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TOPIC: Compound transmission ratios (revisited)

Compound transmission ratios (revisited) 19 Apr 2019 22:45 #200088

  • Dave_64
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Hi All,
Mate of mine recently retired and got interested in that 4X4 box I had converted and we're tossing up whether to have a go at engineering a light duty "compound or married" box as compared to my "divorced or island" transmission. Why? Can't help ourselves!
Anyway we reckon we have enough spare boxes kicking around, so reckon with a bare minimum of machining, virtually only an adapter plate and modifying the input tooth count into the rear box and using the existing gearsets we already have.
On paper came up with the following compound ratios:- Double underdrive or super low, 18.83:1, Underdrive or Low, 9.4:1
1st or starting gear, 6.68:1.........2nd, 5.41:1........3rd, 4.70:1.........4th, 3.34:1....5th, 2.70:1....6th, 2.34:1....7th, 1.66:1....8th, 1.34:1
9th, 1.00:1....10th, 0.81:1.
On paper there's a couple that are maybe a bit close together, 5th and 6th, also 7th and 8th, but at this stage thats all it is, an exercise on paper! Ratios are based on a standard NP435 Dodge/Ford 4 speed driving into an all-synchro "modified close ratio" NP445 Dodge.
Don't know how we'll go, but the assembled modified "island box" seems to be going OK so far, running an added electric oil pump.
Reckon if we have a go at a compound box may try and add an oil pump to the PTO drive somehow, has a std 6 stud SAE plate on either side.
This conversion has already been done in the States, have the US patent drawings here, but the bloke who wrote the plans and diagrams went to a lot of trouble to cut new gears, which gave his design a better spread of gears than we can get using existing gearsets. May never eventuate, but reckon it's doable with what we have here parts wise.
When I was building the original modified box, priced getting gears cut on a one off basis, hellishly expensive. So opted for a wider spread, which had the benfit of utilising standard gearsets, but had the drawback of limiting the actual progressive gears to 8 (9 including double underdrive) from a 4X4, virtually splitting each gear in the main with either underdrive and direct or direct and overdrive as the ratios were too close to each other.
Not worried about weight as it would probably only ever be used in a light hobby truck.
What do you reckon about the posted spread of compound gears above? Would be running something like a 4.5--5.5:1 diff ratio, on probably 7.50X16 tyres with engine RPM of max 3000, but top gear cruise RPM of around 2500 in O/D should sit on around the legal 100kph on the open road.
Dave

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Compound transmission ratios (revisited) 20 Apr 2019 01:01 #200089

  • Blackduck59
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Dave,
Depends on what you want to use it for and the torque of the engine.
With the Ford I used around 3.4:1 to start (4th in the RR), 3.31:1 final and 215/85/16 tyres (rolling radius of around 360mm).
Flat ground 3T of truck plus 3T of trailer and still start out in 3rd (4.38:1)
But have some 400 ft/lb of torque to play with
Cheers Steve
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Compound transmission ratios (revisited) 20 Apr 2019 01:30 #200090

  • BillyP
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All I can say is ,Dave , you are a glutton for punishment ……………Good on you ………..
………………….Billy...………………….
I came into this world with nothing & still have most of it..........
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Compound transmission ratios (revisited) 20 Apr 2019 03:48 #200091

  • Dave_64
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Hi Men! See? This is what happens when you retire and have far too much time on your hands! Sit in the shed looking at collected stock, dreaming up uses for it. That mate of mine is looking for a bit of a project vehicle, something with either a low tray or maybe a little tipper something he can throw a max of about 2 ton of split wood on to replace a bogie tipping towed trailer that he engineered his log splitter onto. Reckons he can scratch around getting enough firewood for a few friends and rellies, without making a commercial enterprise out of it. He mentioned something along the lines of a Dodge, Inter, Ford even a C30 Chevy with dual 16 or 17” duals. Something simple without going overboard.

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Compound transmission ratios (revisited) 20 Apr 2019 07:50 #200092

  • Swishy
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Cogs
M80
U ever thort of just using the standard cog box n chop down a 2 speed diff to suit
Jist a Thort
;)
cya
OF ALL THE THINGS EYE MISS ................. EYE MISS MY MIND THE MOST

There's more WORTH in KENWORTH
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Compound transmission ratios (revisited) 20 Apr 2019 09:43 #200093

  • Dave_64
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Did something along those lines years ago, shortened one side of a Ford F100 9” diff to fit under a CJ Jeep, moved the axle pads to suit, shortened one axle. Just as much ginning around and besides, utilises a wad of spares, keeping me out of the TAB and waterhole!

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Compound transmission ratios (revisited) 20 Apr 2019 11:51 #200100

  • JOHN.K.
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You could once get a two speed diff for a T Ford............and I remember small Inters ,probably D series (pre war) with a hand change two speed diff........the Mazda truck boxes with the splitter in the front worked good,but the split section was pretty weak,and you often see them busted.
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Compound transmission ratios (revisited) 20 Apr 2019 19:27 #200111

  • Mrsmackpaul
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Well I reckon it sounds like a challenge

And Im more than happy to sit and learn as you piece things together
I did have a similar thought once with my old heavy truck
Joining a 8 speed Clark to a 4 speed Spicer joey box
Thoughts were to drop the two speed high low off the rear of the Clark and then close couple the Spicer to the remains

Thankfully it never got any further than just thinking about it lol

Paul
Your better to die trying than live on your knees begging
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Compound transmission ratios (revisited) 20 Apr 2019 20:45 #200115

  • Dave_64
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MrsMack, gather that combo in the Diamond T? You’d have plenty of length between the back of the Spicer and input to front diff/power divider also? Besides, little bit of power loss hardly noticeable? Did you end up with 2 lots of O/D , or was the 4X2 splitter a direct box? Just curious, if not worried about weight or taking up critical space, at least never run out of gears.

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Compound transmission ratios (revisited) 20 Apr 2019 21:21 #200116

  • Morris
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The two speed rear axle for the Model T Ford was called a Ruxtell axle. That was probably the maker's name.

I will ask my Inter owning mate when I see him in a couple of days, about the hand change two speed in the 1930's D series and let you know if he knows anything about them.
I have my shoulder to the wheel,
my nose to the grindstone,
I've put my best foot forward,
I've put my back into it,
I'm gritting my teeth,

Now I find I can't do any work in this position!

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