roversreturn
New Member
When fitting a new VCU and bearings. Is there a need to have the VCU/prop train rebalanced?
No
Alibro
Well-Known Member
In theory no but in practice I had two Freelanders which had an awful vibration from the VCU at anything over 50mph after refurbing them.
The solution was very simple, unbolt the damper and rotate it one hole, if that didn't work then do it again.
I was told I was crazy for saying this before but when the same thing happened with my second one I had confirmation it can make a huge difference.
Of course if you didn't take the damper off the VCU then it shouldn't matter.
The solution was very simple, unbolt the damper and rotate it one hole, if that didn't work then do it again.
I was told I was crazy for saying this before but when the same thing happened with my second one I had confirmation it can make a huge difference.
Of course if you didn't take the damper off the VCU then it shouldn't matter.
Nodge68
Well-Known Member
I would guess that cutting the VCU open and rewelding would induce a degree of imbalance. I had to have propshafts balanced when they were modified for various engine installations, when that was my thing.
Alibro
Well-Known Member
Yes agreed, but if the damper was perfectly balanced itself then turning it would do nothing but I've found it can make a big difference. On one VCU, before I removed the damper I put the VCU onto stands with bearings gently tapped onto each end so I could spin it. The VCU itself was perfectly balanced but the damper had a massive wobble/imbalance in it. This was on a car which had no vibration before I removed the prop shaft. After refitting I had a horrible vibration which was fixed by rotating the damper.
tonytherunner
Active Member
Prop Shaft Dampers are used to reduce or eliminate overlying rotational vibration that is transferred from the internal combustion engine to the drive shaft.
For the design of a prop shaft damper, this means that the first stage is to find an appropriate installation location on the drive shaft or to adapt the design to the existing installation situation. However, the drive shaft absorber should generally be located as close as possible to the origin of the vibration problem, in order to allow the use of a absorber which weighs as little as possible. Generally, a rotational vibration absorber always consists of a hub, an elastomeric element and an inertia ring. For cost reasons, it is recommended to use sheet metal parts for the hub and cast iron for the inertia rings.
I think the engineers at Land Rover took this precaution for VCU ,the idea that silicone inside does not stay in one place, it can collect on the bottom when the car is stationary a long time.
For the design of a prop shaft damper, this means that the first stage is to find an appropriate installation location on the drive shaft or to adapt the design to the existing installation situation. However, the drive shaft absorber should generally be located as close as possible to the origin of the vibration problem, in order to allow the use of a absorber which weighs as little as possible. Generally, a rotational vibration absorber always consists of a hub, an elastomeric element and an inertia ring. For cost reasons, it is recommended to use sheet metal parts for the hub and cast iron for the inertia rings.
I think the engineers at Land Rover took this precaution for VCU ,the idea that silicone inside does not stay in one place, it can collect on the bottom when the car is stationary a long time.
Joe_H
Well-Known Member
Never quite worked that one out Nodge ..... I wonder what the logic was behind that ?Did you try it without the damper? The V6 doesn't use one
GrumpyGel
Well-Known Member
Did you try it without the damper? The V6 doesn't use one
I wonder if it was related to the IRD gearing to the back axle being nearer to parity? Given....
Maybe its because the engine itself vibrated less?
All engines had diferent dampers though:
Petrol KV6 : None
Diesel L&TD4 : Damper on VCU
Petrol K : Damper on VCU and damper on IRD (some only on VCU?)
Joe_H
Well-Known Member
Interesting point..... I forgot about the K series ird blob
.... that sounds about right. - sort of removes the theory of fluid settlement in the VCU - I would have thought any issue there would disappear in a few rotations of the vcu so never be noticeable anyway.
Nodge68
Well-Known Member
There was a theory that the V6 didn't need the VCU damper because the V6 has an inherently smooth output. However the V6 is an automatic, which contains a massive fluid damper, in the form of the torque converter. So I can't see any engine generated torsional vibration getting to the props any way.
I suspect the damper was omitted on the V6, to improve break over ground clearance. The V6 bearings have 25mm spacers fitted to them. This effectively reduces break over clearance by 25mm. Not fitting the damping claws some of that loss back.
Of course the slightly different length of the V6 front prop could alter any resonance enough to make the VCU damper unnecessary.
Alibro
Well-Known Member
I've now confirmed with a second car that the damper can cause massive vibration and rotating it can fix the issue. I can't comment on what would happen by removing it though as rotating it only takes a couple of minutes and removing it a couple of hours.
Note this was with two VCU's that had been refurbed and welded by me so the damper had been removed without being marked for refitting cause I thought it shouldn't need to be. Also as my welding leaves a lot to be desired I could have introduced an imbalance but that wouldn't explain why rotating the damper would fix the vibration.
Note this was with two VCU's that had been refurbed and welded by me so the damper had been removed without being marked for refitting cause I thought it shouldn't need to be. Also as my welding leaves a lot to be desired I could have introduced an imbalance but that wouldn't explain why rotating the damper would fix the vibration.
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Nodge68
Well-Known Member
Maybe the damper is inherently out of balance? Rotating it would then improve or worsen the out of balance VCU.
Alibro
Well-Known Member
The damper may even be balanced in the factory to match the VCU. I remember being surprised how apparently out of balance the first one was before I removed it from the VCU but there was no sign of vibration before the refurb.
Nodge68
Well-Known Member
Maybe. Although with only 3 mounting points, it balance will always be a compromise of the least out of balance position.
I'll mark mine when I remove is this week.
Alibro
Well-Known Member
There are only 3 mounting points but there's a lip on the VCU which centres the damper so the bolts are only holding it on.
Marking it is sensible but where's your sense of adventure?
