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Daimler Roadster Overdrive

Skinnerpot
Posts: 30
Joined: Wed Nov 21, 2018 9:23 pm
Location: Gloucester

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

Sorry to drag up an old thread! Peter did you ever fit an overdrive unit in the end?

I have a Daimler Conquest with the pre-select gearbox and am having the same issue. I love using the car for long journeys, but at motorway speeds it does sound stressed and it makes the journey less enjoyable.

I will soon be completing the Scottish 500 run and I will be starting from Gloucester - so the drive up to the start point will be over 500 miles before I have even started!!

Has anyone fitted one to a Conquest?
Is there enough room?
Do the O/D units bolt straight to the gearbox output shaft?
Is there a rubber coupling?
Is there a different diff that would fit in a Conquest axle to also lower the revs?

Cheers
An age when roads were empty, machines were simple and every journey was an adventure!

Daimler Conquest DHC (DJ252), Morris Minor, Ford Model T, Vandem Plas 1500, Reliant Drag Race Car, Nelson Steam Car, 4.5" Foden Steam Wagon

Peter Grant
Wise Man
Wise Man
Posts: 503
Joined: Thu Mar 10, 2016 10:02 pm
Location: Sydney, Australia

Re: Daimler Roadster Overdrive

Post by Peter Grant »

Hi,
No the Special Sports remains as per factory.
I was only musing about it, to fit a separate per drive unit wold mean swapping out the original gear box I think, not something I would do.
Cheers
Peter

Skinnerpot
Posts: 30
Joined: Wed Nov 21, 2018 9:23 pm
Location: Gloucester

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

Hi Peter,

Thank you for the update. How come you would need to swap the gearbox?

I am thinking about it for the Conquest but I am fortunate to have a lot of spare room under the car behind the box!
Daimler underneath.jpg
An age when roads were empty, machines were simple and every journey was an adventure!

Daimler Conquest DHC (DJ252), Morris Minor, Ford Model T, Vandem Plas 1500, Reliant Drag Race Car, Nelson Steam Car, 4.5" Foden Steam Wagon

Peter Grant
Wise Man
Wise Man
Posts: 503
Joined: Thu Mar 10, 2016 10:02 pm
Location: Sydney, Australia

Re: Daimler Roadster Overdrive

Post by Peter Grant »

Hi,
I think that because the Special Sports gearbox has an overdrive gear set up, while the Conquest does not.
Don’t think you can have an overdrive on an overdrive?
If a separate overdrive was fitted wouldn’t;t a 1m,2 3 T gearbox then be preferable rather that 1,2,T O ?
Cheers
Peter

Skinnerpot
Posts: 30
Joined: Wed Nov 21, 2018 9:23 pm
Location: Gloucester

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

Ah I see, is the Special Sports a Wilson Pre-Select too?

I wonder if they have the same rear axle and if there is a swap that can be done with diff ratios? Although I would prefer not to do this as I can imagine the very high geared 1st will be useful when I am towing the Model T and starting on a hill.

I was under the impression that the Conquest's top gear was direct drive so an O/D would be perfect for it.
An age when roads were empty, machines were simple and every journey was an adventure!

Daimler Conquest DHC (DJ252), Morris Minor, Ford Model T, Vandem Plas 1500, Reliant Drag Race Car, Nelson Steam Car, 4.5" Foden Steam Wagon

Brian-H
Very Wise Man
Very Wise Man
Posts: 1095
Joined: Fri Aug 09, 2019 6:04 pm
Location: UK

Re: Daimler Roadster Overdrive

Post by Brian-H »

In the Conquest service manual (General Information section) , all the Conquests (including roadsters) had the same gearbox ratios
1st = 3.84:1
2nd = 2.21:1
3rd = 1.47:1
Top = 1.00:1

It's the diffs that are different
DJ 250/1 (Conquest Saloon) = 4.64:1
DJ 252/3 (Conquest Coupe) = 4.56:1 (Alternative 4.11:1)
DJ 254/5 (Conquest Roadster) prior to chassis 90500 = 3.73:1 (Alternative 4.11:1)
DJ 254/5 (Conquest Roadster) after chassis 90500 = 4.11:1 (Alternative 3.73:1)
DJ 256/7 (Conquest Century) = 4.56:1 (Alternative 4.11:1)

From the above you can see that the Roadster has the bigger issue at higher speeds i.e. putting it another way, flat out on a motorway, all else being equal, the Conquest Saloon should achieve a slightly higher top speed than the Century, both achieving higher speeds than the Roadster.

But yes, for motorway driving today, I agree that the Conquests (and DB18's) are all under-geared. Depending on drag coefficient (and to a lesser extent, coefficient of rolling resistance) most cars only require 25 to 30 BHP at 70 MPH, so with the right diffs (or an overdrive positioned somewhere), they could all easily cruise at 70 MPH.

EDIT: re top speeds, wrong way round, see next posts
Last edited by Brian-H on Tue Sep 01, 2020 4:32 pm, edited 1 time in total.

Skinnerpot
Posts: 30
Joined: Wed Nov 21, 2018 9:23 pm
Location: Gloucester

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

So a roadster diff in a Conquest Century DHC should make a difference of 740rpm at 70mph! Did all the cars share the same axles?
Snip20200901_4.jpg
Snip20200901_5.jpg
An age when roads were empty, machines were simple and every journey was an adventure!

Daimler Conquest DHC (DJ252), Morris Minor, Ford Model T, Vandem Plas 1500, Reliant Drag Race Car, Nelson Steam Car, 4.5" Foden Steam Wagon

Brian-H
Very Wise Man
Very Wise Man
Posts: 1095
Joined: Fri Aug 09, 2019 6:04 pm
Location: UK

Re: Daimler Roadster Overdrive

Post by Brian-H »

Section H (page 3) of the manual shows the DJ 252/3/4/5/6/7 all have the same rear axle . But surely, putting a roadster ratio into any of the others is going the wrong way for lower revs at 70 mph ? i.e. a Century diff in a roadster would reduce rpm in the roadster
Last edited by Brian-H on Tue Sep 01, 2020 3:58 pm, edited 1 time in total.

Skinnerpot
Posts: 30
Joined: Wed Nov 21, 2018 9:23 pm
Location: Gloucester

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

Isnt the lower the ratio the faster it will go? for the same number of revs?

I thought its would be 4.56 turns of the pinion for every 1 turn of the axle? So a roadster axle only needs 3.73 of the pinion to turn the axle once. Difference with the roadster being a different ratio gearbox?
An age when roads were empty, machines were simple and every journey was an adventure!

Daimler Conquest DHC (DJ252), Morris Minor, Ford Model T, Vandem Plas 1500, Reliant Drag Race Car, Nelson Steam Car, 4.5" Foden Steam Wagon

Brian-H
Very Wise Man
Very Wise Man
Posts: 1095
Joined: Fri Aug 09, 2019 6:04 pm
Location: UK

Re: Daimler Roadster Overdrive

Post by Brian-H »

Yep you're right, roadster diff in a Century reduces Century rpm

So the roadster has the higher top speed, not the other way round :oops:
Last edited by Brian-H on Tue Sep 01, 2020 4:16 pm, edited 1 time in total.

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