Simple Hot Rod Tech...Making a Rear Panhard Bar for a '32 Chassis

You can have as many bends in it as you like, it makes no difference to the action. Having the pivots at the ends out of horizontal is what makes it pull or push side to side a lot.

The bend will merely weaken the structure.

 

I also agree that the panhard rod should be near to level as possible and by bending the bar it may look OK but you really should be ensuring that your pivot points line up level.
This usually achieved by raising the diff point as high as possible and lowering the chassis point as low as possible.
Then the bar should be as long as possible.
Anearlier comment about the spring acting as a panhard bar is only correct if you are running a dead perch set up.

Nice work Brian, you display exceptional hand and workshop skills, I know it is easy for some of us to sit back and be critical of your set up, but please take it the right way.

A straight bar has got to be better than one which has been bent to fit as it goes against the strength factor of the purpose for the bar.
I believe in your particular case the need for the bar maybe more related to the fact that your rear spring has alot of arch in it.
Never the less the panhard bar should remove any side ways movement and I guess time and use will prove whether our comments are justified.

I would actually be interested to read your future comments on the out come once you have used it for a while.

 

thank's for sharing some hot rod tech

 

I've seen several panhard bars bent like Brians and there's no problem with it bending later.
There's not all that much force involved.


As for the round - looks to be 1 1/2" - 2" diameter - rear crossmember, note that SoCal does their chassis' that way and I haven't heard any rumblings about bending there nor do I see any probs with the one 32 I see running around town with a SoCal chassis.

If SoCal, with its quality operation building high dollar cars thinks a small OD rear crossmember is good enough then a careful home builder should be able to do the same with no problems.

People sometimes forget we're building lightweight cars most times and don't need things like 3/8" motor mounts or heavier.


Keep in mind too, the rear axle is going to bottom out on the frame rails and the rear crossmember is doing nothing but holding the weight.

 

Were you testing both the bent bar and the straight bar connected at the same points?

If not, then I suggest your results are flawed.

 

OK, I see what you guys are saying about the bar actually not being level because of the mounting points, which is probably the right way to think about it. Even though the long horizontal part of the bar is going to be level at ride height, it is still technically at an angle....I get that.

However, it's still not at enough of an angle to create all that much horizontal push. I think you guys are confused as to how much a lightweight hot rod can make a buggy sprung rear suspension travel.

Under normal conditions, a buggy sprung ladder bar rear suspension is not going to travel more than 2" in either direction. On a really bad pothole, you might see 3" or slightly more, but I'd even doubt that there is that much travel.

The next time you are driving behind a car on the highway, take note how much the car's rearend housing moves up and down as the car moves at 60+ mph. It's pretty surprising how little it actually moves.

By the time you figure in all the monkey motion and flex going on in the rest of the rear suspension, a very slight amount of horizontal push is not going to be noticeable. It'll be a hell of a lot less noticeable than the shackles swaying side to side and the car shaking it's ass like a dog shitting a peach seed.

There's no need to make this more complicated than it is. Even though the argument is that the bar is technically not level, a 10 to 15 degree angle between mounting points is going to make absolutely no difference in ride quality in this situation.

Andy, early Ford based hot rod rear suspensions are all about compromise!

No matter how you set up a buggy-sprung rear in a '32 Chassis, there is going to have to be some sort of comprimising situation involved. You don't think that there's going to be some bind in the ladder bar set-up as well? Of course there is! But the simple fact is that it still works just fine.

Same for a panhard bar set up this way. Even though it moves in an arc, by making the diameter of the arc as long as possible by making the panhard bar as long as possible limits the horizontal push/ pull....which is exactly what the panhard is there for!

I don't know which hot rod you've been around that has 5" upward and 5" downward travel, but the shocks don't even have enough travel to accomodate 10" of total travel. At least I think that's what you are saying...5" vertical up, 5" vertical down?

Try about 2" vertical up and down with the bar at 10-15 degrees down in the arc and an approx. 28" long panhard, and tell us how much it pushes/pulls up and down. I'm willing to bet that it's not much.

In this instance, to raise the diff point as high as possible would mean making the mounting point taller by about 2-3", which was just not practical. I would then be concerned with leverage bending or breaking the mount where it attaches to the housing.

To get a true straight panhard with this rear suspension would mean making the bar shorter so that it lines up with the top of the housing, or to mount it in front of the rearend, which didn't seem like the best option here.

That is close to the reason for the panhard, the actual reason was because the eye to eye length of the spring is too long for the shackle mounting points on the rear. The shackles are not going to keep the spring in tension, allowing much too much side to side movement.

The need for the panhard would be lessened by either re-arching the spring (which would raise ride height, and we don't want that), or narrowing the main leaf by re-rolling the spring eyes. The latter may still need to be done, but I still think the panhard is a good idea with ladder bars.

I agree with this statement and would say that the 7/8" OD .156 wall tube is plenty strong for this application.

I didn't do the frame, but the tube holding the rear spring is more than enough material to support the weight of a Model A coupe. Have you ever looked at a factory Model A rear crossmember? Probably less strength there than the straight tube used here.

Agreed, there's not enough force involved here to flex the panhard at the bend, because there is just not that much weight on the rear suspension. If I were putting the panhard on a '76 Cadillac, I'd have second thoughts about the bend, but there is just not enough force acting on the bar to give sufficient leverage for it to bend. If it flexes a little, it's really a non-issue.

I do believe that Dirty31 based his rear crossmember design on what So-cal Speedshop does with their chassis. Again, I didn't build the chassis or set-up the rear spring or ladder bars. But I do think it'll work just fine.

 

Also, thanks for the constructive criticism guys...it's what makes us better!

 

Good comments Mr. Bass.

In a way, too bad that sharing some excellent workmanship got a touch astray, but . . . a good discussion and educational as well.

 

When I run mine through its travel, it moves less than 1/4" to the pasenger side at full jounce. It would have been longer but I just happened to have that piece already threaded and that length.

The car came with a panhard bar kit for a 9", and it was 6" inches shorter.

Also dont think that bending one is a capitol crime. If you hit something sideways hard enough to kink it further,,,, you've got many other things to worry about at that particular moment!

 

Good work Bass, your Panhard will work fine. You are right about the minimal travel.

 

Rusty, do you know what the spring you used to set it up came off of? The one that's on the car now is the front spring off of a '40 Ford.

I can pull it off the car and measure it to see how it compares to the one you set it up with, and that would probably be helpful.

And I'm not trying to be critical, but the shackle angle you show in your pic above is already too much angle for the spring to be in tension with the full weight of the loaded body on the chassis. You should have something close to 10-20 degree (from level) angle on the shackles before they are loaded.

It's not really going to be an issue now that there's a panhard bar, but it definitely needs one to keep the rear from swaying side to side.

I hear you there. We both know it's not easy to build a car like this on a very limited budget....especially when you don't have a good understanding of what all it takes to complete a traditional hot rod. The good news is that Bubba's going to have a very nice car when it's all said and done though. Something we can both be proud to say we had a hand in.

 

I would put a cool cheesed out gusset on the underside of the bend area, that would make it a bit stronger if one was worried about that....Thanks for posting Bass!......Littleman

 

Dave, the thought crossed my mind, but I deemed it unnecessary.


Here's an updated chassis pic. The body ('31 Coupe) is actually resting on this frame now.

 

The bend doesnt matter!! It is a simple Pan Hard bar! I think of it as just a little extra pre-caution. I have seen them on dirt track stock cars with a bend in them! And they use there pan hard bars. As a side note Brian, when you make your axle and frame tabs, it always helps to make a little washer out of template paper or some other kind of thin material. You can put the washer in on mock-up and then make your weld spacer a little bigger. That way when everything is done you have a little extra room for paint or powdercoat. Does that make sense? You know my typing skills!!
Jimmy White

 

Great Idea Jimmy! Duly noted! Great Idea I will use on my new toy!!!!!!!

 

Thanks Dude!! I learned that trick when I worked for the Great Boyd Coddington!! It makes assembly just a little bit easier. You dont end up with the dreaded paint chips on the floor.
Jimmy White

 

I started using thin brass or steel shim stock that cuts easy w/ scissors........and at times have been able to reuse them......Great tip to mention Jimmy............Littleman

 

A.N. Washers work good too. How are you Littledude? Sorry Bass we are clogging up your tech. Now back to our regularly scheduled program!
Jimmy White

 

i've been watching this for a while , nice work....but what is the distance on those rear spring hangers? they look too close , i think the spring should have been stretched out more . just my 2 cents

 

NO shit.....after a weekend of progress I feel pretty good, then I look at Brians welds....I feel like the coyote chasing the roadrunner, back to the drawing board.

 

Brian, thanks for the thoughtful reply. a 28" bar at 15 degrees drop moving 2" up and 1" down will try to move the axle .68" a straight horixontal bar .07" ...so how much is that bet and much?

Another bad thing the bent/diagonal bar does is play hell with the roll centre ...http://www.jimmyjudd.com/jimmy/panhard.htm

-Andy

 

Fwiw, flat stainless steel washers are thinner than mild steel.
An assortment doesn't cost much.

A pair of 3/8" stainless flat washers space double tabs out just right for powder coating.

Said washers available most any hardware or big box store.

 

Yes indeed, I just did the same test with a tap measure on my desk top. The difference is about 1/2" for 2" axle movement, but whether it makes a great deal of difference in the long run depends on whether the spring is set up to actually make use of the suspension travel available, or whether it is set up virtually solid like most hot rods. (including mine)

 

OK, to make this a little more accurate...

I just went out and did actual measurements on the panhard bar so that you guys can tell me an exact number on side to side movement. I was "guess-timating" that the bar was 28" long and was at about 15 degrees in my reply above, sorry I didn't make that clear.

The bar is actually 32" long center to center and sits at 8 degrees from center to center with the weight of the body on the chassis. I'm thinking it may be more like 5 or 6 degrees with the rest of the weight of the finished car on the chassis.

Could either of you give me a number with 2" of suspension movement?

I know with the bar already pointing slightly down, it's going to pull a little more to the side under 'full droop'. In 'full jounce' or 'full compression', sideways movement should be almost negligible because the end of the bar will be going over-center on its arc.

Thanks guys...this actually has turned into a pretty informative discussion.

 

The side motion on this set up of a 32" rod with 2" of even travel up or down will yield approximately somewhere around .062"+/- lateral deviation from center on horizontal. This could be more or less based upon the offset of the mounting brackets. This is why it is best to keep bracket centers on the same plane and a panard rod length at least 2/3's the wheel track. This bar could be bent like an "S" and it would still give the same results. The two mounting points form the radius of a circle thus the distance never change.

What does change with panard bars is the relationship of the chassis center line to the longitudinal center of the rear end as it swings thru it's arc. This measurement will vary slightly with the upward or down ward movement of both or individual wheels and the angle deviation from horizontal at ride height, length of the rod and the split between the mounting points. In simple terms the chassis moves back an forth in relationship to the axle during operation .

You should be concerned about the relationship of the chassis centerline versus the relationship to the center line of the axles at ride height under sprung weight or slight load . Considering most of the time you are driving down a smooth road everything should operate on the same center and you don't want excessive movement created by the panard rod during wheel travel.

To see what happens to this chassis all you have to do is take a plumb bob line and center it in front of the axle panard rod mount. Disconnect the rear spring and run the frame up and down and watch the relationship of the bob string to the center of the panard rod bolt. You can do this with a little math but thats no fun and need the measurements of the bracket centers off axle center at ride..

Now my computations with just a tape measure only get about .125 deviation on a 2" bump with a 32" rod at a 20* +- angle, Thats 1/8" or less

 

2" up will have .21" lateral movement, I think you should read that article I linked until you understand why having it diagonal it such a bad idea, those guys only drop it 1", only on dirt, only turning one way, surely you've seen what happens when they unload the outside rear too quick.
Instead of guessing you could take the spring out and determine your desired ride height and travel, put just the main leaf in and play with it and spring it to the desired height when you've got everything on.

 

Pardon me for saying so, but that's not a whole heck of a lot.

I read it and I'm not convinced that it's such a bad idea. It seems to me that the article is geared towards race cars that only turn left....not street driven hot rods.

For instance, it says "A panhard bar that is attached to the right side of the frame lowers during chassis roll. However, a panhard bar that is attached to the left side of the frame raises during chassis roll."

This is only true if the car is only turning one direction.

Roll center seems to be the only drawback that I can see. This car is going to have big and little skinny 16" bias ply tires for god's sake....it's really not going to make any negative impact on the way the car rides or handles.

In fact, I think the panhard bar is going to be a very positive addition to the car as far as handling is concerned.

As an aside, I do appreciate the strictly technical viewpoint being added here. If I were responsible for the entire rearend set-up, I likely would have done things a little differently, but I still may have set the panhard up on a slight downward angle.

Don't like a 5 to 8 degree angle on the panhard bar mounting points? No problem, make yours perfectly level when you build your hot rod. haha

 

Dick, thank you for the very informative post. Could you tell me how it's possible to get a 70" long panhard bar on a '32 Ford Chassis? 2/3 of the 106" wheelbase is slightly over 70".

If you meant to type 1/3 wheelbase, that would make more sense?

 

It looks to me that the crossmember is to light , unless it was made with a moly tube , the shock angle is to great ,if the frame travel 2 ins down think about the angle of the shocks , why was the notch put in the frame , it has a bunch of clearance without it , also it looks like the back of this car is realy stiff beacause of the arc of the spring , banhard bar should be braced ( it will flex ) if you get any up or down travel travel at all , just my thoughts!

 

Super plus, did you bother to read the rest of the thread, or just look at the pictures?

Many of your concerns are unfounded, and have already been discussed in the thread.

But regardless, thanks for all of your insight...the world needs more "armchair quarterbacks."