[taff2]

Mark,the couple of sets of ladders bars I've made have had the bottom bar parallel to the floor,just because it is accepted practice and 'looks' better,one a 13 second car and the other a 10 second car,both worked well(both 1" square box section too). However,as a ladderbar picks the instant centre virtually straight up I can't see it making much difference,just design a front mount with a few adjustment positions so that you can find what the car likes. A friend has a gasser style car along the lines of yours with box section ladderbars that have a kink built into them halfway along,and then a short length of square box section up to the front pivot/rod end,the car has been used like this for over 15 years and runs 11's.

[marks73ta]

Thanks for info. That almost sounds like the bars that Lakewood makes for the coil spring Chevelles and GTO frames. I kind of like that since it gives it a little character. Mark L

[marks73ta]

I bought a 35 spline locker from a member here and it came today.



I picked up a 31 spline locker a while ago but I do not feel safe with only a 31 spine sized axle. I'll feel safer now.

Plus I got all my rod ends and bungs together for a family photo. The 3/4 inch sphericals are from Spohn and the 3/4 inch ends are from "swap meet". Got the weld bungs from Speedway.



So now I can start building the ladders. Mark L

[Jack Gifford]

As for the "physics" of ladder bars, I hope you've thought about the fundamental aspects of them? Ever seen a production vehicle with them? Ever noticed how the old-style factory radius arms ('32-48 Ford, etc.) had the pivot points very close to each other? Ladder bars create an extremely high roll rate at the rear suspension, which is undesireable on the street (the chassis can't roll without distorting something- typically twisting the axle housing).

[marks73ta]

Yes. I've been rolling all that around in my head trying to think of a way to make the suspension more plyable. The street itself is usually flat and the ladders will work with that pretty well. But I have always wonderd what all the involved parts must go through just simple negotiate the turn into a slanted drive way. The roll stiffness is probably a good thing except it has no adjustablilty. I thought about using the long truck arms like GM used on pick ups and early BOP cars. Hot Rods to Hell sells a kit for that. I thought of making my bars on an angle and long to do the same. The longer they are the more they would allow radia lmovemnt of the axle before binding, and the angle would afford some lateral axle control. Still in the designing stages. A fully heimed four link would be the real answer. Mark L

[Jack Gifford]

A single central torque arm is an elegant solution- no binding, very compliant, and eliminates all torque stress from axle tubes other than braking torque.

[BruceWilkie]

Originally Posted by pontiac jack

A single central torque arm is an elegant solution- no binding, very compliant, and eliminates all torque stress from axle tubes other than braking torque.

Bingo! Control side to side "sway" with a "watts" linkage. Control "roll" with an anti roll bar. Length of tq arm and driveshaft pivot points need consideration in the design, but slip yoke helps a bunch.

[marks73ta]

OK, brain storming here. I like the single torque arm but I would still need some kind of additional control arms to locate and hold the rear end in place. My 9 inch is set up for ladder bars. Meaning the brackets have the non adjustable multiple holes for the rear of the bars. Now I could make a 4 link off of these brackets but there would be no rear adjustablility. I can make the traditional ladder bars. OR, what about using the lower rear end bracket holes and run single bars from the lower holes to the cross member. Basically just the lower ladder bar tubing with the rod ends. Then take the top bracket holes, run two bars off of the top but bend them in towards the center of the chassis up to the same crossmember where it bends up over the driveshaft, combining them into a single rod end tube and attach it to the crossmember with one more spherical end. It would place the rear axle, the three rod end points would allow all the articulation needed for full unhindered suspension operation, and using a watts or a simple panhard bar to latteral locating? My only question then is, where is it best to locate the forward rod end on the top two into one bar? Can it set up above the plane of the lower bars and not affect the rear suspension movement? It could be set up as the top bar level with the lowers for a 4 tube suspension? Or do I need to shorten all the bars and make them adjustable so I can set or move the instant center? OR, I can just make a traditional ladder bar and be done with it all. Food for thought. I worked on my bars today. Placing the rearend, measuring and placing the front bar crossmember, cutting and mocking up the bottom bars. Looks like the bottom bars bolt to bolt are going to be 50 inches. Plus the bottom bar will be the level with the frame bars. The top will become the angled bars (in a traditonal ladder configuration). I like the three link type set up I described for the ease of suspension movement, but concerned about the top bars front bolt location and how the suspension will work if not located to the instant center. I hope everything I said make sense. Mark L

[taff2]

With 50" bottom bars they are going to have to be pretty hefty or triangulated like a ladder bar to stop them from flexing,I would put a x brace between the bottom bars no matter what system you go with(as in a ladder link system). Decisions,decisions,eh.

[marks73ta]

Yea been thinking about that too. Plain old time ladder bars are still looking the best. They will be heavy enough as it is. I just have to figure out how to make the top bar. Bottom bar level and top bar a straight shot from the rearend bracket down to the front of the bar? Level out of the rearend bracket and then bend down to the front of the bar? Once I figure that out and maybe get the bar bent then I can tack it all together, adding the triangulating bars as I go. I still want to add that plate in the middle with either the Pontiac Crest (V), or if I can find a water jet cutter maybe a Pontiac silouette. Mark L

[marks73ta]

Did some fabricatin' today. I made a plywood template/pattern for building the 50 inch ladder bars. Just mapped out the bolt up points and located 1/2 bolts thru the points to located the rod ends.



Then put the rod ends/weld bungs on the template bolts to measure for the main rails. Cut the rails and mocked it all together. In this pic the top bar is not yet angle cut to fit the bottom rail at the front.



Now the top rail is sliced to fit to the front of the top rail. Still needs some grinding and fitting to get it right.



Next up after fine fitting the slice, I have to make the reinforcing tubes to tie the bottom and top rails together. Then tack it all together and finally decide if I want to try the final welding or take them to a good welder. We'll see.

Mark L

[bankbook]

Looks good Mark.

[Jack Gifford]

Originally Posted by marks73ta

... building the 50 inch ladder bars...

To each his own. It's not something I could live with- knowing the axle housing is getting twisted every time one rear tire hits a bump or hole, or body-lean occurs while cornering.

[Tom Vaught]

Personally if I were starting from scratch, a torque-arm 3 link suspension would be my first choice for a street car with a lot of power. Ladder Bars suck on any real street car.

Tom Vaught

[marks73ta]

Pulled the rear end out from under the car and put it on my work table. Mounted the first ladder I made on the rearend bracket and it slid on perfectly. So I set up the template with the second ladder bar and tack welded it together. Placed the second bar on the rearend brackets and it too slid on like I actually knew what I was doing??? HA.





Now I have to put them back on the template and build the crossbar supports. Mark L

[twinturrbo406]

... very nice, have you decided on the Turbo's you'll be running ??? ... i might know a guy ...

[aronhk_md]

Looking good Mark! And yeah he decided on the turbos and picked up a sweet pair....its a few pages back

[marks73ta]

Thanks Bill and Aron. Bill, twin Turbonetics 76MM ball bearing turbos. Now I have to either sell Jeffs headers I bought (for the singe turbo) and build new headers, or cut the set down to make twin turbo headers out of them. First I want to get these bars in and the rearend placed and in so I can roll the car around on it's own wheels. Pontiac Heaven is coming again and I want to put it in the car show again. The coverage for last years Pontiac Heaven is supposed to be in an upcoming High Performance Pontiac and a pic of my car is supposed to be int it. It'll be the first time I've ever had a car in a magazine. I hope it gets a favorable comment, if any. Mark L

[BruceWilkie]

Glad to see you finally got out of hibernation there Mark. Things are looking good.

[marks73ta]

Hey Bruce. Final configuration. Got the bars all tacked up except for the front catch attachment. Will talk to the welder on how he makes the catch.

I'll probably take them over tomorrow. Mark L