Rebuilt Driveshaft - Thumping After Install

[ShortCST]

Marked all driveshaft components. Removed the driveshaft to replace carrier bearing. Replaced all u-joints with Spicer 5-1310-1X Life Series units.

Reinstalled. Tightened carrier bearing mounting bolts with truck on the ground. At 20mph +, I have a thumping under the cab.

Could it be the driveshaft length? The C10 is lowered 3” in the rear.

Here’s where the shaft mounts in the transmission:

[Toms67]

Could be the pinion angle. After Lowering it. Can you put it on jackstands? And have someone look. To see if the driveshaft is whipping. But if it's an automatic transmission I don't know if you can do it. Maybe someone else can chime in. Good luck.

[indymachinist]

Was it thumping before rebuild? What was it doing that prompted a rebuild?

[ShortCST]

It was thumping, which I attributed to the worn carrier bearing rubber isolator.

[AussieinNC]

Sounds like the trans mount is broken...try putting a jack under the trans and lifting the trans up to check...

Also, have the cab mounts collapsed ? Placing the cab too close to the driveshaft.

[ShortCST]

I haven’t seen a photo of a collapsed cab mount, so I don’t know if mine are. They aren’t disintegrated.

Thanks for the tip on the trans mount!

[BCOWANWHEELS]

Bet shaft is out of time in u-joints

[ShortCST]

Originally Posted by BCOWANWHEELS

Bet shaft is out of time in u-joints

You may be right. But I don’t know what that means.

[Arnulfo]

Originally Posted by ShortCST

You may be right. But I don’t know what that means.

Its how the u joints line up relative to eachother. Think of it like the 4 arms of the ujoints being at 12:00, 3:00, 6:00, and 9:00. Some driveshafts require that one of the ujoints not line up at those positions something like 2:00,4:00,7:00 and 10:00.

[B. W.]

You must run u-joints "in phase" with one another. (the yokes should be in line with each other) If they are not they cannot cancel each other out (pertaining to vibration). In some cases (not common) u-joints are "cross-phased" meaning one yoke is turned 90° to the other.

Your yokes should line up, doesn't matter if it's a 1 piece driveshaft (2 u-joints) or a 2 piece driveshaft (3 u-joints).

[ShortCST]

So do I need to pull the shaft back out, and make sure all of the grease fitting line up?

[B. W.]

you don't have to remove it to check, you can just "eyeball" them. If they are not lined up you'll need to drop the shaft & slide the slip yoke off to re-index it.

[BCOWANWHEELS]

Best to pull it and lay it down on a flat surface.that will show you if your even 1 tooth off on your slip yoke timming.

[harpo231]

http://67-72chevytrucks.com/vboard/a...1&d=1506899740

[ShortCST]

So is that definitely something that everyone does when they reassemble a two-piece driveshaft?

And is it as easy as just lining up the grease joints?

And is slip yoke timing a separate issue?

[71cheyennesuperlongb]

If you will look it up in the assembly or servise manual you must rotate your front shaft 4 teeth to the left. They are not supposed to be inline.

[71cheyennesuperlongb]

What I mean is to rotate your slip joint 4 teeth to the left on the front shaft

[ShortCST]

Crap. I’ll see if I can figure out this slip joint timing wizardry from the chassis manual.

[BCOWANWHEELS]

In 45 yrs i never herd of anything but all joints being clocked the same

[ShortCST]

Originally Posted by BCOWANWHEELS

In 45 yrs i never herd of anything but all joints being clocked the same

Well, I know that I definitely didn’t make sure that the grease fittings were pointed the same way. In fact, I know that there are at least two that are pointed 180 degrees from each other.

[71cheyennesuperlongb]

In the 28620 Chilton Full size trucks 1970-1979 repair manual on page 7-42 you will on 71-72 two piece drive shaft I was wrong.You rotate the rear shaft 4 splines to the left. It shows this in fig.38 at the top of that page.

[B. W.]

Originally Posted by 71cheyennesuperlongb

If you will look it up in the assembly or servise manual you must rotate your front shaft 4 teeth to the left. They are not supposed to be inline.

I'll be a monkey's uncle! Just looked it up in the factory manual - it says to clock the rear shaft 4 splines to the left. GM wanted you to run your driveshaft out of phase! Learn something every day!

(I'm still going to run mine in phase)

[BCOWANWHEELS]

all 4 of my trucks the u-joints are aligned FWIW

[Keith Seymore]

Originally Posted by BCOWANWHEELS

In 45 yrs i never herd of anything but all joints being clocked the same

Originally Posted by B. W.

I'll be a monkey's uncle! Just looked it up in the factory manual - it says to clock the rear shaft 4 splines to the left. GM wanted you to run your driveshaft out of phase! Learn something every day!

(I'm still going to run mine in phase)

Originally Posted by BCOWANWHEELS

all 4 of my trucks the u-joints are aligned FWIW

It's a design philosophy that comes and goes.

Some think that the added "windage" compensates for any deflection in the shaft; others do not observe the deflection and design the shafts "straight up" with all the joints in line.

Depends on when the parts were designed and manufactured, and who the leadership was at the time.

K

[Keith Seymore]

Originally Posted by harpo231

attachment

This is a pretty good chart, but could use some explanation:

"Perfect - inline": this is true from a u joint acceleration/deceleration aspect, and would be ideal in theory but not in practice. The issue is twofold: 1) without any u joint working angle the rollers do not rotate inside the cup, causing them to "brinnell" a low spot in the cup and resulting in a disturbance, and 2) there is rear axle pinion nose windup during vehicle acceleration and deceleration, (and in trim height due to cargo loading/unloading) so the shaft doesn't really stay straight during vehicle use.

"Parallel; moderate strain/minimal vibration": This is ideal, with angles equal and opposite and less than 3-7 degrees. However, "strain" is not really the right word choice, as it is not a strain issue but the disturbance caused by the acceleration and deceleration of the u joints as they rotate. The equal and opposite characteristic allows the accel/decal to cancel out (while one is accelerating the other joint is decelerating the same amount) resulting in no disturbance and no vibration, and also provides some windage so that if the angles are set up like this statically then you come closer to the "inline" setting during vehicle use.

"No! High strain/bad vibration": again - it's not "strain" but accel/decal of the joint. Angles higher than 7 degrees are greater than what a single cardan joint can accommodate. Differing angles front and rear do not allow the accel/decal pairs to cancel each other out.

"Absolutely not! etc": the issue here is that the angles do not cancel each other out and are, in fact, additive. "Poor pinion vibration" has nothing to do with this.

K