Vibration under acceleration

vipergts · Post by **vipergts** » Tue Aug 18, 2015 8:19 am

What could this be.

Can feel it through the seat but only properly at about 50 onwards when it becomes more intrusive but very much so when accelerating.

Obviously not wheel balancing plus wheels and tyres have been changed.

Could it be prop?

christopher storey · Post by **christopher storey** » Tue Aug 18, 2015 8:40 am

Propshaft is usually throttle sensitive and frequently shows by blurring the rear view mirror i.e. it is a high frequency vibration . Why not wheel balance ? Particularly the rears again often can be felt through the seat

mark10337 · Post by **mark10337** » Tue Aug 18, 2015 8:54 am

Is it revs sensitive or speed sensitive?

e.g. if above 3000 revs in any gear you always get it, it is probably prop/drive shaft related. Check simple things like the bolts on the prop shaft ends are tight. I've seen them become loose and cause this.

If it is above a certain speed rather than revs, more likely to be wheel/tyre related. If you feel it through the seats, rather than on the steering wheel, it could be wheel alignment or suspension related.

Gfhug · Post by **Gfhug** » Tue Aug 18, 2015 9:50 am

Mark, forgive me for disagreeing, surely the propshaft rotation is directly related to road speed not to rpm, 3000rpm in third has lower prop rpm than 3000rpm in fourth. It would certainly be worth checking whether changing down and maintaining speed changes the vibration.

Geoff

mark10337 · Post by **mark10337** » Tue Aug 18, 2015 10:15 am

Hi Geoff

Surely they are all related to each other.
Engine - gears - prop - diff - drive - wheels
just with different ratios.

So there is always a correlation between RPM and prop / drive etc. as well as prop to road speed.

I fully agree, the prop will be turning at a different speed at 3000rpm in third and fourth. What I was trying to highlight (perhaps poorly), was in the past I have seen that the connection between the prop and diff had been loose that showed up roughly over e.g. 3,000. depending on the gear selected it did move a little, but not as much as by road speed.

Hope that made it a little clearer.

PeterCrespin · Post by **PeterCrespin** » Tue Aug 18, 2015 10:35 am

mark10337 wrote:Hi Geoff

Surely they are all related to each other.
Engine - gears - prop - diff - drive - wheels
just with different ratios.

So there is always a correlation between RPM and prop / drive etc. as well as prop to road speed.

Nope. Geoff is right.

Prop speed is only 'always correlated ' to road speed and factors 'downstream' of the gearbox output shaft. You could have a 3000rpm diesel under the bonnet or a 19,000 rpm Formula 1 engine - or no engine at all - and the correlation would remain identical.

Pete

Quattrofrank · Post by **Quattrofrank** » Tue Aug 18, 2015 10:58 am

I had the same issues as yourself. Tried changing everything but in the end it turned out to be loose bolt at the propshaft to gearbox flanges in addition to a worn out u/j at the propshaft.

Only noticable when accelerating or crusing uphill, if I put in in neutral or pressed the clutch it would disappear

mark10337 · Post by **mark10337** » Tue Aug 18, 2015 11:08 am

Excellent. I'm glad you found the problem.

And thanks to Peter and Geoff for correcting my perception of the propshaft.

Now if only I could work out where the noise is coming from on my backend :)

vipergts · Post by **vipergts** » Tue Aug 18, 2015 2:34 pm

Thanks Guys

It's not engine revs related and it's definitely not a wheel balance issue as the problem is identical with brand new set plus it's doesn't behave like that. I feel it's always there even at a lower speed but obviously the faster the car is travelling the more prominent it becomes. For example accelerating in 3rd and I feel it progressively more, swap into fourth and carry on hard accelerating and it continues to increase, If I step of the gas the vibration is still there but not nearly as harsh. So I agree, can only really be output shaft backwards. You have given me some stuff to check, first being prop nuts and UJ's

Many Thanks

David Oslo · Post by **David Oslo** » Wed Aug 19, 2015 12:58 pm

It might be what I have on my car. New tyres, all nicely balanced with adaptor cones from Fosseway, I was supervising the guys when they did it, all came out at zero on the machine. But, I have a vibration that comes in through the seatback, and it actually easiest to see when I have one of my kids in the front seat. Due to their lighter weight they bounce up and down on the seat foam, visibly, even although it is only an ever so slight vertical movement.

The vibration comes and goes when driving on twisty roads, or after roundabouts, junctions, etc.

I identified the problem to be the wire wheels being slightly out of round. This doesn't stop the balance machine from getting them into (near as damn it) perfect balance. But when you put them on the car you have in essence four eggs (or elipses). And they can be in phase or out of phase, or somewhere in between. This explains why it seems to come and go when on twisty roads, roundabout and traffic lights with sharp turns - the wheels are going into different phases. So the vibration can apparently dissappear for a while.

I've spun the wheels with the car jacked up and can see the "out of round" on the rim. So I'll be adjusting the spokes this winter, got nothing to lose by trying.

andrewh · Post by **andrewh** » Thu Aug 27, 2015 1:25 pm

Lee I have the same wheels as you and feel my wheels need re truing at MWS maybe we should stuff them all in that big black truck of yours and see what they say. Mine vibrate at 80 mph upwards

Post by **Heuer** » Thu Aug 27, 2015 1:46 pm

I had a set of MWS wheels serviced by MWS because of loose spokes - ?100 each + VAT! They have really lost the plot - try Dayton.

andrewh · Post by **andrewh** » Thu Aug 27, 2015 1:53 pm

Ok. Thanks David I will look into that. does one need to remove the tyres to true them?

Post by **Heuer** » Thu Aug 27, 2015 3:18 pm

Yes, and pretty much a specialist job but you will be giving the wheel back to the people who did it wrong in the first place.

You could also try Turrino or Borrani. I think I may have a similar problem to you on my FHC which has MWS wheels.

vipergts · Post by **vipergts** » Thu Aug 27, 2015 3:53 pm

andrewh wrote:Lee I have the same wheels as you and feel my wheels need re truing at MWS maybe we should stuff them all in that big black truck of yours and see what they say. Mine vibrate at 80 mph upwards

Two different sets of wheels though Andrew.....same vibration

Post by **Heuer** » Thu Aug 27, 2015 5:06 pm

I think you will be lucky to find any set of MWS wheels running true! Should be fairly simple to test though. Set up a dial gauge with the pointer against the rim and gently spin on the hub. ?15 on eBay:

christopher storey · Post by **christopher storey** » Thu Aug 27, 2015 6:01 pm

In fact, David, you don't really ( for these purposes ) need a dial gauge. Any fixed pointer will do which you set to the outermost part of the rim, and then rotate it . The run out can then clearly be seen and if need be measured with a rule

David Oslo · Post by **David Oslo** » Sat Aug 29, 2015 9:21 am

Knowledge base, 13 Wheels & Tyres:

http://dl.dropbox.com/u/8496016/Service ... 0Tyres.pdf

page 6 and 7 explains how to check, true, replace spokes etc.

allowable tolerance is +/- 1,5mm (1/16") from the nominal, in all three axis

vipergts · Post by **vipergts** » Sun Nov 08, 2015 5:17 pm

Just to put a lid on this

I concluded it MUST be the Prop out of balance

Replaced it as it was only ?180 rather than send of the existing one for balancing.

Job done....drives beautifully......It's a different car

jagwheels · Post by **jagwheels** » Sun Nov 08, 2015 6:14 pm

Can the prop be changed with out taking out the engine. I think I have the same problem

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