Technical Rear Suspension/Ladder Bar Question.

I have the more crude, cheaper version of that. Factory monoleaf springs from 55 years ago, and home made "caltracs" linkage.

 

I have seen (and repaired) the carnage from under-engineered ladder bars and brackets. While the Pete & Jakes style bars can probably take a few 9 second passes in a light car they were primarily designed for a 2600 lb car with street tires and 300 hp. If I was determined to drag race my street hot rod I would certainly build beefier bars and double shear bracketry with at least 5/8" grade 8 hardware.
Another reason non-parallel 4 link systems came about was lack of space and the additional adjustability of the IC.

 

This is my set up in my 30A Coupe
Still trying to dial it in..... lots of learning.

It seems to be under a lot of tension when I unbolt it but it's perfectly square according to the alignment machine....


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We ran 9's back in the 70's with a 67 Firebird with a mono leaf and a Jones and Young slapper bar setup. All you do is cut the rear portion of your slapper bar that is behind the the rear end and weld it into the front section to make sure the snubber hits the front eye bolt and not deflect the spring .
We ran 9's in big block Camaro just by using Mopar super stock springs and a pinion snubber. People couldn't believe we could run that hard without traction bars. Made a lot of money grudge racing that car.
I have seen ladder bar ends that bent when the driver was backing out of a parking place and turned sharp. Put it into a bind and tweaked the bar ends. A spool on pavement puts quite a load on suspension

 

The Art Morrison ladder bars I have been using for the strip are about 33" long.
I like them because it's an easy and simple adjustment of the front mounting pivot bolt location that will let me choose how much the car body rears back and plants the tires when launching, or keeps the nose down, whether it slips a bit then grabs, or simply super-bite right off the bat.
These bars make it simple, but I wouldn't want to street drive them much if I had more than the smallest amount of body lean.
I was really impressed by one of the early mustang guys that showed up one day and was getting superb tire-plant and traction on every launch with a simple set of clamp on slapper bars. It looked pretty stock looking, but then it really stood out when he kept getting better launches than the other more elaborate cars at test and tune. You could actually see the rear tires getting pushed down harder on the track as it first started moving. The other cars rigs didn't seem to be quite that effective.
I tried to get closer looks to see if there were any clues having to do with modified mount locations, pre loads, or any other helpful hints, but it looked so "ordinary slapper bars" that I didn't discover any of his tuning secrets other than he used a small 3/4 gap before the snubbers hit. but nothing else easy to spot.
His car had the perfect balance of tire pressure, windup, and plant to make it stand out from the others.
just an interesting observation......


WHY BE ORDINARY ?

 

It does not matter how much the ball can rotate in the heim, for the rear end to rotate on the longitudinal axis one heim has to move down and one up or something has to flex---frame, mounting brackets, ladder bars, rear end housing etc. In the bushed P & J deal one bushing is compressed on the top and the other on the bottom to allow the rear to articulate. With the close lateral spacing of the front mounts and the length of the bars the displacement is not very much but it must happen for the rear to rotate (without the hard parts flexing)--simple physics.

Roo

 

The deal is 10 second motor or 10 second chassis. If you can't build a 10 second motor make your chassis go 10s.

Not likely I am going to own a blown 427 any time soon so if I want to keep up I'll have to do it with the chassis. Chassis tuning is an art, or if you're me sometimes you just get lucky.

 

Good lord....i have had street/strip cars w ladder bars for years....no leaf springs, just coil overs....i take it easy on uneven transitions like driveways, parking lots, etc. My 30 Coupe is set up with 32" adjustables, has 582 hp, set in middle bracket hole, 30" drag radials, hooks hard and rolls out....ladder bars can be run on the street. Never have bent the end of a bar or broke heims, of course i check them frequently

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Of course race car suspensions can and have been used on the street. As I said earlier, it's all about your tolerance level.
Jim's car, being an original leaf spring deal, made it all easier for him. It probably rides decently, for a 9 sec. car.
The original Tempest conversions were usually a big car rear and goofy looking leaf springs sticking out the back. There was no way to hide them.Again, not for me.
The ladder bars were a compromise, that ultimately, I couldn't stand.
Your results may vary.

 

Many many years ago when I was 19 and working part time for Carman Pisano at Wedge Engineering we were discussing a new rear end for my '33 5w. I wanted ladder bars, he said they ride like crap and suggested ladder bars angled towards the driveshaft with Heim joints in each bar attached to a third Heim joint attached to the center cross member. That would allow the rear end to articulate like a wishbone.
I never did try it (I went with Corvette IRS), but considering what Rooman said, he may have been on the right track.

 

Yep. Main goal is prevent wheel hop from springs wrapping up. Many ways to git 'er dun!!

 

This post clears up a lot of my questions.

 

Thanks to everyone for all the great information. My build is going to have coil overs. I expect to have about 450 hp and a lot of first gear. This is a street car that will be raced two or three times a year. So... How about bars shorter than the P&J stuff with urethane front mounts, triangulated, with the mounting points as close together as possible? Would this be a good compromise of traction and drive-ability.

 

Ideally, the traction bar forward pivot point should be at, or very near, the same plane as the front u-joint. That to keep the rear axle arc the same as the arc of the driveshaft therfore keeping u-joint angles the same during suspension travel.

Ray

 

You sorta want the front pivots close to the front U joint.
Granted this drawing is for a 4 link and
Grabbed it quick. The rear attaching point are a little bit offset. But the lines of action are the same. So far I've always been able to get to neutral with P&J bars.

Short bars always seem to force a connection above the line

 

Due to the fact that the rear end is anchored to the rear of the bar and not able to rotate as it arcs the rear u joint angle will be virtually unchanged throughout the suspension travel. The vertical offset of the front joint and the forward pivot of the arm is all that makes this different from an original Ford torque tube driveline where there is no rear u joint. Therefore the front u joint will be seeing a lot more angle change (relatively) than the rear.

Roo

 

^^^^^^^...oops !........you are, of course, correct........I short circuited the thought process

Ray

 

31Vicky with a hemi, thanks for the excellent drawings. Very informative!

 

To make it better to understand, there should be an arrow pointing right at the centre of gravity and an arrow pointing left at the instant centre.
These are the 2 main forces [thrust and resistance]
Pinion torque reaction is minor compared to axle thrust [traction torque reaction] due to mechanical gearing.
Leaf spring wrap up [previously mentioned] is a combination of "Forward Axle Thrust" and "Pinion Torque Reaction" on the same spring causing it to "S" shape itself.
Slapper bars help keep the spring straight by controlling the pinion torque reaction, but the majority of the force is forward axle thrust.

For example: A 300ft/lb engine in 1st gear of 2.54 ratio [Muncie m21] with 4.56 rear gears and 28" tyres has 2978lbs of thrust at the axle centreline. Or 1489lbs thrusting force at each front pivot.[enough to accelerate a 3000lb vehicle at 0.992G]
With a pair of 36" long ladder bars the same engine in 1st gear will only create 127lbs lift at each front pivot.[this lift is caused by pinion torque reaction, and is not a factor of the rear end ratio but gearbox ratios]

Squat is actually a factor of resistance at the Centre of Gravity Height vs Accelleration at the Point of Thrust . If you have the Point of Thrust at ground level there will be a lot of "Overturning moment" in the chassis [Lift at the front & squat in the rear]

 

4-linked my 40’

 

A more correct (and common) description would be "parallel four bar". In the hot rod/drag racing world the "four link" definition generally refers to packages that have an "instant center" as illustrated in 31vicky's post above. Then you also have the "triangulated four link" that may or may not be parallel in side view depending on the packaging required to get the top bars to clear the rear floor pans. In that case even though the top bars are generally angled outwards towards the front in plan view there can be an intersection point when viewed from the side and the information in 31vicky's post applies.
Kerry, in the case of the parallel four bar with no actual instant center would the "thrust line" ( for want of a better term) be at the mid point between the bars?

Roo

 

The thrust line would be parallel with the bars but directly in front of the axle centreline.
The 2 bars [on 1 side] share the thrust in proportion to their distance from the axle centreline.

Similar to standing on a plank supported by 2 blocks, it is equal if you stand in the centre but as you stand closer to one block the proportions change

 

I am assembling a SoCal triangulated ladder bar kit with 9" for my 32 chassis to go under my 31 coupe. The body and chassis are already assembled, so Im hoping to take the assembly to our most excellent hot rod shop to have da man swap out a 40 Ford/radius rod located rearend for this SoCal kit. I've been reading a lot but can't find good guidance on how high to locate my front crossmember for best traction. I've estimated my CG location and run some string lines to try to make a good guess at where the 100% antisquat line will fall. Unfortunately, the SoCalkit does not have multiple holes for the front pivot, so I hope to get it right on the first try. Suggestions?

 

I plan to run this car hard. I have ordered ladder bar adjusters and a left handed tap to allow adjustment of pinion angle and an adjuster to make the panhard rod adjustable as well. The SoCal 45" ladder bars and panhard bar use 5/8" clevises.

 

Choppedcoupe,
it should not be too difficult to modify the brackets on the SoCal cross member to allow some adjustment.

Roo

 

There's at least 2 different crossmembers. Straight and dropped. Yours looks like a bigger drop than standard 5" - might be camera angles though.

You'll probably end up with the drop crossmember mounted as high as you can get it. Like this, showing the dropped bar. Maybe higher by cutting the top of the tube flat, capping it and flush to the top of the frame rails.

Straight bar below.
If you're looking for multiple IC holes I think it would be easier to do with a straight bar and make your own brackets on a locally sourced piece of DOM tube.

Dropped bar.


Also, study the rear brackets. Different folks locate the holes differently in relation to axle centerline.

 

Agree....the pic w front of bar heim on the line is correct


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Thanks fellas. My car is pretty high in the air with no dropped axle and limited ability to lower the rear cause I have the fuel tank on the floor right over the axle (poor foresight there on my part). All these lines and angles are relative to planned ride height, I'm pretty certain. Also finding conflicting info on whether locating IC above or below the line increases "hit", which I kinda assume means "pushing tires DOWN" into the pavement. But most of the guys I'm reading say they have to move their IC (front pivot) lower than anticipated and are now running in the lowest mounting hole available. Also found a reference that suggests that those gospel drawings are drawn backward, and that moving the IC down increases hit and that moving it up increases squat. I certainly don't know from experience of my own. I have some caltracs on my S10 and it is cool that the rear of the car LIFTS under hard acceleration-I can feel my arse going up!

 

great info here, you guys just answered alot of questions that i need needed for setting up my ladder bars. Can anyone give me some incite as to some decent fitting more than performance built fenderwell headers. say under $300. Lots of them on ebay that seem too cheap but if last 3-4 years on a weekend hot rod i would be happy. sbc, 40 plymouth, straight axle w/6" drop

 

What do you mean by "more than performance built fenderwell headers"?
Regardless of where you buy them, cheap is cheap, study the welding in the head flange area between name brand headers and those "too cheap" ones, this will show you why the price difference.