Weird vibration
Discussion
I originally posted this on the general forum under technical and caught no luck.
I have received my 98 XJR back after a Dinitrol treatment and it has a drive issue, it definitely was not like this before it went in.
It was up on a ramp and the wheels have been off.
At 45 mph and especially at 50mph there is a deep trembling / vibration feeling from the car, it doesnt feel like front end.
I have done the pressures and balanced all four but its still there. Tyres look fine.
Its really difficult to describe, it could be a diff issue.....I have never felt anything like this before. Its doing my head in though. It doesn't affect the steering wheel and still does this in Neutral.
Is there anything that anyone can think of that could cause this ?
I have received my 98 XJR back after a Dinitrol treatment and it has a drive issue, it definitely was not like this before it went in.
It was up on a ramp and the wheels have been off.
At 45 mph and especially at 50mph there is a deep trembling / vibration feeling from the car, it doesnt feel like front end.
I have done the pressures and balanced all four but its still there. Tyres look fine.
Its really difficult to describe, it could be a diff issue.....I have never felt anything like this before. Its doing my head in though. It doesn't affect the steering wheel and still does this in Neutral.
Is there anything that anyone can think of that could cause this ?
45-50 MPH is classic prop vibration speed on a X308. It might possibly be knackered rear shocks allowing suspension resonance - that can occur at the same speed or something damaged inside the diff.
Prop balance symptoms are a constant high frequency fairly light (compared to unbalanced wheels) vibration felt through the rear of the car at those speeds. A really bad case will also produce a kind of thudding buffeting you hear more than feel at the same speed similar to that you get when driving fast with a rear window open. Find a smooth bit of road and play with the vibration for a bit to familiarize yourself with the exact symptoms.
If its consistent on/off load/steady speed and coasting in neutral in that speed range then chances are it's prop balance. Wheels and tyres are usually more of a issue around 60-70MPH but I'd still rule them out by balancing and substitution first though just to be absolutely sure.
To diagnose a unbalanced prop first jack the rear wheels up and run up in Drive to the vibration speed. Observe.
Remove the rear wheels and do the same again. Observe again.
Remove the calipers and rear discs. Run up and observe.
Match mark then disconnect the half shafts from the diff. Run up and observe again.
If you still have the same vibration - probably in a much purer form now then yes, it's either the diff or more likely the prop. Next step is to find out why, there will be a cause as props don't suddenly go off balance for no reason.
Prop balance symptoms are a constant high frequency fairly light (compared to unbalanced wheels) vibration felt through the rear of the car at those speeds. A really bad case will also produce a kind of thudding buffeting you hear more than feel at the same speed similar to that you get when driving fast with a rear window open. Find a smooth bit of road and play with the vibration for a bit to familiarize yourself with the exact symptoms.
If its consistent on/off load/steady speed and coasting in neutral in that speed range then chances are it's prop balance. Wheels and tyres are usually more of a issue around 60-70MPH but I'd still rule them out by balancing and substitution first though just to be absolutely sure.
To diagnose a unbalanced prop first jack the rear wheels up and run up in Drive to the vibration speed. Observe.
Remove the rear wheels and do the same again. Observe again.
Remove the calipers and rear discs. Run up and observe.
Match mark then disconnect the half shafts from the diff. Run up and observe again.
If you still have the same vibration - probably in a much purer form now then yes, it's either the diff or more likely the prop. Next step is to find out why, there will be a cause as props don't suddenly go off balance for no reason.
I would recommend that you look at the propshaft for masking tape left on the shaft or a deteriorated centre bushing. If those are o.k. typically propshaft imbalance manifests itself at the 110 mph level.
50 mph vibration is more likely to be a tyre and bushing harmonic and the rustproofing process is more than likely to be the culprit. The bushings need to be checked for failure induced by petrochemicals. Clearly this is a lot of work but it is probably the only way you can figure out what's going on.
50 mph vibration is more likely to be a tyre and bushing harmonic and the rustproofing process is more than likely to be the culprit. The bushings need to be checked for failure induced by petrochemicals. Clearly this is a lot of work but it is probably the only way you can figure out what's going on.
GavinPearson said:
I would recommend that you look at the propshaft for masking tape left on the shaft or a deteriorated centre bushing. If those are o.k. typically propshaft imbalance manifests itself at the 110 mph level.
50 mph vibration is more likely to be a tyre and bushing harmonic and the rustproofing process is more than likely to be the culprit. The bushings need to be checked for failure induced by petrochemicals. Clearly this is a lot of work but it is probably the only way you can figure out what's going on.
Now that's interesting - I chased exactly this to death on my previous X308 and found prop vibration periods at both 45 and 90 and deliberately them worse by fitting a jubilee clip on the shaft to throw the balance out further as a aid to diagnostics. That's after I'd replaced the rear shocks, A frame bushes and Jrdid couplings as well as fitting a known good substitute diff and propshaft. I played around with shims on the centre bearing bracket too just to see what influence changing the UJ operating angles had.50 mph vibration is more likely to be a tyre and bushing harmonic and the rustproofing process is more than likely to be the culprit. The bushings need to be checked for failure induced by petrochemicals. Clearly this is a lot of work but it is probably the only way you can figure out what's going on.
The original shaft was precision balanced by a specialist and went back on after I'd balanced all the coupling nuts and bolt sets to within 1gm of each other.
Still no improvement.
I eventually got some improvement by several hours of fiddling about with another Jubilee clip on the rear of the shaft by the diff with the half shafts disconnected and found a sweet spot where the symptoms dissipated completely... for a couple of weeks and then returned.
The centre bearings aren't replaceable on the X308 as far as I discovered and new props are no longer available either. That was the nail in the coffin for me and I got rid of the car.
If the handbrake is too tight, sticking, or discs corroded it can cause this.
Those non believers pull your handbrake up at about 50mph and you'll feel it, the cable might be loose but the shoes can still be tight. Remove real wheels and back handbrake right off to check this isn't the fault.
Those non believers pull your handbrake up at about 50mph and you'll feel it, the cable might be loose but the shoes can still be tight. Remove real wheels and back handbrake right off to check this isn't the fault.
Update : I thought I'd get the car back to the garage that completed the Dinitrol treatment and I asked them to remove the treatment from both drive shafts, propshaft and UJ's.
It worked, the vibration has gone.
The garage were very helpful and had never come across this before.
I thought I was in for a long pain in the arse fault diagnosis time !!
It worked, the vibration has gone.
The garage were very helpful and had never come across this before.
I thought I was in for a long pain in the arse fault diagnosis time !!
Zippyworld said:
Update : I thought I'd get the car back to the garage that completed the Dinitrol treatment and I asked them to remove the treatment from both drive shafts, propshaft and UJ's.
It worked, the vibration has gone.
The garage were very helpful and had never come across this before.
I thought I was in for a long pain in the arse fault diagnosis time !!
Good news. I guess they'd got a strip of treatment fluid along the prop. Shows it only takes a few grams to throw the balance out.It worked, the vibration has gone.
The garage were very helpful and had never come across this before.
I thought I was in for a long pain in the arse fault diagnosis time !!
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