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2 overdrives?


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Has anyone though about the possibility of adding overdrive to overdrive?  Not at all sure about the way it might work.  But a short length of splined shaft to replace the output shaft straight into the next overdrive, perhaps?  And if it would,  just bolt the flanges of the 2 together or an adapter plate?  Might need to move the handbrake to the back seat.  That won't matter as they seldom do much any way on heralds/vitesse.   0.8 x 0.8 = 0.64 reduction in revs for economic cruising.

 

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Given the extra length/width of the overall gearbox unit you'd end up with and resulting chassis mods I can't help thinking fitting a modern 6 speed gearbox would be a similar cost/effort option with better results (like being able to buy a replacement gearbox for less than the cost of one of the O/D units if anything went wrong).

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46 minutes ago, Prince Brainier of Meccano said:

Might need to move the handbrake to the back seat.  That won't matter as they seldom do much any way on heralds/vitesse.

If you do MOTs it will have to work and would they accept the new location? It’s bad enough adjusting them let alone hacking the cables and mountings about.

Doug

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I think that will require re-modelling of the g'box tunnel to accommodate the 2nd OD. Even the ORS self contained jobbie will need somewhere and there's little or no room between the chassis arms down there. (We are talking Herald, Vitesse or other small chassis, aren't we?) The Borg Warner T5 gearbox is available with a really tall 5th gear - that might be an option.

Cheers, Richard

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4 hours ago, dougbgt6 said:

If you do MOTs it will have to work and would they accept the new location? It’s bad enough adjusting them let alone hacking the cables and mountings about.

Doug

And if you're MOT exempt but make a change that WOULDN'T pass an MOT I'd say you're NOT maintaining it in a "roadworth condition", so not eligible for the MOT exemption.

I'd also question if this would count as a "substantial change" or not, which could again invalidate the MOT exemption.

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32 minutes ago, Mjit said:

I'd also question if this would count as a "substantial change" or not, which could again invalidate the MOT exemption.

I don't want to start the slippery slope... again.. but weren't owners claiming that modern gearboxes were an essential upgrade as the originals weren't available any more? 

Anyway if you put the two overdrives on, but in opposite directions, so that one cancelled out the other, couldn't you just claim it was non-overdrive? :)

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6 hours ago, Pete Lewis said:

its a heck of a lot easier to change the diff for a higher ratio  

how you would tandem a 2nd OD on the back of the former is not meccano 

Pete

Having looked at the diagrams of the guts it is indeed a bit of a job.  I thought all the epicyclery went on in the parallel section but it extends into the cone bit at the back as well.  Shame.  I was quite looking forward to some fun.  As to the meccano comment I remember in a hot car mag from the 70s a boy racer asking for advice on bodywork mods.  He finished with the a statement "I'm quite good with a hack saw and dreadnaught file as I've done a hairdressing apprenticeship."  You have to admire a tryer.

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so get an auto box about the same length  as one Overdrive much less hassle 3 times shorter  

using a overdrive on low gears is restricted as the torque would overcome its design .

TR use it in 2nd gear but thats with an A type , different kettle of fish to the D types used on small chassis ,

and J type probably has the same limitations ,   

pete

 

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1 hour ago, Pete Lewis said:

TR use it in 2nd gear but thats with an A type , different kettle of fish to the D types used on small chassis ,

We put 2nd gear overdrive on my brother's Mk2 Spitfire with a D-type. I know all the torque arguments but, having checked the figures, I concluded maximum torque from a Mk2 Spitfire in 2nd is about the same as a Vitesse in 3rd, and the factory allowed that on a D-type so it's probably fine.

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Nobody has mentioned that a 4 cylinder car would struggle with 0.64 or similar gearing. (I remember somebody trying a 3.27 diff with overdrive on a 1300, hopeless)

It may just work on  a 2 litre and a 2.6 would be ideal *you could use a 3.89 diff, so brisk acceleration and a relaxed cruise) 

Very lows revs at 70mph is not everything. And is unlikely to help economy much. Kipping did lots of real-life research on economy, and found long ratio diffs didn't help.

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True, but amusing to see people keep trying ideas that are doomed. 

The thing that amuses me is an obsession with many owners to be able to drive with the engine doing little more than idle speed. As if 4K will kill an engine (it really won't) And there is a 3 way aberration. The same people often don't ravel long distances. And thirdly have also stuck a variety of performance mods to make the car more powerful. Nuts.

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Seems to be current trend we were in Taiwan for our sons wedding and his father in law arranged one of his chauffeured cars to take from Taichung to Taipei 2hrs freeway driving.

The young driver had a Merc 250 which did 1500rpm at 110kph it was raining like hell 2in on the freeway what a great driver he was maintained speed without getting close to any other vehicle

By comparison our Jag does 2100rpm at 110kph

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Indeed, modern diesels trundle along at under 2k rpm quite happily, but have 3-4 times the torque of a triumph 4 cylinder car, and at those revs probably 5-6x. 

The Triumph factory bods got the gearing pretty well accurate for the cars, as proved by kippings research. 

On my present car, I have fiddle with diff ratios. In its previous iteration, it would pull a 3.7 diff quite happily, BUT, and it is a huge but, changing from 2nd-3rd, or indeed 3rd-4th, if you were approaching the red line and changed gear, you were out of the power band and it felt odd. A change of diff to 3.9 sorted that. I guess I could have used bespoke gearbox ratios, but that gets expensive very quickly. Latest engine has a much broader power/torque spread, so changed back to 3.7 which is a really good ratio. Will cruse at 5k+ rpm all day (that's bang on 100mph, trouble is the fuel gauge seems to visibly move at that speed)

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Like Peter and Clive  I think this move to more road speed for less engine speed comes from modern vehicles.

People are not used to engines doing high revs.
My VW Amarok 420 BiTDi rarely goes above 2000rpm and at our strictly policed 100kmh speed limit it doesnt get much chance.
And it has the amazing ZF 8 speed autot hat is found in may  modern cars.

This is all to make engines more efficient and with a narrower clean economical band.

 

Adrian

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22 minutes ago, ahebron said:

Like Peter and Clive  I think this move to more road speed for less engine speed comes from modern vehicles.

I don't think that's true. It was very much a thing when I first started driving Triumphs, back in the 1980s. Most modern cars of the time were not geared any longer than my Mk1 Vitesse - in fact the Rover 214 (same power, same weight) was nearly identical and the 216 was even shorter. The big difference was that both the Rover K-series and the Honda unit would rev smoothly and quietly up to 7000RPM (the Honda could even go higher) so it didn't "feel" as if you were screaming the nuts off. Granted the diesels and the 820 turbo were long-geared... almost the same as a 2500S, in fact.

My daily driver - a 1.8 Mondeo - is geared very similarly to the Spitfire 1500. It doesn't feel short-geared only because it's a moderately revvable engine (nothing like the Honda ones but much smoother than the 1500 Triumph lump) and has lots of attention to NVH.

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An overdrive x 2 sound like more trouble than it's worth both in the short term fitting it and the long term dealing with it. A diff change is the best way to go. Back in the John Kipping days he offered, if I remember correctly,  a J type conversion with 25% reduction in gearing. 

For road use a broad torque engine is easier to live with, as are lower revs on a dual carriageway.

Dave  

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