Car hits bumps in the road and tries to rocket off the road. Normal for classics?

So I have a 55 Plymouth. New shocks, tires, tie rod ends, and leaf spring bushings. It was wandering around the road and had terrible steering. Thanks to you gentleman I now have her smoothly tracking straight. Except for when I hit a bump in the road way. The car feels like it wants to rocket off the highway when I hit the smallest of bumps in the roadway. Is this normal for a classic? Is the suspension that crazy? Or do I have something I'm way overlooking

 

55 Plymouths are not classics, but were good driveable cars when new and didn't dart off the road. There is something wrong and I would start with an alignment.

 

Have you had a front end alignment? What kind of tires are on the car? Non radial tires could cause the car to lurch when you hit a bump.

 

Sounds like the caster is off...........if the caster is too straight up it will make it dart cause it makes it almost run Pigeon Toed when it hits a bump.......make sure it is aligned right first.......Toe is just part of it....Caster is the main thing when suspension travels.

 

bumps should not but ruts will/ can cause erratic behavior, especially with bias plys and stock susp/ steering if not rebuilt

 

Would a worn pitman/idler arm cause this?

 

There should be a rubber isolater pad between the steering box and the frame. If this is mushy, no amount of new parts and alignment messages will work, as it will allow the steering box to slop around. There is also an adjustment on the steering box that will take some play out of the worm and roller in the box itself. Assuring these thisng are correct will along with a proper alignment keep your car handling and driving properly. Also if you are running bias ply tires, what are you running for air pressure?

I have a 46 Plymouth with radials and it tracks well over bumps and despite of some slop in the steering box it goes wher I point it. The front ends are pretty much the same. So you have some checking to do.

 

Have it professionally inspected and aligned.

 

Its not normal for an old car. And on another note, bias plies wont make it dart off the road. All they do is follow deep cracks..

 

You definitely need to get it to an alignment shop.
Going off you tie rod thread, just take it in and have them set it up and check it out for you.
Tow it there if its that badly out of wack.

 

Check the caster.

 

I would really shake it down for something loose first. Caster would have to be ridiculous for this type of behavior, but the aligmnent should be al least checked and compared to specs. What is the tire air pressure set at? Too much can make it jumpy like that.

Bob

 

Well the majority of the guys are correct on one thing and that is the fact that you need to have the whole steering and suspension checked out by someone who knows those front ends.

But you can still check things out yourself and see if you can spot something.
Start with checking the Isolator for the steering box that Ply 46 mentioned. You should be able to have a helper rock the steering wheel back and forth while you watch the box to see if it moves. If it does mark that down as needing attention.

move on down to the pitman arm and see if you have excess movement in the wheel before the pitman arm moves.

Next check the connection between the pitman arm and the steering link and see if you have movement there that shouldn't be.

Each component in the steering and suspension needs to be checked individually to make sure that it is good or see that it needs replacing. Several slightly worn things may not be issues on their own but added together they create a loose front end.

It's not a tire issue unless you have a bad tire or maybe mismatched tires. Or you are trying to run radials on one end and bias on the other.

And the new tie rod ends may actually be magnifying what is wrong now. I just found that out on my ot daily driver when I replaced the tie rod ends and ball joints but hadn't replaced the pitman arm yet. Hit the famous highway 97 ruts by Parker on the way home and the truck wanted to change lanes on it's own.

 

No car should experience this behavior! Whether it is a "true classic", or just an old car it should not be erratic. This sounds to me like slop/ or slack in the steering linkage. The best way to check this is to crawl under the car and have someone turn the steering wheel back and forth, just the amount where it feels like there is slack. Any movement should show up like this.
Also check the rear suspension, as the rear doesn't have to move very much to really steer the car. Do the same on the rear, but have someone push the body side to side while watching for movement.
Look for loose bolts. Look for a dusting of rust around bolt heads and nut, as this is indicative of movement.
Check the shocks for loose bolts or worn bushings.

~Alden

I am just ribbing you about the "classic car" business. The term has too many meanings to be clearly defined. One group or entity says it means one thing, others have other meanings. For this forum there is no reason to be so fussy! Old car, classic car what difference does it make?

 

One opinion and the thread gets Hijacked.

How to start an internet argument:
Step 1. State an opinion as fact
Step 2. Wait.

 

One opinion and the thread gets Hijacked.

How to start an internet argument:
Step 1. State an opinion as fact
Step 2. Wait.

 

One opinion and the thread gets Hijacked.

How to start an internet argument:
Step 1. State an opinion as fact
Step 2. Wait.

 

I agree. Get an alignment. Then you'll know.
Tom

 

Probably the same people that came up with FoMoCo............

 

Probably the same folks that came up with FoMoCo................

 

Probably the same folks that came up with FoMoCo................

 

First let me say that I really appreciate the help guys. I'm a medical student with zero real buddies around to wrench with. My pop wasn't a car guy at all and I'm learning all this as I go. Excuse the ignorance of my questions. This is all new to me.

My tires are not bias belted, they are new and are aired to 32lbs, disk brake swap up front, and ford 8" rear out back.

I followed the gear box adjustment procedure according to the factory service manual and it appears to be in spec. With the tires off the ground there is two pounds of resistance with the turning of the steering wheel. It was hard to observe any play in the steering as I was turning the wheel via a pulley system in my garage alone when I was checking it. I'll have to bribe the kid next door to help me and check the gearbox mounts/ tighten everything down there real good. Called around and was told that my car did not come with a pitman arm by several parts places. Am I missing something? I'll be getting a new alignment with my inspection as soon as I can get some windshield wiper arms that will fit. Sounds like I am on the right track though.

I know I could take this right to a pro and have it fixed in a day but I enjoy trying to figure out stuff like this as it will be the only way I learn for myself right? I have considerably improved the ride since my first drive and am Definetly making progress.

Anyone know if 55's had reverse lights? I don't have any and will need to rig up some if so to pass inspec.

Thanks again for the mentoring guys!

 

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