The VP Vibration Project.

[Circlotron]

I'm fast coming to the conclusion that VNs/VPs are a poorly designed car in some respects. I'm on a mission to make the VP as whisper quiet inside as possible so I am cataloging various sources of noise and vibration. What I am looking at at the moment is the rear gearbox mount. On my HJ the rear crossmember went right from one side of the car to the other. Got in the way of the exhaust but is a great place to connect to the car because the car body is relatively strong at the edges. The VP by comparison has a short crossmember that joins to what is virtually the floorpan, and not that far from the centre either. The bad thing about this is if you apply vibrations to the floorpan near the centre it has very little resistance to flexing. It is like a trampoline almost. Like a 6 foot by 10 foot loudspeaker covering the entire bottom of the passenger compartment.

We can't easily brace up the floorpan so I got to looking at the crossmember. It is hollow and rectangular somewhat, so I got to thinking about blocking up the ends and filling it with molten lead to make it much heavier. That would add about 4kg to it in my estimation. The purpose is to make the rubber gearbox mount work a bit more by making the crossmember more difficult to vibrate. Not going to do anything to low frequency "shaky" vibes but should help a lot with higher frequency "tingly" vibes. It's just like a very heavy car and a very light car having identical springs - the heavier car is much less able to follow the bumps than the light one.

Now, just gotta track me down a lead smelter.

[Jonno]

i thought the cross member on all commodores was done to the floorpan............................

[Circlotron]

I didn't mean it was only confined to VN/P.

[VK SL 3800]

You are never going to get the natural vibrations out, and most vibrations are from the engine and even more so if its V6 powered, they are simply not engineered as well as some little rice burner or modern European car and will never be as nice and smooth, even the good ol 5ltr vibrates a little but thats half the reason you have one, you literally feel the power!

The reason the HQ-HZ series has the mount all the way across is because it has a separate chassis and the body is not strong enough to go hanging engines and gearboxes off.

[88GreenVN]

Change engine mounts every 100,000kms to reduce in car vibration. Do the gearbox mount at the same time. (V6 that is)

[Circlotron]

Engine and gearbox mounts both just done.
Got V8.
Still not happy because 6 cyl HJ was smoother.

[monkeys437]

So you brought a 20 y.o V8 and your unhappy that its not smooth enough? What were you expecting mate

[MasterOfReality]

Just go nuts with the dynamat.

Its a car that shares engineering aspects with the VB commodore - its always going to feel like a dog, especially when the floor pan was widened and stretched and was noted for feeling sloppy even when new. There is a good write up about the VN in the last issue of Unique Cars.

[ryan21]

Just go nuts with the dynamat.

Its a car that shares engineering aspects with the VB commodore - its always going to feel like a dog, especially when the floor pan was widened and stretched and was noted for feeling sloppy even when new. There is a good write up about the VN in the last issue of Unique Cars.

i read that "the vn commodore was an exciting ride but usualy for the wrong reasons" i loled so true. that thing is dangerous with a v8 thottle body and bald rear tyres in the wet

[Circlotron]

So you brought a 20 y.o V8 and your unhappy that its not smooth enough? What were you expecting mate

I was expecting it to be smoother than the 35 year old 6-cyl Kingswood that it replaced.

[Circlotron]

Big update.
When I first got the car I got a wheel balance done and they pumped all the tyres up to 36 psi. I asked the guy about this and he reckoned that's what they put them all at nowadays. 2 months later I am thinking the car is as bumpy as all crap because it also has FE2 springs and pretty hard shockers/struts so last night I let the tyres down to 30 psi. So now it rides somewhat smoother, but here is the =REALLY= unexpected part. The vibration I had at ~1500 rpm is now perhaps two-thirds gone! Just as a result of letting down the tyres! Before you say "nonsense" remember this - the car body has mass, the tyres have springiness. Here we have a system that will resonate at a certain frequency. 1500rpm = 25 Hz. If the body mass and tyre springiness resonated at 25Hz then the vibe would be greatly magnified at 1500rpm. Letting down the tyres would lower this resonant frequency to where it did not matter as much. You may not believe the above but that is exactly what happened. The source of the vibration I still think is a wobbly crankshaft pulley (1/2 mm runout) so I am still going to have a look at that.

[alpha_au]

Just a question, what sort of tyres have you got on there? If they're low profiles I find that the ride is severely affected. I run the standard 205/65/15 tyres and they act almost like an extra shock absorber compared to having low profile 235/35/17 wheels on there.

[Circlotron]

I think they are 205/65/15. Looks as normal as can be.
Yeah, I know what you mean; low profiles are as noisy as.

I would love to have soft and squooshy springs and shockers too so it rode like a 70's Cadillac but that's lotsa money and mucking around.

[Brett_jjj]

With my VS, I had a vibration about midway along the car,around the transmission area at around 80 km/h,I replaced the engine mounts,the trans mount,the uni joints and centre bearing,and I still had the vibration there,though not quite as bad.I then replaced all the rear control arm bushes and panhard rod bushes as Id heard that if the diff is slighly out of alignment from worn bushes,it could cause vibrations to occur,I was a bit sceptical about this being the cause,but the bushes were badly worn anyway,so I replaced them with nolothane type bushes and the vibration has completely gone and has never come back..

[Circlotron]

Id heard that if the diff is slighly out of alignment from worn bushes,it could cause vibrations to occur,

That's interesting. On a one-piece tailshaft at least, the front and rear uni joints are meant to be at an equal angle. The effect is (the greater the angle the greater the effect) the transmission yoke rotates smoothly, the tailshaft rotates 1/4 turn slightly fast, 1/4 turn slightly slow, and the diff end uni joint undoes this fast-slow effect, but ONLY if it is at the same angle as the tranny end. If the diff housing rotates backward a bit under acceleration because of worn bushes and makes the diff uni joint some weird angle then it would probably become vibe city.

BTW, this fast-slow bizzo is why FWD cars have =Constant Velocity= joints on the axles, not uni joints.

And my car does vibrate a bit on hard takeoff.

[agrsv8]

+1 for dynamat,

if you want a 20 year old car real smooth and quite, why don't you wear ear plugs and sit in a bean bag :P

[Warranty Void]

If you wanted to go smooth and quiet in a relatively cheap car you should have got a 10 year old Magna or Camry for 3-4 grand or a Toyota Cressida and shove a 1-2 JZ in it or a VT commo for 4-6 grand if you must have rear drive V8. Or fill the interior with doonas and look out through a periscope.

[bj42turbo]

IMHO 30psi is to low......any high performance driver course will say at least 35psi...infact they spend a lot of time on tyres pressures...

Keep up the quest though on a vibe free commodore, would be interesting to see what you come up with......

My first VN I bought when they first come out...I was looking to buy a second hand VL but ended up buying the VN as they were the latest model....Even brand new they were not what I would consider refined espessially when up against a VL for example...However there is something about there quirks and lack of refinement I like.....




Dazz

[Circlotron]

Righto, time to try something new. On my car at least, at some rpms you can feel this ~slight~ tingle of a vibration coming through the steering wheel. At some rpms the p/s pump hoses send vibes to the steel lines and onward to the rack. Then from the rack, up the steering column to the wheel and thence to my delicate little fingies.

So, the plan was to attach some extra mass at the end of the hoses so the hoses would find the mass more difficult to vibrate. For the pedantic among you, we now have a second order low-pass filter that reduces vibes as they go up in frequency by 12dB per octave. Second order because (1) the springiness of the hose stores potential energy and (2) the moving mass stores kinetic energy. But I digress...

So what I did is attach a steel rod weighing about 270 grams to the metal collar of the high pressure hose. The high pressure one because it is by far the stiffer of the two and so would more readily transmit vibes. Haven't taken the car for a drive yet, but just sitting there it seems good. Cost practically nothing too.

Edit --> Took it for a little drive and yep, I reckon it improved things. The car feels just that little bit nicer. More refined. I say try it

[monkeys437]

So your saying the vibration from the high pressure hose was actually noticeable and was significantly reduced by adding a dampening weight? How'd you arrive at 270g? Trial and error or was there method to the madness?

[Shearer]

Just go nuts with the dynamat.

Its a car that shares engineering aspects with the VB commodore - its always going to feel like a dog, especially when the floor pan was widened and stretched and was noted for feeling sloppy even when new. There is a good write up about the VN in the last issue of Unique Cars.

Good write up?!!?? It would be THE MOST negative article written about these cars

Unique Cars publishes a lot of mis-leaded and incorrect information, typical of the Media in general

[Reaper]

Just go nuts with the dynamat.


Its a car that shares engineering aspects with the VB commodore - its always going to feel like a dog, especially when the floor pan was widened and stretched and was noted for feeling sloppy even when new. There is a good write up about the VN in the last issue of Unique Cars.

Good write up?!!?? It would be THE MOST negative article written about these cars

Unique Cars publishes a lot of mis-leaded and incorrect information, typical of the Media in general

Which bit of that is incorrect or mis-leading? The VN-VS was built on the same platform that was the VB-VL and started life in Europe as the "V" car platform. The VN chassis was terrible for rigidity and was gradually improved each model up to VS. That said, even the VS wasn't great.

Reaper

[m1lky]

So your saying the vibration from the high pressure hose was actually noticeable and was significantly reduced by adding a dampening weight? How'd you arrive at 270g? Trial and error or was there method to the madness?

That's what I was thinking.

Have you checked the obvious sources of vibration out first?
Rims are well balanced and aren't buckled. Tyres are good quality and in good condition? No play is suspension or steering arms?

[Shearer]

Which bit of that is incorrect or mis-leading? The VN-VS was built on the same platform that was the VB-VL and started life in Europe as the "V" car platform. The VN chassis was terrible for rigidity and was gradually improved each model up to VS. That said, even the VS wasn't great.

Reaper

Everyone knows the platform basis.

Improved in rigidity with each model?? Show me where in pictures

[Circlotron]

So your saying the vibration from the high pressure hose was actually noticeable and was significantly reduced by adding a dampening weight? How'd you arrive at 270g? Trial and error or was there method to the madness?

Very technical approach. Dug out the only bit of steel bar I had in the junk box and cut it to the max length that would fit tidily. Probably about double the weight would have been the ideal, but too much more would make it inclined to waggle in the breeze as the car went over bumps etc.