Help with setting up a four link rear suspension

[Oldphart]

I'm in the process of installing my first ever triangulated four link suspension in my 27 Tudor using a Ford 8" and coil over shocks and I have a few questions. I've read lots of posts on the subject...to the point where I'm a little confused...maybe more than a little but I have a plan.

1. I can fab brackets to get the lower control arms parallel to both the frame and the ground, keep the driveline relatively flat and still stay well above the scrub line so I think I'm OK there. My frame is 27" wide and the axle 54" at the flange. It would be easier and probably a bit stronger to mount the bars directly to the outside of the frame but I could fab brackets to move them out further. Is there an advantage to spacing them further out toward the ends of the axle?

2. The longest lower arm I can get to work without major mods to the body and frame is 19" the upper would be 14". I believe the proportions are correct but are they long enough assuming 3" of upward suspension travel? That may be a silly question because there's just no good way to go longer.

3. By welding the brackets for the upper arms to the center of the axle housing I can get about 90 degrees (45 per side) with a slight upward slope to the attachment point on the frame. I've read conflicting info on the best angle some say 90 is best some said more like 70 degrees. Anyone have experience here?

4. As I mentioned I'm planning for 3" of upward suspension travel. When I buy the shocks should they then have 6" of travel with the suspension sitting at halfway with the weight of the car on it?

Thanks in advance for any input.

 

[Old Iron]

1. The suspension will be more stable the farther out they are positioned.
They don't have to be parallel, You can angle them out from the frame to the rear axle, just don't get them so far out they interfere with the tires and wheels.
Shock angles should not exceed 10 degrees either for them to work like they're designed.
2. That will work since you only have 3" of travel. Pinion angle change through suspension articulation is what you have to keep under control.
3. A slight angle down towards the front of the vehicle is the best.
Around 10 degrees.
4. I like a shock with 9" of travel. Less likely to bottom out.

 

[Oldphart]

1. The suspension will be more stable the farther out they are positioned.
They don't have to be parallel, You can angle them out from the frame to the rear axle, just don't get them so far out they interfere with the tires and wheels.
Shock angles should not exceed 10 degrees either for them to work like they're designed.
2. That will work since you only have 3" of travel. Pinion angle change through suspension articulation is what you have to keep under control.
3. A slight angle down towards the front of the vehicle is the best.
Around 10 degrees.
4. I like a shock with 9" of travel. Less likely to bottom out.

Thanks a lot for the advice, just what I was looking for but more information brings more questions .

1. It makes sense that wider would be more stable. I thought of angling the lowers outward and making them longer but I was concerned that having different angles on the upper and lowers would cause binding. It sure would be easier and stronger than adding outriggers.

2. I know it's important but how could I change my set up to better control pinion angle?

3. Oops, I got confused between reading and trying to fit those ideas on my frame. Is the reason because it improves the roll center?

4. 9" shock travel with the suspension centered in the travel?

I plan to mock it up and just tack weld then work the suspension and see what I've got but I sure would like to get it right the first time and this kind of input sure helps. Thanks again.

 

[Old Iron]

1. It'll have less bind than if they were straight as it articulates over uneven surfaces.
2. Pinion angle changes even on factory vehicles. A small amount is acceptable on street driven vehicles. I wouldn't be concerned with it since you only have 3" of travel.
3. No, the roll center is controlled by the front end geometry and the panhard bar in the rear, which you will not have with a triangulated 4 bar.
With the upper bars angling in from the framed back and the lower bars angling out from the frame back, it gives a little more control of holding the rear end centered under the vehicle.
4. I set my shock travel at 5" up and 4" down travel.

 

[Oldphart]

Thanks a bunch for your input Old Iron. I think I have a good plan now. The geometry of the suspension will probably make more sense to me when I get it mocked up and can see it move in 3-D so to speak. You've got me thinking about the amount of suspension travel I planned for and I think I'll look for a bit more.

 

[Old Iron]

You're welcome
On vehicles with fenders, I use a shock with enough travel to let the tire drop to a point I can get it off the axle without unhooking the shock, don't be afraid to use longer ones.