81 Hopping Around

[cmegga]

I need to do some suspension work on my 81, trying to figure what exactly I need. I dont really want to do the entire system, just what is necessary to make it ride decent.

The problem Im having is highway driving, I have a nice 20 min. highway ride to work. I usually cruz along at 65-70, at this speed when ever I hit a bump it feels like the whole car whats to lift up and hopp a foot to the side. Not large bumps eigher, even a little bump will make this thing jump fairly good.

I wonder how t correct this, would this be as easy as some decent gas shocks or shocks / springs or more ??

Around town is not to bad, I do get alot of window shake on the little bumps, but nothing too major.

 

[Bob Chadwick]

How are your shocks? If you push down hard on the corner of the car does it bounce several time or just pretty much return to position?

Bob

 

[Yoda]

Is this the rear end doing the jumping?

What happens when you are running about 40-45 and nail it? Does the rear end want to move around?

If yes to these, it may be shocks,,, but my money would be on the trailing arms being worn...

BudD

 

[78SilvAnniv]

Sounds more serious than shocks

When you accelerate and/or let off the gas pedal, does the 81 want to pull from the rear wheels to one side or the other?

If so, things that could be worn out:
bushings/bearings
trailing arms
yokes
or maybe these items just need an 'attitude adjustment'!

Now as for these bumps being 'little' bumps that are causing your 81 to want to change lanes mid-flight.
I've noticed that certain sections of roads, with or without bumps and/or standing water will cause my 78 to change lanes on her own. It's why I ususally drive with two hands. Sometimes those large tires are just grabby and want to go where the road takes them.
Silver

 

[cmegga]

Well if I push the front down it does go right back up, but there is not much bounce at all.

Im not getting a pull when I left off the gas, and I have no issuse nailing it at 45 unless my back tires cut louse.

And its not really that it changes lanes it has a decent alignment ans stay on course on the smooth roads. It just jumps the bumps over 60. And it may be just the back end because I usally have to give it a little turn to get it straight, but its hard to tell from the drivers seat.

Its almost scarry like the car is going to come off the ground.

 

[69MyWay]

You are suffering from a condition called "bump steer", and you can see by the definition that it is exactly what you have.

It is a very dangerous condition. It usually happens when the geometry of the car is different left to right, and or the suspension travel is not equal left to right.

If it was wheel bearings, I think you would know by now from the sound, smell, and fact that one of the rear tires would be physically loose.

Do a quick check. First grab the back tires one by one and bear wrestle/tug/pull/ and see what movement if any you can get. Then, jack it up one side at a time. Grab the tire first top to bottom and pull, then side to side. Have a spotter there recording the results of any movement, and where they movement is coming from.

Now, get a large pry bar and stick it up in the pocket where the trailing arms pivot in the frame next to all those pesky shims. Gently pry and record any movement left and right.

Now, jack the car up and watch the movement in the rear lower rods that go from the center of the diff out to the wheels. Look at the ends where the bushings are and measure/note any movement you see through the above noted tests.

Finally, lower the car down, go around the block to settle the suspension. Now, take a level, put it against each tire top to bottom, center the air bubble, then measure from the edge of the level to the top side of the rim or tire (rim is better, and make sure tire pressure is the same in each wheel), record the difference if any. This is one of many ways to shade tree check your camber angle.

Bottom line is that you have two major areas of wear. One being the trailing arm bushings up in the frame pockets, two being the bushings at either end of the rear struts. This is really all that holds the rear of the car in spec other than the pressure from the spring and any assistance you get from the sway bar (if equiped). So, you are looking for any movement that is more on one side than the other, then looking for the source of the movement. However, if it ends up coming from the trailing arms, you might as well plan on replacing all the rear bushings.

Could shocks cause this problem?---I really don't think so. They might make the car bouncy, and loose, but a sudden bump should not cause the car to bump steer as a result of uneven wear on the shocks.

Good luck.

 

[bioandy]

I feel that I have the same handling symptom in my 70 Roadster, but my car hops over bumps at much slower speeds than highway. I have recently completed a total rear suspension rebuild for other reasons, and had a suspension shop go through the front-end to do what was needed along with the 4 wheel allignment.

The shop replaced upper control arm bushings, sway bar links, and one lower ball joint. Car drives and stops straight. Handles great all around . . . but still hops/jumps when hitting small bumps/potholes.


I plan to replace front shocks to match new rears, steering piston, and idler arm. I''ll let you know if any of this makes an improvement.

Good Luck

Andy

 

[cmegga]

Thanks for all the great adivse. Chris as alway your vast knowledge of the cars has overwhelmed me. You know more about these cars then any shop or mechanic I have been to so far.

I took a look at the rear and everthing is fairly close to symetrical. The bushing all looked faily beat up. Especally the rear above the the back tires. Im not sure which bushing this is, but you can see it inside the rear wheel well, to the top right, it bolts to th frame. The bushing is toasted, and the plate below it is all rust and the side are about to fall off.

To rebuild the suspension can I do just the shocks, springs, rear bushing and control arm bushings?? Of should I be doing more while Im having it done. I just want to make sure Im getting all I will need to get some decent control so I can do 1 order with VBP.

 

[jbonifas]

I had the same problem. I replaced the shocks. No change. I then replaced the bushings and front springs and I believe that fixed it. I also had some spacers and oversized tires that I replaced, but the bushings were the trick.

 

[69MyWay]

cmegga,

I think you have found it then, just naturally worn bushings letting the rear change position on a hard bump.

I have seen several stories now where fellows have done either the rear trailing arm bearings, then had to do the bushings, or visa versa. This can get very expensive at a shop, and you can do it at home by taking your time and gathering plenty of info, as well as buying the tools you need to press the bushings, and bearings.

I would suggest a complete rear rebuild, then you know it is good to go for another 20 years.