Thread: 101 Front Driveshafts

Garry your work is proving what I have been saying all along and no one (especially the poms) will listen to the truth.
The fix is not easy...........landrover would have done it if they could with the design and money constrains of the time.
Fix 1
Roll the front diff and use a tailshaft with a double cardon joint on one end at the transfercase.
Lower right hand side front engine mount slightly.
Fix 2
Double cardon joint on each end of the tailshaft.
( the whole thing will most likely be slightly weaker and will become very unsteady when worn.)
Fix 3
Drive the vehicle and dont wory about it like 95 percent of 101s on the road.

Changing the position of the sliding joint, unijoints, shaft size etc will not solve the problem as the basic laws of operation of the unijoint have not changed.
Diffs and transfercases have operational play in between the gears for safe operation.
Diffs and transfercases run at constant speeds per revolution.
The tailshaft itself does not not run at a constant speed, but speeds up twice and slows down twice per revolution and this speed up and slow down effect increases with angles of operation.
For a normal tailshaft to deliver a constand speed per revolution from one end to another using two normal UJs the angle of operation of the UJs must be the exactly the same , but opposite to one another to cancel each other out.
Even with a correctly set up and angled tailshaft using two UJs as operating angles are increased you will lose constant drive efect though the tail shaft as the maximum possible angle of operation is 45 degrees for constand drive effect.

At high angles of operation the tail shaft is speeding up and slowing down and as is the tail shaft weight or inertia.
The effects of inertia increase with speed.
The 101 runs low diff ratios and the tail shaft runs at higher speeds than most 4WDs if driven down the highway like we tend to do in civilian use.
When a load is on the tail shaft like on drive or backing off and using engine braking all the play in the diff pinion gears , transfercase and tail shaft sliding splines is taken up by the forces of the drive and the effect of no play.
When on the float going down a hill or coasting any inertia effect and slight misalignment causing more speed differential effects will unleash themselves in the play in sliding splines and gear clearances as there are no forces to control them until the play in the drive system is taken up and it will then release and find the play in the other direction.

The effect of reducing gear clearances in the the front diff is interesting.
I did this when I fitted my front locker.
The standard front diff pinion gear clearence is something like 12 to 6 thou and mine was reduced to 4 thou ( I didn't mention this on my locker thread).
The effect was it made to front tail shaft vibs higher in pitch and and any thing slightly worse than before as the frequency effect had less play to bounce from one side of the gear clearence to the other.
The effects on the drive drive with this viberation is one that the tailshaft bolts and drive flange nuts will tend to come loose and wear in the drive flange splines will be heavy and this in turn will lead to the seal on the transfercase leaking.

Tailshaft splines and any other part of the front drive on a 101 will wear quicker than normal.
I note the front tailshaft on my defender, whisle it doesnt viberate or cause a noise, it does suffer from the above problems to some extent for slmilar reasons.
When replacing the diff pinion seal or front transfercase seal use a Loctie produce on the drive flange splines and nuts.
Use Nyloc UNF nuts with Loctite on the tailshaft bolts and check bolts frequently.

The effect of a overdrive with standard tail shaft and diff ratios is interesting.
When going down a moderate hill in a 101 cruising at 80 kph we tend to back off as the vehicle is picking up speed at getting out of the friendly engine rev range.
If we float down this hill we tend to induce the the tailshaft buzz, so we tend to back right off and use the engine braking effect to load up the drive line again and stop the buzz,
The problem is with the low gearing the engine braking is too good and we have to drive though the buzz and put the power on again and the cycle starts.
With a overdrive you would tend to be cruising higher down the hill anyhow at say 100 kph.
Due to the increased wind drag (box shape) and drive lines losses you need to keep the power on and can do it for as long as needed as the motor is not reving too hard.
A good example was driving my 101 down to the Hawksbury on the F3 freeway.
A normal 101 would have to back off going down keeping to 90 kph.
On my 101 I kept a small amount of power on all the way down (just enough to stop the buzz) and reaching 120 kph on the bridge at the bottom and then used the momenum to help carry me up the other side.
With overdrive the engine revs are less than 3800 rpm at 120 kph

Thanks Ron - most of what you have said ties in with what I have found, however I do not believe a double carden will actually fix things in the front. As you have indicated there is more that one thing going on which manifests itself in the noise and vibration.

If it was just a drive shaft issue - the rear drive shaft would be worse - in all the forums I have posted this issue the same question has never been acknowledged or answered - and that is if the rear drive shaft is shorter and steeper than the front, why is it that it is only the front shaft that has the issues. I suspect it has something to do with a rear salsbury diff being put in the front but I have no evidence.

I find the 101 extremely tiring to drive in undulating country where you are constantly trying to either drive through or slow down through the rumble - as it does not appear to actually damage the shaft I find I am no longer driving through it just driving at a speed appropriate to the conditions - my new earmuffs help.

When someone can work out why the front shaft rumbles and not the rear when it should be the rear shaft that makes all the noise then we may be on the track. The rubber in my new shaft certainly takes most of the vibration out but not the noise.

Garry

As for the rear shaft I have experimented here and so did Landrover.
The prototypes had rear tailshaft problems and so the 101 short bell housing was developed to lenghten the rear tailshaft on production models.
I have played with UJ joint angles in the rear by the use of castor correction wedges under the rear springs to see if I could induce vibs in the rear tailshaft or see if any effects the rear shaft could have on the front being a constant 4WD system.
The rear shaft has no effects vibs wise on the front one, but I could easly induce vibs from the rear shaft by slightly placing the UJ angles out.
The fact is the rear shaft is on its limits too and I think we are luckly it is not more of a issue as well.
The front tailshaft has more play advailible to it for harmonics due to the presence of the front axle CV steering joints.

Originally Posted by 101 Ron

The front tailshaft has more play advailible to it for harmonics due to the presence of the front axle CV steering joints.

Thanks Ron - good information - I am beginning to find I am getting more out of you and the other 101 owners in Australia than all of the 101 owners in the UK.

I am with you on the front end - while the noise and vibration may manifest itself in the front drive shaft - I think the entire front end has to be considered as a unit as I think all components contribute to the issue.

I will be interested to see how Peter P's new drive shaft works in his truck when it gets onto the road.

Cheers

Garry

Dunno the first thing about this stuff, but I'm curious if anyone has put a locker in the front of a 101? Just as another way of changing the setup.