Vibration!!

[FinFury]

One vote for the transmission mount. The new rubber mounts are incredibly poor quality. I wasted one in my Challenger in less than 5000 miles, went for polyurethane bushings after that. The sagged and ripped mount caused significant weird vibrations 50mph+ velocities.

Also I think that bad torque converter can cause noticeable shudder on light to moderate acceleration.

 

[Big_John]

Since you brought the rear up I'm not sure how you can install that wrong. Without customizing a bunch everything " falls" into place.

I will watch the video...

Yes, it does "fall into place", but you have to look at the whole picture.

We have to understand factory tolerances. That is how much the bits and pieces can deviate from "perfect" and still be good enough to put on a car.

The perches were welded on to the rear housing on a jig at the rear factory. There's a tolerance to where they are positioned. The front and rear spring mounts are drilled in the frame at the factory with a tolerance, then the frame structure is welded in place with a tolerance. Leaf springs are arched with a tolerance. On and on.

You can have what they call "tolerance stack up" where one piece is off the maximum, the next one is too, followed by the next one... and before you know it, the end result isn't quite right.

So, you could have the front mounting holes up a little too high, the perches off just a little, the spring arch not quite right... In theory, it's should be good, but let's say that the perches aren't right and were never caught by inspection. Now let's even make it more complicated and drive the car around for a few years, get new springs, have the car sag a little... Suddenly that angle might be bad enough to make a difference.

Hope that explains one scenario of why the angle could be off. That's not taking about crashes, changing rears, welding new perches, re-arched springs and on and on. I knew you were really wondering about how a stock setup could be wrong.

 

[polara71]

I completely understand all of that BJ. My response was to the engine and transmission not being aligned .
Everything you posted was already understood, informative , interesting, but already understood.

 

[Big_John]

I completely understand all of that BJ. My response was to the engine and transmission not being aligned .
Everything you posted was already understood, informative , interesting, but already understood.

Gotcha..

The engine/trans alignment comes into play with a stick car where the center of the bellhousing, particularly an aftermarket one, needs to be checked to keep it all in alignment. Again the stack up of tolerances and in the case of a stick, there's a need to have it align better.

While I have seen a procedure for checking the alignment with an automatic car using an empty trans housing, unless there's some other stuff going on, there's enough allowance for misalignment built into the convertor and flex plate that you never need to do this. At least, I've never seen anyone do it.

 

[Chrome58]

I'm not sure about later C bodies, but in '57-'59, that engine/transmission alignment was a serious thing. Below, an excerpt from the '58 Plymouth service manual. Measured runout must not exceed 0.010 inch (0.254 mm) total dial indicator reading.

I must say I didn't do it when I reassembled the engine and transmission on my '58. But I do have some vibrations at idle that leads me to believe that I should have.

 

[Big_John]

I'm not sure about later C bodies, but in '57-'59, that engine/transmission alignment was a serious thing. Below, an excerpt from the '58 Plymouth service manual. Measured runout must not exceed 0.010 inch (0.254 mm) total dial indicator reading.

The major difference being that trans would still have a separate bell housing and everything was less forgiving of any misalignment. The later trans is one piece, making for a more accurate alignment as you have less parts to align and (I would suspect) the trans case is machined more accurately.

Just for chuckles, I looked at my '65 FSM, and the spec for a manual trans bell housing is .008" TIR which is slightly tighter than your .010" TIR. Of course, nothing is said about the auto trans alignment.

 

[oldkimmer]

I have never checked TIR on any auto trans car. Manual trans yes. My buddy did his auto. It was within spec. Kim

 

[John Kirby]

I've spent many hot afternoons under cars replacing auto transmissions. Never gave any thought to an engine/trans misalignment. The dowel pins are very precise, the trans only goes in one way. The bolt holes will not line up otherwise. The only headache is getting the torque converter to slide all the way into the front pump and not fall out while jockeying the trans into place.

 

[hotroddinwillie]

Hi. Just my 2 cents. Check the transmission extention housing bushing that the driveshaft slip yoke slides into for excessive play. I had a 1966 Dodge Coronet that suffered from a vibration similar to yours. Replacing the bushing took care of said vibration.
Willie

 

[OldWarHorse300]

Hi. Just my 2 cents. Check the transmission extention housing bushing that the driveshaft slip yoke slides into for excessive play. I had a 1966 Dodge Coronet that suffered from a vibration similar to yours. Replacing the bushing took care of said vibration.
Willie

That was same thing with my -66 300, how ever that vibration wasn't that bad but new bushing helped anyway.
Regards
Mika

 

[ggarrett]

My '68 300 has some vibration in the drive line. It does it when you are on the throttle or off the throttle, but at steady speed it seems to go away. I've already posted a thread on this forum about it and received a lot of advice. I'm leaning towards it being a problem with the differential and rebuilding one looks complicated. So, I was wondering, is it possible to get one already rebuilt and just swap it out? Kind of like a rebuilt transmission, engine, steering rack, etc.
Or would I be better off just taking it to a professional mechanic? Thanks!!

 

[ggarrett]

Hi. Just my 2 cents. Check the transmission extention housing bushing that the driveshaft slip yoke slides into for excessive play. I had a 1966 Dodge Coronet that suffered from a vibration similar to yours. Replacing the bushing took care of said vibration.
Willie

My '68 300 has some vibration in the drive line. It does it when you are on the throttle or off the throttle, but at steady speed it seems to go away. I've already posted a thread on this forum about it and received a lot of advice. I'm leaning towards it being a problem with the differential and rebuilding one looks complicated. So, I was wondering, is it possible to get one already rebuilt and just swap it out? Kind of like a rebuilt transmission, engine, steering rack, etc.
Or would I be better off just taking it to a professional mechanic? Thanks!!

 

[ggarrett]

MY 74 NYB had the same problem,I installed new U-Bolts and the vib went away.
Should have said U-JOINTS.