2-Piece Driveshaft, Phasing and Angles

[t walgamuth]

My only comment is that a two piece driveshaft does two things that I know of:
1. It reduces unsprung weight for a better ride and handling.
2. It allows for a slightly tighter ds tunnel since the front portion of the shaft does not move around at all.

[JoeHall]

My only comment is that a two piece driveshaft does two things that I know of:
1. It reduces unsprung weight for a better ride and handling.
2. It allows for a slightly tighter ds tunnel since the front portion of the shaft does not move around at all.

Agree with the advantages, but it's a trade off with the 1-piece, so also has disadvantages.

Spicer's way of setting the 2-piece up is to align jackshaft (short front shaft) with transmission main shaft (as if it were an extension of the main shaft), then misalign it by about 1/2 to 1 degree (so the u'joint bearings will rotate to avoid brinneling). If in perfect alignment, phasing would be a non-issue, but the 1/2-1 degree misalignment makes it a slight issue. As you say, the jackshaft hardly moves, BUT it must be aligned properly. To be in phase means the jackshaft and driveshaft's u'joint ears are all aligned perfectly. The driveshaft's ears are phased and welded in place at the factory, but the Studebaker jackshaft can be rotated 360 degrees, one spline at a time, since there's no blind spline. Max out of phase is at 90 degrees; past 90 degrees and it starts to come back in phase. The more out of phase, the more elliptical the rotation of the driveshaft, end to end.
After setting up the jackshaft, Spicer says to align the differential pinion angle parallel with the jackshaft angle (can use wedges under the axle perches). Set up that way, it is almost a 1-piece driveshaft, excepting the 1/2-1 degree misalignment of the jackshaft.
That's the basic Spicer setup for vertical alignment. But stir in horizontal misalignment (various sources), drive train flutter, carrier bearing flutter, rear spring flex and pinion shift under acceleration/deceleration, bind at the slip joint etc., and it's just more prone to vibration than a 1-piece, which is the 2-piece's main disadvantage.

Today's mission is to get the 56J up on ramps, level. Then measure everything for base read, including horizontal alignment. Then install a new rear transmission mount, carrier bearing & mounts, and all three u'joints, and measure again. I will then attempt to make any adjustments needed to align vertically per Spicer's method. Several ways to adjust: shim the transmission mount; raise/lower the carrier bearing mount and/or shift it sideways; use wedges under either end of the rear spring perches. Will start with jackshaft and driveshaft in phase, and may try 90 degrees out later, if needed. I will also use a string from end to end to check horizontal alignment; hopefully no adjustments will be needed, but will shift the carrier bearing sideways and drill new holes, if needed.

No matter what, I am sure the new components mentioned above will improve things, after 150,000 miles. Not expecting perfection, but hoping for improvement, especially if I can make some fine tune adjustments which Studebaker did not bother with in mass production.

From what I have read, Jackshaft alignment and phasing is most important for reducing low speed vibration, and driveshaft alignment is most important for reducing higher speed vibration. All 56Js I have driven with OEM 2-piece shafts vibrated on both ends, so I am sure there's some improvement to be made. Gonna stop rambling and get out into the garage now.

[NMJack]

I don't understand why Studebaker used a 2 piece shaft in the FIRST place...and then tried to put a band-aid on it, rather than throwing in the towel and installing 1 piece shafts...

It was done to reduce un-sprung weight.

[JoeHall]

Yesterday I spent 10 meticulous hours on the 2-piece shaft: I used a phone ap (accurate within 1 degree) to measure angles before disassembly, and happy to say Studebaker did an EXCELLENT job on the geometry. Using the T85 output flange as base, the jackshaft angled down rearward 1/2 degree (so phasing is a minimal issue, no matter the setting); the driveshaft also angled down rearward one degree more than the jackshaft; but the pinion shaft angled 4 degrees down FORWARD at a, "broken back" 7 degree angle with the driveshaft. Per what I have read, this angle must be 3 degrees or less to avoid road speed vibration. So the pinion needs adjusted upward 4-5 degrees, and can be done with degreed wedges installed below the axle perches. I've read the wedges nearly double in degrees at the pinion, so ordered 2.5 degree wedges from Summit last night.

After rebuilding the entire assembly yesterday (new u'joints, carrier bearing & bushings, and rear T85 mount), a test drive showed about 50 percent improvement. I anticipate more improvement from adjusting the rear pinion angle.

Lessons learned from this high mileage 56J: the slip joint and carrier bearing was original at nearly 250,000 miles; the (grease able) u'joints about 150,000, the T85 mount about 100,000, and the carrier bearing rubber bushings about 25,000 miles. The slip joint is still as new; the carrier bearing was toast, the front two u'joints were brinelled, the T85 mount had sagged 1/4", and the right side carrier bearing bushing was lightly sliced. Moral of the story: re-grease the u'joints and slip joint at least every 10,000 miles; rebuild the entire assembly at least every 100,000 miles; replace the rear mount when it sags 3/16" and/or hardens with time; and check the carrier bearing rubber bushings anytime under the car.

Noteworthy: Though not perfect, I now believe Studebaker did as well in the 1950s setting up a 2-piece shaft, as Toyota has done lately.