Vehicle & Technical > Discovery
Bad Vibrations
nzoliver:
Howdy all, Something to ponder.....
I have a harsh vibration under medium to hard acceleration at 55km/h (31MPH) and it comes in again at 100Km/h (62MPH). SO far we have tried this to no avail:
Remove rear prop shaft - problem stays
Remove front shaft - problem gone
Install brand new front shaft - no difference
Dissasemble and check centre diff - all just fine
Dissasemble front diff - all fine
Checked both CVs and front wheel bearings - all fine
Changed the wheels for some from another vehicle - no difference
Put the truck on a hoist and run it up to 55 - transfer case starts shaking - engage diff lock and the problem is almost gone.
Where to next??
Any clues?? It is a '98 300Tdi with 80000km.
:cry:
Range Rover Blues:
That's a good one. Obvioulsy the vibration at 100 is a harmonic of the main vibration at 55.
Now you've almost answered this yourself because the transfer box is vibrating, unless you engage diff-lock :-. curiouos :-k
But I think the T-box is your problem.
3 questions, was the truck on it's axles whilst on the ramp or were the wheels "dangling" from the chassis? this will effect the front propshaft UJ angles badly and wear in the T-Box would be shown up worse than usual.
And is the truck lifted above standard, have you done any suspension work recently?
Finally, how quick did the problem appear?
I'd be looking for a collapsed bearing, a bent or loose shaft/flange or chipped teeth somewhere in the T-box.
nzoliver:
Howdy! :lol:
The axels were in dangle mode. The truck is bog standard as supension goes. I'm not sure how quick the proble appeared but it appears to be gettimg worse. It is less noticable when cold. Once the trans. box is warm then it is very evident. More so when it is hot.
Hmmm, its a doozy alright! :doh: We pulled the transfer box out and all looked good. Same with the centre diff. Took the plate on the bottom of the t/case off and no 'bits' or spare parts so no broken teeth etc. Oil was clean etc.
This is a damn nuicance!! :-k
nzoliver:
Howdy again.. :roll:
The brand new front driveshaft that turned up was 'in phase' and probably ballanced as such. Would shifting to phase the 45deg that it is meant to be alter the ballance of the shaft? :-k If so that would make the new shft out of ballance and therefore useless. :doh:
Range Rover Blues:
Err, hmm.
I tried for ages to get my head round why the UJs appeared to be out of phase, on early RRC it's about 30 degrees but by the 90s it was 45 degrees.
The best that I can understand it's because the T-Box and axle diffs are at different distances from the centreline of the truck, so that the UJs are in fact in phase, because of the unusual way the front prop is installed.
Anyhow, the difference it would make is minimal, a droning from the front end during coasting is the most obvious. When I was trying to sort out oour lifted truck (before castor correction etc) I re-aligned the front prop so that the UJs were in line, because it was lifted 2" this helped. I didn't experience any out-of-balance issues.
If the prop was built properly (no punn inteneded) then the balance issue will be minimal.
I've been trying to figure out why engaging difflock when it was on the ramp made any difference :-k, the first answer is that perhaps the 2 axles were running at different speeds and engaging difflock changes the speed of the front axle :?
If you can be bothered trying it again stick the truck up on axle stands rather than a lift so the weight is on the axles and they are in their normal position.
Meanwhile, check that none of you engine mounts have become damaged or gone soft, oil contamination can do this but check none are split either.
Do you off-road? could it be damage from striking something hard :-k
Does the gear you are in make much difference? obviously it effects the rate at which you accelerate but I have seen a combination of engine vibration and propshaft vibration that's worse in some gears than others.
You tried another set of wheels, so I take it you can't identify exactly what's vibrating. How good are your shocks and do you feel the vibration through the steering?
Lastly for now, check the rubber coupling on the rear prop, both the doughnut and the spigot bush inside the back of the prop.
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