Projects Mocking up rear suspension for my Bantam - opinions please

hi guys

I am mocking up my rear suspension for my Bantam roadster project. I am currently planning to use ladder bars with helms at both ends, coil overs and a panhard bar to connect my narrowed nine inch to my chassis.

Bantam's are small cars and my seat will be only a few inches forward of the pinion. Thus no room to move up into the passenger compartment and use a tri-link or triangulated four bar. With a regular four bar (parallel to frame rails) the top link would only be a few inches long. So, all of those options are out at least in my humble opinion.

Here is where I could use the input from the HAMB. I would prefer to put the ladder bars parallel to the frame to keep out of the passenger compartment. See pics below with driver side ladder bar mocked up.





Or, should I angle the ladder bars to the tranny tail shaft like in this photo? Note that the bantam is such a short wheelbase car that my current ladder bars actually extend past the tranny tail shaft. Also note that I will intrude into the passenger compartment a little to make this angle work.





Lastly, here is a photo shooing the two different ladder bar placements:



Appreciate your thoughts and thanks in advance for your help on this.

- Bantam






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Shorten the bars and mount them to the back side of the trans crossmember. Run your track bar (panhard) parallel to the ground.

 

To give yourself some room inside I'd mount the bars outside the rails.
I would shorten the bars (in fact I'd go 4 link) so they pivot flush with the rear of the trans.
As stated panhard parallel with the ground.
Do some Googling to get anti-squat in the rear correct or you may start doing wheelies.

 

Three things

1. The ladder bars should be close to parallel to the ground..."at finished ride height" (fully loaded/finished car). Make the front mount with at least two fastener locations, three would be better if you can.

2. The Panhard bar should be parallel to the ground at "finished ride height".

3. The Panhard bar should be as long as it can be made, not the little 18" ones as sold to unsuspecting builders. The car will be MUCH more controllable under power with a longer the bar.

I've built /rebuilt several chassis and in ALL cases, the Panhard bar goes from the frame rail on one side to...as far as it will go on the other side of the car. Like bracketed on the axle right against the frame rail on the other side.

Make yourself a "paper doll" layout with pins and cardboard to see how much the rear axle moves...side to side.
This assumes that you have more than 2" of axle travel..!

Mike

 

Looks like the ladder bars are chromed and the threaded insert is welded in. Any modification to them throws the chrome out the window.

Sell the chrome ones and make some that fit. Running on the outside will give you more trouble geometrically than triangulating towards the center.


You didn't ask but the Trans mount is welded in and that's likely to give you an ass ache eventually. You could move it toward the front and get your chrome bars working. The top of the bar should be about centered in the axle and the lower bar close to level with the ground.

A Z will bring the cabin closer to the ladder bars

 

Tight little buggers back there, aren't Bantams ? I had fits trying to get all the suspension tucked back there on the project drag altered I have sitting around. Funny as it seems, T buckets have so much more room back there.

Don

 

I would go with ladder bar by frame rails and like said above - longer panhard bar. Panhard laid on frame rail for pictures - you are going to stand it up right??? not flat on frame rail. Heim joint move few degrees up and down or if stood on top of frame would move - allow few degrees fore and aft like ladder bars need. Hard to explain in words. Also like idea of "paper doll" lay out and try moving rear end as you want it to move.

 

Consider eliminating panhard bar and running a diagonal from right rear lower ladder bar bolt to front left bar attachment point? This would pass under driveshaft. More of a drag configuration ,but should work on a light car.

 

Don - I was following your build as you tackled the same problem. I am making mine a two seater (wife is more supportive of the hobby when I put in a seat for her which only makes it more challenging to make everything fit.

 

With the ladder bars installed parallel you will have no roll compliance in the rear (unless the frame twists) as you have a truss configuration. With the bars triangulated and mounted to the trans crossmember (street rod style) you can get some roll compliance if you use urethane bushes or such at the front mounting point. If you use the heims you will be putting some bending load on them while cornering as the frame tries to roll (the same applies to the parallel installation but more so). If you do use the triangulated configuration keep the forward mounts as close together as possible.
As stated, the longer the panhard bar the better so a standoff mount on the right axle tube would be better than the tabs on the center of the housing. If you have limited rear suspension travel this becomes less critical--if the bar is parallel to the ground a 12" center to center bar will only move the housing 1/8" or so laterally through 3" of vertical travel.
The suggestion to use a diagonal locator between the parallel ladder bars will work but the brackets to mount it need to be stout for a street application as compared to its more normal use on a drag strip where (hopefully) there is minimal lateral loading.
Finally---please try to build it with some sore of compliant bushes at least where the bars mount to the frame. Heims are OK on race cars but pretty harsh on the street. Remember that (paved) race tracks usually do not have chuck holes, manholes, abrupt surface transitions etc like the average streets.

Roo

 

The question becomes what are you building a performance oriented car (think really fast from point A to point B in a straight line) or a cruiser.

Roo gave you a pretty good explanation of the workings of what you are building. So it becomes are you going to drive it most of the time and race it once a year or are you going to race it most of the time and drive it once a year.

On the roadster the raven runs his ladder bars parallel to the chassis on the outside of the frame, he likes it real well. His chassis is pretty wiggly and he mostly only races it other then the trip to the track.

One other thing to consider is packaging, looks like your real option is to run them parallel so using a bushed end for a little give is your other real option.

 

Have you considered parallel leaf springs? That would allow you to put the suspension outside the passenger compartment, or below it. It would also eliminate the need for a panhard bar.

Or, you could bolt 1/4 leaf springs to the back of your ladder bars. In other words, the ladder bars would take the place of the front half of the parallel leaf springs. Then you'd have the simplicity of the leaf springs without the wind-up that causes wheel hop.

 

will it be multiple choice?

 

Sorry, my Android randomly wouldn't let me post a reply. I've edited it so there's actual content there now instead of just the word, "test."

 

Actually Big John ran quarter elips on his Willys. it was a good suspension and handled the power well.

LOL I figured it was something like that and I just couldn't resist.

 

As narrow as you are I think I'd go with a Watts Link instead of a panhard bar.

 

Thanks for input on bushing ends vs heirs. Is this what you would recommend rather than a heim?

http://www.speedwaymotors.com/Rod-End-Supply-FBE12-3-4-Inch-Four-Bar-End,60385.html

 

First thing I would do on a narrow car is get the coil overs as far apart as possible. If it were mine I would put them outside of the frame rail and do whatever I needed to do to the frame rails to make it happen. (notch them or step them in). If you can picture in your mind the coil overs right next to each other in the center of the car it would just be a pivot point, so the farther apart you get them the more stable the car will be (less body roll).

 

The more I look at the pictures, the more I like the parallel leaf springs idea. It eliminates a lot of problems like where to mount the panhard bar, the coilover springs, & the ladder bars.
If you mount them under the frame & axle they are not in the passenger area. With adjustable spring shackles the ride height is adjustable. With Wedge shims on top of the springs in between the axle pads you can adjust pinion angle. And you can slide the axle forward or backwards on top of the springs to play with the amount of possible spring wrap. You could even add or remove leafs to fine tune the spring rate. I likeit! I like it a lot!

 

Think it thru - all the way.
Can you envision where the rear spring mount is going to go.

 

Actually if I were going to run a quarter elip I would run it forward inside of the ladder bar, and I would use a shackle mount on the axle end of it.

If I were going to run coil overs I would run the vertical as near the inside edge of the cassis as possible. This will require using a lighter spring and perhaps even a shorter shock but it would work better then leaned toward the center of the car.

 

Yes, sir. I think I would mount it to the inside vertical surface of the rear most crossbar on the frame. If you weld two plates to the crossbar going up vertically, you could drill bolt holes at different hieghts to mount the spring shackle mounts up or down wherever you want or need them.

 

You could actually install a reversed spring over the top of the axle running from the front of the C to the rear of the C. See arrows. I suppose that would be an option and it would maybe work better then a standard leaf spring.

 

This would get back to what Kiwi Kev is talking about re the coil overs, a narrow spring base. It would be better to put them under the frame rails (as per your first post) to get them as far apart as possible. The problem that I see with using leafs is that the back of the spring (behind the axle) is going to be very short due to the extremely short overhang of the Bantam body. That is the exact opposite of what you really need. The best leaf springs available for performance applications are the ones used in sixties Mopars. The have the rear end about a third of the way back from the front hanger and the result is that the front of the spring does not wind up and the long rear makes for a better ride.
The quarter elliptic top link deal sounds good until you look at the relationship of the components. It would have to mount inside the frame rail and even then the axle attachment point would have to be on the front side of the housing, at or below the center line. It can't mount to the inside of the kick-up to get it higher because that is too close to the rear end to get the length of the spring in place. That reduces the spread between the upper and lower attachment points unless you make a really long bracket for the lower trailing arm to mount to and that in turn introduces geometry issues with the lower bar angle unless you put a corresponding long bracket off the bottom of the frame for the forward mount.
I personally would go with the Pete and Jakes style triangulated ladder bar deal with compliant front mounts, a long panhard bar and the shocks spaced as wide a possible and as close to vertical as you can get them as suggested by Kev. The Watts link would be a good idea except for the fact that there is nowhere to put it and clear the rest of the components/frame.

Roo

 

How long are leaf springs ?


I'm guessing he's about 20" short on the frame behind the axle for leaf springs.

 

Use a long Panhard bar and instead of running Heims, use RUBBER bushed rod ends on the parallel ladder bars.
You will get enough compliance to allow a reasonable amount of chassis roll thru the suspension and as a bonus the rubber bushed rod ends will keep ride harshness to a minimum without getting complicated.

 

First question that needs to be asked - Is this going to be a street cruiser or a Race Car? - BIG difference in how I would set it up

 

Earlier the OP mentioned that he was making room for his wife to ride in it--- "I am making mine a two seater (wife is more supportive of the hobby when I put in a seat for her which only makes it more challenging to make everything fit." so I was working on the assumption that it was for street duty and made my comments on that basis.

Roo

 

I would run locater bars with heims on both ends outside the rails. I would run a torque arm next to the driveshaft to take all the wind up loads. It would need a shackle at the front. It needs a long, low panhard bar instead of that short high one. Think Camero. You will need a really strong sway bar to stabilize the rear with the short mounting span of the shocks.