drive shaft alignment problems

[captain69]

So I took the truck out for its maiden beating and I can feel the trans or the drive shaft almost step out every once in awhile. Im not sure if its the locker in the rear end but its real bad with a little gas and taking a corner. I tried the trans brake and it almost seemed like it was in nuetral when I let off hope I didnt smoke the converter. Can some one show me a pick of there auto tail shaft height. I think the rear of the trans needs to come up.

[captain69]

Since lowering it something has changed bad look at this angle does it seem right?

[kwmech]

1 piece? 2 piece? tight u-joint? shaft alignment out (in phase?) carrier bearing jumping, slip yoke frozen?

ah, posting pics while I was typing, yeah, trans has to come way up, put the x-member inside the frame rail? Shaft appears too short also.

How far did you drop it?

[captain69]

1 piece new drive shaft 4"

[captain69]

Im looking more at the angle its just so low hard to show the angle

[kwmech]

Trans has to come up, maybe more than 1/2. How does it look at the axle?

[captain69]

Was thinking about raising the rear mount 1/2

[Keith Seymore]

It's angled the wrong way (assuming your pinion nose is down in front).

The front and rear u joints are adding their disturbances together rather than canceling each other out.

Rear of the trans has to come up quite a bit.

K

[Keith Seymore]

D@mn. Tree'd by kwmech.



K

[captain69]

Looks good in the rear. I guess always having it jacked up in the air I never noticed and when I was putting the super panhard in it seemd low.

[Keith Seymore]

I'd be more comfortable if you had more slip yoke engagement, too (yoke farther into the trans).

K

[captain69]

Ok ill jack it up put some spacers in and try it . Thanks just wanted to make sure I wasnt nuts.

[captain69]

I had three shafts made freaking nightmare.its a coan reverse manual and the tail shaft has been a problem for fitment either the yoke wont fit or bottoms out

[captain69]

Theres only a small amount it will go in 1/4 inch max

[captain69]

Want to say its a long input shaft on a short tail its been awhile cant remember.

[88Ironduke]

Just from the outset, I assume a turbo 350. Having made a trans cross member I can pass on a couple of things. I would figure out the process of getting the tail shaft up higher. Nothing else will work right until that is resolved.
I would rework that cross member to either bolt from the top of the frame or at least bolt to the sides of the frame with four Grade 8 bolts supporting the trans tail shaft. A nice large mounting pad to spread the loads out will ensure that transmission tail shaft is transferring rotational loads to the cross member/frame and not into the body of the transmission. It doesn't have to be pretty, just solid and reliable. GM put in a robust cross member into our trucks from the factory. The tubing you have chosen is sufficient to do the job it just needs more structure for when the pedal hits the floor.

Bring a new cross member inwards high up and drop it to the center and pick up the transmission. Doing so will also provide extra clearance for the already low hanging exhaust.

Good Luck.
88Ironduke

[captain69]

Ok well I have tried to move the th400 till its aligned but its hitting the firewall. Equal length headers are maxed this is what im doing. Putting the mount up top and recessing it. Already cut all the bolts to the shifter for room . But still not straight theres no way I can see

[captain69]

Jacked up smashing into the firewall best it gets

[captain69]

More

[davepl]

Time for some schoolin'

First, yes, lockers are annoying on the street. But they're either locked or not, more or less, so don't cause

But as for U-Joints, it is completely irrelevant how it looks (within reason). It does not matter what the angle is. What matters is that the angle is the EXACT same angle as the other end.

Which is why, boys and girls, they invented the constant velocity joint for applications such as front wheel drive (and IRS) where you can't guarantee the output shaft is parallel to the input. But with a standard U-Joint, any difference in angles will show up as a vibration.

Think of it this way: as one u-joint cap goes around it's furthest outward point, it's speed is different than the innermost. So the whole deal speeds up. But when aligned properly, the exact opposite (kitty corner?) cap on the other end of the shaft is on its inside sweep, so it exactly compensates. If the angles are different, they do not cancel each other out and you wind up trying to constant accelerate and decelerate your rear axle (or trans, I suppose) with every driveshaft rotation and that's never good.

If you care about vibration, I wouldn't try to eyeball it. You really need to get a magnetic angle finder, which is probably available at the dollar store, though if you value accuracy you might want to spend double that.

On my leaf spring truck the axle has a 'nub' that fits into a receiver in the spring pack, so you really cannot change the pinion angle on the rear axle (haven't looked at a coil spring truck in a long time so can't recall). That leaves you with only the angle of the engine & trans to work with.

I will assume you've got the basics covered, like the right trans hump (TH400s like mine came with the tall hump) and crossmember and mount.

With all the right stock pieces it should, as you would imagine, be right on the mark or close enough to it. But once things start changing, the onus is on your to keep the angles right.

BTW, same deal for left-right (as viewed from above) but I've never run into that. Then again I'm the last guy left at stock ride height so I never have these kinds of issues :-)

[Keith Seymore]

Originally Posted by davepl

But as for U-Joints, it is completely irrelevant how it looks (within reason). It does not matter what the angle is. What matters is that the angle is the EXACT same angle as the other end

Almost. It has to be the exact same angle but in the opposite direction. I hope/think this is what you meant.

The reason is because each time the u joint passes it maximum articulation it creates a disturbance. The rotation creates a disurbance that is sinusoidal in shape.

If the two u joints are at maximum articulation in the same direction then the amplitudes are additive (they double). If the joints are articulating in the opposite direction then the amplitudes cancel out and the net effect is zero.

I can't draw pics here but I will post the attached for reference. http://67-72chevytrucks.com/vboard/s...d.php?t=522180 Figure 4-20

Captain69 - you may want to peruse/memorize/become very familiar with the attached link.


K

[davepl]

Originally Posted by Keith Seymore

It has to be the exact same angle but in the opposite direction. I hope/think this is what you meant.

It is.

[captain69]

Originally Posted by Keith Seymore

Almost. It has to be the exact same angle but in the opposite direction. I hope/think this is what you meant.

The reason is because each time the u joint passes it maximum articulation it creates a disturbance. The rotation creates a disurbance that is sinusoidal in shape.

If the two u joints are at maximum articulation in the same direction then the amplitudes are additive (they double). If the joints are articulating in the opposite direction then the amplitudes cancel out and the net effect is zero.

I can't draw pics here but I will post the attached for reference. http://67-72chevytrucks.com/vboard/s...d.php?t=522180 Figure 4-20

Captain69 - you may want to peruse/memorize/become very familiar with the attached link.


K

Great article thank you.

[ItsRandy]

What was wrong with the stock cross member? I have a '69 C-10 which was a small block/TH350 truck w/low hump cab. It is now a BB 502 w/4L80E using the stock automatic cross member and I have plenty of room between the floor and trans.
I too think the trans yolk needs to be farther in the trans.

Oh...ya gotta' love Keith!

[captain69]

I have magnetic levels theres just no way its going to happen unless there is something else like lowering the motor. The pulleys up front are almost touching the electric fan.