Bad vibrations (Part 2!)

[ckessel]

Something that might help you pinpoint the amount of off center/crooked etc angle would be to drop the driveshaft out and put a laser bore sight on the end of the output shaft. Do you own any guns or have friends who may have one? Use the type that looks like a dummy round of ammo.

 

[Dave145]

I'll have to crawl under the turd once we get home tonight to measure the center lines of everything so see how it all lines up. Measurements or not, the motor/trans is definitely cocked toward the driver's side of the car.

 

[the mississippi madman]

I'll have to crawl under the turd once we get home tonight to measure the center lines of everything so see how it all lines up. Measurements or not, the motor/trans is definitely cocked toward the driver's side of the car.

Are you using a small block transmission crossmember or have the big block one backwards if that can even happen

 

[Dave145]

I should hope that it's a small block cross member. None of the bolts look like they've been touched and it's still got it's numbers matching 318 for now

 

[Brewzer67]

I think the pinion nut issue may have been mentioned before but I don't recall seeing an answer. When you changed the driveshaft over to the new one did you either tighten, or loosen then re-tighten the pinion nut? This would change the pinion preload which could definitely be causing your issues. Have you opened up the rear end to check what the current gear contact patch looks like?

 

[Glenwood]

Are you using a small block transmission crossmember or have the big block one backwards if that can even happen

I'm using the original from the sb on my big block. The two transmission tails look identical to me. Unless the kframe is a later b body, i don't think you could reverse the mount and still bolt on the old transmission.

 

[Dave145]

I have not opened up the rear end at all, nor did I touch the pinion nut. The K frame is original as well to my knowledge, but I'm frankly assuming it is because all the bolts that hold it on look like they've never been touched.

 

[the mississippi madman]

I'm using the original from the sb on my big block. The two transmission tails look identical to me. Unless the kframe is a later b body, i don't think you could reverse the mount and still bolt on the old transmission.

I would think the big block trans crossmemeber would have an offset to it like the motor and rearend?

 

[Glenwood]

I would think the big block trans crossmemeber would have an offset to it like the motor and rearend?

I don't know if there is a different mount for big blocks but mine fit perfectly.

 

[the mississippi madman]

It was just a thought

 

[Sixpactogo]

I do think it's odd how the tailshaft sits in the trans tunnel. Looking at the motor from the top down it doesn't appear to be overly cocked to me.

I'm aware of the age and wear on the car. I don't dispute that. All I'm disputing is this idea of flinging money at a problem hoping it goes away. When I bought my truck it had two shot motor mounts in it. The motor would literally lift right up out of the bay and come at you if you tried to rev it. It never vibrated at all, except for at idle. So I don't believe it's motor mounts causing this. The trans mount in the same truck shot itself a few weeks back. Started clanking real bad going into gear. Crawled under there and the layers had separated! Still it never vibrated.

The noise sounds like front u joint failure. The shudder while coasting/decelerating between 40&30 sounds like front u joint. The violent shaking is a mystery to me.

Here is a shot of the underside of the car as it sits in front of me. The driveshaft looks quite angled to me.

View attachment 607712

It certainly does appear the drive line is not centered properly. I don't know how it can get that way. It should be centered in the tunnel and appears to favor the left side of the tunnel. I also understand your frustration but side to side angle can be just as bad as up and down angle.
Your trans cross member should be centered under the transmission but looks like is is not. I would drop the cross member and see why.

 

[khryslerkid]

Last time I'm going to ask this.

Did you try to jack up the rear of the trans and see it the mount is broke?

 

[5.7 hemi]

For that matter, put a jack under the oil pan and see if the engine will move.

 

[mopar 3 B]

If nothing else take it to a frame shop and have it checked. You maybe looking for something that may show no other way. At least you will have piece of mind knowing that after all these years everything is a ok.

 

[Ski 61701]

Here is a cheap test for drive shaft balance. Mark the back of the driveshaft up about 6 in from the rear of the back ujoint. Then place 4 marks around driveshaft at this point. Take a hose clamp, place it so the screw is at on of the marks. Slowly accelerate up to where it starts to vibrate. You might not get it up to speed if it really vibrates. You want to repeat the test for the 3 other marks and see what happens. If the vibration lessens you found your problem, doesn't cost you anything other than time.
Might want to try and mark a straight line down driveshaft and find a go pro camera and mount it so you can see the length of the driveshaft the line should give you a visual clue to things. Ive seen people put a poly in and they put engine mount bracket in wrong on passenger side. The mounting ears on bracket can go either in front or behind casting ears on block, this can cause things to get a little bound up.

 

[Dave145]

I have jacked up both the engine and transmission to check this awhile back. Nothing looks broken. Do they look old? Sure. They're 60 some years old. The rubber is still bonded to the metal and there aren't any chunks missing.

This week I will loosen the motor and trans mounts and see if I can pull the engine and trans back into place. That side to side angle I would guess is a good part of the problem.

 

[Ski 61701]

When I've seen the motor mount get installed wrong if you unbolt the trans mount from cross member it would either one be somewhat stuck when you try and jack up tailshaft because of excessive tension, or two when you jack tailshaft up it would spring one way or the other. When you jack up tailshaft it should go straight up with minimal effort

 

[Dave145]

Correct and it does. It goes pretty much all the way up to the trans tunnel without much effort or resistance.

I checked out the motor mounts tonight as well. They are both mounted the same on both sides.

My thoughts are that if I loosen the mounts up, I should be able to wrap a ratchet strap around the tailshaft housing and tie it to the frame. Then using the ratchet straps I should be able to slightly pull the motor/trans over where it should be. This will also allow me to look at all the mounts with the motor in the correct position, to see if any of them are cracked or warped. If anything else I should be able to see where everything should be in relation to where everything currently is.

 

[5.7 hemi]

So when you jacked the engine up, the mounts were tight and tried to lift the car at the same time?

 

[miller]

At least your getting some ideas on this, Dave!
Another little thought. Might take a look at the cross member mount 'box', to see if any of the welds are cracked, or broke.