[Josue]

That's what's somewhat reassuring about the issue, it's coming from something that's rotating, so that narrows it down quite a bit there.

Furthermore, it's something that I just changed in this round of mods, so it's either the wheels, converter, driveshaft, or rear end.

It was $70 to balance the shaft at this local shop, so I'll likely start there, after rotating it the 180 degrees first to see what that does. It seems too violent to be a wheel shimmy, but it's been a while since I've experienced one of those, so I don't have any recollection of how bad an unbalanced wheel could feel.

[JLMounce]

Originally Posted by Josue

That's what's somewhat reassuring about the issue, it's coming from something that's rotating, so that narrows it down quite a bit there.

Furthermore, it's something that I just changed in this round of mods, so it's either the wheels, converter, driveshaft, or rear end.

It was $70 to balance the shaft at this local shop, so I'll likely start there, after rotating it the 180 degrees first to see what that does. It seems too violent to be a wheel shimmy, but it's been a while since I've experienced one of those, so I don't have any recollection of how bad an unbalanced wheel could feel.

Is the vibration high frequency with low amplitude? Meaning the vibration is fast and shallow? Or does the vibration tend to be slower with greater amplitude? The latter, I'd be looking at wheels/tires. The former, I'd be looking at the driveshaft.

If the vibration is rpm dependent where it always occurs at a specific rpm range, but not based on vehicle speed, I'd be looking at something in the engine/transmission. If the vibration is speed based only, it's a good bet it's occurring after the transmission where rotation increases with vehicle speed as opposed to engine speed.

For what it's worth, on my 2008 Mustang GT/CS this occurred after a gear swap from the factory 3.23's to a set of 4.10's. Clocking the driveshaft 180 degrees from the pinion cured the vibration.

[Josue]

Originally Posted by JLMounce

If the vibration is speed based only, it's a good bet it's occurring after the transmission where rotation increases with vehicle speed as opposed to engine speed.

^This.

If it is happening at low speeds, it's not enough for me to notice. It really only comes on around 50mph and up, and increases with vehicle speed.

Anything engine related would be hard to understand, since I didn't touch that over the winter, and it wasn't doing this last year. Unless it's somehow in the converter and/or the way I installed it?

My money is on either the wheels or the drive shaft right now, I'll get overt there tomorrow to try rotating it. Weather's been on and off for a week now, so I haven't even been driving it....eff.

[JLMounce]

Yeah so what I'd do is clock that driveshaft and take it for a drive in the general direction of a tire shop. If the vibration is still present on the drive, have the rear wheels balance checked.

If that still doesn't cure the vibration, I'd be take the driveshaft out and make sure it's actually balanced correctly.

[Josue]

I'd like to think it's not the tires, the shop I use has some top of the line equipment, and a great reputation, but stranger things have happened, so I'm not ruling it out!

[Squidward]

What's your rpm when vibration comes in? Does it vibrate hard at that same rpm but when in 1st or 2nd gear? When you get up to 50+ and the vibes start, does it go away or stay when you put it in neutral and coast? Just trying to half split to whether it is in front of the trans, or behind it.

I had a bad vibe on my 67 FB after blindly installing the wrong size ujoint. Yeah, it rattled my teeth at 45-50. I had it centered on first install, and then it shifted after I first started driving. Not a proud moment when I discovered that boo-boo a few days later.

[Josue]

That I'm not sure of, I haven't specifically noticed. If I had to guess, I'd say above 2,000.

And, maybe another clue is, it mainly does it when I'm on the gas. When I let off, it all but goes away.

[JLMounce]

Originally Posted by Josue

That I'm not sure of, I haven't specifically noticed. If I had to guess, I'd say above 2,000.

And, maybe another clue is, it mainly does it when I'm on the gas. When I let off, it all but goes away.

If the lash in the gear set is off you could be creating the tolerance stack when you're on the throttle. As you get off the throttle the pattern contact in the gears change and may relieve that stacking.

Trying to clock the driveshaft could still cure that. I know you put a second hand rear in the car. Did you open up the cover to inspect the carrier and gears?

[Josue]

I had a GM master tech friend of mine come over and pull it apart with me, to inspect the bearings, gears, and whatnot. Even thought the rear end had been sitting around for well over a decade, it was full of fluid and everything checked out in his opinion. You never know the history of a part when going used though, who knows what's been done to this rear end in it's 40+ years.

I put it back together myself though, first time messing with the guts of a rear end, but I can't imagine I screwed something up? I put the shims back where they belonged (only 1 per side anyway), and torqued the carrier caps accordingly. What else is there to putting a rear end back together that had a basic tear down/inspection?

[JLMounce]

It's a bit broad, so here's a read on the subject.

The basics of it is there are two contact points in the ring and pinion. One side of the ring gear contacts the pinion during acceleration, the other side contacts the pinion on deceleration. If the contact pattern is uneven what typically occurs if you get a bit of noise, but there's other issues that can come in to play. I'm not an expert here, except for my experience with changing gears in my mustangs.

https://www.ringpinion.com/Content/B...h-Patterns.pdf

[Josue]

Alright....here's more.

Rotated the drive shaft, and voila! All was good! Short of now being able to hear/realize all the other noises a 48 year old car makes. haha Now that I have more miles on it, I remember it having a little shimmy in the front end last year. The thing hasn't been aligned in over a decade though, so there's probably some stuff going on there...

The vibration/wobble seemed to have returned though, but only intermittently?! I don't know if it's something I'M doing to manipulate the car and get it to go away...but sometimes it'll go down the road at 60-65 and be fairly smooth. Other times, the wobble is back something fierce, again, when I'm on the gas. As soon as I let off, it's like flipping a switch, it goes away....quiet as a mouse.

[Josue]

- update -

Been enjoying the car as much as I can! Finally was able to hit up my first cruise-in of the year. Up till then, I was mostly just driving it to work, and running errands in it.



The vibration got worse though, to the point where I just parked the car until I could tackle the next thing on the list of possibilities....those pads.

Ran to Summit and got some polyurethane ones...



Finally got a good "clamp", so hopefully the rear end doesn't move anymore. (I cut those sockets back out)




Didn't help the vibration though, so on to the next item...pinion angle. Trying to research it, but there's a bunch of contradictory stuff. As of now, my angles aren't matching, the trans is pointed down a little over 3 degrees, and the rear end is pointed up a little over a degree and a half. Some say the angles need to match, but in order to do that, I'd need to tilt the rear end up even more than it is, and some say it needs to be pointed down as it is. Maybe tilt the trans up, by shimming the mount?

My brand new conversion u-joint DID take quite a beating though, so I'm sure that didn't help the issue. I figure this happened when I drove with the rear end out of whack for those few miles, then the vibration all this time did it in...

[TedRamAirII]

Those are pics before you tightened the bolts I assume. When torqued down the bottom plate should be flat with the rear axle mounts. As for the driveshaft, the angles should cancel each other out. +3 at the trans, -3 at the axle, etc. I dont think it matters much what they are, as long as they are equal. The issue is all looks good until you accelerate and the axle tries to twist upwards and the angles change. That's why you want down angle on the axle. I am thinking I want cal tracs to keep mine where it should be, but I'm cheap and dont want to spend the money. I have not tried clamping the leaves but may try that, its cheap and I "hear" it works.

[Josue]

Yes, those were before I tightened down the u-bolts. Before, I could just about hand tighten them to the point where the plate was touching the perch! Now, with the proper pads, it made a world of difference....and hopefully the rear end stays in place without any trickery!

I threw some shims under the trans mount at the cross member, and got the trans angle and the rear end angle to under 1 degree of each other. Installed the new u-joint as well, and all seems well now. Put around 30-40 miles on it tonight, and it definitely went away. There might be a little shimmy when taking off, but again, it's a 48 year old car, so I'm not holding my standards too high. haha

My trans mount is shot too, so I'll be replacing that soon. Maybe a new one will give me more in the way of evening out those angles. Otherwise, I'm really not trying to mess with much on this car, because I'll be replacing it all when I overhaul the suspension, likely getting rid of the leafs all together.

[Squidward]

Yikes! That ujoint was BROOTALIZED! Glad to see you have that knocked off the list. I will stay tuned on how your pinion angle work goes.

I liked the cruise in pic, wheels are looking good! Having Summit in your backyard must be a bonus.

Thanks for the update!

[Josue]

It's weird....it's not like I'm a pioneer of this swap, it's been done thousands and thousands of times before me, you included. But, not once have I seen a thread where someone had to mess with their pinion angle like this! I hate the little things that pop up once you start messing with stuff....haha

My old man wants a set of 17" Rally II's for his '69 now too, so I have to keep an eye out for any deals. They don't seem to come up too often though, my set have been the only used ones I've come across. I need to show him some examples though, so he can decide which style he wants....there seems to be 4 or 5 different ones!

And yea, Summit is definitely a playground!!! They have a clearance section that's got some steals. They also have a few car shows there that are pretty huge. Midwest living FTW!! hahaha

[TedRamAirII]

Originally Posted by Josue

Yes, those were before I tightened down the u-bolts. Before, I could just about hand tighten them to the point where the plate was touching the perch! Now, with the proper pads, it made a world of difference....and hopefully the rear end stays in place without any trickery!

I threw some shims under the trans mount at the cross member, and got the trans angle and the rear end angle to under 1 degree of each other. Installed the new u-joint as well, and all seems well now. Put around 30-40 miles on it tonight, and it definitely went away. There might be a little shimmy when taking off, but again, it's a 48 year old car, so I'm not holding my standards too high. haha

My trans mount is shot too, so I'll be replacing that soon. Maybe a new one will give me more in the way of evening out those angles. Otherwise, I'm really not trying to mess with much on this car, because I'll be replacing it all when I overhaul the suspension, likely getting rid of the leafs all together.

If you have a shudder on accel try putting the pinion angle down more. That should be easy to try. Loosen the u bolts and get a shim of some kind, maybe a couple flat washers at the rear to change it and see it that helps.

[Josue]

So, shim the rear of the perches, to get the rear end to tilt down more in the front?

There's a local shop that sells rear end shims, in all varying degrees, I could hit them up if need be.

[TedRamAirII]

Originally Posted by Josue

So, shim the rear of the perches, to get the rear end to tilt down more in the front?

There's a local shop that sells rear end shims, in all varying degrees, I could hit them up if need be.

Yes. I just thought maybe use a couple flat washers as a test. Then you could see what thickness you need before buying anything.

[Josue]

Gotcha. They go between the leaf and pad, right?

Seems like a weird concept to me, to shim a rear end with pads like this. Seems the pad would squish down over the shim, rendering it useless in achieving any kind of angle change? I guess with enough shims though.....