Calling all vibration detectives?

vince · Unread post by **vince** » 29 Jun 2009, 22:54

Tonight i finally got the rev counter working with a new sensor

Since owning the car it has never worked so i have driven "by ear" and it seems rather conservatively

Once completed, I went out for a spin on the motorway using the rev counter to see how many revs the car was doing when i reached the maximum speed ive ever taken it (90mph)...it was just over 3000rpm.

Then i pushed a little harder

......the car drives faultlessly and always has apart from a slight knock when going over speed bumps or down pot holes. This i presume would be either anti roll bar links, or arm bushes...? Anyway....i decided to drive the car using the rev counter and pushed it to 4000rpm...doing about 100mph. Now, when i backed off the accelerator without touching the brakes, it suddenly felt and sounded like i was driving over a lightly cobbled road....ie like the road was a bit lumpy with some feedback coming through the steering wheel and the accompanying vibration noise this would cause.

Once down to around 90mph and lower it stops....

It doesnt do it at lower speeds, and it doesnt / didnt do it when accelerating even up to 100mph....ie not when the power is on.

Now normally id go for control arm bushes, but these tend to wobble under braking from high speed (which doesnt happen) or wheel balancing...but then that would happen before that speed. Driveshaft wear would also happen before that speed, and a knackered CV Joint would usually groan when the gas is lifted off and again even at lower speeds.

It is worthwhile saying that the box remained smooth and the engine seems smooth also...so im looking for someone who has experienced this before and found the cause....

If it cant be found, im not hugely bothered as i dont ever drive that fast or have any need to....i want my rev counter to work so i can strive for better economy.

Any ideas guys?

Unread post by **RichardW** » 30 Jun 2009, 07:53

I had a hideous overrun vibration on my VSX that I thought was the front end about to fall in half - turned out to be an out of round tyre - eventually worked it out when I found it had a near bald spot on it, about 2" wide and 6" long, about 2" from one edge, when the rest still had 4mm or so on it

Can never have been right from the day it was made! Also had weird vibration noise from a failed track rod end that took me ages to track down.

citronut · Unread post by **citronut** » 30 Jun 2009, 09:12

you NAUGHTY BOY Vince TEA HE,

seriously though i would be very carefull statting those sorts of speeds especialy when you no BIG BU***R (BROTHER) almost certainly could pick up on it

regards malcolm

Brigsygtt · Unread post by **Brigsygtt** » 30 Jun 2009, 13:23

Id say balancing or duff tyres.

vince · Unread post by **vince** » 30 Jun 2009, 20:53

Thanks guys, it is interesting you should mention tyres because you would have thought that it would be an issue at lower speeds also...?

On and Malcolm, im not worried about the speeding thing because i dont speed normally it was a one off.....no honestly...

I usually travel at 70mph tops due to fuel economy and plus i read somewhere that we are allowed a 10% increase for overtaking manouvers and speedo's always read over usually by about 5mph at motorway speeds anyway?

I gave up my speeding days a while back when i sold my T5 Volvo within which i did do some silly speeds

I fell out with the idea when looking over at my wife and kids at well into 3 figures and thinking "what if i had a blow out"?

Neilsouth · Unread post by **Neilsouth** » 30 Jun 2009, 21:10

vince wrote: I gave up my speeding days a while back when i sold my T5 Volvo within which i did do some silly speeds

I'm selling my mr2 turbo though i've not given up on speeding days lol , just need something reliable and good on fuel. Till my money situation is better! , mr2 turbo's are not cheap to run

Unread post by **Peter.N.** » 30 Jun 2009, 23:27

Could possibly be worn inner drive shaft joints, tends to be worse when the engine is hot.

vince · Unread post by **vince** » 01 Jul 2009, 21:25

Hi Pete....on just 122K miles?

I must say i have never been asked for these since joining GSF a couple of years ago. We usually come across most faults in our line of work....

How can they be tested by the home mechanic? if at all?

Unread post by **Peter.N.** » 01 Jul 2009, 22:30

My experience comes from a CX estate I had many years ago and I must admit I have never had to replace them in anything else, that had probably done 200k or more at the time, but after trying everything else - that's what it turned out to be. When it was cold and the grease was thick, no problem, it didn't start to vibrate until it was well hot. If you took the joints apart you could see the wear point.

Xantidote · Unread post by **Xantidote** » 03 Jul 2009, 00:12

Hi Vince, not really part of your original thread, but you suggested speedos over-read. If a speedo is not going to be spot-on, then obviously better designed to ensure they over-read, and good for the ego.

However, my Xantia's speedo under-reads, according to the satnav (and a friendly policeman whom I overtook in a 30). Basically under-reads about 1-2 mph at 30 and 2+ at 60mph - not explored higher speeds. Runs on standard steel wheels & tyres.

Cheers - Martin