OK, let's assume that my engine is running OK. I have a vibration that starts at about 40 mph and gets worse at highway speeds. It doesn't seem to be consistent, sometimes it's really bad, other times not so bad, but I can always feel it in the steering wheel.

It's not front wheel bearings, tires out of balance, sticky brake calipers, warped rotors or suspension parts, I checked all of those.

Let's assume its the drive line, more specifically, let's assume it's the transmission. I had a blown head gasket and during which time the motor was shaking violently and it tore up the motor mounts and tranny mount. I changed those, and noticed the tail shaft bushing was damaged (the tranny tail section was cock-eyed toward the driver side about 1/2 inch before I changed the mounts). I changed that bushing and the tail shaft seal. Test drove again and had the vibration still. I swapped the drive shaft out for a new balanced one, and I still have the problem. I checked the drive line angles, they are very shallow, 0.65 degrees and 1.45 degrees, if I'm recalling correctly, can't recall which was front and which was rear, but I don't think it's too steep of angles.

OK, what could cause a high speed vibration in the tranny? Bent tail shaft, torque converter issue, band too tight or worn? I'm not a transmission person by any stretch. What have people experienced in this regard? The tranny seems to be shifting fine, up and down shifting, fluid level is good. I can check the flex plate and torque converter bolts now, see if any fell out or if the flex plate is damaged, but if I don't see any issues, what else might be the cause, assuming it's the tranny?

Brian

_________________
https://tinyurl.com/yynpj4v2

The tranny was rebuilt a few years ago, fyi, the filter is clean and the fluid was recently changed, say a year ago.

brian

_________________
https://tinyurl.com/yynpj4v2

If it is indeed coming through the steering wheel, I would suspect front end, probably a slipped belt in a tire.

_________________
Official Cookie and Mater Tormentor.

+1.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

A belt in the tire should do it all the time I would think.

I was going to ask if someone thought it could be something messed up in the transmission, but I do not know enough to ask it intelligently

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I had the tires checked at the shop; that's what I thought it was first too...they said the tires were balanced (they are also fairly new). The wheel bearings turn smoothly, and the rotors are snug, no play that I can feel if I yank on them. I don't feel anything in the steering wheel when I hit the brakes when there is no shaking, rotors are fairly new. I did the brake upgrade well before all this started, they seem fine.

When it's shaking on the highway, it keeps shaking, even when I put it in neutral and coast. I can rev the engine and it sounds smooth.

I pulled the inspection plate, all the flex plate bolts (crank hub and torque converter) are in place (I used thread locker when I installed it) and i don't see any cracks in the flex plate. Can't tell if it's warped at all, seems OK by eye balling it.

My working assumption is that I damaged something in the drive line when I drove it with the head gasket blown (it was the engine shaking then, no doubt). Certainly I damaged the motor mounts and the tranny mount during that episode. I suppose I can pull the tranny and have someone check it out; or take the care to a drive line shop and see if they can find anything.

Brian

_________________
https://tinyurl.com/yynpj4v2

I'll take it to the drive line shop this week, see if Larry (local guy) can find anything. I'll let you all know what he finds (or not).

brian

_________________
https://tinyurl.com/yynpj4v2

I know I don't have the car to look at, but this tells me it's not in the drive line.

_________________
Official Cookie and Mater Tormentor.

Have you moved your tires from front to rear to see if anything changes?
Also, a completely blown shock could do something that felt like that as well.

You could pull and check your u joints to make sure you didn't drop a needle from your needle bearings, but you shouldn't feel that up front, you should feel that in the back.

Based on what you have said driveline and trans don't seem like a likely source.

Maybe not your problem here, but: On my drive home from buying a 76 Valient Brougham, the steering wheel would rock side-to side 1/2 inch at about 50 mph in a slight turn. I did everything you did to troubleshoot. Then went back to the U-joints again and carefully noted some excess slop. Replace the U-joints, the vibration went away. Resonant vibration showing up at the steering wheel. That's my story.

_________________
"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)

Say the pinion angle is parallel to the ground, you want the driveshaft to raise at a 10 degree angle from that (no matter what, the pinion to shaft should be 5 to10 degrees) and front angle should be 2.5 degrees or less from shaft to the output shaft of trans.
For out of balance drive shaft;
Try marking the drive shaft in 4 equal spaced points near the rear joint and install a hose clamp with the screw on one mark to see if vibration changes, move it around and test each mark location for change, add another if it does better but doesn't go away, then split the location of them if it gets worst or stays the same, do the same on the front joint.

_________________
Advise should be taken as ongoing, that way, when you get to realizing what you are doing you can include yourself.

Wait, we need to qualify that: all we can say is it's definitely not the front (engine/flywheel/converter/inputshaft) portion of the drive line. But it could involve anything that's still rotating while in Neutral at highway speed (outputshaft/Ujoint/driveshaft/Ujoint/pinion/axle.)

I chased a similar gremlin in an engine-swap car for a long time before I finally found it -- it was a vibration that seemed to come from everywhere, at times indistinguishable from the steering wheel or the floor or the seat. It became audible by about 30 mph, and visceral by 40-50. I measured and tweaked and remeasured driveline angles 'til the cows came home, but it never improved much.

It turns out that service manuals mention the vertical angles, presumably because those are the most likely things to get messed up when people swap parts. There's seldom a mention of lateral angles; apparently we presume that the factory got it right when they built it. In this case, when the previous owner had welded new motor mount perches, he had not considered lateral alignment, or at least not well enough. When I finally measured the real issue, it became blindingly obvious -- I moved the transmission mount a mere 1/4" (either left or right, I don't recall which), and all seat-of-the-pants vibration disappeared. Bingo!

Regardless of the exact angles involved, the important criteria is that the engine centerline and the rear pinion centerline match. And they have to match both vertically and horizontally. In my case, I made the assumption that the rear axle was an exact 90* angle, so aligned the engine perpendicular to the rear axle.
... and that's my clue. Let me know if it triggers any success.

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Right, the drive line was out of lateral alignment a good deal and I hadn't noticed it. I believe I had that straightened out (double entendre) prior to the engine rebuild, but if I fire this new one up and there's still a shake, then I can look again to the drive line issue, maybe I didn't get it straightened out as well as I thought. Certainly my engine had some internal problems, that's why I had the crank checked, fixed and rebalanced for the rebuild. start from the core and work my way outward...

Brian

_________________
https://tinyurl.com/yynpj4v2