12 replies to this topic

[Steve77]

My N15 Pulsar has a slow pulsing vibration, about once per second or a bit quicker. It only happens between about 28 and 32 km/h, and is worst at 30km/h. It happens both in gear and in neutral, regardless of whether the brakes are applied or not.
It's not noticeable most of the time, but if I have to stay at 30 km/h for any length of time in slow traffic it's very noticeable, and bad enough to rattle my car keys a bit.

I'll have to take it to a mechanic soon, but just wondering if any of you know what could be wrong with it?

[Big_Valven]

A few possibilities:

• Warped brake rotor and sticking caliper
• Worn engine mounts causing lurching as the engine rocks (not necessarily since you say it happens in neutral)
• Sticky handbrake cable / calipers / mechanism

That's off the top of my head...

[Steve77]

Thanks BV. It shouldn't be the rotors, because they were machined 3 or 4 months ago. Also there is none of the usual pulsing at higher speeds while braking.
Hmmm I just hope that whatever it is, it's not too expensive to fix

[Lunchbox.inc]

Steve77, on 20 July 2011 - 10:51 PM, said:

My N15 Pulsar has a slow pulsing vibration, about once per second or a bit quicker. It only happens between about 28 and 32 km/h, and is worst at 30km/h. It happens both in gear and in neutral, regardless of whether the brakes are applied or not.
It's not noticeable most of the time, but if I have to stay at 30 km/h for any length of time in slow traffic it's very noticeable, and bad enough to rattle my car keys a bit.
I'll have to take it to a mechanic soon, but just wondering if any of you know what could be wrong with it?

considering you say it's happening both in, and out of gear, that takes the driveline out of the equation... kinda... could still be the issue, but for the obvious stuff, we'll look elsewhere...


my 1st instinct was to say your tires... specifically your fronts... could simply be off balance... usually the problem gets worse the faster you go, but i've had pulsing @ 75-85kph before and barely anywhere else... could also be quite worn, especially if the car has some toe/camber issues, eg wearing the inside of the tire significantly...

another option could be your tailshaft/drive shafts, this is a BIG spot for vibrations, you could have a work uni or center bearing, with uni's you'll generally hear a nice clunk when you put the car into gear/release the clutch, especially from a drive gear to reverse... the center bearing you'll generally notice more when the car is under a higher load... so accelerating in a higher gear etc (just noticed you said a pulsar so FWD, ignore this bit as it's more for RWD cars)

i've heard of worn shockers causing vibrations at certain road speeds before, but this is getting less likely, as it sounds to me as if a moving/rotating part of the car is causing the issues...


and now to REALLY stretch the possibilities, you could find that at certain speeds, the frequency of the vibration (remembering anything that vibrates, has a frequency it's doing so at) could actually be super closer to the resonant frequency of the car it's self... i know this soulds far fetched, but my corona made this horrible droning @ 110kph, we got the termlab in the car and it was 108db @49hz or close enough, which is roughly where the cars peak frequency was, speeding up or slowing down slightly, would change the speed of the pulsing warble like vibration...

this showed that some part of the car was vibrating in almost complete harmony with the frequency of the car, and changing a few hz would create the warble...

altho i doubt this is the issue here, as i've never known it to be an issue before for anyone else, i thought it was interesting enough to post up lol

[Steve77]

yeah i had wondered about the tyres too, but i assumed (maybe wrongly) that if they were out of balance the vibration would get worse as speed increased.
The fronts are fairly worn and need to be replaced soon, but they are evenly worn - no excessive wear on inside edges. Still, they haven't been balanced for over 18months/30,000 km, so maybe that is the problem.
Could also be a drive shaft. I'm hoping its the tyres because they need replacing anyway

[Captn_Awesome]

could be bearings.
But I'd bet a balance issue - quite often they get missed because you can drive through them at "normal" speed.
Other than that I dont know a lot about FWD cars and their steering geometry to make too much other assumptions

[ubernoob]

I'd go with tyres too, have you checked for marks on the rim to see if a balancing weight has let go recently, both the glued and clamed types fall off occasionally.

[Steve77]

Found the problem, the driver side front wheel is out of balance. When I swapped it for the spare wheel the vibration stopped. It's now a bit smoother at higher speed too, though the main problem was at 30km/h. I'll get them all balanced soon when I have time.

But now I have another question. The out of balance wheel has weights at 3 different positions, a total of 100 grams. That seems like a lot of weight to me - my car's other wheels have a lot less weight, and only in one position.
Does that sound abnormal? Like maybe that wheel has been very difficult to balance in the past, maybe a manufacturing fault in the tyre or something?

[The Toad]

Steve77, on 02 August 2011 - 11:41 PM, said:

Found the problem, the driver side front wheel is out of balance. When I swapped it for the spare wheel the vibration stopped. It's now a bit smoother at higher speed too, though the main problem was at 30km/h. I'll get them all balanced soon when I have time.

But now I have another question. The out of balance wheel has weights at 3 different positions, a total of 100 grams. That seems like a lot of weight to me - my car's other wheels have a lot less weight, and only in one position.
Does that sound abnormal? Like maybe that wheel has been very difficult to balance in the past, maybe a manufacturing fault in the tyre or something?

If ballanced correctly there should be a wheel weigh/weights on both inside and outside of the wheel, however the weights should only be in one place on the wheel. Not three.

Weights in different parts of the wheel is incorrect and acts as a counter ballance.

Take it in to your local tyre store and get all four re ballanced.

[ubernoob]

You can't always get a whell and tyre balanced correctly with the weight in just one spot, if is done old school(static balance) or if it is done on a newer dynamic balancing setup they may have to put weights in a couple of locations especially if the rim has had some sort of previous rough treatment.

When they balance your rims just ask if any were buckled, one of mine has a bit of lateral runout but it balances fine.

[The Toad]

ubernoob, on 03 August 2011 - 10:38 AM, said:

You can't always get a whell and tyre balanced correctly with the weight in just one spot, if is done old school(static balance) or if it is done on a newer dynamic balancing setup they may have to put weights in a couple of locations especially if the rim has had some sort of previous rough treatment.

When they balance your rims just ask if any were buckled, one of mine has a bit of lateral runout but it balances fine.

If your placing Weights in multiable locations on the wheel, then you create a counter ballance bias. Sorry, but If there not in the same location on the wheel then its not being done correctly.

[268669♫]

I've had a couple of badly buckled wheels and they were unable to balance them. Had the same effect as you describe but at anything over 70. New rims were required.

Ant

[ubernoob]

The Toad, on 03 August 2011 - 10:49 AM, said:

If your placing Weights in multiable locations on the wheel, then you create a counter ballance bias. Sorry, but If there not in the same location on the wheel then its not being done correctly.

OK, nice one , I stand corrected.