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Old 07-30-2006, 08:16 PM
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Rear Suspension: Will it work?

After a few hours at my local adult beverage establishment, I came up with a design for my RPU. It's loosely based on the trailing arm suspension described in the latest issue of R & C. It uses a pair of Ford 'bones as trailing arms welded to the rear end, a pair of coil springs, panhard bar and shocks. My questions are, will this work, and is the desired pinion angle 5 degrees up? If you have any questions, please ask, as I am unsure what you need to know. BTW, it's hard to tell in my drawings, but the panhard bar will be level with the ground at ride height, but the control arm will be pitched up in the front just like it is drawn.
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Old 07-30-2006, 08:22 PM
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It will work....its been done before.
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Old 07-30-2006, 08:34 PM
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Yes, that will work. The pinion angle, however, will be dependant on the angle of the motor. When you set the motor tilt, be sure to set it no more than 5 degrees, or no less than 1 degree.



http://carcraft.com/howto/91758/
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Old 07-30-2006, 08:40 PM
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My plan was for the output shaft of the trans and the pinion of the rearend to be almost level with each other except for the pinion angle. Looks like I could pitch the rear of the trans up a few degrees and the pinion up a few degrees and I'll be OK. Right.

As for the design of the suspension itself, my main question is since it wont be a four link, or ladder bars, is there enough support on all planes(X, Y, and Z)? Is there enough triangulation for it to work?
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Old 07-30-2006, 10:49 PM
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I wouldnt recommend pointing the tailshaft of the tranny up. You motor has to tilt back at least 1 degree. That means your tranny will tilt back that much as well. If your driveshaft is level, tilt your tranny down 2 or 3 degrees, and the pinion up 2 or 3.

Essentially that setup is a 2 link. That will provide enough support in all directions but side to side, thats where the panhard bar comes in to play. You'll be fine. I'd make the panhard as long as you can though.
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Old 07-31-2006, 03:58 AM
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Joe, if you were to bring the front ends of the links together at the center of the car, you'd have the suspension used in the NASCAR Cup cars. (This isn't by their choice. It's dictated in the NASCAR rules.) Unfortunately, that which you're proposing would require a birdcage at the rear of one of the links. In other words, one link would have to be free to rotate about the axle housing. If this were not done, there would be severe linkage bind during cornering. (While cornering, one wheel is going up and the other down. This means one link is attempting to rotate the axle housing clockwise and the other counterclocwise. Not good!! With the NASCAR design, the two links become one.)
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Old 07-31-2006, 06:22 AM
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Quote:
Originally Posted by BillyShope
Joe, if you were to bring the front ends of the links together at the center of the car, you'd have the suspension used in the NASCAR Cup cars. (This isn't by their choice. It's dictated in the NASCAR rules.) Unfortunately, that which you're proposing would require a birdcage at the rear of one of the links. In other words, one link would have to be free to rotate about the axle housing. If this were not done, there would be severe linkage bind during cornering. (While cornering, one wheel is going up and the other down. This means one link is attempting to rotate the axle housing clockwise and the other counterclocwise. Not good!! With the NASCAR design, the two links become one.)
If I bring the front ends together they'll be in the way of the driveshaft, or contact the frame. That's why I'm running them on the outside of the framerails. I'm very limited on space. There is only 24" between the framerails, and I have a driveshaft, springs, and shocks to fit in there. There will only be only a few inches of suspension travel, anyway, so wont the axle pivot at the front joint? It is a ball joint type connection, just like any split wishbone.

Last edited by bigjoe; 07-31-2006 at 06:31 AM.
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Old 07-31-2006, 06:29 AM
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Quote:
Originally Posted by Twisted Minis
I'd make the panhard as long as you can though.
I heard I should do that, but because of the space limitations between the frame, the only way I could to that would be to run the end that's connected to the differential all the way over to the other side near where the shock mounts up.
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Old 07-31-2006, 06:37 AM
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Set the engine/trans in the frame so that the carb base of the intake manifold is level front to rear and side to side. This usually results in the centerline of the crank/trans mainshaft 4 degrees down toward the rear as per factory design. Set the pinion at four degrees up. (See photo of Small Block Chevy below) The crank/trans mainshaft and the pinion shaft should be parallel.

In your sketch the trailing arms appear too short. They should attach to the frame closer to being in line with the front u-joint. The coil springs are also too close together and would result in some serious roll that close. Spread them as far apart as the body/frame will allow.


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Old 07-31-2006, 07:46 AM
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[QUOTE=Frisco]In your sketch the trailing arms appear too short. They should attach to the frame closer to being in line with the front u-joint. The coil springs are also too close together and would result in some serious roll that close. Spread them as far apart as the body/frame will allow.
QUOTE]

That is all the space I have. If I mount the trailing arm even with the u-joint, it'll be in the front seat with me.
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Old 07-31-2006, 10:23 AM
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Quote:
Originally Posted by bigjoe
There will only be only a few inches of suspension travel, anyway, so wont the axle pivot at the front joint? It is a ball joint type connection, just like any split wishbone.
This isn't a bushing/Heim/ball joint problem. Consider the car as it turns left. The right side wheel moves up into the chassis. As it does, the right side link rotates clockwise (as viewed from a position to the right side of the car) and, since it is welded to the axle housing, the axle housing also tends to rotate clockwise. But, on the left side, the wheel is moving down and away from the chassis. The left side link is then rotating counter-clockwise and so is the axle housing where its welded to the left link. This turns the axle housing into a big torsion bar.

If you can't copy the NASCAR setup, there are some other options. One would be to weld only the right side link and use a bracket and bushing on the left (with a Panhard, of course). What this would really amount to is a 3link, with the two right side links having the same forward pivot point.

Another would be to simply go to a 3link. See my blog for some 3link variations:

http://home.earthlink.net/~whshope
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Old 07-31-2006, 11:04 AM
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Quote:
Originally Posted by BillyShope
This isn't a bushing/Heim/ball joint problem. Consider the car as it turns left. The right side wheel moves up into the chassis. As it does, the right side link rotates clockwise (as viewed from a position to the right side of the car) and, since it is welded to the axle housing, the axle housing also tends to rotate clockwise. But, on the left side, the wheel is moving down and away from the chassis. The left side link is then rotating counter-clockwise and so is the axle housing where its welded to the left link. This turns the axle housing into a big torsion bar.

If you can't copy the NASCAR setup, there are some other options. One would be to weld only the right side link and use a bracket and bushing on the left (with a Panhard, of course). What this would really amount to is a 3link, with the two right side links having the same forward pivot point.

Another would be to simply go to a 3link. See my blog for some 3link variations:

http://home.earthlink.net/~whshope
Thanks for the link, looks like I might be able to make something work. Would I be OK if I just make a bracket and bushing for both trailing arms, instead of welding them both to the differential?
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Old 07-31-2006, 11:09 AM
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[QUOTE=Frisco]Set the engine/trans in the frame so that the carb base of the intake manifold is level front to rear and side to side. This usually results in the centerline of the crank/trans mainshaft 4 degrees down toward the rear as per factory design. Set the pinion at four degrees up. (See photo of Small Block Chevy below) The crank/trans mainshaft and the pinion shaft should be parallel.

In your sketch the trailing arms appear too short. They should attach to the frame closer to being in line with the front u-joint. The coil springs are also too close together and would result in some serious roll that close. Spread them as far apart as the body/frame will allow.
QUOTE]

I agree...this is the correct way to set up the driveline geometry. Don't just play with numbers. Actually check the setup with gauges, then set the pinion angle to compensate. Inland Empire Driveline recommends 3* (full weight & ride configuration), and that's what I use with my setups.

You have problems with the engine mounting IF your angle gauge(s) reads in excess of 5 degrees.

Also, (just curious...not picking it apart), why not go four-link? It's no harder to do than your setup, doesn't require any more room, and will prevent wheel hop better than two-link.

George
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Old 07-31-2006, 11:32 AM
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Quote:
Originally Posted by gdubstub
Also, (just curious...not picking it apart), why not go four-link? It's no harder to do than your setup, doesn't require any more room, and will prevent wheel hop better than two-link.

George
NO, I welcome the picking apart! That's how I'm gonna figure this all out. I decided to use the lower link setup because I already have a set of split wishbones on hand that are too short to be used as a frontend setup, and I want to: A) Keep cost down, B) Use as many old or OEM parts as possible, and 3) I have a hard time doing "what everyone else is doing". I like to be different.

As for wheel hop, this thing is NOT, NOT going to be a powerhouse, nor do I drive like a fool, so that shouldn't be an issue.
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Old 07-31-2006, 12:35 PM
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Quote:
Originally Posted by bigjoe
Thanks for the link, looks like I might be able to make something work. Would I be OK if I just make a bracket and bushing for both trailing arms, instead of welding them both to the differential?
Only if you locate a third link above the axle.

If you're intent on fabricating something, I'd strongly recommend a 3link. If you follow the instructions at my blog, you have the opportunity to dynamically cancel driveshaft torque.
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