driveshaft upgrades?

[BerniniCaCO3]

Because I spent approaching $800 and considerable time rebuilding a transmission core, only to find out that, despite coming from a mustang, some previous owner had somehow installed a longer tailshaft aod into it... I've got a transmission that's 1" too long and need to cut down my driveshaft. Of course i could uninstall it, tear down both transmissions, and put in the output shaft from the aod I uninstalled, but I'm not a fast worker and I could be looking at around 12 hours of time to R&R the transmission, AGAIN, and tear down two transmissions for the swap. Lots of wasted time and nothing to show for it, but the ability to refit my stock drive shaft with 125,000 miles and 22 years and original u joints on it.


As with anything, while you're working on it, might as well build it better!
I'm looking at $200 to shorten and rebalance, with new u joints, at the better shop in town. New u joints in themselves are better, and since this guy is a driveshaft specialist, I imagine the balance might be better than factory too?

Now, I'm not going to go quite that fast, not on the east coast anyway.... but I remember an earlier discussion about how at 120mph+ the driveshaft is actually one of the earliest and most egregious weak points at high speed for our cars. I think I was reading something about either the balance, or, the bearings in the u joints coming apart?
So if I wanted to improve, would certain performance-marketed heavy duty u joints be the biggest upgrade?

The other option is aluminum. I know it's rotating mass, which for good reason it is much more beneficial to reduce than the non-rotating inertia of the rest of the car, and I understand that; but is the weight reduction/ strength improvement going to be so very dramatic?
Is it worth spending $300 on an aluminum driveshaft?

I can try and find a junkyard driveshaft from a p71, it has been advised, but I mostly struck out today. Unless someone here has one to sell and ship ASAP

Give me the skinny on performance driveshafts!

[BerniniCaCO3]

I'm wondering if I ought to buy this:

http://baltimore.craigslist.org/pts/2855410324.html

which will really depend on how much it will subsequently cost to make it the right length (for one, I'm not sure if a mustang driveshaft is too long, or too short, or if lengthening a driveshaft is even that much more expensive than shortening anyway).
I know that welding aluminum is harder than welding steel, so it might be more than the $55 the shop's going to charge me to cut down a steel driveshaft, and I probably would want it rebalanced right? (another $55).
I could end up with a $350 driveshaft instead of a $200 one.

[bigbeigeboat]

The other option is aluminum. I know it's rotating mass, which for good reason it is much more beneficial to reduce than the non-rotating inertia of the rest of the car, and I understand that; but is the weight reduction/ strength improvement going to be so very dramatic?
Is it worth spending $300 on an aluminum driveshaft?

not really.
I'd have the one you already have shortened and balanced with good quality greasable u-joints and save yourself a bunch of time and cash.

[BerniniCaCO3]

Thanks for the advice.
I wonder if I'll get a better balance than factory now?

I've been reading up on driveshafts. I understand the sine wave vibration, that you get with U joints. I suppose you could have rzeppa/ cv-axle style joints instead in your driveshaft :-P Seriously, I wonder why not? That would eliminate the inherent vibration in a u-joint style driveshaft! I know some cars do, and I know cv axles for fwd cars can still be cheap cheap cheap, many times anyway.
But anyway.
So of all the rotating mass in a car, the driveshaft is going to be one of the worst if it's heavy.
But it looks like aluminum has very very modest weight savings,
AND it looks like that vibration is only a serious issue at very high rpms, like going 120mph with 4.10s in the diff, for 20 minutes straight. Maybe related to harmonics. And it seems to be a question for guys on mustang forums producing 500hp. Probably not a question for my mildly modded 4000# wagon.
I don't ever do that.... The most I do is take off from a red light or going on to the highway, and then come to a cruising speed by 80mph not really ever faster.

[bigbeigeboat]

Thanks for the advice.
I wonder if I'll get a better balance than factory now?

If they have a Hines or Universal machine (and most dedicated driveline places do) it will be dead nuts on. the factory is only close enough to remove felt vibration

[86VickyLX]

Find a Mark VI two door and take it's driveshaft.

[BerniniCaCO3]

another question...
I've heard from several people, and they have also all "heard," that it's important to put a driveshaft back the exact way it came out, not 180 degrees off.
This could ONLY matter if it were balanced to match some other part of the power/drivetrain, I initially assumed.
The fact that the shop will be balancing my driveshaft by itself, that he doesn't need to balance it on the car with the crankshaft or pinion gear considered, also directly undermines the idea that you need to install the driveshaft the way it came out-- why and how could it possibly ever matter (which 180 degree position you reinstall a driveshaft in)?

I've been thinking deeper on the question. I know that the driveshaft is accelerated and decelerated, with an average rpm of whatever the engine speed is, but going faster and slower alternatingly in a sine curve. So it's constantly accelerating and decelerating all the time, even when the engine is going at a consistent speed. I presume that mainly puts stress on the needle bearings in the u-joints, but probably isn't felt elsewhere. And a heavier steel shaft will take more force to accelerate and decelerate, so it puts more stress on the u joint bearings than a lighter aluminum shaft?
Now, could this have any relation at all to the engine? Does the firing order produce perfectly evenly spaced, 360 degrees divided by 8 pistons, impulses? If it's the slightest bit uneven, then, I see that you would want the moment of higher engine torque output to correspond with the moment of driveshaft acceleration. Maybe. Because obviously the engine speed is static, and the output at the wheels is static, if you're cruising at a maintained speed: it's only the driveshaft that's accelerating and decelerating. So even if you had an unbalanced engine that produced more torque at one portion of its rotation than at another, I'm not sure that the center section of the driveshaft could necessarily take advantage of that when it needs to accelerate in its sine wave?

But if our 302 v8s fire every 45 degrees, I can't see that that could matter at all anyway.
And the u joints are going to always, always, be 180 degrees opposed, in all makes and models of driveshaft ever manufactured? (the driveshaft guy was assuring me he'd put them in the same spot with respect to the balancing weights, even before he rebalances; I was confused, because I figured as long as they're opposed, it doesn't matter where the hell they are?)

So I've thought myself full circle and still can't imagine that orientation for a driveshaft can ever help or harm vibrations.
Wondering then if it's just a perpetuated myth about putting the shaft back the way it came out, and there's no math to back it?

[jaywish]

You ask good questions. I don't know any of the theoretical answers. I can say for sure it does matter if the driveshaft goes in 180 out. I have forgotten to mark driveshaft positions several times over the years and sure enough some of the time I have had to remove, rotate and reinstall the shaft to remove the vibration.

Jay

[sxcpotatoes]

Wouldn't it be crazy if the two members on here (1 asks about shortening, other asks about extending it) had the right length driveshafts for each other and could just trade them?

[Southern_Pride]

The 180 out thing only applies to 2 piece driveshafts. Not ours.

[gadget73]

What he said. The driveline is not dynamically balanced. The shaft is balanced, maybe with the yokes but probably not, and thats it. It doesn't matter what orientation you put it to the flange at the diff or at the trans. If the entire thing were balanced as a unit, then it would matter.

[zoomie]

to be honest, i would have made sure that my trans, was from another vic,me i didnt have much of a choice, mine is lincln specific, unless i use a markvi driveshaft for the shorter crownvic trans. btw the police ,truck and townie all have extended tail shafts so it could be from any one of those. the only sure way is to measure the tail housing.

[86VickyLX]

unless i use a markvi driveshaft for the shorter crownvic trans. btw the police have extended tail shafts so it could be from any one of those.

WRONG AND WRONG! Mark VI driveshaft is for a Lincoln trans with vic/gm wheel base. The police AODs are the same length as the Civilian Ford ones...

[zoomie]

they made 4 diff tail housing lengfths for the aod, also which driveshaft was it then that you saqid i could use in my linc with a crownvic trans?

[86VickyLX]

NO. I said (when you wanted to buy that grand marquis with no trans), get a two door mark vi driveshaft, as it uses a Lincoln AOD but has the wheel base of a vic or gm... And where do you get 4 tailshaft housings?