The Hairpin vs Four bar discussion

[RexRod]

Please bare with me on this one. I know it's something that's discussed from time to time on other forums. And I know the topic can sometimes get ugly. Because those discussions often turn for the worse, I end up not completely satisfied with the end result. I figured it would be safe to talk about it here.

I occasionally stumble across discussions about the dangers of using hairpins or wishbones with tube axles. I am not going into the details of why, I'm assuming the rest of you know what I'm talking about. I completely understand the logic in the idea/concern of others, but what I have never seen is evidence of the catastrophic failures claimed due to metal fatigue.

There are sooooo many rods out there with hairpins and tube front axles. Is this something we should be thinking about? Or can I relax, assuming safety in numbers.

Thanks in advance for your thoughts.

The forum worry wart, David

 

[all-world1]

Great question....looking forward to the response from the guys that have built lots of these.

I'm starting a build using hairpins and tube axle. I don't plan on doing any offroading so I'm very optimistic about steel integrity.

 

[Youngster]

David ...you can relax. When questions of this nature come up it seems everyone thinks of the extremes. A 4 bar is by far the most efficient set up. At the same time the hair pin works well in the parameters that we drive our cars. How many time dose the axle on a T bucket go to full travel? Unless your 4 wheelin', not often enough to cause sleepless nights.

Ron

 

[donsrods]

Ron's answer is 100 percent correct. Period. The hot rod world is full of "things that won't work" and yet people are driving those very cars down the road every day with zero problems. My '27 was my daily for 7 years with hairpins front and rear. After being on the car for 20 odd years there are no signs of any fatigue or any other problems with that setup. Also have split bones on my '23 front and rear, same deal. My Son is running a chrome tube axle with hairpins........supposedly a big no no because "tube axles don't twist properly like a beam axle", that is a big crock IMO.

Like Ron said, MAYBE if these axles were rising and falling 6 inches each way there might be some stress issues, but if a typical front end goes up and down an inch or two each way that is a stretch.

You worded your question very well and it looks like you have asked it elsewhere and have gotten the doom and gloom reports. Have a cold one and don't worry about it, they work fine.

Don

 

[RexRod]

Thanks guys. I had a feeling it was OK, but I just wanted to hear what others had to say.

You will see literally hundreds of hairpins connected to tube axles for every four bar setup. I guess some people just like to scare others.

Take care,

David

 

[donsrods]

I say this all the time, but there is the PERFECT WORLD, then there is the REAL WORLD. What I mean is that stuff like four bars may be better in some respects, but in reality hairpins work just fine too. Same with Ackermann. It is better to have the tie rod in back, but sometimes you need to put it in front, and they work well too.

I live in the REAL WORLD. :yay::lol::lol:

Don

 

[Todd]

Some of the less technical fights over these are due to eras and astetics.

split bones - 50's and earlier
hair pins - 60's & 70's
4 bars - 80's & up

 

[GAB]

Hmm?

 

[donsrods]

Hmmm??? what?

Don

 

[GAB]

Just food for thought.

 

[RPM]

Just food for thought.

I ain't never been hungry enough to eat a clevis.

 

[Todd]

Hmm?

Wheres the rest of the threads on the clevis, and in the tube?

 

[GAB]

Turned off of the clevis and not tapped in the tube.

 

[GT63]

Hmmm??? what?

Don

I think what GAB is brainstorming is a clevis that can slide in one of the hair pin tubes, just enough to relieve any twist. The nut still allows you to adjust caster.

Am I close GAB?

 

[GAB]

Does the term "3 link" ring any bells?

 

[RexRod]

Has someone done that? I wonder what that would be like under hard braking. I can imagine the axial spring in the front axle making things a bit jumpy/jerky. As one side gets more bracing from a two sided hairpin, the other is sort of left open to twist.

Back to the original configuration, I did conclude that the longer the hairpin, the less twist on the axle when one wheel lifts more than the other.

David

 

[Youngster]

I've heard and read about these slip type ends. I don't have any experience with them but this is what I have thought about doing;

It might need some tweaking. I haven't been comfortable with something that would be able to come completely apart. Maybe someone here could explain that concept to me.

Sorry, I don't have a program for the drawing.

Ron

 

[GAB]

O.K., since RPM is hungry (just not for clevises! :lol how about some cakeas in having your cake and eating it too

This idea was intended for the guys that just HAVE TO HAVE the hairpin look but like the fact that 4 bars allow the suspension to do what it is supposed to donamely allow for a wheel to react to a deviation in the roadway independently of the chassis structure.

By using a slip joint on one of the 4 tubes, you are creating a 3 link arrangement. This is a configuration that has been used on sprint cars for many years. It originated to save weight, but fits all of the requirements for the location of a straight axle assembly. The two bars on the drivers side control the wheels fore/aft location and the caster angle of the kingpins. The right side bar controls the fore/aft location on that side of the car. A track bar controls side to side location.

The left side hairpin is in effect, two bars of the three. The top and bottom bars just happen to have common rear mounting points. While these would preferably be two points which make the linkage into a parallelogram, this will work and the only drawback is a very slight change in caster as the axle moves vertically (10ths of a degree). Assuming that the slip joint is used on the lower radius rod on the right side, the top tube becomes the link and the lower tube is just along for the ride. By freeing this connection to move lineally within the tube, you have introduced a degree of flexibility to the suspension locating mechanism.

The nut on the modified clevis is just to maintain appearance continuity. Just Loctite it on after the extents of travel have been determined. After thinking about this some more, I think that I would use rod ends on the front also. To be able to allow the clevis to rotate on the batwing, the attaching bolt would need to be left loose, even though it is lock nutted or cotterpinned. A rod end would be securely fastened with the rotational movement a result of the parts design.

Has anybody tried it? Well, they arent in Speedy Bills little book of Chi-com goodies, so Id have to say No. "Ingenuity in Action" died long ago.:razz:

 

[GAB]

Ron,

What you are showing in your drawing is most commonly found on locators for side to side movement. These are compensating for conflicting arcs. The slip joint is controlled as to its sideways movement by the triangular assembly. It need not share common mounting point centerlines or link length as the slip joint takes care of that job. The urethane isn't necessary but might quiet things down a little.

George

 

[Youngster]

Thanks George. I see what your getting at now. Please don't think I was disputing your design. I just wasn't familiar with that type of set up. It makes sence to me now and have added it to my files. Hope you don't mind.

Ron