Thread: Uni's out of phase?

I haven't even checked the alignment of the uni's, I was just thinking that if the uni's are no longer parallel then it would cause a noise/vibration.

It did it when I first got it with standard suspension, but only slightly, then after the lift it got worse / seems to be getting worse. Only happens at that point between accel and decel. Maybe the uni's are buggered, will have to investigate further.

The thoery for uni joint phasing is: the shafts at both ends, that a prop shaft is attached to, parallel then the unis are in phase.
;if the shafts are not parallel, eg coil front diff pinion, then the unis run out of phase.
For most spring lifts on road vehicles around 22 to 24 deg is fine, thats turning the shaft 1 spline on the slip joint.
If you are at right angles then 45deg is used.
Most of the vibration will be felt at trailing throttle or overrun.
I have turned dozens of front shafts on Landies and Rangies to cure this problem, with no detrimental effects

My 1991 3.9 ZF/vc transfer case has this annoying vibration at the point between power and coasting as described and the shaft is already out of phase. I will check how many splines (looks like 45 degrees) and change it if necessary.

It spoils an otherwise smooth running vehicle. It does have "heavier" springs - will try and id the colours if that will help.

(just had a look in the workshop manual and it does not specify the angle to set the unis - just align the arrows. It does mention also making sure the front wheels are balanced correctly)

Bob

For the non technical i see people saying that 23deg is turning the shaft 1 spine out of phase - so does that mean to get the ideal 45 deg off set one turns the shaft 2 splines out of phase??

Is that the simple rule?
Skiboy

You need to be sure which way you change the splines: my clear understanding is that for the front prop shaft the rear UJ LEADS the front UJ by 2 splines in the normal direction of travel, while for the rear shaft the UJs are in phase.

I discovered this information the other day in regards to my P38, and having changed things around to reflect the above, I have now removed the vibration that has been bugging me for the past 4o+ thousand Km!

Originally Posted by Skiboy

For the non technical i see people saying that 23deg is turning the shaft 1 spine out of phase - so does that mean to get the ideal 45 deg off set one turns the shaft 2 splines out of phase??

Is that the simple rule?
Skiboy

This is what i done to mine on the weekend, moved diff end 2 splines forward. Mostly cured the slow speed vibe (rear shaft needs a new uni) and as a bonus has reduced the noises/clunks in the transfer to near nothing

for a discussion re. the geometry of a U-joint (known as a Hooke's joint) check out Driveshafts and U-Joints - Tom Sotomayor

Also see Pirate4x4.Com - Extreme Four Wheel Drive for everything you want to know about u-joints including lots of pics re. maintenance, rebuilding, applications etc

Originally Posted by Hoges

You need to be sure which way you change the splines: my clear understanding is that for the front prop shaft the rear UJ LEADS the front UJ by 2 splines in the normal direction of travel, while for the rear shaft the UJs are in phase.

I discovered this information the other day in regards to my P38, and having changed things around to reflect the above, I have now removed the vibration that has been bugging me for the past 4o+ thousand Km!

I've been thinking about this phasing on and off for the last 5 years or so (when I rephased my front shaft). I've mostly convinced myself that leading or lagging gives exactly the same input/output pulse cancellation/excitation.

If you offset two sinusoids, then it doesn't matter which leads or lags, you've still got two offset sinusoids.