model t 4-bar insanity check

I am currently designing up my 4-bar set up for my model t. To make everything work I have to make all of the 4-bars 12" long and the panhard bar 12" long also. I have never designed a 4-bar system with this short of geometry and want to make sure it will work properly. so my question is has anybody built a 4-bar with this style of geometry and how did it work. attached is my 3-d model I am playing with.

 

the 4 bars are short but if the travel is not too great will be okay. You should have the top bar nose down & try to have it intersect a line drawn from the bottom bar at the transmission . If you can, build a centering yoke to the rear end instead of the panard bar. What you have will work okay if the travel of the rear is not a lot.

 

Panhard bars like to be longer than that, watt's link could be better for you.
Why did you limit the panhard though?

The Locost/ Seven replica uses a very similar 4 link. My panhard will be 32".

 

I have limited the panhard for room I guess it could stretch from on side to the other side of the axle but i figured I would center it. I am used too useing a buggy spring and not to familiar with using a panhard or watt's link so that is why i mounted the panhard bar off the rear end center. I will have to look up what a watt's link is and see how I can incorporate it into the design. I will also align the bottom bar with the transmission to get a better design. thanks for the help.

 

I think a 12" panhard bar is going to limit suspension travel.

 

There are two variations on the 4-bar;
4 Link, which is what drag racers use. These generally have longer lower bars angling up and shorter upper bars angling down. They has multiple mounts for height at the front mounting points (and sometimes at the axle) and can be adjusted to move the instant center along with creating front end lift, neutrality, or by exerting a lifting force between the rear axle and chassis, transfer weight to the front end while simultaneously adding downforce to the rear.
Parallel 4 bar, which is very common on street rod type applications, uses 4 equal length bars that are parallel to each other as viewed from the side. They act like a parallelogram and keep the pinion angle quite constant. They do not create an instant center and therefore do not aid in traction or rear axle downforce. they are very easy to set up and the angle of the bars (within reason) isn't too important as long as they are equal length and parallel to each other.

A longer Panhard bar will create less side to side movement of the rearend, but i would imagine on a T with little travel it won't make much difference.

 

I think the short panhard will cause the rear to move side to side too much as the car raises and lowers. My Son was going to do what you have shown in your picture ,and even bought a special bracket to bolt onto the 9 inch center section, But he decided to put on a longer panhard and weld a bracket on the passenger side tube to mount it.

Don

 

nice rendering. which program did you use to produce that?

 

Don,

thanks for the advice and after seeing your pic I think I will go with a longer panhard bar like the figure below. I always like seeing your rides because they are my style. I lenghten the panhard and attached a figure of the new conceptual design.



nashvegas,

the rendering is just AutoCAD but plan on throwing the design into Solidworks once I get my concept done, then I can check movement and constraints.

 

Thanks. Mucho better. The arc will be less severe as you have it in the second drawing. Nice way to lay out a car in advance, if only I were smart enough to run one of those programs.

Don

 

Just thinking out loud, if you mount the lower 4 bars on the outside of the frame as you drawing and the uppers on the inside you might not need a panhard bar. That might give you enough triangulation.

 

I think that as long as the amount of travel is not too great it should work fine and I also completely agree with the added length of the panhard bar. Suspension stuff is very critical to make sure you get it correct, but also remember that you can also overthink it and make it much too complicated for the application.

 

hey guys thanks for the advice, I just have one more idea I thought i would run by you guys. I am thinking about making it trianulated like the pic below. The pivot points are the same so it woul still keep the pinion angle correct but I might be able to eliminate the panhard bar. this is my last thought then it is time to decide and get on with it.

 

That's what I'm doing on my T, would be nice if the short bars will work. When you think about it , factory bars can be pretty short too.

 

HOLY CRAP!!!!!!!!!!!!!!! I looked at the AutoCad and good gosh....I would have to take out a loan to take out a loan to buy that program. guess that's why i am a troll and only look at other posts and pin them to my desktop for future reference. I learn a lot.
I think the triangulated set up looks nicer and cleaner.

 

Triangulated 4 bars are very common and do eliminate the need for a Panhard or Watts. Most OE's have done it with the uppers considerably shorter than the lowers, in fact most aftermarket are done this way as well

 

nashvegas99,

There is really no cheep CAD software anymore that you can do 3-d models. I do Cad for a living so that is the only reason I have it at my disposal. For most it is not cost effective to own. you can buy AutoCAD light which does 2-d for arround $1200 but that is as cheep as you can go with AutoCAD.

hotroddon,

I have looked into a triangulated 4-link and just cant grasp how it works with short bars on top and long bars on bottom. wouldn't your pinion angle change as your suspension goes up and down. I have been looking at some info on this method and found that they use a 70 percent length upper to the lower bars.

 

==================================

In my experience learning any of the CAD programs is tough, and takes a lot of work. Classes can help a lot. Sometimes U get a demo or student copy of the software when you take a class.

there are some cheap CAD programs around that are plenty useful.

I have access to high end software, so have not looked into Google "sketch up", but some folks like it. It sounds like more of a "visualization" tool than a design tool

http://www.techsupportalert.com/best-free-cad-program.htm

If you have a son/daughter/nephew/niece who is a student they may be able to score a student version of Autocad or Solidworks etc.

http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=14185424

 

I can't figure out how unequal length upper and lower bars work either, but they evidently do. We just pulled the rear suspension out of a Fox Mustang and the uppers are shorter and mounted in a different spot fore and aft. Not sure how they articulate that way but they do.

Don

 

Just for your information I have been doing AutoCAD for 15 years for a living and 20 years using it. AutoCAD is not the easiest to do 3-D models but I do use it. Anybody wanting to learn 3D should use inventor or Solidworks. like Dan said you can get student copies and learn how to use the software but they do have limitations in what you can produce like drawings etc. I really feel the best way to learn is taking class its alot cheeper than buying the software and would teach you the basics.

Don,

thanks for the comment, i have been doing engineering design for years and don't understand how triangulated 4-link works. I think I will have to throw my design into solidworks and check movement to maybe better understand how it works.

 

Cardboard and push pins works pretty good....

 

spoken like a true redneck.....haha

 

Long lower and short uppers on a tri 4 link do go through some pinion angle change, and also in extreme cases, like the fox mustang, some bind. The OE's make up for some of that with very soft bushing's in the upper arms to help with bind. This is usually done because there isn't enough room for longer upper arms - they would go into the passenger compartment, especially with the way the OE's like to angle them upwards for roll understeer for safety factors for the average bad driver. The reality is the car does not spend much of it's life traveling very far off of ride height and the travel is not very large, and at that point the pinion change is minimal

 

That makes a lot of sense.

Don

 

I'd try the triangulated setup and make the front bar attachemnt point double shear.

 

Factory cars have big bushings and flexy stamped arms, so they can get away with it.

 

I like GM's tri 4 link- Used from 1964-1987 on the Intermediate chassis (GTO, Grand Prix, etc.)- but the mini trucker guys have an interesting design too:
A "Wishbone" has two frame connections and one differential connection. The diff. is a fairly wide (maybe 6" wide?) mount, and it seems the "Y" intersection is not two equal angles- In other words, one of the arms is shorter and at a slightly greater angle where it hooks to the other arm vs. the two arms being at 45* where they meet the section that hooks to the differential. Hope that makes sense...

 

I do have a gm chassis under my merc and I am thinking of taking some measurments off of it. the idea of a wishbone style top connection sounds fine except what do you do for side to side role and does has anybody use this type of suspension on a hot rod.

 

The cardboard worked pretty good. Usually make this stuff myself, but by the time I get taps, ends,tubing, etc. decided to order 'em up. Besides, the rear is taking a long time to put together, by the time I do everything myself, there won't be enough lifetime left to finish this damn thing..

 

Here is another solution for a center locating device, with limited space. I didn't want a short panhard bar, a friend of mine came up with this. It is hard to tell from the pics, I welded a threaded boss, dead center on the rear of the housing, to mount a 2.5" roller wheel. On the rear crossmember we mounted 2 angles, one welded solid, the other bolted on for side adjustment. It was adjusted for just enough clearance for the wheel to turn during suspension travel, it worked perfectly, keeping the rearend centered, without bind. This was 35 years ago.