

you have your spring end bolts on in reverse, supposedly you cannot remove them now to reverse them w/out disconnecting the Aarm from the spindle.

I wondered if that would work when I saw a picture like it in the VB&P catalog. I think it looks cleaner for sure. However, the instructions that I have clearly show installed as done in my car, so I guess it just a matter of preference.

Thanks for the photo, all your bushings are red, are they poly?

 

[cascotty]

No need for the rear sway bar indeed, and you can use a thinner one at the front also.

TT do you have an opinion as to why VB&P would put together this kit with a 1.125 inch dia. bar in front and a 0.75 inch dia. bar in the rear? BTW I noted these are the same size as sold with their autocross kit, actually it looks like it is the combo for all the kits. Do you think that the level of sophistication in the design of the stock fiberglass Chevy springs used in the later Vettes is superior to what the aftermarket might do, or not really? The above states designing a spring can be a complicated business.

 

[RossLato]

I wondered if that would work when I saw a picture like it in the VB&P catalog. I think it looks cleaner for sure. However, the instructions that I have clearly show installed as done in my car, so I guess it just a matter of preference.

Thanks for the photo, all your bushings are red, are they poly?[/QUOTE]

yep poly. my instructions said the other way wtf? guess it depends on which way the winds blowing.:nuts:

 

[cascotty]

So I've done some research and have a expanding to-do list. VB&P in their installation instructions does give a minimum for the thread length that should show past the nut on the bolt that runs through the spring. It is 1 1/2 inches. Also, VB&P recommends that the rear be 1 inch higher than the front. And lastly VB&P recommends that the adjustment for spring rate be kept the same front to rear. The installation instructions are only two pages long, I guess I could have spent a little more time reading them before starting the thread huh. :blush: Anyway, if all those recommendations are followed the number of adjustment options narrow down a lot. We will see if that is a good thing.

Also, I dug up some factory specifications on the standard 71 coupe:

Front swaybar = 0.750 inch dia.
Rear swaybar = 0.562 " "

Now I wish I had kept my stock bars to test.

Wheel travel
Front
Jounce = 3.82
Rebound = 4.02

Rear
Jounce = 2.87
Rebound = 3.99

It is interesting to me that the rear jounce is 1 inch less than the front. Add to that VB&P recommends adjusting the rear 1 inch higher than the front.

 

[cascotty]

I wondered if that would work when I saw a picture like it in the VB&P catalog. I think it looks cleaner for sure. However, the instructions that I have clearly show installed as done in my car, so I guess it just a matter of preference.

Thanks for the photo, all your bushings are red, are they poly?

yep poly. my instructions said the other way wtf? guess it depends on which way the winds blowing.:nuts:[/QUOTE]

Did you have to pay extra for the Poly or was it an option. I forget if they gave me the option or not, I placed the order a year and half ago.

 

[RossLato]

I wondered if that would work when I saw a picture like it in the VB&P catalog. I think it looks cleaner for sure. However, the instructions that I have clearly show installed as done in my car, so I guess it just a matter of preference.

Thanks for the photo, all your bushings are red, are they poly?

yep poly. my instructions said the other way wtf? guess it depends on which way the winds blowing.:nuts:

Did you have to pay extra for the Poly or was it an option. I forget if they gave me the option or not, I placed the order a year and half ago.[/QUOTE]

just my sway bar links are red poly. as for the spring bushings there what VB's sent w/the kit, can't remember if there poly or rubber, installed the kit 3yrs ago.

 

[mrvette]

LONG time ago, I had a 1.125 bar in front, and a 3/4 bar in back...VBP, and so it was stiff as hell in the back just a center mount 360 VBP glass spring in back 460 coils in front....the car got away from me, ass end going around nasty in a quick corner once....

got that rear bar outta there, went to the roughly 7/8 front bar and a 9/16 rear bar....

car is much more friendly to me now....

:shocking:

 

[gkull]

Before the internet and I was young and dumber I bought the VB&P street and slalom kit

I had a 1.125 bar in front 550 #, and a 3/4 bar in back a center mount 360 VBP glass spring sway spring ends and poly everything and smart struts.

Best thing you can do with upgraded tires and wheels. I thought. It did do great for many years. although I went to a 420+ pound rear spring for drag racing and road courses



After 20 years of this setup I now have no rear sway and front semi coil over QA-1

My lap times are not that much faster, but what I do have is much more confidence. I went from skating around to over the rumble strips in every turn.