Bad vibrations...

[moparsrul]

Well said Centerline I agree with you! I haven't dealt with the wide blocks much, but have been following this tread. I have seen a few problems over the years with miss match parts on the big blocks with cast or steel cranks. I have leaned toward that from the beginning. Dave 145 my hat is off to you for getting after it. I would just suggest take a little break. Sometimes just backing away for a little bit ansd starting off with a fresh start.

 

[Dave145]

Well, we stuck with it. Enough to go and get a new driveshaft made. Unfortunately, that did not fix it. The vibration at 35-40 is gone, but anything above 65 makes the whole rear end shudder like jello in an earthquake.

At 60 you can feel a slight shimmy in the floor, but above 65 it vibrates mostly the rear of the car.

 

[Ski 61701]

Without rereading 9 pages of ideas. Have you loosened up your motor / trans mounts and try to resettle your motor, maybe its cocked enough to throw things out of wack. If you haven't already have someone brake torque the motor while you look at the mounts to make sure they aren't torn.
Next thing, I vaguely remember you saying leaf springs are flattened out. I'd jack the car up putting jackstands under front spring perch and jacks under front of car level it as best you can. Get a 3rd set of jacks and now that rear end is hanging, jack it up some and put the 2 other jack stands under to support it. Do your road test this way and see if vibrations change or go away. You'll have a pretty good range of adjustment considering the amount of teeth on the jackstands holding axle up. If you luck out and vibrations go away look at replacing leaf springs and or trans mount.

 

[440+6]

Put a timing light on it and run it up to rpms when it vibrates and see if timing is jumping around or if it's steady, kinda sounds ignition related to me, maybe cross firing in the distributor.

 

[Dave145]

I've had a timing light on it up to 3200 rims to watch the timing curve. It's rock steady. Distributor and brain box are new from Proform. Plugs and wires are new too, with the plugs being from ngk and the wires are oreilly masterpro. I've never had an issue with any of these parts on past cars I've had, so I highly doubt that's the issue.

 

[Dave145]

Well after the let down from the driveshaft swap, for science we put the other set of rims and tires on. No change in vibration at all. Vibration is constant at all speeds above 65 and gets worse as the speed goes up. As soon as the car slows to around 62, the vibration disappears completely. While up at 70, I shifted the car into neutral and took my foot off the gas. The vibration did not change one bit. Revved the engine while costing...still no change. But again, as soon as I hit 62mph, the sea calmed and she sailed away without issue. The vibration begins in the front floor and then can be felt most predominantly in the tranny tunnel and seats. Hell, even the steering wheel is solid while she vibrates along.

Why 62 Mph?

Why only the floor and seats?

What else is left here to look at?

Why is E.T. brown?

Why does it still vibrates even while costing in neutral?

 

[khryslerkid]

I know you checked the motor mounts, how's the trans mount? Place a jack under the trans and see if the mount separates. Even if it's real oil soaked or spongy, it will allow the tail shaft to move and create a vibration.

 

[oldbee]

Well after the let down from the driveshaft swap, for science we put the other set of rims and tires on. No change in vibration at all. Vibration is constant at all speeds above 65 and gets worse as the speed goes up. As soon as the car slows to around 62, the vibration disappears completely. While up at 70, I shifted the car into neutral and took my foot off the gas. The vibration did not change one bit. Revved the engine while costing...still no change. But again, as soon as I hit 62mph, the sea calmed and she sailed away without issue. The vibration begins in the front floor and then can be felt most predominantly in the tranny tunnel and seats. Hell, even the steering wheel is solid while she vibrates along.

Why 62 Mph?

Why only the floor and seats?

What else is left here to look at?

Why is E.T. brown?

Why does it still vibrates even while costing in neutral?

Well it's gotta be suspension/driveline minus the engine.

 

[miller]

Why does it still vibrates even while costing in neutral?

Just tossing out ideas. Any chance your rear axle housing is bent? Probably already checked rear spring bushings.

 

[jim ritchie]

I have been reading from the start,all good advise,but now down to rear end and axles,if everything you say and done is correct,,no more changing parts in rear end,if you don't know where to look.Find a used rear end ( at best price,,or,maybe someone has one in club,they know was good and willing to let you try,before you buy it)Only takes your time,hell ,you've done everything else.As you know,everyone will say ,YA, I KNEW THAT after you find and fix it.But the good thing is you can forget it for the season,or drive it only up to 62 mph,,and look cool doing it,because others will think you are just out cruz'n in your classic Mopar and enjoying the ride!CHEERS

 

[Dave145]

Well today we opted to put new shocks on in the front and rear. I decided to put air shocks on the rear to help aid my saggy springs and restore my ride height. This way if I really need to I can use them to raise and lower the car incrementally to try different pinion angles.

The right front shock compresses and expands without any resistance, the left front shock went down and wouldn't come back up on its own, and both rear shocks went down and also wouldn't come back up on their own.

I concur that if the issue persists, we will be pulling the rear end to check for monkey business back there.

 

[Ski 61701]

If you read my post about jacking car up, and levelling it and putting jack stands under the rear end and changing the height of the axle while running it ,is a cheap way of seeing if your angles are off and seeing if vibrations change.

 

[Jcharger]

Well after the let down from the driveshaft swap, for science we put the other set of rims and tires on. No change in vibration at all. Vibration is constant at all speeds above 65 and gets worse as the speed goes up. As soon as the car slows to around 62, the vibration disappears completely. While up at 70, I shifted the car into neutral and took my foot off the gas. The vibration did not change one bit. Revved the engine while costing...still no change. But again, as soon as I hit 62mph, the sea calmed and she sailed away without issue. The vibration begins in the front floor and then can be felt most predominantly in the tranny tunnel and seats. Hell, even the steering wheel is solid while she vibrates along.

Why 62 Mph?

Why only the floor and seats?

What else is left here to look at?

Why is E.T. brown?

Why does it still vibrates even while costing in neutral?

Use the first to eliminate anything that wasn't spinning above 62 mph. And then assume it has something to do with a harmonic. Then you are stuck with process of elimination. If it is two things causing it, then you might have to cycle on it.
You see the same with 2 sets of tires so not tires.
You swapped the driveshaft for another, so not driveshaft balance.
I didn't look back but believe you checked driveline angles. The up down might respond to load/no-load, but side side I don't know.
rear of transmission/output shaft I assume has been checked.
You checked U joints.
Yoke in the differential? (could these be checked by looking at runout?)
Is the frequency such that you can put it before or after the differential? Can the axles be messed up.

 

[miller]

Can the axles be messed up.

Wonder about that, too.

If the housing is bent, rear wheels are out of line, trying to walk. That would cause vibration. Or, if one of the rear spring line-up pin/bolts is broke. Have seen that, too.

 

[Dave145]

Well everyone, the shocks actually helped. I can now take her up to 80 before the vibration sets in. Still the same vibration, just now happening much later for some reason.

When we were under the car yesterday, it's apparently clear that the rear axles has met the body quite a few times. Both bump stops on the outside are actually shaped funny from it hitting them or sitting in them for awhile, and the bump stop above the pinion yoke also has a rather obvious wear mark above it on the body. Makes me wonder what could've caused that to happen and what could've gotten messed up from it.

 

[Ski 61701]

Weak or broken leaf springs will cause the deformation of the body stops. I'd bet you have a cracked leaf spring or two. Which at different speeds can occelate back into the body. Think about it, you put new shocks on, problem is starting to go away. Jack car undo your shocks and let the housing hang. Take a big screw driver and start poking at the spring pack you might have to undo a leaf spring clamp. Ive had more of these springs have a broken leaf, especially being 53 yrs old.

 

[jim ritchie]

At this time,after 9 pages of thoughts,ideas,possiblities,seems to be a combination of issues with this car,all of which needed to be repaired,from ball joints,driveline,tires,wheels,shocks,springs etc.For others to learn from this,if you have a vibration when driving at different speeds.First, put the rear up on jack stands,under axles ,remove rear wheels,block front wheels,have a buddy start engine & put in gear, slowly speeding up till you get vibration,,,OR NOT. NOW you know if it is in the drive chain(engine,trans,drive line,diff.)You cut the problem in half,,,and you can look at drive line(if you have vibration) or if no vibration, start looking at the other areas that weren't moving,such as ball joints,tie,rods,tires,wheels,shocks,springs,etc,etc.That's what makes the club great,,,,we can all learn from it! CHEERS

 

[Ski 61701]

At this time,after 9 pages of thoughts,ideas,possiblities,seems to be a combination of issues with this car,all of which needed to be repaired,from ball joints,driveline,tires,wheels,shocks,springs etc.For others to learn from this,if you have a vibration when driving at different speeds.First, put the rear up on jack stands,under axles ,remove rear wheels,block front wheels,have a buddy start engine & put in gear, slowly speeding up till you get vibration,,,OR NOT. NOW you know if it is in the drive chain(engine,trans,drive line,diff.)You cut the problem in half,,,and you can look at drive line(if you have vibration) or if no vibration, start looking at the other areas that weren't moving,such as ball joints,tie,rods,tires,wheels,shocks,springs,etc,etc.That's what makes the club great,,,,we can all learn from it! CHEERS

Suggestion sounds very familiar....

 

[jim ritchie]

Suggestion sounds very familiar....

Read you posts,,,,,and agree with them all,,,,enough said!CHEERS

 

[Dave145]

The problem we had in determining what was causing this wasn't because of neglect to test something, it was more so because the car exhibited vibrations no matter where or how it was.

On stands, with the shaft in, supported by either the body (to let the axles drop) or the rear end (to simulate road height), it vibrated at speed.

On stands again, now with the driveshaft removed, it still had an oscillating vibration felt in the floor of the car....

...so we removed all the belts to isolate the accessories from the engine. Vibration diminished some, but still there.

Then went on to check the harmonic balancer, which was moot because this is an internally balanced engine. Either way, at least it hadn't slipped. De-gunked the heads and set the valves. Sure idles nicer now!

Moved our search to the tranny. Everything appears in order.

Tried a different brand new driveshaft. New rims and tires. Rebuilt front end.

Tried shocks because we knew they were bad, and the air shocks were for cheap science.

All in all, the thing I guess I took away from this (besides all the new knowledge) is that definitive testing procedures sometimes still don't highlight an issue.

Here's hoping the leaf springs fix it when I get to purchasing them....