I have a strong vibration ( worse as engine torque is incresed) at 1500 - 2000 rpm in 2nd gear ( approx 20 km/h ) . What does the clooective wisdom diagonise this to be ??. I suspect transfer box mounting but how do tell be inspection as they look OK?
PEter Merle
I have the same symptom, as do amny other Gs I've driven. Mine seems to be drive shaft wear. Transfer case mounts may help how much of the vibration is transfered to the chassis, but the mounts aren't a SOURCE of vibration. Regardless of the condition of the mounts, the forces that create the vibration are there and damaging to components. Drive line components are either out of balance (may result from loose, bent, broken, missing components), or out of proper alignment (meaning flanges not parallel). In the first case the vibes come from an ecentric weight and in the second case, they come from U joints being unable to properly cancel each others' angular velocity variations and cyclicly speeding up and slowing down the output end of the shaft.
Now that the front end of my G is so nice and all rebuilt, my drive line vibes are jsut that much more annoying, though they are actually a little less in magnitude, because I KNOW the truck can drive perfectly with just a little more work.
I'm planning to get a local drive shaft company working on a whole new set of three for me. I fiure with 300,000 miles on these shafts, they've served their time in hell and deserve a break.[:)]
I'll also be updating my t-case mounts to the newer style that seem to be stiffer. At that time I'll get the flange alignments tuned up as best I can. Vibes should be a thing of the past at that point.
On my axle rebuild I also discovered my calipers could use freshening up, so I'll be after that one of these days.
Have you guys checked the parallism between the transfer output flange and the rear diff flange? Mine is out by about 4 degrees! I am trying to rectify this am nearly ready to do a test to see if this is the vibe source. I need to drop the diff front to move toward parallel. I'm goind to replace a control arm bushing bolt with one that has a smaller diameter. My plan is to drop the nose of the diff a little and then tighten things and test drive it. If it reduces the vibration problem the two options that I see as realistic are: Redrill new holes in the axle flanges or find a company that can make offset hole control arm bushings. I thind my G is off about 12mm! Has anyone been down this path? I've balanced every shaft and the harmonic balancer. They are perfect. The frond drive shaft flanges are insanely out of parallel and that is why there is an out of phase in its construction I think. I think the major bad vibes com from the back of the truck. Any thouhts?
By driving with the rear shaft out and finding no vibes?
You could also experiment with U-joint phasing at the rear to make up for your out-of-parallel.
OME made eccentric control arm (axle end) bushings with the idea of adding back caster to a spring-lifted front end in Land Rovers. They didn't work very well the thin side of the bushing is too thin and wears prematurely. The biggest gripe with them was they didn't hold up.
The trailing arm can also be bent a bit, but you need to find somebody who knows what they're doing to get this right on the first shot. The drawback of that approach is that it'll put more bind on the chassis-end trailing arm bushings.
Just a few things to try. I'm driving around with 4 bolts per flange at the t-case as I know I'll be swapping it again soon, so now would be a good time for me to play with phasing angles to see if they help. If you're going to do this though, you definitely need to do it one shaft at a time with the other one removed in order to be able to identify the best position for each shaft. Then put them both back.
Spinning up the transfer case without drive shafts.
Have either of you ever (briefly) spun up the transfer case, that is, without the two drive shafts attached, to see how it behaves in a static spin?
I know that the front shaft operates the tc pump, and one would not want to do this for more than a moment. But would that be diagnostic of alinement and short shaft issues?
Never thought to try it, but I guess you could. As long as you keep the t-case in 4wd while you do it there shouldn't be any problem at all with oil delivery. Not to mention the fact that with no drive shafts attached, there's next to no load on the bearings anyway. But no matter. Keep it in 4wd and all is well with 1 or 2 shafts attached.
Yes I removed the rear shaft and ran with the front. It is clearly a rear problem. I did not spin the transfer with no shafts but I don't think it's the issue. Creative thinking with the other ideas you have. I'll let you know how the small bolt test works. Thanks a lot,
Regarding the two sources of vibration - eccentricity and out of balance described I would imagine out of balance would manefest itself as a high speed problem and eccentricity as a low speed problem. With that in mind I should be looking at parallessism of flanges and alignment and/or phasing. Its interesting that the LWB G have a 120 deg phasing on the rear shaft as I guest the parallessism is not perfect.
I di dnotice that my phasing is not perfect - out by about 4 deg as the shaft has been repaired before and I guess they didnt line it up right.
Regarding the parallessism problem as mention by Dai I think it was - one can achive correctly canellation of non linear angular velocity if the one flange is say 2 deg above the normal and the other 2 deg below the normal or infact 4 deg difference in parallessism betwen the two. Perfect parallessism is just a special case of the one I just mention. So before you drill holes in your axle mounts find out if the "out of parallessism " meets the criteria I just mentioned. I can imagine that the axle has moved by 12 mm without a good reason.
Thanks Peter, I will not be drilling things without looking at the alternatives first. I am going to try taking the rear shaft apart and introducing 'out of phasing' to see if that has a positive impact. Its a great idea and it makes sense to try it first. My flanges are 4 degrees off in one direction. In otherwords if you jack up the truck and make the face of the transfer flange plumb or exactly 90 degrees off the floor of the shop the flange of the rear diff points slightly up toward the transfer case by 4 degrees. If I understand what the driveline folks tell me and what Dave and others have said the diff should ideally 90 degrees too or plumb as well. I was told they need to be within one degree. If not there will be a fast-slow oscillation because the u-joints are tensioning against each other as they pass through the out of parallel point. Makes sense to me. I've checked this out flat of the ground with angle finders under normal spring tension and its the same. To get correct orientation with my truck the nose of the diff needs to drop a bit. I will try to trick the driveshaft into not noticing this first. Thanks for the ideas, this is tricky to solve.
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