Properly aligning 2-piece tailshaft?

[George]

I had to use 2-piece tailshaft in my engine conversion project but failed to understand anything about centre bearing adjustment. Could someone point me in the right direction?

More details below
Previously I used single piece shaft, and I couldn't suppress the vibration at high speed due to shaft's essential properties (length/diameter) giving too low resonant frequency. It was perfectly balanced however , AND engine / axle were aligned properly as per the picture below


2-piece shaft doesn't vibrate at any reasonable speed anymore, however it turned out that I must align center bearing thoroughly, otherwise the car would shake wildly upon heavy load conditions (quick start off the line, for example). Engine and axle are aligned just like before (so the two angles compensate each other)

I eventually had to align the bearing purely by feel and it doesn't look like the picture below


Any ideas?

[dnegative]

Work out the JWA for what you have

[George]

that's the 1st URL that Google has for JWA
http://jwa.org/

I bet they will be of little help hehe

[dnegative]

Joint working angle
Joint operating angle

You measure and add up all the angle of your driveshafts and it will determine how fucked your setup is. You should be within a few degrees max


This is a really good read from Dana

[George]

As I said above, joint working angles are perfectly equal both at transmission and axle. (so their centerlines are perfectly parallel as per your manual)
HOWEVER finding out the correct angle to install the centre bearing is the problem
It doesn't work if I just align 2 pieces of the shaft in one line

The document does have some valuable info on multiple shafts, thanks!

[George]

p/s my current setup only gives slightest vibration upon hard acceleration from standstill, so that's more of general curiousity than real problem

[andrew_mx83]

Use a Dial Indicator and measure the runout at the centre bearing, and each end of the shaft. Adjust centre bearing position until runout is less than 0.5mm, job done

[George]

andrew_mx83 I'll try , thanks, but how can a perfectly centered shaft have any runout? Will do however

[andrew_mx83]

You answered your own question buddy... if there is no runout then it (the centre bearing) is perfectly centred
If there is runout, then she's not centred...

[George]

I was referring to alignment problem rather than centering regarding the bearing

So the bearing is perfectly centered around the shaft, and there's NO vibration at ANY speed, low to medium load, no matter how I mount the bearing (higher/lower)

HOWEVER low speed, high load vibration somehow depends on centre bearing position

[Duk]

As I said above, joint working angles are perfectly equal both at transmission and axle. (so their centerlines are perfectly parallel as per your manual)
HOWEVER finding out the correct angle to install the centre bearing is the problem
It doesn't work if I just align 2 pieces of the shaft in one line

The document does have some valuable info on multiple shafts, thanks!

This is very true! Universal joint's output doesn't actually turn constantly compared to it's input..................... Weired I know, but why do you think that Constant Velocity joints exist and are made very differently???
Uni-joint equipped tailshafts work smoothely when, as mentioned, the gearbox output shaft is parallel to the diff input shaft. That way the 2 uni-joints operate at the same angle and cancel out each others pulsing behavior.

Watch this! https://www.youtube.com/watch?v=T4P75ZQvpws

[George]

Duk
You'll notice that axle and trans are aligned in exactly that way if you read what I typed above
That video does not address my problem however, b/c there're 3 u-joints, not just 2 of them

[Duk]

See how you are using 3 uni-joints? Lots and lots and lots of cars with 2 piece tailshafts have a rubber coupling at the gearbox or a CV joint somewhere in the tailshaft. But the key is that only 2 uni-joints are in use.
How much does the gearbox move around when under heavy acceleration? Surely there is some torque related movement that will incure some angular misalignment of the front section on the tailshaft when under heavy acceleration???
If/when that happens, you now have 1 uni-joint that has an operating angle that will introduce the pulsing behavior that was shown in the video.

[TooQik]

Duk
You'll notice that axle and trans are aligned in exactly that way if you read what I typed above
That video does not address my problem however, b/c there're 3 u-joints, not just 2 of them

Your problem is caused because you've aligned the transmission and axle centre lines, this is not correct for a two piece shaft.

In the Dana manual that dnegative linked, go to page 14 and look at figure 9. You need to align the centre line of the axle to the centre line of the first shaft, move the centre bearing position to do this. Once these are aligned check that the angle between transmission and first shaft centre lines is correct (1 to 1-1/2 degrees), if not you'll need to find a way to adjust everything (trans, centre bearing, axle) so they all align.

[George]

Duk thanks, that does make sense.
TooQik I also noticed that , but strange thing is that I sense no vibration at whatever speed, no matter how bad I adjust the bearing. The only difference it makes is when RPM of tailshaft is close to zero.
The second strange thing is that I sense very noticeable vibration even if I *temporarily* set the bearing so the 2 pieces of the shaft line up.

Overall, I will try to set trans and axle per the Dana manual, though I'm disappointed a bit with the manual only declaring the proper setup and not explaining it.