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V8-250 3.54 diff conversion

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classiclife
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V8-250 3.54 diff conversion

Post by classiclife »

Hello.

I am considering, at some stage, replacing the current 4.27:1 diff ratio in my 1968 car (auto) with a more user friendly 3.54:1 crown wheel & pinion set. There are a couple of companies who provide this conversion service, but I'm always keen to do such work as I have a decent mechanical knowledge.

Have any owners carried out this conversion personally and if so how did you get on with it; straight forward or a gnashing of teeth ?? !!

Is there a particular vehicle I should be identyifying to obtain a 3.54 such as a "S" type, hopefully there are others to widen my search area ?? The other option would be to have a 3.54 manufactured.

I know I will need to recalibrate the speedometer but other than that nothing spring to mind.

Any information / experience on undertaking the job will be gratefully received.

Thank you in advance.

Regards.

Richard.
1968 Daimler V8-250 Saloon
DLOC East Sussex Branch Secretary
DLOC 2.5L V8 & V8-250 Registrar - https://www.dloc.org.uk/v8-250
DLOC 2024 International Rally - https://www.dloc.org.uk/rally-2024

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captain bobo
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Re: V8-250 3.54 diff conversion

Post by captain bobo »

Robert Grinter changed the ratio in his V8 250 rear axle. His car now cruises at speed at significantly lower revs. He advertises in the club magazine or you can google him, I'm sure he'd happily tell you what he did and how the car performs.
Best wishes, Dave B

classiclife
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Re: V8-250 3.54 diff conversion

Post by classiclife »

Hello Dave and many thanks for the suggestion - much appreciated.

As it happens I spoke with Robert, very nice chap, the other day and have advanced my enquiry somewhat now.

Best wishes.

Richard.
1968 Daimler V8-250 Saloon
DLOC East Sussex Branch Secretary
DLOC 2.5L V8 & V8-250 Registrar - https://www.dloc.org.uk/v8-250
DLOC 2024 International Rally - https://www.dloc.org.uk/rally-2024

silverdart
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Re: V8-250 3.54 diff conversion

Post by silverdart »

Hi Richard, I have not changed axle ratios, but I have rebuilt axles.

There are three important points to note. Great care must be taken to achieve the correct tooth contact, the min. backlash [ie. no less] and the preload setting on the drive pinion.

With these achieved you should be fine.

Dave.

classiclife
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Re: V8-250 3.54 diff conversion

Post by classiclife »

Hello Dave,

Many thanks for the info, much appreciated and very useful to know come the conversion.

All the best.

Richard.
1968 Daimler V8-250 Saloon
DLOC East Sussex Branch Secretary
DLOC 2.5L V8 & V8-250 Registrar - https://www.dloc.org.uk/v8-250
DLOC 2024 International Rally - https://www.dloc.org.uk/rally-2024

tjt77
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Re: V8-250 3.54 diff conversion

Post by tjt77 »

well..firstly there is a good reason that Daimler /jaguar chose the 4.27 diff ratio..the cars weight is heavy and the engines power and torque was matched axle ratio in order to provide what devlopment engineers calculated would provide optimum performance for normal average conditions on Uk roads.. . in actuality they started production with a 4.55 diff.. ratio was raised after premature engine issues caused by over revving .(high oil consumption among other things) ... top speed was limited by valve bounce.. early cars had issues that called for production changes.. increased valve to guide clearance.. and issues with pistons.. (never fully resolved.. but later cars went to a multi piece oil control tiring in an effort to reduce oil consumption)
The manual overdrive version came with a 4.55 diff also.. but the overdrive gives an 'overall ratio' of 3.54 when engaged..making for a much more relaxed gait than the manual cars ( and longer engine life to boot) a 3.54 diff on an auto gearbox car will make for really sluggish acceleration because there is just not enough power to haul the car 'off the line' fast.. and the car will struggle on hills too.. a far better compromise would be to fit a 3.77 diff from a Mk2 3.4 of 3.8 'manual overdrive' jaguar.. these are still fairly easy to find in UK and more common than the 3.54.. If you use the 3.8 manual overdrive axle you also get the benefit of the 'powr-lok' limited slip diff. which was standard on all 3.8s..
a far more sensible upgrade (which obviously is going to cost more..but well worth it) would be to fit a ZF4 hp 22 gearbox.(conversion kits are available in UK do do this) that way you retain the standard diff.. and gain a far taller cruising gear due to the 'overdrive' in the gearbox.. 3.9:1 would likely be the 'optimum' diff.. but this is not a common ratio in the salisbury 4HA axle.. Dana 44 gears can be adapted to fit though and are available in a number of different ratios.. ( the GKN/'Salisbury 4HA' is in actuality a UK made GKN /'Dana 44' axle )
BTW..its 'false economy' to just clean and fit a 'used' rear axle .. to do the job 'right' it is essential to replace all the oilseals before installing.. otherwise yo¨ are likely to encounter oil leaks.. those seals get very hard and brittle after 30-40yrs.. and simply cannot do their job.. an axle specialist can change them all out in less than 1 hour.. NOT a job to do at home as it requires special tools..

tjt77
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Re: V8-250 3.54 diff conversion

Post by tjt77 »

typo above.. I meant 'auto box' when referring to the overall ratios in comparing manual cars to auto cars .. non overdrive manuals used same ratio as auto :- 4.27.. the overdrive up's a 4.55 ratio to 3.54 'overall ratio' when engaged.. I have 4.27 axle in my manual/overdrive car (converted from auto) and its pretty much perfect as regards gearing for the roads in my area
Again.. a 3.45 diff on an auto car will make for very sluggish acceleration.. and it will really struggle on hills as well ..
You need close to 200ft lb of torque to pull a 3.45 diff 'off the line' on a car of this weight ... i.e... the power of a 3.4 or 3.8 litre jaguar engine.. the cars that had that ratio from factory..

classiclife
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Re: V8-250 3.54 diff conversion

Post by classiclife »

Mmmmm,

That's an interesting alternative suggestion with the 3.77, not interested in the ZF4 conversion.

I can certainly see the logic in this and one that perhaps I need to investigate further.

Would I benefit from a 3.8 "powr-lok" on my V8 auto, I do not know the answer to that and more than happy to hear advice / rationale.

Accept fully your advice regarding full axle overhaul - it's the only logical way and a golden opportunity missed if not done.

Thank you for your help, much appreciated.

Best wishes.

Richard.
1968 Daimler V8-250 Saloon
DLOC East Sussex Branch Secretary
DLOC 2.5L V8 & V8-250 Registrar - https://www.dloc.org.uk/v8-250
DLOC 2024 International Rally - https://www.dloc.org.uk/rally-2024

tjt77
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Re: V8-250 3.54 diff conversion

Post by tjt77 »

there is definite benefit from the 'powr-lok' diff.. especially on damp roads when pulling out of a junction etc.. it was standard fitment on Jaguar 3.8 litre cars.. an 'optional extra' on the others..

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