L Series Vibration/Booming

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Well to be honest I was gutted but it could have been worse, i.e. if I bought an IRD or gearbox and fitted them and it didn’t stop the vibration then I would be seriously ****ed off and gutted! Driveshafts didn’t take long to replace and I am sure they will be knackered some day so I have a spare set now!

The facts I know about this problem are –
1) The driveshafts are not causing the problem!!!
2) It is definitely rev related between 1500-2000rpm, not road speed related.
3) When the complete propshaft is removed it makes it a lot better to a point that is
live able with but the problem is still there. So whatever is causing the problem
is transmitting itself down the prop and up into the drivers seat and through the
body of the car. Also this rules out the propshaft/viscous/centre bearings.
4) It does not have the problem when revving when stationery.
5) When the problem occurs if I press the clutch pedal down but keep the revs
between 1500-2000rpm the problem disappears. So basically when the driveline
is removed from the engine the problem goes.
6) If I apply light pressure on the clutch when the problem occurs it does not stop
the boom/vibration.
7) When at 1500-2000rpm (with the problem evident, for example in 4th gear), if I
shift it back into neutral and let the clutch back up the problem goes.
8) Gearbox and IRD oil levels are fine.
9) All 4 tyres are relatively new, they are micheline synchrone 4x4, the newest tyres
are on the rear
10) I have had numerous people drive the car, from engineers to LR techs that I
know and all have different opinions which doesn’t really help me. Some say it’s
the IRD, others say driveshaft, some say engine mounts and one said flywheel!

To summarise, it only happens when the driveline is connected to the engine, as
soon as the clutch is pressed, disengaging the driveline from the engine the
problem goes.

I have on order a lower rear tie rod because there appeared to be some play in that when I checked it, be surprised if this causes the problem but guess I will find out next week when I fit it, nothing would surprise me anymore. I can only think there is more stress/engine movement on this tie rod when the engine is connected to the driveline amplifying the boom/vibration, that is what I am hoping for anyway!

Noise/vibration/booms etc are difficult to diagnose from on line but its good to get people's opinions, especially if people have had very similiar problems that have been rectified.

Will keep you posted, and thanks to Dave for the input to date.
 
Hi Tank,

I have to admit I really felt I had let you down as I was so sure you had the same problem without a doubt. I was totally stunned when you stated your problem was still there.

One thing that is much in common is that both problems occur when the engine is on-load at 1500-2000 revs. How do you find out though? We know it is in the engine / transmission assembly from the propshaft experiment. Vibration is normally something out of balance. Rev related means that it is most likely either engine / clutch / input shaft on gearbox. I don't have the information but try this thought. Your problem occurs in 4th and 5th gear. Are these two gears on the same gear set in the box? (Sorry I don't know the correct terminology). Where I'm going is, could this be these gear parts that have the problem.

Obviously this means gearbox out, and replacement I guess is the easiest way. Serious work and cost. Anyone who knows gearboxes better than I care to comment on this possibility before Tank bancrupts himself.

I hope this helps.
 
No worries, the way I look at it is that is one more component out of the way that is not at fault and now I have spare driveshafts. The problem is there in all gears, but its more prominent in 4th-5th but it is there in 1st/2nd/3rd.

I am not going to get downbeat about it as that will achieve nothing. Its a challenge and hasnt cost me vast amounts yet, that time will come when/if I have to start thinking about IRD, gearbox etc.

I will update next week when the lower tie rod has been replaced.
 
No update as yet, might never have an update if all I am left with is the IRD/gearbox as I will just live with it as the cost of a new IRD or gearbox is way too much. Anyway will be the weekend before I get to look at it again. I have got quite accustomed to the boom now to be honest, the car wont feel the same if when I finally cure it, after the driveshafts didnt cure it last week i think the car is telling me something!!!!!!
 
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