Monaro – Bad Vibrations
Discussion
If the vibration is prop shaft related then the first thing I would do is get under the car and re check the bolts at both ends of the prop, also check the bolts at the centre bearing.
Next on the list would be to check the rubber donuts for splits and general damage.
If Roger has said the prop has been balanced then cross that off the list
However, I seem to recall that before you remove a prop shaft from a vehicle you should make a scrib mark on the prop and the flange. When you come to put the prop back on you need to make sure the scribe marks are ln alignment. This keeps everything in balance.
Since you have replaced the complete propshaft you couldn't do this, so I'm wondering if you unbolt the prop and rotate it one bolt hole then tighten it all up again and test drive the car. Keep doing this until the vibration has gone, or you have rotated the entire prop. Basically you are trying to find the sweet spot in the balance of the prop. It's going to be a right feck on but you never know?
Hopefully someone will come on here and correct me if I'm wrong, or you could ask around before you try out that theory!
John
Next on the list would be to check the rubber donuts for splits and general damage.
If Roger has said the prop has been balanced then cross that off the list
However, I seem to recall that before you remove a prop shaft from a vehicle you should make a scrib mark on the prop and the flange. When you come to put the prop back on you need to make sure the scribe marks are ln alignment. This keeps everything in balance.
Since you have replaced the complete propshaft you couldn't do this, so I'm wondering if you unbolt the prop and rotate it one bolt hole then tighten it all up again and test drive the car. Keep doing this until the vibration has gone, or you have rotated the entire prop. Basically you are trying to find the sweet spot in the balance of the prop. It's going to be a right feck on but you never know?
Hopefully someone will come on here and correct me if I'm wrong, or you could ask around before you try out that theory!
John
John,
We cannot get it upon the lift until tomorrow morning, but will certainly check all that when we do. I don't think 'my garage man' will have left any of the bolts loose, but you never know.
My best guess at the moment is that one of the donuts has failed, and that caused the original split in the centre bearing rubber mounting. Of course when we were under the car and saw the destroyed centre bearing mount we were certain that we had found the cause, and didn't look for anything else!
Tomorrow we will look at everything very carefully!
Steve
We cannot get it upon the lift until tomorrow morning, but will certainly check all that when we do. I don't think 'my garage man' will have left any of the bolts loose, but you never know.
My best guess at the moment is that one of the donuts has failed, and that caused the original split in the centre bearing rubber mounting. Of course when we were under the car and saw the destroyed centre bearing mount we were certain that we had found the cause, and didn't look for anything else!
Tomorrow we will look at everything very carefully!
Steve
Had the car up on the lift this afternoon, and everything underneath looks absolutely fine. New centre bearing is good. Donuts at both ends are good. Bolts all tight. No excessive movement at gearbox or differential end. Backlash in transmission is minimal. While we were there we went around all the rear suspension bushes and they were fine. Drive shafts also looked good. (If there was anything like this amiss I would expect a few clonks when manoeuvring the car, and there are none.)
So I am just left with the possibility that this recon prop shaft is out of balance.
I will try and get Roger on the phone tomorrow and discuss it with him. What else, other than the prop shaft, could this vibration be? Is it possible that this recon prop shaft was not balanced? Might there have been some confusion between them and Dave Mac Propshafts (who reconditioned it) around the time of the closure of the Monkfish business?
If it is out of balance I can probably get it rebalanced locally. There is a prop shaft specialist just a few miles away.
I suppose the other possibility it to get the car onto a rolling road and get underneath it at 70+mph to watch what happens!
Steve
So I am just left with the possibility that this recon prop shaft is out of balance.
I will try and get Roger on the phone tomorrow and discuss it with him. What else, other than the prop shaft, could this vibration be? Is it possible that this recon prop shaft was not balanced? Might there have been some confusion between them and Dave Mac Propshafts (who reconditioned it) around the time of the closure of the Monkfish business?
If it is out of balance I can probably get it rebalanced locally. There is a prop shaft specialist just a few miles away.
I suppose the other possibility it to get the car onto a rolling road and get underneath it at 70+mph to watch what happens!
Steve
So I spoke to Andy at Monkfish last Wednesday, and he thought it very unlikely (though not impossible) that the recon prop shaft would be out of balance. He recommended some proper vibration diagnostics before spending any more time/money on more parts. He mentioned Vibration Free in Bicester, and I will give them a call next week.
However, in the mean time I had all the wheels re-balanced – they were not perfect, but a test run on the motorway revealed the rumble was still there.
I then did some calculations of wheel and prop shaft frequencies and found that the prop shaft is rotating at about 56Hz at 70mph and the road wheels are rotating at about 16Hz. It seemed to me that the rumble was much more like 16Hz than 56Hz. This focussed my attention back on the wheels.
I decided to swap front right wheel with rear right, changing the direction of rotation as well as the position front to back. I also measured the eccentricity of both tyres by rotating them against a straight edge. Both tyres were only out by about 1mm, but I have no idea what might be considered acceptable.
HOWEVER, after the wheel swap I took the car for a test drive on the motorway and the rumble has gone! At least it did not appear during 5 minutes at high speed. I will swap the other two wheels across the diagonal tomorrow and go for a longer test drive.
So this residual vibration or rumble seems to be a tyre issue. They are Continental 5P’s (not directional) and have done about 5,000 miles on the car. Anyone else had tyres do this?
Steve
However, in the mean time I had all the wheels re-balanced – they were not perfect, but a test run on the motorway revealed the rumble was still there.
I then did some calculations of wheel and prop shaft frequencies and found that the prop shaft is rotating at about 56Hz at 70mph and the road wheels are rotating at about 16Hz. It seemed to me that the rumble was much more like 16Hz than 56Hz. This focussed my attention back on the wheels.
I decided to swap front right wheel with rear right, changing the direction of rotation as well as the position front to back. I also measured the eccentricity of both tyres by rotating them against a straight edge. Both tyres were only out by about 1mm, but I have no idea what might be considered acceptable.
HOWEVER, after the wheel swap I took the car for a test drive on the motorway and the rumble has gone! At least it did not appear during 5 minutes at high speed. I will swap the other two wheels across the diagonal tomorrow and go for a longer test drive.
So this residual vibration or rumble seems to be a tyre issue. They are Continental 5P’s (not directional) and have done about 5,000 miles on the car. Anyone else had tyres do this?
Steve
Steve when you changed tyres round I would leave as it is with just the two tyres changed and if it cures problem then you just have to do no more than check the two changed, for wheel to hub clean faces, wheel not buckled, no untrue tread patten .
Then leave alone until tyres are ready to change. With the tyres not been directional, may be manufactures dont take the same degree of attention to detail in the tread moulding, which may cause a problem as in yours.
Hope you leaeve alone and car is vibration free
Ade
Then leave alone until tyres are ready to change. With the tyres not been directional, may be manufactures dont take the same degree of attention to detail in the tread moulding, which may cause a problem as in yours.
Hope you leaeve alone and car is vibration free
Ade
The handbrake was adjusted, but over a year ago, and the vibration is a relatively recent problem. We know we have a problem with the front right hub, so will fix that first before looking for something else.
With a sticky front calliper it is just a shame I cannot take part in the Bathurst 1000 this weekend!!
Steve
With a sticky front calliper it is just a shame I cannot take part in the Bathurst 1000 this weekend!!
Steve
We were able to service the front right calliper yesterday, and confirmed that one of the two pistons was sticking. There was no corrosion but there was a ring deposit in the cylinder, which was easy to clean off, and all was fine when reassembled using the service kit provided by Pedders. The whole braking system was flushed through with new fluid.
I still don't easily connect this sticking calliper piston with the intermittent vibration I was experiencing at speed, but a test drive on the motorway today was completely free from any vibration. Let's hope it stays that way!
Steve
I still don't easily connect this sticking calliper piston with the intermittent vibration I was experiencing at speed, but a test drive on the motorway today was completely free from any vibration. Let's hope it stays that way!
Steve
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