Building an adjustable panhard bar

[RallyBob]

Here's a pictoral step by step buildup of an adjustable panhard bar for those who may need one.

There are a few reasons for wanting/needing a new panhard bar. First, the stock Opel bars are made from thinwall steel tubing that bends very easily. Second, if the ride height of your Opel is changed from stock (usually lower), the length of the panhard bar must be changed to compensate, otherwise the rear axle will sit crooked in the chassis. Third, by using alternative bushing materials the handling of your car can be made more predictable and precise due to a reduction of deflection.

The first step is to locate a stock panhard bar as a donor. I like to use one polyurethane end bushing and one heim joint in my panhard bars. The reason for this is I've found that using heim joints at both ends on a road-going car can be a bit unforgiving. For example, if a solid item were encountered in a sideways motion, there is very little yield....parts tend to break this way.

Next, a few hits with a hammer will knock the stock rubber bushing from the eyelet.

The eyelet should then be cleaned of any undercoating, paint and rust. I used a wire wheel and sanding rolls to do this, a sandblaster or glassbeader would do a better job in less time, if you've got access to those machines.

[RallyBob]

Once cleaned, the eyelet must be cut off the panhard bar. My favorite way of doing this leaves about 1/2" of the panhard tubing still attached to the eyelet.

After cutting, I drill a hole through the tubing for greater strength when welding. Using plug welds will greatly reduce the chances of the welds breaking away.

A hardened grade 8 bolt will serve as the right hand threaded portion of the panhard bar assembly. It's 2.5" long, and will require grinding the head down to fit inside the panhard bar tubing. Measure the tubing ID first, as GT's and Manta's have different panhard tubing diameters.

[RallyBob]

I used a bench grinder with a coarse wheel to grind the head of the bolt down, and fitted it tightly to the 'stub' of the panhard eyelet. If you have access to a lathe, it will do a much more precise job and probably in a lot less time.

I was able to get the fit close enough with a bench grinder that I had to tap the bolt into the tubing with a plastic mallet, so it's a good tight fit with no slop.

I TIG welded the bolt head into the eyelet stub, welding 360 degrees around the bolt, through both drilled holes in the tubing (plug welds), and for good measure I added a few more beads at the transition from the tubing to the actual eyelet. For a strong weld, all plating, paint, rust, etc must be removed if you are using a TIG welder. MIG welding is a bit more forgiving, but the parts should still be as clean as possible.

Here you can also see the thick wall aluminum tube I used for the panhard bar. For a Manta, I've found a 30" long tube does the trick. For a GT, 26" works well. This tubing is tapped left hand thread on one end, and right hand thread on the other. This allows you to adjust the length of the panhard bar while it's in place on the car. I got mine from a local circle-track supply shop, for about $14.

You'll also need to get some thin-head jam nuts, one left hand and one right hand.

And you will need to buy a left hand heim joint. Do NOT be tempted to use the cheaper commercial grade rod ends, as they have a lot of slop in them and will only get worse with time. Go for the stronger precision-grade chromoly rod ends with teflon liners. They do not require lubrication, and they are built to much tighter tolerances. They cost anywhere from $28-$40 depending on the brand.

[RallyBob]

A pic of the chromoly heim joints I use (Aurora), and of the polyurethane eyelet bushing I use from Opel GT Source.

I've used two different options for the rear axle attachment (the body attachment uses the polyurethane eyelet so there are no hardware changes required).

Option 1: I remove the stock attachment stud from the rear axle, and weld a 5/8" nut to the backside of the mounting surface. Then, a hardened bolt is used with appropriate tapered spacers (also bought from the circle-track supply shop) and a lock washer to hold the panhard bar to the axle housing.

Option 2: Simply remove the stock attachment stud, and have a machinist turn the OD down to fit the heim joint. You'll still need the spacers to prevent the heim joint from binding, but this fitment is arguably easier and stronger.


That is pretty much it for the panhard bar. For initial fitment, adjust the center to center length of the bar to the same length as the stock panhard bar with the jam nuts still loose, and then fit it to the car. Try to find a flat surface area for adjustment, as uneven ground can skew the results.

Have the driver sit in the car with the gas tank 1/2 full. Jounce the rear suspension of the car a few times, and have a helper spin the new panhard bar in either direction until a 'neutral' tension zone is felt. That is, there should be very little (if any) resistance felt. At this point, the axle should be centrally located under the car. Once this is confirmed, the jam nuts can be locked into place and you're ready to go.

Bob

[bosco]

Thanks Bob,

I have a lowering spring for my GT and am just waiting for enough available time to do the job. In recent posts I was made aware of an adjustable panhard rod and your instructions above make it very understandable, as well as being convincing to me that it is something I could actually put together, with the help of my local machine shop.

Your time and effort in this forum is always appreciated.
Mike

[tekenaar]

AWESOME!!!, Bob.

[kwilford]

I moved this thread to the "Performance" Forum, where it will better appreciated. Nice work Bob.

[nobody]

Just two quick questions. Where did you get the tapered spacers and would a solid ali rod work?

[RallyBob]

Just two quick questions. Where did you get the tapered spacers and would a solid ali rod work?

I got the spacers and the aluminum thick-walled tubing (already threaded at each end left and right-hand BTW) from a shop in NY, www.behrents.com , but any circle track shop should be able to supply the same stuff.

Bob

[N61WP]

Bob,

would the Panhard rod be an item you would consider building as a sale item?
James

[RallyBob]

I presented this thread as a DIY project because I can't sell any suspension or brake parts. I figured the next best thing was a step-by-step how-to article.

Bob

[nobody]

I think from seeing so many GTs with old and tired springs this is an important upgrade to be taken seriously. For every bit of drop in the rear springs it pushes the rear end out of square. I think everybody should go out and take a look at thier cars with a straight edge and tape measure. How far off center is your axle?

[GTJIM]

I presented this thread as a DIY project because I can't sell any suspension or brake parts. I figured the next best thing was a step-by-step how-to article.

Bob

Great stuff, Bob. You need to produce a line of "garden equipment" including ali adjustable bean stakes and "A"-frame strawberry cloche supports.
"NOT TO BE USED FOR ANY OTHER PURPOSE - BY OPEL OWNING GARDENERS"

[azopelnut]

I think from seeing so many GTs with old and tired springs this is an important upgrade to be taken seriously. For every bit of drop in the rear springs it pushes the rear end out of square. I think everybody should go out and take a look at thier cars with a straight edge and tape measure. How far off center is your axle?

Hey Ron Can you elaborate on how exactly the measurements should be taken??

[nobody]

the quickest check is to have the car on a know level surface and use a plumb bob or weight on a string. hold that on the outer fender and measure to the wheel or preferably the axle itself. Keep in mind that from side to side you need to be at the same point so a reference measurement off the door opening adds to the accuracy.

Ya know I have problems with the bean stakes I have and could really use one like that. Just for gardening purposes of course.

[simplemind7]

i know this might seem like a stupid question to most of you, but what exactly is a panhard bar? from what i gather by reading this it moves the back axle side to side, is that it or is there something else? and when would you need/want to make one? gotta learn these things sometime.....

[jeff denton]

That is step one, nobody. While you're checking this out, put a level on your panhard bar. You want to see it a bit higher on the end that attaches to the chassis.
Now you need to know what your suspension travel is. Put a zip tie on the shock absorber shaft right where it slides into the shock body. Get it nice and snug. Now go drive your GT hard thru some corners, then look at how far away that zip tie is from where the shock body pushed it up the shaft. Mine got two and a half inches. So two and a half inches is my suspension travel.
Now you need to simulate this full travel, called "full bump". Racers do it by replacing the shock absorber with a length of All-Thread so they can pull the body against the spring to simulate this full bump setting. Now how level is your panhard bar? You want it to be "off level" as much as before only the opposite way. Theoretically. The actual amount of difference is all trial and error. This is the adjustment you see the pit crew on TV racing coverage do when they stick the wrench down a hole in the right side of the rear window.
While you've got "full bump" simulated, do nobody's plumb bob measurement again and you should get the same reading as you did at "ride height" if your panhard bar is adjusted right.
Keep in mind this is all silly busy work if your GT is just a cruiser. It is very important only if, for some reason, you really need the ultimate in handling control out of your GT. In which case you are driving in a controlled environment and have all your safety equipment installed, etc.
Simplemind, the panhard bar is that rod that attaches to the axle housing at one end and the chassis at the other end. It holds the car's chassis from sliding away sideways from the tires. Keeps the car centered between the tires, put simply.

[jeff denton]

Now I'll try to explain what this thread is really about, that is Bob's adjustable panhard bar. This allows you to adjust it's length, the adjustment I described before is adjusting how high or low one end attaches to the chassis.
If you do noboby's plumb bob check and find one side measures differently from the other, you can adjust the length of the panhard bar to fix this.
But nothing is fixed if you haven't done the test I described first. The two adjustments screw with each other.
Then there are the lower control arms. Guess how important they are?
Look at them when you're doing these tests. As the axle moves from "ride height" to "full bump" they are moving the axle slightly from front to rear, causing a condition called "roll steer". This is something you need to study carefully if your goal is a good handling car!

[RallyBob]

Great stuff, Bob. You need to produce a line of "garden equipment" including ali adjustable bean stakes and "A"-frame strawberry cloche supports.
"NOT TO BE USED FOR ANY OTHER PURPOSE - BY OPEL OWNING GARDENERS"

Holy s**t Jim, laughing my ass off at that one.....!

Bob

[jeff denton]

It's not funny, Bob. That kind of stuff is where the money is! Think about how many people with money need that stuff compared to how many people without money are dreaming of building a hot rod. We are both in the wrong business.