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Old 01-08-2006, 06:31 PM
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4 Link rear suspensions



I've started an upgrade to me 57 tbird. The biggest and most radical change is a 4 link fixed rear axle with coil over springs from Comp Eng.
The suspension needs to be aligned - front and rear. The front end is from a '70 full size ford and is aligned in the same way as the original tbird.
The rear end is going to take extra care. There are two links on the top of the axle that angle inward and forward; and two links on the bottom of the axle that are level and pointed straight to the front.
How do these two sets of links work with each other?
And what are the critical adjustments?
...
Had this posted under "Welcome" and took me a while to find how to post here !!!
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Old 01-09-2006, 12:26 PM
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So it is a triangulated 4-link with no Panhard (aka track) bar set up like this?
|/\| (with the top of the screen being the front of the car)

IMO the easiest way to set it up is to disconnect all the links from the axle, position the axle and chassis where you want them to end up (side to side, front to back, pinion angle, etc...) and then adjust all the links so they will bolt in without moving anything.
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Old 01-09-2006, 08:12 PM
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triangulated 4-link

This sounds easy... And your diagram is right on...
Does ride heigth effect these adjustments?
Should the front end be aligned before the rear adjustments?
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Old 01-09-2006, 09:29 PM
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I don't see that the front end alignment would make much of a difference - as long as it is in the ballpark.

Yes it would have to be at ride height. It could of course be at ride height with the axle 2feet off the ground so you can slide around under it.
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Old 01-10-2006, 05:56 AM
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Front end alignment does not factor in. Pick points on either side of the frame that are identical. Place the rear axle evening the distances up by continually adjusting the lower bars. The top angled bars will have more of an adjustment for pinion angle than the lower bars. When you get consistent measurements on each side relative to your frame reference then measure the length of each of the 4 arms to see that they are the same. I cannot stress enough the continual measuring.

Vince
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Old 02-24-2006, 12:43 AM
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Two questions I'd like to ask regarding 4-link setups:

1. How does triangulated compare to "straight"?

2. Does the top and bottom have to be the same length or did you mean that both tops must be equal and that both bottoms must be equal?
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Old 02-24-2006, 04:22 AM
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Neo, the axle assembly must be located both fore and aft and laterally. To locate the assembly laterally, the straight 4link requires either the addition of a Panhard OR a fifth trailing link which goes from the rear of a link on one side to the front of a link on the other side. As has been pointed out, the triangulated setup does not require an additional link for lateral location.

The triangulated arrangement also has an advantage in that it has the potential for eliminating binding during cornering. (I say "potential" in that binding can only be totally eliminated when the "V" comes to a point and is not truncated. Usually, however, the two angled links pivot at four points...not three...and some binding is still present.)

Many would say that the straight 4link has a competition advantage in that the links can be individually adjusted. The triangulated arrangement is generally considered a "street" setup. There are, however, some "tricks" with the triangulated links that can make it very suitable for competition.

For instance, if the lower links of Black-Hawk's arrangement were individually adjustable, the lower right link might be angled up more than the lower left, resulting in a possible cancellation of driveshaft torque unloading of the right rear tire. To test the effectiveness of such an adjustment, I would recommend use of a traction dyno.

Asymmetric adjustments and the traction dyno are discussed at:

http://home.earthlink.net/~whshope

As for link lengths, the rule of thumb is "the longer, the better." Longer lengths mean a more stable setup during changes in ride height and while encountering track surface irregularities.
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Old 02-24-2006, 05:44 AM
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Thanks! Made perfect sense and I'm happy. Much appreciated.

The thing is that I've got a triangulated 4-link axle that I want to put into one of my other project cars. I didn't know if I had to keep that setup or go for a straight setup. Now I know I can keep it and just make new links once I've modified the chassis and floor a bit. I'm planning on channeling the '48 Fleetmaster I'm getting to get it nice and low without sacrificing too much ground clearance on the chassis.

The axle I've got is a 3.42 (I think) with limited slip (maybe posi) from an Australian Holden Statesman. I've been wondering if I should use that or the spare Jaguar IRS I've also got. I've actually got two Jag centres, one a 4.45 and the other 3.32 but neither with lsd. But, due to cost of overhauling the Jag stuff and the lsd the Holden axle won.
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Old 02-24-2006, 03:31 PM
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lower bars

you guys are givin some good info for people who are starting to do rearend chassis work.

take heed and listen to all that has been posted.
as z28 said, CONSTANTLY MEASURE!!!

there are 2 points that i would also like to stress in a rearend set up.

1, when mocking up a rear suspension, weld the rearend to the frame where you want it at ride height,
use angle, box tubing, or whatever you got to locate the rearend with pinion angle set. (dont eyeball it, call speedway,summit,etc. and spend 10 dollars on a pinion angle finder) that way it wont move during suspension mock-up.

2, no matter if you have a triangulated or normal 4 link, ALWAYS KEEP YOUR LOWER BARS LEVEL TO THE ROAD. the reason?, if you dont have your lower
bars parallel, you run a greater risk of wheel base change during suspension travel. and could cause binding .
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Old 02-24-2006, 08:28 PM
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Quote:
Originally Posted by h0trod389
2, no matter if you have a triangulated or normal 4 link, ALWAYS KEEP YOUR LOWER BARS LEVEL TO THE ROAD. the reason?, if you dont have your lower
bars parallel, you run a greater risk of wheel base change during suspension travel. and could cause binding .
Here's a case where the wheelbase change would be large, but there would be absolutely no binding during cornering: Suppose the lower links are parallel to the upper links and all links are angled up at a 45 degreee angle. As you turn left, the right side wheelbase would be lengthened and the left side wheelbase would be shortened. There would be no binding, however, because of the parallelogram linkage. Another way of putting it is that there is no binding because the instant center is at infinity. (Parallel lines meet at infinity.) As the instant center is brought back from infinity (approaches the centerline of the rear axle), the binding increases.

Manufacturers of 4links often recommend that, for the street, the upper and lower links be parallel to each other and to the ground. The "parallel to the ground" business is to minimize roll oversteer. While extreme roll oversteer can take a little getting used to, there is no inherent danger. If your car pushes at the limits of adhesion, you can add as much roll oversteer as you like and it will still push at the limits. The "oversteer" in "roll oversteer" is due to the SAE definition of oversteer, which involves steering wheel angle. Roll oversteer does not, however, affect the wheel loadings, so handling at the limits is unaffected. There are none of the stability problems normally associated with oversteer.
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Old 02-25-2006, 08:16 PM
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Neophyte, if your Statesman rear end is a live axle from an early 70,s 350 S/man it will be 2.78 or 3.08 lsd - very weak side gears, the one wheelers are much stronger (larger gears in the same size hemisphere). 3.36,3.55 and 4.44:1 were available in Monaros and 1 tonners.
If you have a Statesman irs - like my 96 daily driver it will be a 3.08 one wheeler. The HSV Grange (345hp) had a 3.46 hydra/track . Standard wheelbase Clubsport/GTS 6 speed manuals came with 3.46/3.9 centres which are a bolt in, same would apply to the Oz built Pontiac GTO (Monaro)
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Old 02-25-2006, 09:27 PM
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Thanks Ian,

Yes, the car it came from is early 70's but was known as the Chev DeVille here is South Africa which basically is the Holden Statesman. An HQ if I'm not mistaken. For some reason my memory tells me that the ratio was shorter than 3.08 but I could be wrong. I'll go and open it up again to count the teeth.

But at the end of the day you're telling me it's not all that strong? Would a mild 350 break it then?
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Old 02-26-2006, 01:33 AM
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My late father ordered a Statesman De Ville the day he sold our dairy farm in august 73, we picked it up on my sisters birthday - oct 25 73.
He died of golden staf infection following major surgery on dec 25 1973 - hard day to forget.
My mother, a farm girl from birth had driven cars, trucks, tracktors and earth moving eqpt from her teens but didn't get a licence until may 74 when, with 4 kids under 20 she had to. She blew the first centre in oct 74. By the time I was 15 I had replaced the lsd with a one wheeler, recurved the delco (moroso kit), fitted headers and 430 Buick secondary rods. With a standard 2.78 ten bolt it ran 14.4 at calder with air and p/steer.
No, the diffs aren't strong, if it's an lsd or you plan on burnouts then use the Jag. A one wheeler will live in a MILD application but if lean on it it will shed pinion teeth. Having said that, the 1 tonner axles are MUCH stronger than 28spl ford, I have a 9 in centre with custom housing and 1/ton axles (equalish length) in my 400 sbc HQ ute with nary a problem.
Here we called those 350 Statesman/Chevs an export Statey as they wound up in NZ, Sth Africa (rhd) and sth pacific, se asia (lhd). I'll bet Billy Shoppe's next meal your ratio is 2.78.
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