four link suspension, need the correct angles for the bars. 1

[opiesrodshop]

I am building a 1936 Ford street rod. I am wanting to build my own four bar, three point rear suspension. But I am not sure of the correct angles for the bars, or the proper place to mount them to the frame. Can anyone please help me?

 

[GregLocock]

Is this the suspension with 4 mounting points on the body, two with just a normal longitudinal rod, under the axle, and two in a V shape to a single point on the axle, on top? Do you have a Panhard link or Watts link as well? Coilsprings or leafs?

The trick with multilink suspensions is to keep everything square and equally spaced, until you have to change it. Also maximise the dimensions if possible, but not by sacrificing squareness.

So for a starting point

in side view make sure that the length of the two longitudinal rods equals the length of the A arm, and that they are mounted as much below the axle centreline as the A arm is above, and that at design height everything is parallel tot he ground (ideally).

In plan view make it all symmetrical, and keep the arms square to the axle.

Now the fun starts.

Back in side view, that arrangement will keep the diff parallel to the gearbox output shaft (which is good), but if you have a lot of suspension movement the propshaft or the diff or the pinion nose may hit the floor, or the UJ may over-articulate. So often you shorten the upper arm to dip the pinion nose as the suspension rises, or move the body mounting point for the A arm down. You need to make a model or draw it out to make sure that you aren't plunging the prop shaft too much if you do this.

In plan view on our four link beam axle we angle the upper arms in a bit, but you've already got that in spades, so I'd leave the lower arms parallel.

You'll need to post some more details and dimensions if you want to go further than that. Incidentally from the drawings I've found most non racers angle the upper and lower arms towards each other in side view.

oh one other thing - what is this suspension supposed to do? How much suspension travel does it have?









Cheers

Greg Locock

 

[opiesrodshop]

Thank you for your reply. This is the style that has two v-shaped bars meeting at a single point above the axle. I do not currently have plans for a panhard bar. Is this something I should look into further? The spring set-up is coil over shock.
This street rod will not be used for racing, only touring. So ride quality is what I am going after with this set-up. I would be more than happy to get you bar lengths, angles, and axle travel if that would be helpful with more advise.
Again, thank you for the information.
Thanks
Opie

 

[GregLocock]

I don't recognise that suspension layout, I'm afraid (not very surprising). If you send a jpg of a sketch with dimensions on it to me at greglocock at yahoo dot com dot au then I'll have a look. While you are at it details like the front suspension travel, spring rate etc would be handy.

I forgot to add that in side view the links are often angled upward to give anti-squat on acceleration, and anti dive under braking.
Cheers

Greg Locock

 

[c2s]

Opie,
I think I recognize the configuration you described ... same as on the late 70's & early 80's full size Chevy and Ford. If so, the side view will define the instant centers for the upper and lower arms. The line between the two IC's will describe the roll steer. If this is the correct configuration, let me know & I'll shoot you a link to a webpage that will be helpful.
Kevin