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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 »

Im confused! haha.

So assuming we are always talking about 1:1 gearbox ratio as that is 'Top' in the Conquest, I thought:

3.73 diff meant that the engine has to turn 3.73 revolutions to turn the wheel once.
and....
4.56 diff meant that the engine has to turn 4.56 revolutions to turn the wheel once. Meaning the 3.73 would have lower engine revs at the same road speed as the 4.56 diff?

Does the Roadster have a higher diff ratio because the roadster has effectively an overdrive ratio in top gear in the 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
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Location: UK

Re: Daimler Roadster Overdrive

Post by Brian-H »

According to the service manual there is no overdrive in any of them.

But yes I got it wrong way round, the lower roadster diff ratio gives the roadster longer legs in each gear. I guess it could do that because it was lighter.

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

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

Sorry I dont mean a true overdrive unit, but does the Roadster have a different gearbox with higher ratios in it?

I think someone suggested that top gear in the Roadster was geared to act like an overdrive i.e. a ratio lower than 1.
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
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Re: Daimler Roadster Overdrive

Post by Brian-H »

According to the service manual they all had the same 4-speed gearbox with same ratios.

Roadster is lighter by 3 cwt (150 kg)

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

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

Very interesting! might see if I can source a Roadster axle or diff and go from there as a test.

Not holding my breath though. I doubt they are easy or cheap to come by!
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
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Re: Daimler Roadster Overdrive

Post by Brian-H »

That overdrive is on a Special Sports (Peter Grant, end of page 1 of thread and into page 2). Special Sports is of the DB18/Consort range, so not a Conquest type, but chassis/engine of DB18/Consorts are not drastically dissimilar from Conquests. Special Sports ratios are 1st 3.0:1, 2nd 1.64:1, Top 1.00:1, O/D 0.73:1 with a slightly higher diff ratio than the Consort saloon (which had a 4-speed without O/D ratio i.e. 1st, 2nd, 3rd, Top).

So a Special Sports gearbox with a Conquest Roadster diff would be interesting.

All the other info I've given is in the Conquest service manual that I have (a true paper original). Note that there's someone selling them on CD on ebay btw.

Maybe I ought to scan the relevant pages ?

HenryC
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Re: Daimler Roadster Overdrive

Post by HenryC »

The 'best' option would be to go for the diff/axle from the DJ260 automatic Century. The ratio is somewhere between the Saloon and the Roadster.

I can't lay my hands on the ratio at the moment but I went through this process 3-4 years ago. The roadster ratio would be too 'tall' to push the Conquest saloon along at higher speeds.

It took me 2 years to get my hands on an axle from an automatic Century but I came across 3-4 in the process of looking. I was planning to fit it this year but haven't got round to it yet.

I'll look for my notes on the ratio.
Cheers, Henry Curwen
Registrar for Conquest & Century Saloons (DJ250/1, DJ256/7, DJ260/1)

Conquest (Drop Head) Coupe DJ252

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

Re: Daimler Roadster Overdrive

Post by Skinnerpot »

Hi Henry!

Thank you for the info and reply. So you have a DHC Conquest too?

Interesting to hear that you think the 3.73 diff would be too tall? from my calculations it would put the engine revs at 3220 at 70rpm which is a drop of 740rpm. I actually wondered if that still wouldnt be enough?

Being the 100hp version I felt that it would have enough grunt, ive always found it to be a very quick classic.

Trouble now is finding one from a roadster to try.....
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
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Re: Daimler Roadster Overdrive

Post by Brian-H »

The DB18/Consort Saloon only has 70 BHP and the DJ 250/1 Conquest Saloon only has 75 BPH, and with torque curves that fall away quite a bit after 2500 they would possibly struggle to reach and maintain 70 mph with a reduced ratio in either the diff or gearbox.

However, the DJ 252/3/4/5/6/7 all have the 100 BHP engine achieved by having a higher compression ratio and flatter torque so they would be ok I think, mainly because the torque is still relatively flat up to 3500 rpm

Note that there is no torque curve for the Special Sports but it's rated at 85 BHP and the handbook states 80 mph at 4500 in Top for that car, which is possibly why there is an overdrive for cruising at say 60 mph, possibly 70 mph ? (a Special Sports with an engine out of a DJ 252/3/4/5/6/7 would be a very nice car to have)

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