Prop shaft and overdrive Vitesse 2.0

[Bobo63]

Hi all, getting to the end of the show season, so consider it’s time to sort the prop vibrations. Think the consensus of opinion when I first mentioned it, is to get a new prop. We fitted new joints and it helped, but it obviously out of balance as well. Before jumping in and buying a shaft, is there any way of fitting an overdrive or altering the gearing.? Car is mk1. Any more than 50mph seems to be reviving like hell. I know our MGB od makes a huge difference. Any ideas welcome.

[Pete Lewis]

you can convert the gearox to add an overdrive but you have to strip the box and replace the mainshaft

then theres a relay for D type  no relay for a J type  the chassis   mounting plate and rear mount together with a shorter propshaft and a coulmn switch

the gear remote needs the front cam to operate the inhibitor switch etc.

but its quite doable 

as  another idea  a lot simpler to swap to a 3,63 diff 

Pete

[chrishawley]

Where to start?

In the original setup at 2.0 Vitesse without overdrive would be operating at 4100rpm at 70mph. Subjectively that can sound markedly 'fussed' to  modern ears: With overdrive 70mph would be 3300rpm. Far more modest. Originally both od and non-od Vitesses had the same differential ratio of 3.89. So at lot be be said for overdrive. I have experience of having added o.d. to formerly non o.d. Spitfires and GT6s to great advantage in both cases.

Another line of thinking is to put a 3.63 diff (ex Spitire 1500) in place of the 3.89 diff.  Although not quite a straight swap such would be feasible for must less cost and effort than replacing the existing gearbox with an o.d box and its acompanying overdrive. But not such a great effect: 70mph would now be 3850 rpm - still pretty whizzy. A greater effect would, in principle, be had by using a 3.27 diff from an non od Triumph GT6.  But never plentiful they are now very rare and hard to get hold of. In any case this might be a step too far and make the car feel boggy in lower gears.

Before embarking, might it be an idea to check on a road test what rpm are being obtained at 70 mph (or calculated by proportion at a lower speed)? I'm wondering whether it's possible the car has picked up a 4.11 differential ratio sometime in it's life in which case that would be a (probably quite unpleasant) 4350 rpm at 70mph.

[Nigel Clark]

The easiest way to convert to overdrive is to buy a complete gearbox and overdrive from another Vitesse or GT6. However, these are quite rare and therefore expensive now. I sold a sound GT6 gesrbox with overdrive last year for £400, and should perhaps have asked more.

You will also need the switch gear, wiring and a shorter prop shaft to complete the conversion.

Nigel

[johny]

Another possibility is to not drive at 70mph. I find wind noise to be a major factor in a Vitesse so 50 - 60 is my preferred speed and the sound from the engine is much more acceptable even with the standard axle...

[trigolf]

I'm part way through the same prop vibration issue investigation on my Vit. A brand new prop reduced vibration, but I also noticed an improvement after swapping the wheels around ( original fronts to rear). So a wheel rebalance is worth trying intially. I have also discovered a specialist company near Bicester- Vibration Free- that specialise in all aspects of vehicle vibration elimination.(engine and transmission). Speaking to their boss (Steve), I have confirmed that they routinely balance props on the car. It's not cheap (what is nowadays), however, I think much safer and quicker than pratting about with jubilee clips under the car!

[Pete Lewis]

dont forget any vibrations the frequency is dependant on rotational speeds the prop frequency is related to engine revs  the wheel and drive shafts arein relation to the diff ratio  so wheel related are around 4 times slower than the prop   

so any vibration is  a va va room   or  a  wibble wobble  should give you a clue   

dont discount bent drive shafts   always worth run on a jack/stand and at idle observe the rear trunnion is not getting a good wagging 

Pete

[Pete Lewis]

just to add a prop  will make the whole body 'live' at a variety of speeds 

wheels and shafts give it a more  of  wobble around 45/50 mph 

if really bad dont discount a failed tyre banding .looks fine till you apply torqure then the tread flops around  in an alarming way .

and to add  more  excess Toe  be it front or rear can make the suspension kick as it keeps correcting 

Pete

Edited August 17, 2023 by Pete Lewis

[daverclasper]

On 17/08/2023 at 07:54, Pete Lewis said:

dont discount bent drive shafts   always worth run on a jack/stand and at idle observe the rear trunnion is not getting a good wagging 

 

Hi Pete.  Assume that's with wheel off and jack under the upright?

[Pete Lewis]

why take the wheel off        just raise the car 9jack /stand on the diff x member    put in gear at idle   and watch  that all is rotating nicely no wobbles   

if the shaft has a bend  you will see the trunion do a wobble as the shaft turns    and you  can view wheel tyre runouts 

easy

pete 

Edited August 18, 2023 by Pete Lewis