7 Litre Driveshaft

[Diogenes]

I have a spare 7 Litre driveshaft that came with the toploader I purchased from the same. I was looking it over this morning and noticed what appears to be a rubber insert where the differential yoke meets the driveshaft tube, as if it is some sort of a vibration damper built into the driveshaft--does anyone have any knowledge of these shafts? 

The driveshaft currently in my Galaxie does not have this feature; it was installed in the car when I purchased it, a Z code 390 C6 car originally. I'm just curious if this was a 7 Litre part to help make it the "smooth brute" Ford advertised

[galaxiex]

Yes, I've seen those "2 piece with rubber insert" driveshafts on various Ford products.
Basically a tube within a tube joined by a rubber insert.
Apparently they can slip (not desirable) from lotsa torque.
Never seen that happen...

A friend had a 71 Mustang convertible with 302 C4 3.00 diff, that had one of those shafts.
We later made it a 351C w/top loader and 3.25 diff.
Reused the same driveshaft.

Vibration damping is the purpose.

[shady]

I had a 64 with a t-10 that had one of those. I assumed it was to kill noise from clutch loading and drive line harmonics coming back through the shifter handle. Always wanted to cut one apart to see how it was constructed. GM had a service bulletin where on manual transmissions if a customer complained about noisy trans. they would fill the drive shaft with expandable foam insulation. Real problem was weak clutch disc hub springs.

[Heo]

It acts like a harmonic damper somewhat like the one on the engine
Its just two different size tubes vulcaniced together with the rubber
I have seen one explode when a guy decided to heat one up with the
oxy acetylen torch why i dont remember but it was a loud bang
the inner part came flying the guy squelig face full of freckles of
melted rubber

[WConley]

I wouldn't trust that two-piece driveshaft, even on a stock vehicle.  The rubber has had 50 years to break down, and the rubber-steel interface has probably corroded from trapped moisture.

As stated above, these were intended to absorb driveline vibration.  The 7-Litre was a premium boulevard cruiser trim level 

[cleandan]

Yes.
The 7-Litre cars were originally equipped with a "torque tube" drivesahft.
This was used as additional noise, vibration and harshness abatement to end with a really quiet, smooth driveshaft......that eventually fails due to the rubber going bad over time.

Quiet and smooth were part of the goal in 1966 and this is but one portion of the whole.

I spent way too much money and time trying to get my original 7-Liter's driveshaft in owrking order.......don't bother unless you are building a real, 100% concours competition show car.

The trouble with the torque tube driveshaft is they will slip and the yokes will become out of phaze and this will cause a vibration.....from slightly noticeable up to chipping your teeth as you drive.
They don't usually get too long, or too short as they slip but once they are out of phaze the balance is ruined.

I had my torque tube driveshaft redone and as soon as I had my 428 rebuilt, with a bit of extra power.....nothing special in my car (420ish HP and 480ish TQ) it twisted the newly redone driveshaft because the rubber insert could not hold the torque.

I swapped in a solid driveshaft and have never looked back.

Yes, the solid driveshaft rings when hit....like they all do.
Yes, the solid driveshaft transfers more noise than the torque tube, especially when shifting into driver or reverse......you hear the clunk more that with the torque tube driveshaft.
But none of that is beyond anything every other car with a solid driveshaft experiences, so yes, it is noisier, but it is not noisy by most measures.

Remove, tag and keep the original torque tube driveshaft if you desire.
Then get a solid driveshaft from a non-7-Litre (LTD's used them too) or get a driveshaft made and never look back.