Projects Mocking up rear suspension for my Bantam - opinions please

Once again---heims on the street are not a particularly good idea. As for the "short mounting span of the shocks", in the OP's initial photos the one that is mocked up is simply tied to the cross member with some wire so I presume that he will take Kiwi Kev's advice and mount it as far outboard as possible. Mounting a "long, low panhard bar" is once again a packaging issue and in the same vein there is no need for a "really strong" anti roll bar as this obviously is not going to be an autocross car. With the extremely low sprung weight at the rear of a car like this a stout anti roll bar would simply put it back in the parallel ladder bar situation with little/no roll compliance and a twisting moment on what is basically a single plane frame with little resistance to that sort of torsional input. Remember that this is not a 3500 lb car (more like 2000lbs) with a lot of mass above the c.g. to create much of a roll moment. The are hundreds (maybe thousands) of hot/street rods out there with the triangulated ladder bar/panhard bar package and none of the ones that I have ridden in seem to have any issues in a real world street situation.

Roo

 

Guys - Thanks so much for all of the input. Based on everyone's back and forth dialogue I plan to do the following:

1). Space shocks as wide as possible. And as vertical as possible.

2). Panhard bar mounted level at ride height (knew that but good reminder in the event I started to compromise because of space limitations)

3) Longer panhard bar if I can fit it. Probably can if I mount it near the front of the pinion not from the top of the housing.

3) Rubber bushed ends, rather than heims on ladder bars. Could use a specific source, p/n recommendation here?????

4) Clevis ends where ladder bar attaches to rear end. Agree/thoughts????

4) Re-do tranny mount to use existing ladder bars ( I've been saving them since 1993 for this project, old school look and I love them) with them angled-in provided I don't lose much floor space as they articulate. Otherwise, going out on frame rail.


Appreciate input on items in bold above.

Bantam

 

Just a point of clarification; while the total unsprung rear end weight is low compared to bigger cars, the unsprung/sprung weight ratio is quite high. That 9" is HEAVY. The sprung weight is very low.
As Rooman said, in the real world, it probably won't be a problem.

In stock car racing it IS A BIG DEAL!

 

Thanks mate! Typing this too early in the morning and got it backwards (just went back and fixed it). Years ago (about 40 of them) I got "smart" and replaced the Salisbury style rear in my girlfriend's 23 "T" with a 9" to make it stronger. Big mistake on what was basically a street driven car with a "Y" block and auto and did not need the extra beef of the bigger rear end. There was a noticeable difference in the ride quality with that heavy 9" back there bouncing around with no car weight on the other end of the springs.

Roo

 

My thoughts in RED

 

"I would keep them inside the frame rails, as far apart as you can get them. I don't think it would be worth the work to move them out by 2-3 more incehes. I would also angle them out at the bottom, this will help with body roll"

"I would stay with the out side mounting. You are not going to have a lot of wheel travel to start with, especially with the light weight. This will also keep the body roll to a minimum.

If he stays with the outside mounting there will be NO body roll (unless the frame twists).
As for the shock mount angle, at anything less than straight up and down the shock and spring rate will fall off as the travel increases. With limited travel this effect is less pronounced but still there. Moving the lower mount outboard of the upper just accentuates it, especially if there is any body roll. Between 10-15 degrees of angle usually looks better but will not stop body roll--it actually makes the car more prone to roll as the outboard shock will lay down more (and lose rate faster) as the frame rotates.

"Level and lower than you are showing it. Move it forward over the pumpkin so you can lower it"

Good idea. The lower the better (within reason) as any lateral load will try to push the frame sideways and the closer that you can get to the vertical c.g. the less it will try to roll the chassis around the longitudinal axis. On most full bodied cars the c.g. is about camshaft height, on this package it may be a little lower.

Roo

 

He stated he is using coil overs... so no leaf mounts are required.

 

Something got lost in the translation I guess

Someone mentioned leaf springs as a better idea than the coil overs.

 

I used home made ladder bars with #RB110 rubber bushings in the front. They are rubber with steel inside and outside, leaf spring front bushings.

 

I'm thinking singular (each side) links parallel to the frame and a rear facing a arm providing the upper link and thus removing the need for a panhard. The likely minimal suspension travel should minimise pinion angle changes with the short top link.

Chris

 

With that minimal space that'd be a good candidate for Jag IRS.

 

A few more thought in RED Don

 

I've never liked the 'outside the rails' mounting for radius rods/ladder bars on a rear end for the reasons mentioned.
Until I had a T bucket with CCR's rear end design (exactly as the OP is planning) - it was no problem at all.
So I tried the same design on a Model A project - with not so good results. Slightly wider frame & rear end mounting, so zero body roll. A jack under one side of the rear end would lift both wheels - but not so on the T, same action would lift one wheel at a time.
As mentioned, it's all about theory vs real world. Given the even narrower frame on the Bantam, go outside the rails & give your wife a decent seat!

 

In theory this Might be true, In real world it is Not. Many companies have made and thousands of Pro Street cars (including my own) have run parallel ladder bars for many thousand of miles. Although there is not a Lot of articulation, there is some and enough to drive a street strip type car without it lifting the inside wheel each time you turn in a driveway or such. Large urethane bushing are Best for this application, but high angle heim's will work, but they do wear out faster.

Nope! Aside from the compliance in the bushing (1/8"-1/4" maybe with front spring eye type) there is NO articulation unless the ladder bars bend (in beam) or the axle housing twists. High angle heims would be a waste of money as the truss that is created by the ladder bar/rear end housing is simply rotating around the front mount in one plane. In fact a solid "rod end" as used in some drag race ladder bars would do the job just as well if not for the potential frame twisting of a single plane chassis. Why do split rear wishbones have a tendency to break as had been discussed in other threads? It is because chassis roll tries to push one forward mounting point up and the other down in a cornering situation. The triangulated design of ladder bars acts as a truss and the longer they are the more leverage they have to twist the frame. In a multi rail drag race style chassis that does not happen but with a single plane street rod design any tendency for the car to roll around its longitudinal axis while cornering will try to twist the frame. The fact that this style of car is generally light with a relatively low c.g. allows them to survive on the street.

I didn't really explain my comment about the angle and body roll very well. If given the choice between mounting the lower mounts closer together to keep the shock vertical versus spreading the lower mounts out and slight angle to make the top mounts fit his frame, I will take the slight angle. Having the lower mount further out lessens the tippy feeling and body roll associated with coil overs that are mounted to close together. I think it is the lesser of two evils. And on this car, which I doubt will see more than about 2" of bump travel, I think it will work fine.

Nope! The mounting spread overall is the only width that will have any effect on the "tippy" feeling with a live axle and even that is dependent on spring rate (and the tendency for the car to roll about the longitudinal axis which is not going to happen with wide based ladder bars). As I commented, the limited travel envisaged just about negates the scenario but with a live axle, when moving the lower shock mounts outboard relative to the uppers, the extra width of the spring base at the axle is most likely balanced by the fall off in shock and spring rate.
With a Pete and Jakes style triangulated ladder bar package and especially with closely mounted shocks an anti roll bar is a good idea to enable the spring/shock rate to be at the level simply needed to hold the car up (and not control roll--aka "tippy feeling") but in the case of the wide based (parallel) ladder bars the rear end housing is the ultimate anti roll bar.

Roo

 

A 4 link would work in that space. Work really good and wouldn't get into the passenger area. Wouldn't need a panhard bar and plenty room for an antiroll bar.

 

OJ,
I presume that you are suggesting a triangulated four link and if so the angle on the upper bars (in plan view) is going to be pretty extreme. Due to the narrow frame there is really not enough room on the left side to bring the top bar off the axle tube outboard of the pumpkin and get enough triangulation for lateral location. Coming off the top of the housing above the pumpkin is also an issue as the frame kick-up is too close to the rear axle at the point and the upper pivots on the frame will be too close to get any front to rear spread on the mounts.
As already discussed (at length) the parallel ladder bar deal will work as plenty of cars are that way but it is not ideal. The triangulated ladder bar is a proven package as well and I feel that for street use it has a lot of plusses over the drag race style version, roll compliance being the biggest one. looking at the OP's photos with the bar mocked up in the triangulated configuration it looks as if it will clear the floor OK depending on how it is mounted to the axle. I know that the OP was hoping to use what he already has in some form but the Pete and Jakes deal puts the top bar at the axle centerline for that reason as well as to allow the bar to attach to the transmission crossmember without extreme side view angularity.

Roo

 

Oh look...a formed steel parallel ladder bar setup with compliant bushings...on a solid axle.
On a PRODUCTION truck.
All Ford Super dutys are set up like this, and have been for the past 10 or more years.

 

I thing those big bulges on the front of the arms contain rubber bushings to allow articulation.

 

Yep. Real big bushings at every point.

Just like the rear of my motorhome. Even shorter arms. But mounted with huge bushings at frame and three at axle.


Posted using the Full Custom H.A.M.B. App!

 

Yep, that would hold up in your hot rod quite well

 

A triangulated four bar can fit [your mock up already proves that]
You just need to think outside the square mate!

Put the triangulated links on the underside of the axle, and run the parallel links along the outside of the frame rails [preferably at the axle centreline height or slightly above it]

It doesn't really matter if the triangulated links point together at the front or the rear, as long as all 4 links resemble a basic "K" shape.
Doing this eliminates the need for a panhard bar or watts linkage

Having a narrow spring base softens "Roll stiffness", you can add a rear anti-roll bar to increase rear roll stiffness without stiffening the suspension
The closer the spring base , the stiffer the rear anti-roll bar needs to be.
Imagine a single coil mounted to the diff head with a rear anti-roll bar , all the roll stiffness would be controlled by the rear anti-roll bar and non via the springs

 

Good thinking mate!

Roo

 

That looks like the best configuration for that car to me, too!

 

Yes...well the attempted point was that parallel ladder bars with compliant bushings would give plenty of articulation for a street driven vehicle...as proven by OEM useage.
Landrover also used a similar setup with inline bushings on arms that ran under the axle tubes...both front and rear axles!
1st series Ford Bronco used something along the same lines with a rear bushing to the frame and a front cushion that wrapped the axle tubes. All of these vehicles have proven themselves quite capable on AND off road as well for at least two of them!
There are many ways to skin this cat!

If you feel that particular arm itself is suitable for the job then....knock yourself out!
I certainly wouldn't run it! LoL
It's made the way it looks to allow it to be punched out simply and accurately in large numbers.
Attractiveness was never a consideration!
A regular ladder bar setup with sensible sized rubber bushed inserts would be fine for our needs.

I'm toying with the idea of changing the rear mounting plates on my Roadster to allow for the use of rubber bushings at the axle while retaining the Heims up front. That, and angling the coilovers a tiny bit should really improve the ride. I'd like to drop the car an inch or two as well, and this mod would help that as well.
In the mean time...even if I don't do anything to the rearend over the winter I'm quite pleased with the driveability and handling of my T with Ladder bars and Heims.

 

I used the Ford Bronco arms on my hot rod & they work very well. I used the factory mount to the frame & made my own mounts to the 3rd. member. The bushings are cheap ( 7.99 a set.) & easily replaced.

 

The amount of compliance in the bushings in all of the examples that you cite is way more than in a typical hot rod bushed end and that is why they work.
Adding rubber bushings to your car will take some of the harshness out of the ride over rough surfaces and putting them at the axle end of the bars will be much more effective in allowing at least a little roll axis motion as a small amount of movement at the axle will be amplified by the length of the bars. If you only put compliant bushes at the front you will not make much of a difference in that department.
Again, I know that there are lots of ladder bar cars out there but it is definitely not the best solution and the light weight of a typical T bucket is its salvation. Progressive rate springs will do more for your ride quality than changing their angle and if you are doing that to lower the car you are just accentuating the rate fall off.

Roo

 

Absolutely WAY more...but they are intended to give as much articulation as possible in off-road situations. Street use on a Hot Rod would require much less rubber deflection.

I 100% agree that parallel ladders are not the best solution in most cases and that it is the light weight of a T (or a Bantam!) that allows it all to work. A much heavier car with Heims all around would most likely snap things off on a regular basis.
The bushings I think would offer enough deflection to prevent this problem and give a little bit of articulation besides. You really don't need a whole lot on the street to make things survive. Many, many T's are surviving just fine with Heims and clevis ends!

I'm just looking at the OP's requirements compared to his needs...and it seems like the parallel bars will meet his needs with the least amount of problems caused to other parts of the build.
Sometimes you just gotta compromise...and given the car its going under, this seems like the way to go to me.
The other suspension I see working with few issues would be the idea of two arms and a center torque arm as mentioned several times. Just might be able to squeeze that in there.
Super short 4 bar arms I'm iffy on. If you do get a lot of roll you will also get a lot of rear steer effect.

In my personal setup, adding bushings to the front would be difficult anyway as the Heims in use now are mounted in single shear. NOT the way I would do it myself given the choice but the Heims are large, the car light and the bars are long. This setup survived a lot of drag racing over the years and I replaced all the Heims and bolts 6 months ago just to be safe...along with adding some support tabs under the front Heims to support them and reinforce the tip of the bar itself. Also...drag racing days for the car are over. Period.

The lowering would be made possible by relocating the position of my ladder bar, relative to the axle tube. Right now its too high and lowering the car would have the ladder bar hitting the floor on bumps. My coil overs apparently have a 225lb rate(!) and are an older 'odd" diameter that isn't used anymore. This is what I'm told...didn't determine this myself.
I'm dealing with it but figure a bit more angle will soften things up just a bit. With two aboard and a full tank its not so bad. Solo and a 1/4 tank will definately have you bouncing around in the seat! LoL

 

Bill,
I can understand why you would want to get away from 225 lb springs in a lightweight roadster.
The 23 T that my girlfriend had back in the early 70's had 4 Monroe load leveler shocks on the rear ( the ones that were designed to boost leaf spring load capacity) and after the chrome plated springs sagged (yep, we were clueless back then) I simply shimmed one per side with a sleeve on the spring seat to get the ride height back. It made for a progressive rate as the unshimmed spring did not come into play for the first couple of inches of travel. The rate on them was probably less than 75 lb/inch and the car rode great apart from the huge unsprung weight of the 9" rear end hammering up and down.

Roo

 

Like Roo said, I recently redid an old bucket Tee and used 100# as they were the lightest available chromed spring for the coilovers, It rode good but 80# would have let the shocks do their job better.

 

OJ,
I forgot to mention that on that 23 T I also drilled a hole and drained all of the fluid out of one shock on each side as the damping was a little excessive with two.

Roo