front end bounce issue

[PotvinGuy]

The Panhard is the only thing I see that is different from most T front ends. Being "loose" horizontally would make the front end more dynamically unstable, and might lead to the behavior you've seen at high speed. I'm grasping at straws, everything else looks kosher.

 

[Wild Mango]

As Potvinguy observed, your front end has no transverse control. You need a Panhard bar. The symptoms you describe are of the front axle oscillating from side to side, bump steering itself to even greater excesses until the front end components contact each other. IMHO that pretty little front end is a disaster looking for someone to happen to. Just looking at the kingpin angle in the photo, it could be you are a little light on caster as well, but that ain't the problem. It's the front axle oscillating transversely that's giving your bucket the hippy hippy shakes.

 

[PotvinGuy]

The missing Panhard seems the only difference from typical T front ends. The lessened horizontal control would make the front end more dynamically unstable. Shaking side-to-side on the spring shackles could transfer weight violently from wheel to wheel and might cause what you've experienced at speed. I'm grasping at straws; everything else looks kosher.
Speedway has a Panhard kit that might fit.

 

[409T]

You don't need a panhard bar with your current setup. Panhard bars are used to keep the drag link from pulling the axle to one side or pushing it to the other. Your drag link runs perpendicular to the axle and is stabilized by the radius rods. You said "the axle would jump up and down to absolute limits". Think about it. What makes things go up and down when the wheels are spinning? The first thing I would look for is out of balance or out of round something that spins, assuming you don't have 1/2" bolts in 5/8" holes or something like that.

 

[TriodeLuvr]

... The symptoms you describe are of the front axle oscillating from side to side, bump steering itself to even greater excesses until the front end components contact each other.

There is no discernible side-to-side movement when this happens. There is also no vibration in the steering or frame unless the components make contact. Even when the wheels are moving up and down a half inch or more, nothing can be felt by the driver. This is occurring strictly in the vertical plane, and I'm sure it has nothing to do with bump steer.

 

[TriodeLuvr]

The first thing I would look for is out of balance or out of round something that spins...

Right, that's why I had the balance checked again. Do you think lateral runout of a wheel could cause this? I don't feel anything in the steering, but I can see that one of the wheels isn't quite true. There's no out-of-round, just lateral movement.

Jack

 

[PotvinGuy]

FYI, I called Speedway. They had to do some digging, but the Panhard assembly is 916-35101, for $160 in chrome. You can't find it in the catalog or online. It's the same one used in their 4-bar front end 913-39026, which I have in my car:

 

[Mike J]

There has to be some side to side even with the short shackles, I.M.O. I vote for panhard bar instead of damper.

 

[Ma_n_Pa T]

Right, that's why I had the balance checked again. Do you think lateral runout of a wheel could cause this? I don't feel anything in the steering, but I can see that one of the wheels isn't quite true. There's no out-of-round, just lateral movement.

Jack

I had the same problem with mine, pissed around trying to change part to the fount end for dam near 2 years. I also tried balance beads, different air pressure, changed alignment, caster, toe in-out with no fix. It ended up being the rear tires.
I had MT 29x15.5x15 biases tires with tubes. I had a chance to pick up some new Hoosiers, 29x 15.5x15 for half price, took them in and had a good “force spin balance” job done on them. Bingo!! No more bounce in the front tires, I have put over 15,000 on it since with no problems. The balance job is not cheap but works very well, give that a try first before adding new parts unless there worn.
Jerry

 

[Wild Mango]

Don't forget the steering damper is parallel with the tie rod. Rapid lateral axle movements will move the tie rod and thus steering arms as the damper does its work and very little is felt in the steering. I have had the exact same problem, learned the hard way. There are very good reasons why manufacturers dropped the beam front axle early on, and this is one of them.
If things were out of round or out of balance they would progressively get worse as speed increases, not suddenly go beserk.
If you apply moderate brake when the shakes come to visit, what happens? If things suddenly damp out, good bet its a stability issue. JM2CW
As an aside, as screamin' will tell you, plenty caster will tame an unruly beam front axle, look at any race car so configured and there's lots of caster so the front wheels tend to be "led" and so stabilise themselves.

 

[RESINATOR]

This is a Checklist of sorts that may help go thru and fix the common causes of front end bounce and shimmy. We give this to our customers when they call about these issues. This is a work in progress and this might be a good place to further it's helpfulness to people with some added input. This is a PDF file, I hope it works similar to uploading photos.

 

[dalekc]

Thanks for the information I think it help a lot of T BUCKET'S

 

[PotvinGuy]

This is a Checklist of sorts that may help go thru and fix the common causes of front end bounce and shimmy. We give this to our customers when they call about these issues. This is a work in progress and this might be a good place to further it's helpfulness to people with some added input. This is a PDF file, I hope it works similar to uploading photos.

Jerry, thanks for the checklist. One question: it says to set toe at 1/8" out. Shouldn't that be 1/8" in?

 

[RESINATOR]

First, your welcome. Second, when the tie rod is behind the axle we always start with toe out, just as we would start with toe in on a car with the tie rod in the front. This preloads the rod and seems to calm the front bouncing down more often than not, especially with larger/heavier front brakes or wheels. The toe adjustment will not fix a dimensional or design problem. The toe in or out is really the simple part of the ordeal (easy to adjust and try) and some tires like more or less. The most common issue is out of square or not triangulated components (dimensionally). It's easy and common for people to work on one part of the car at a time (front end / rear end ) and forget that the relation to each other and the frame.
When a frame comes out of our fixture we can simply match the bars by laying one on top of the other, leave around 1/4" to 3/8" of thread, and by dropping a bolt thru all three ends, they will match.. we know we are close and start from there. If some one has brackets that are not quite the same side to side the bars would be adjusted to fix that.
One more thing I already see the list overlooks is to always check the tires for out-of-round or misalignment on the rim. Jack the car up and spin the wheel, it will be obvious if this is a problem. The guy we used to have do the spin balancing "on" the cars would check this before starting anything else. He would simply deflate the tire, break the bead, rotate the tire back and forth a bit and reinflate it.

 

[iajjpop]

Well, I'm having the same problem, and this will keep me from having to start my own thread on the same topic. So, maybe it's not quite for nothing...

As background, I think the frame and suspension in my bucket are from Total, just like the OP's. When I first bought the car a couple months ago, the front axle would oscillate (seesaw) like crazy when I hit 60 mph or so. The problem was really severe, so bad I thought parts would break. The axle would jump up and down to the absolute limits, smacking the tie rod into the radius rods on both sides several times a second.

It turned out the car had been sitting a long time, and the front tires, which were more than ten years old, had developed a few flat spots. I also found that the friction shocks weren't working, even though they'd been tightened down at some point by the proverbial 300 lb. gorilla. Replacing the friction pads and adding a lot of air pressure to the tires helped, but the problem was still there. Since then, I've replaced the friction shocks with hydraulics and replaced the front tires (MT Sportsman Front 26 X 7.50 - 15) with smaller Nexen 165/80r15 radials. Because I put radials on the front, I also replaced the huge MT rear belted tires with somewhat smaller MT Sportsman S/R 29 X 15R15LTs. The rear rims were changed at the same time.

Through all of this, I've been careful not to drive the car too fast. The oscillation is really scary, especially in traffic, so I've been sorta easing her speed up gradually since making the changes. Sadly, the problem is still there. The new shocks control it enough to prevent the tie rod slapping other front end parts, but the wheels otherwise oscillate just like before. I'll add that the company that changed the front tires really botched the job (another story for another day). I was sure that among other things, they hadn't balanced them correctly. Today I took the car to another service center, and they spent a lot of time inspecting the wheels and tires. One tire was out of balance more than five ounces, the other out by four. The most disappointing thing was when I left. The first time I hit speed, the oscillation started up again. In fact, despite the improvement in balance, there was virtually no "before and after" difference.

Below is a photo of the front end (still has the MT front tires). I'm at the point now where I'm considering whether to replace the leaf spring. If anyone has any ideas, I'm all ears.

Jack

 

[iajjpop]

I see on your rod you have mounted reg. shocks . they look real good. Where did you get the top mount at ??? Thank You....

 

[TriodeLuvr]

This is a Checklist of sorts that may help go thru and fix the common causes of front end bounce and shimmy.

Thanks Jerry, that's very helpful. This car wasn't set up very well, and I've had a few unpleasant surprises. No doubt it needs all the items described in that PDF checked out. I tried an experiment today, and I think the bounce is due to the lateral runout of one front wheel. I also think the Nexen tires I just bought may be out of round. Anyway, I've decided to replace both front wheels, remount the tires, and go from there.

Jack

 

[TriodeLuvr]

I see on your rod you have mounted reg. shocks . they look real good. Where did you get the top mount at ??? Thank You....

I'm fortunate enough to have a small CNC mill in my garage. I cut the brackets from 3/8" aluminum plate and mounted them using the same attachment points as the original friction shocks.

 

[TriodeLuvr]

You said, " The axle would jump up and down to the absolute limits, smacking the tie rod into the radius rods on both sides several times a second." Maybe I'm missing something here, but the tie rod and radius rods are virtually tied together with the tie rod going relatively equidistant between each "arm" of the radius rod and should not move independently, therefore, I don't see how the tie rod can be hitting the radius rods.

Sorry, that was an assumption on my part, based on the extremely violent behavior of the front end when it oscillates. Guess I didn't think it through all the way. Yes, I had caster and toe checked/adjusted right after I bought the car last month. That helped the steering stability, but it didn't do much for the bounce.

 

[iajjpop]

Triodluvr would you happen to have a paper template of your front shock mount ?? Also what shocks did you use ? I really like the look. Thank You....