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Old 04-21-2009, 11:32 AM
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Setting up a four link

I am building a 1928 ford model A, although the only thing model A anymore is the body. It is going to be low and mean. It has 400 hp. and 400 lb. ft. of torque and it will only weigh around 2,000 pounds. I would like to be able to take it to the strip and have it do well (when I had the engine dynoed they put all the cars specs into some sort of calculator and they said I should be able to make 10 seconds... If I can hook up). So, my current project is to get the four link set up and I am not sure exactly how to go about this. I was originally going to just set them parallel to each other and parallel to the ground at ride height, but I'm not sure if this will be adequate. It seems like most drag cars have the top bars level and the bottom bars angled up. I have been trying to find out how important this is and if it is what I need to do.

I know this is not a very simple question to answer and it depends very much on the specifics of the car, but any info, help, or resources you guys can give me would be great. Thanks.

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Old 04-21-2009, 01:08 PM
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Here is a good resource, Billy Shope has a website that has all kinds of info regarding setting up 4 links as well as a ton of info about suspension design and adjustments for getting your car to hookup.
http://home.earthlink.net/~whshope/

There are calculators included there as well as how to find the input numbers you'll need to use them.

Another good resource is Herb Adams book, called "Chassis Engineering" , published by HP books...I have another suspension design book by Steve Smith, but IMO it is not as good as the Herb Adams book.

I'm sure there are more good resources, in print as well as online, I'm sure you will get a few more responses from other members here.

Later, mikey
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Old 04-22-2009, 12:13 PM
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Chester...you are on the right page to get away from the parallel link that is so popular. These work great for cruising, ride nice and don't get choppy in the corners.

For drag racing or just plain brutal acceleration you can not beat the true 4-link. Now setting them up is whole chapter in itself. There are a couple programs available but be prepared to spend about $100 for them. You will have to do a search as I just don't have them right now.

I installed a true 4 link on my 41 Willys for the same reason you are. There was an Excel program someone made a long time ago but I think it has been taken down. I used it to calculate a number of what ifs for my car. right now I'm in the middle of trying them out. I don't have a spool or locker rear end so it become pretty clear when things start working. So far I have gone from 1 wheel wonder to both rear tires digging in and a straight line launch. It digs really hard now even though it it does slip the tires. I only weigh 2550 with 1150 on the rear end. 400 hp motor (on paper)

Rear roll stiffnes is important so plan on making a rear anti roll bar. The front needs to be soft. I'm currently working on a variable rate front roll bar so I don't have to disconnect it for racing.

Definitely use adjustable coil overs at all 4 corners.

4 link kits are availabe from several mfg. Summit and Jegs Chassis eng come to mind. I made my own.

My ride is a little on the stiff side but I may add softer rear springs. Nothing I can do about the front. I already have the softest available. It's acceptable. Braking really surprised me. With a couple twists of the proportioning valve I now can lock up all 4. With the big Hoosiers on the rear and 7 in wide front tires It really stops quick. I;m sure it is very competitive with the best on the road except the sports cars.
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Old 04-22-2009, 07:43 PM
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OK guys since I have been driving my 34 I have tried a few hard launches (when the wife is not with me). My 34 has a triangulated 4 bar rear with a Ford 9" Ford Racing Trac-Lok 3:50 ratio. Transmission is a 700R4. Both times I am in D with my foot on the brakes and the throttle to the floor. Release the brakes and the car starts to leave hard but then violently lurches to the left. One time I made a complete 180 in the middle of the road before I could get it shut down.. This is on a country road with no one around. It seems it pulls hard until it shifts into second, and if it's still spinning when it shifts into second then it gets really squirrelly. Any advice?

Vince
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Old 04-22-2009, 11:35 PM
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I love the color of your '34 It's close to what I'm going to paint the Willys.

I'm assuming you have checked all the rear suspension bolts, brackets, bushings and shock adjustments and alignment. This has always been a concern of mine...to break an axel or spider with a locking or spool rear end.
For the problem I would look at the rear end. I assume by lurching to the left you mean as though turning left. I suspect the Trac-Lok is not locking up correctly and applying all the power to the right side causing the car to try to turn left. Is it possible you have a broken axel and the Trak-Lok is strong enough to drive the car with just one wheel??? Maybe an axel is not even engaging the spider gear on one side or there is a broken spider gear. Clutch pack messed up.?? Possibly the rear brakes are not releasing completely. My Dodge dually has a limited slip that will lock up nicely in the mud or snow if you just lightly apply the e-brake.


I couldn't imagin anything wrong up front unless you are yanking the steering wheel. Not likely with a long time hotrodder.

Last edited by bentwings; 04-22-2009 at 11:41 PM.
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Old 04-23-2009, 12:05 AM
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this will help ya
http://mysite.verizon.net/triaged/4l...tml/index.html
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Old 04-23-2009, 12:46 AM
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I'm guessing it's about weight transfer , and if your car is set up for good cornering left or right, and not alot of anti squat at the rear, (usually how it works with the TCI un adjustable trangulated 4 link) it will mess up your launch.
Do you have a front and rear swaybar? I'd try unhooking the front one. You can't do much more than that without preloading your springs, (but that will make it handle better turning one way, and suck turning the other.)


Here is something that might help understand what's going on.

http://racingarticles.com/article_racing-50.html

Another gem from Billy Shope.

Whatever you do to make it pull straight when you are hammering on it, will take some away from your everyday driving experience.

Of the 2 '34 coupes I worked on in my shop for customers, the one with the front straight axle and no front swaybar went much straighter when both back tires were smoking than the IFS equipped car with front and rear swaybars.

Both cars had limited slip rears, and the parallel 4 bar setup with panhard bars.

Later, mikey



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Old 04-23-2009, 07:40 AM
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Thanks guys, the car has no front or rear sway bars. I am certain both rear wheels are pulling as it leaves two strips of rubber about the same length on the road. When I put everything back together after painting the frame I made the length of the four bar components equal to each other as I set the pinion angle. The front end is IFS. I am not too concerned with how it does on hard launch, as I will not be doing that very often, but I would eventually like to see what it would do on a quarter mile strip. If it goes crazy like that off the line it could be disastrous . If it someting simple I could check or look at that would help.

Vince
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Old 04-23-2009, 09:18 AM
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Possibly you just hit a goofy spot on the road. Maybe it's just the new tires.

My big Hoosiers were a bit slippery until we burned them in.

Just be careful, we don't want to read any bad news.

I had a fuel funnycar do a right turn just off the line on a concrete air port drag strip. No good reason at all but I totally demolished the tree and a 2 concrete blocks. The next run same lane it ran perfect.
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Old 05-04-2009, 10:39 AM
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Thanks guys for the helpful replies (at least the first few anyways). I have checked out the resources some of you gave and have a much better understanding of what I need to shoot for in building my rear suspension. I do have one more question though.
Where do you want your instant center to be?
I couldnt find anything about this in the Herb Adams book (he only explains how to find your instant center, not where to put it). And on the Billy Shope site, he talks about instant centers but to be honest I didnt completely understand it so I may have missed the answer I'm looking for. So, if anyone can help clarify this then that would be great. If not, then I guess I keep trying to decipher Billy's super-technical writing
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Old 05-04-2009, 10:49 AM
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FWIW, Circle Track magazine has been running a series of suspension/handling articles for quite some time.

IIWY, I'd visit their site HERE. Root around some and even though they are using different rear suspensions for the most part, instant center and roll centers and such is discussed at length.
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Old 05-05-2009, 10:24 AM
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I got to put some time and testing on my Willys last week end. I don't have a limited slip yet so it is a one wheel wonder until set up.

I just added a 2800 converter so the torque curve is much better matched. The converter really hits hard now.

I started by adding 2 turns to the left front coil over and 2 turns to the right rear coil over and left the front sway bar hooked up.

This gave a good start with the left tire leaving marks and the right still much darker. Pretty straight launch.

I added another turn and a half to each shock and lowered the rear tire pressure to 17 psi. This was even better as the tires now are both hooking better but the right tire is till unloading.

Next I loosened the front sway bar so there is about 1 1/2 inches of free travel. No other changes. This really helped. Both rear tires hooked hard and evenly. It drifted to the right ( rear end moved to the right) about a foot in the 100 feet of tire marks. the marks are not really burned into the pavement. Just clearly there. The car is really moving hard even though the tires are slipping.

We made several launches in opposite direction in the same area to make sure of our adjustments. It's dead consistent so I still have a little adjusting to do but I'm really happy now. It really doesn't blow the tires off at all even with the converter.

I still have 2 more adjustments to go on the 4 link so I can get even more positive body lift. Hopefully it won't do some crazy wheelie.

I reconfirmed that the motor will not perform unless it is over 180 deg and it takes at least 1/2 hour driving to warm up. 180 thermostat too. The air gap manifold just needs heat radiating from the motor. Once it is warmed up it runs great.
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Old 05-05-2009, 03:09 PM
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Vince, what is your pinion angle set at, and what is the angle of your transmission yoke?
I vaguely remember about 6 years ago, a buddy's GTO wasn't hooking up straight, similar to what you're explaining. We adjusted his pinion angle and it helped the problem immensely, although he had a ladder-bar setup.
From what I've always been told, if you're using standard u-joints at each end of the driveshaft the pinion and transmission yoke should be parallel to eachother, and if you're using one standard u-joint and one double-cardan joint, your pinion should point at your trans yoke.
I'm not sure if this is exactly your issue, or if my information is exactly correct, so please correct me if I'm wrong.
This also doesn't factor in any slight degree's of axle wrap you're getting on launch that could possibly change the angle enough to cause it to go crooked like that.
When I had a locker in the back of my jeep, my pinion angle was off, and if it down-shifted in traffic it would almost jump into the other lane.
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