Shudder at highway speed

Some of you may remember my broken spring problem from a couple weeks ago? Well, I got my new rear leafs back for the 55 Ford and put them in, along with new KYB shocks. Well, it rides pretty nice, now, over bumps and such, but on the highway there is a noticable constant shudder. There was always a little vibration, not necessarily constant, but I summed it up to being a product of a slightly bent rim.

I'm not sure if it is front end, driveshaft (which seemed to rub the body a bit when the springs were broken), or maybe road bumps from the rear suspension being so much stiffer. On the same note, I'm wondering if maybe the stiff suspension is making the bent rim more noticeable.

Now, when I put the springs in, I left the passenger side springs connected while doing the driver's side. Then did the passenger side. The pinion angle should not be any different, right? The car seems to sit about 1.5" higher in the rear than it used to. That shouldn't change the pinion angle, would it?

Does any of this make sense? I guess I'm just wondering what to start looking at, or if I'm just imagining a problem.

 

Check the driveshaft as it may be bent due to hitting the body.
You said you suspected the rims - might be time to actually change it??
I do not think the pinion angle would change enough to cause this, unless it was marginal to begin with, check it.
Check also the tyres for bead shift.
Cosmo

 

I've run into this before. I lowered my 49 ford [stock mavrick rear axle] and didn't pay attention to my pinion angle. The angle was severe enough [like yours would be with a broken spring] that I did damage to my rear U-joint in less than 500 miles, causing a bad vibration. I had to cut the spring mounts off the axle housing and reset my pinion angle.....installed a new U-joint and had no further problems with it.
Might want to examine your pinion angle and U-joints..

 

To find out if it's a rim, borrow some rims from another car--a buddy's, your late model, whatever fits. If the bad vibes are still there, you know it ain't the rims.

If your pinion angle was marginal, you can correct it with some wedges from Chassis Engineering, Inc. These are basically thin lowering blocks that taper, so you can adjust your pinion angle by sticking them between the spring and the perch on your axle. They are available in a couple different "pitches". Howver, I would not use these with more than 2" of lowering blocks. http://www.chassisengineeringinc.com/universal_components.htm

If it's the front, then you should feel the bad vibes in your steering wheel.

 

I remember from my previous life as an alignment tech that too much negative caster will cause a high speed wobble, similar to racing shopping carts where the inclination angle is is to far forward.

This would make sense in your case since the rear of the car is higher therefore increasing the amount of neg castor.

Just a thought, but you may want to lower the rear of the car or drop the rear of the split bones to correct.

My .02

DOGG

 

Here's what I THINK might have been causing it, and I don't know what the actual name of the items are, so it is going to be really confusing.
The way my rear is set up, the spring is "sandwiched" by a carrier of sorts, a flat tray with a very thin rubber sheet on it, and the spring pack nut on top, has the same type of tray. That top tray piece has a locator pin that keeps it in place at the spring pad on the bottom of the rear axle housing.

On the driver's side, that pin sticks up very prominently maybe 1/2" into the hole at the spring pad. On the passenger side, it is JUST barely sticking through, although I'm not quite sure why.

Also, I cannot understand what difference it would make to the pinion angle to shim the springs. If the wheels are on flat ground, and the ground is somewhat constant, the body is just dancing on top via the springs. As long as the spring pad is not moved, and it is welded to the housing, how can it affect pinion angle, assuming the tranny angle is the same.

The springs were built "custom" using the old springs that I gave him, so they should, in essence, be identical.

 

Just replaced the springs in the convert and the "little" touching of the body with the driveshaft with the old springs turned out to be enough that the whole driveshaft, less the yoke, was not repairable and completly shot.

 

Miles, was there a dent or any kind of marking on the driveshaft? Mine looks like it is just the paint that is scraped off.
I'm going to be super pissed off if this one is fucked up. To the point that I might not bother replacing it. I would seriously think about parking the car for awhile or speeding up the Gasser plans.

Deyo

 

Try taking it up to speed , then shift into neutral. If the vibration stops it's a u-joint. If it doesn't stop it may be the drive shaft or a rear wheel bearing. Also, if you did any welding on your rear axle housing it may be that the welds pulled it out of line with itself causing a bind in your axle bearings. Have you checked the wheel balance?

 

I suspect the bent wheel.

They don't have to be bent much to give you shit. Now with everything fresh and tight the vibrations should be more prominent. I may have a old Ford wheel you can use if you need it.

Remember the conversation about the spring perch insulators, I showed you a picture in the T-bird Headquarters catalog. If those bushings (flat rubber) are shit or missing the pinion angle will change under acceleration and cause the driveline to buzz.

 

Steve, I tried that suspension place, but there was no talking to the idiot behind the counter. He didn't have half of a clue, it is a story in itself. I asked if he could find a KYB for a '55 Fairlane, and also added that it would be the same as a Tbird. He looked it up and said it only goes back to 1962. Then I had him look up the Tbird, because he obviously didn't figure that out from my previous remark. He finds the number and says, "I don't THINK we have it," as he comes over and stares at me. "Well, could you go look?" I asked.
"Oh, you want me to look?" Well, he didn't have them, they'd need to be ordered, no Ubolts, nothing, so I pretty much gave up on that kid. BAP had my KYBs and they are pretty badass.

Well, I'm not sure but I think it is better. The insulators on the passenger side were trashed, so what I'd done was split an old radiator hose and use it as the top insulator. I think that acted like a shim since that rubber was about 3x the thickness of the isulator on the other side. So, today, I took it all apart and used the radiator rubber on the bottom side and put the good insulator on the top side. I THINK it is smoothed out, but I"m not sure. I can't feel a thing at 2200 RPMs in high gear, but I think I can at 2500. Which is a difference of about 60 MPH to 70MPH.

It feels no different in neutral than it does in gear.

 

Try what just dug said. I had a U joint that was real dry and did'nt know it and went lowered my truck aq little more (which changed the pinion angle slightly) and I immediatlely had vibrations. Took me a week to figure it out. Even sent it up to Lincoln Tech when my nephew was going to school there and they thought the drive shaft was bent but I knew it was'nt.

When the angle got changed it pretty much just finished the ujoint off. It only did it at 45 to about 75 mph. I could also change the spacer between my carrier bearing and get it the vibration to change at different speeds. It was just a weird thing all together for me.

Anyway, thats what I would check.

 

Yeah, thats Jerry allright. He is a prick but I have learned to deal with him over the years. I wish I would have known..

Vintage Ford/SoCal or T-bird Connection here in town should have the new replacements. I know you don't want to throw more money at it but I belive the stock bushings have a metal reinforcement sleeve in them to help locate the rear axle better on the spring. They are a bit thicker than radiator hose too.

Acceleration to coasting not making a difference in vibration tells me it's more likely a bent drive shaft or the bent wheel!

 

I am a technician at a Chevrolet dealership. Each Chevrolet dealership in the country is required to have what is referred to as an "EVA" (Electronic Vibration Analyzer). It will measure the frequency of the vibration. Depending on the vibration frequency, you can pin point the vibration. Drive shaft vibrations have higher frequencies than a wheel vibration for example. In the hands of a trained operator, it is quite a useful tool. It can even pinpoint the cause of engine vibrations.

Now I know some people have reservations about taking their vehicles to a repair facility (dealerships are no exception), but I'm here to tell you, THIS IS THE TOOL YOU NEED TO FIND THE CAUSE OF YOUR VIBRATION. Go to your local Chevy dealer and ask if they will diagnose your vibration, and then make the repairs yourself. It would be money well spent, rather than throwing parts at it. Plus, it will save you some brain damage trying to figure it out the old fashioned way. We work on any make, model or year of car at our dealership, I would HOPE that any other dealer would also. I've found the cause of several vibrations on my own, as well as a couple of my friend's hot rods using this tool.

...for what it's worth to ya...

LP