terrys6t8roadster

Some good ideas here on the forum. T

Gunfighter13

The only time that bar is doing anything, and that is a stretch, is when the link bottoms out on the rear bolt head holding the bracket. It is also only working in one direction so yea it does nothing.
Extend the trailing arm out so the link is vertical and you would have something.

ronarndt

C3batmobile- the heim joint size will depend on the bushings you use. I used 7/16 inch from Summit Racing part #SUM-MSM7

C3batmobile

Thank you very much sir !

I plan to try this first, since I already have that aftermarket bar (with the 'matched' (intended to be, anyway) front bar - if it doesn't feel like what I want, I'll save-up for an OEM 9/16" bar and maybe go back to my OEM front bar too.

ignatz

I went out and looked under my car and have to agree with Gunfighter here, mostly. The stock setup has the end links nearly but not quite vertical over the pivot point on the trailing arm. If the aftermarket arms are shorter than the OEM arms (and that isn't clear from just this picture), then the link is rotated more to accommodate the shortness in arm length. And I think they have to be shorter, based on originally being designed to mount a bit behind the trailing arm. Given that arm difference, a lot of the motion that would be given to pushing up on the bar instead goes over to pushing back on the bar. Vectors at work here. I wouldn't say the rear bar is now completely useless but I would think its authority is diminished. As he said:

C3batmobile

I smell what ignatz & Gunfighter are cookin' - & I very much appreciate their expertise and input, of course (& everyone else's input).

The 'arms' (with the horizontal bushing 'eyelets') on the ends of my aftermarket bar look like they will be roughly 90 degrees vertical (maybe just a bit less) directly above the end link mounts on the rear of the trailing arms. My aftermarket anti-sway bar 'arms' are about 9" long from the frame bushing bracket mounts to the center of the end link bushing 'eyelets'. I'll try to remember to add a photo or 2 here after I complete the bar installation (I'm waiting on the OEM-style end links and heim joints).

How long are these 'arms' on the OEM anti-sway bars?

Anyway - if I do end-up with geometry that diminishes or negates the effect of the bar, I'll then start looking for a 9/16" OEM anti-sway bar (I think my '69 coupe was an L-46 350/350, not due to the $12 console plate, but due to the tachometer redline. The block numbers point to an early 70s 'truck block' 4-bolt main, and I'm certain that the compression is far less than 11:1, as she runs well on today's low-octane unleaded fuel).

Anyway, much appreciation for everyone's discussion & input !

Mooser

Stock setup with the TA hanging down a bit (not all the way, close to where it would ride)
The link is mainly straight up/down

The stock link shown

with the aftermarket bar is going to try to push the bar backward if anything until something locks up (link hits TA or binds solid) rather than transfer load straight to the bar. If the modified mount plates move the link mount location back farther to be under the aftermarket bar ends they would work correctly again I think



M

Kid Vette

I think this pic is showing full droop which makes a big difference. Here's a pic of mine at full droop.



And loaded.



At full droop the bar appears to be pretty much ineffective.

ronarndt

The position of the sway bar ends at full droop on both sides would only happen when the car is jacked up or if the rear tires go completely airborne, at which point no sway bar will work. Going into a hard turn, the weight transfers to the outside, which causes the car to lean to the outside and put weight on the spring and sway bar on that side. This weight transfer is partially controlled by using the weight on the inside, the end of the inside sway bar and the inside spring resistance to limit the leaning to the outside. The sway bar never gets to the full droop position. If the sway bar is stiff enough the inside wheel will actually lift off the ground instead of going to full droop.

C3batmobile

Finally got my rear anti-sway bar attached, with excellent ideas from this thread. I won't know until I can finish my power steering installation, but it looks like I should get some anti-sway function (see photos; both are at ride height) - though maybe not as much as with an OEM bar. Maybe I'll throw another couple hundred at her and get an OEM bar someday - if I like the change in feel, and want to see if an increase in that direction is desirable.

Thanks again for everyone's ideas/discussion.

ignatz

I have my doubts. An interesting experiment would be to remove the poly bushing and see how much movement you see at the chassis mount. That will tell you how much force is going where you don't want it to go.

C3batmobile

Yeah, I need to mount a camera under there & see what's happening under various scenarios. Maybe after I finish my power steering Borgeson conversion project.....I'm still waiting on my pump kit.....

leigh1322

The angled link would "soften" the bar. A 45 degree angle link would split the vector force in two directions and only half of it would be vertical. Now those links aren't 45 degrees, but they aren't 90 degrees either. So maybe 30% softer??

Using a combo of both methods you could put a piece of angle iron on the T/A extending the lower pivot, and then the heim joint/GM link combo could be almost vertical. See the rancho bar picture above with the three mounting holes on the lower "c" shaped bracket.

Basically yeah, the aftermarket bar must be shorter than a GM bar. I am tempted to go measure my OEM BB 9/16 GM bar for a reference point. Wait I already did: It is 13.5 inches long.

Measurements: Rear Sway Bar
W 43.75" (width)
arm 13.5" (arm length)
MR 1.136 (unusual motion ratio since the spring and sway bar are located behind the axle center)

C3batmobile

Thanks for the OEM 9/16" bar measurements. On my aftermarket VB&P bar (3/4"), I get approximately 45" of width and 9.5" from the bend to the tip (about 8.5" from the bend to the center of the hole). It looks like another 3 or 4 inches would push my bracket beyond vertical, but I have mine mounted without drilling holes (i.e., using the big center hole and hanging about an inch off the back of the TA). The centers of the end link brackets are above the trailing arm proper though.

I was thinking about 'combining the methods', as you mention - but I'd want a pair of ronarndt's 'improved' aftermarket mounts for that. I think I like that Rancho bar mount best (& it's adjustable at the mount and where the mount clamps to the bar). Another idea might be to extend the ends of the bar forward by slipping a foot of 3/4" inside diameter pipe onto each end, drilling & bolting through the aftermarket hole and then drilling a horizontal hole to use the OEM connection. I'm picturing 8 to 9 inches of bar inside the pipe and an extension of just 3 to 4 inches to get 90 degrees vertical. However, 2 things, 1) it looks like if my bar ends were another 2.5" long, they'd contact my calipers, and 2) the bar is flattened at the hole, such that a 3/4" ID pipe would not 'slip' on......might take a full inch ID, but then it'd be a 'sloppy' fit on the rest of the bar.

Also, I'd be going to an awful lot of trouble to avoid spending $200 on an OEM bar !
Anyway, I appreciate the discussion, etc.

leigh1322

I loved the adjustability of the Rancho bars a lot. I ran one on my Pro-Solo 1970 Z28 for 27 years and was very competitive with it. OTOH it was very stiff, too stiff actually. I wound up gradually changing the adjustable links and softenening it over the years. It barely leaned even with both bars on full soft. At that rate it was still significantly stiffer than the stiffest OEM WS6 bar. IIRC it was 1.25" dia in the front. The rear bar was at least .75 " and may have been 7/8 or 1". I wound up removing the rear one and substituting a smaller custom made bar.

I don't know how it applies to their Vette bars, but my Z28 felt incredibly flat and barely leaned. It had razor sharp go-cart like reflexes. If the Vette Rancho bars are the same diameter as the factory Gymkhana bars, but with shorter links, I would guess they act the same. My car did work very well on billard table smooth concrete courses. But it was so stiff, and it shock loaded the tires so suddenly, that traction was easily lost. It would "snap" into a slide. The car was a real wild handful on a bumpy course, and virtually undriveable in the rain. I made a short drive home one day on the "DOT" race tires, with the stiff suspension, in the rain, on I-95, with 11 inch wide rubber "skiing" on the puddles in the 7 inch wide grooves & puddles left in the asphalt from the passenger cars. I have never been so scared in my life!! It would randomly dart 3 FEET to the right or to the left. At 40 mph. The car got "softened" after that.

It wasn't until I drove a couple of the other national champions cars, and they mine, and we compared notes, that I understood how their softer bars let the car be more compliant on turn in, on bumps, and in the rain, that I softenened the Rancho bars up by half their original stiffness, and made an even softer rear bar. It became much more manageable on the bumps or in the rain. The snap oversteer vanished. It pulled the same G's! but wouldn't lose-it on a bump. Eventually I even came up with softer bar & shock settings and different tires, just for the rainy days.

ronarndt

I mentioned earlier that I had a chance to talk to Dale Earnhardt, Jr about how to properly adjust the suspension on a car. His answer "If I knew the answer to that, I would probably win all the time" sums it up. We amateurs trying to solve an issue that full time professional drivers have trouble with is a lost cause- but we will still try.

cagotzmann

What is everyone expecting the rear sway bar to-do ?. From reading most of the posts I get the impression "bigger is better". Meaning get the 90 degree angle or its not going to do anything / soften the effect. And what's wrong with that.

Its not what 1 connection is doing its a number of factors. Dia / Length of the ends / Length / angle of the connect points / travel the connect allows etc. Compression vs extension movement.

So if during the compression at one side very little force is transfer to the opposite wheel (angle is not 90 degrees) that could be a good thing. eg. one wheel hits a bump. If too much force is transfer to the other wheel its noticeable and feels as if you hit a bump on both wheels. So lets say you want some body roll to slowly transfer weight there are many ways to make this happen. But the point is what are you expecting the sway bar to assist with.

As for street driving the most common situation you will experience is one for both wheels hitting a bump. If you plan on other driving conditions auto-cross / road track days / drag strip each may require different setups.

So the best setup you can do is adjustability and not introduce a restriction in the arm movement. But until you know what you are trying to fix , you cannot make any adjustments towards the goal.

Start with the setup as is. Drive the car in the conditions you see fit, and then introduce changes as required.

eg my setup started with the aftermarket VBP setup and then I changed to the factory links and a heim joint to the VBP sway bar. ? Why well because the aftermarket setup (providing a 90 degree setup) transferred to much force to the opposite wheel causing more over steer on high speed cornering. By changing the angle between the trailing arm and the sway bar (very little force almost none ) is transfer from the compression side and additional force is transferred from the extension side as the body rolls net effect less over steering feel of the car in high speed cornering. (track days). Also note many racers remove the rear sway bars during track days to get the driving feel they want.

The factory setup is a compromise of different conditions. Ride quality vs cornering under steer vs over steer.

Drive the car and feel free to make adjustments in the setup as required. You might enjoy the ride quality better with the bar using the factory location vs extending the connection to get the so called 90 degrees.

There are many different rear sway bar setups for the C3, some have 3 different locations to install a connection arm, also if you look at Ridetech website and how they are engineered for adjustability you get the idea

1 setup doesn't fit all conditions.

ignatz

The point here, at least to me, is that the mechanism transmits almost as much force backwards or forwards as upwards or downwards. The vector components are sine and cosine of the angle and resolve vertically and horizontally. The bar will be pushing or pulling against the bushing as well as rotating. Ideally one wants as little resistance to rotation as possible.

cagotzmann

That is why I believe the heim joint vs the ( straight bar / bushings ) can work better, but the angles are different and 90 degrees may not be the best setup depending on what you are trying to achieve. The original poster has not driven the car yet so I am not sure what the final goal is, but looking at the options presented he can still make adjustments with very little effort. Ideal is adjustability.

ronarndt

"The original poster has not driven the car yet" Actually I have driven it. With the heim joints installed, there is no perceived difference in the "flatness" during hard cornering compared to what I started with. My original concern was the cheap bracket included in the aftermarket kit was bending. Both the channel iron bracket and the heim joint bracket corrected the chance the bracket would continue to bend and perhaps break. I like the heim joint set up so I can use the factory parts that were gathering dust on my work bench and the setup looks more professionally done. I'll let you guys argue which works better.