Confessions of a compulsive tinkerer.

Daveman
Gudday M8

I can rehash the # ifn U can supply:

Tyre size (as the speed is calculated on tyre loaded radius)

Diff Ratio :1

Engine RPM ( Governed or max desirable RPM )

n R the Cog Box ratios Correct

cya

Swishy,
Unsure if this is the right way to do it, but I measured a 31" X 10" X 15" tyre with a dressmakers tape and the outside circumference comes out at just on 95 (ninety-five) inches The tyre is roughly half worn out , say 50%, and that would be the length of distance the wheel would turn in ONE FULL revolution
Standard unaltered diff ratio is 4.10:1
I am working on 2500 max desirable RPM
Went back over the ratios and I am pretty confident I have them right:-
7.93---4.56---3.96---2.28---2.10---1.74---1.21---1.04---1.00---0.86:1
And thanks for going to the effort, Cheers,
Dave

Here Go Dave
Me jist on the way out the door can xplain L8R

https://lh3.googleusercontent.com/onIZUWp6I3ungy9_7zFU627YFyk7PanIAMHsPuDiPjzu-IeZvfo=w601-h393-no

cya

Dave RE: Part 2
Back again ........ took the HandBrake out fir 'T'

:lol:

your collection of gears has not much in the way of evenly spaced gears so U can progressively change gears
a cupla gears R lookn fir over a 1000 rev drop n nuther only 96 rev drop..... it would keep U on u're toes remembering wot gear u're in n how fast to change depend n on gap B tween them cogs

the 2nd part of chart shows a cogbox available wiff the 1st lot of Kenworths in Australia ovr 50 years ago
they were progressively changed with not a lot difference in rev drop
jist to sho U wot can B achieved .... but this is for big wagons way back wen

the combination of gears U sho. ..... R they in the one box or R U swap n 2 stik to achieve the result
any chance can U put up all the ratios BTween boxes

Cya

Hi Swishy,
Thanks for the relevant info. OK, here goes. Two individual fully self contained transmissions.
Transmission (A):- !st-4.56:1---2nd-2.28:1---3rd-1.21:1---4th-1.00:1
Transmission (:- 1st-3.48:1---2nd-1.74:1---3rd-1.00:1---4th-0.86:1.

I simply multiplied each ratio in ( by each ratio in (A). Theoretically, you could have 16 individual ratios, BUT there are some way too close to be of any real value, some overlap.
As previously stated, this started life as an exercise on paper. I got to the stage where I wanted to see if it was feasible, using up as many parts as I could from what's laying around here.
The input housing(for the 2nd transmission) has been completed and awaiting pick-up early next week. I used the Spicer 7231 as a 'template', and if you know that particular transmission, it is a 3 speed, 0.85-1.00-2.14 so in reality, was really only a two speed splitter with a deep reduction in underdrive, albeit behind a 5 speed main transmission, but I digress.
No doubt I could come up with more suitable ratios, If I wanted to have gears cut specifically, there are still a few blokes around who do, do it. Machining costs run out about $100 an hour, so it doesn't take long to run the clock up!
Just going by those charts you posted, there are some glaring discrepancies between the two. Given that one, the 12 speed Synchromaster was purpose built from scratch and mine was simply a hash of ideas thrown together with what gears I had available. This has probably NO commercial value whatsoever, nor was it ever intended to be so. I'm not defending myself, have made plenty of blues in the past, probably will continue to do so until I fade away into that great wrecking yard!
I'm still having trouble getting my head around the road speeds you listed though. Jarrods previous post seems more realistic. As I wrote earlier, I realise that in some conditions, e.g. the gap between some ratios as well as the rev drop between gears leaves a lot to be desired.

Going to strip one of the spare transmissions down probably this weekend and have the input shaft bearing housing bored out on a mill to accept the newly completed adapter housing, (has to be enlarged approx 1/2 --3/4 "). If the whole thing lays an egg, well, I am out a few quid and a bit of pride.
The second transmission I am going to assemble back to it's original configuration (and ratios)
for the time being,just to see how it works. I have a half dozen (boxes) or so here either complete or in various stages of strip down. depending on just how much machining involved will dictate whether I will try and use the set of gears I have here, or if I spring for a set to be machined from scratch.
If I do go that way, I'd probably opt for a more suitable set of ratios.
By the way, in it's UNMODIFIED form the ratios in the second transmission are as follows, 1st-6.68:1--2nd-3.34:1--3rd-1.68:1---4th 1.00:1,a stock standard NP435. Which at first glance, probably would have been the better ratios to start with, modify the 'close ratio' box around them. Bit late now, already spent quite a few quid to get this far. Isn't hindsight a wonderful thing??

Cheers, and thanks again,
Dave_64

Her's my quick calculations.
31" tyres: theoretical circumference 31 x 3.14 = 97.34" (of course, this will vary somewhat)
1 mile = 5280 feet (hope I remember that correctly)
5280 x 12 = 63,360"
63,360 / 97.34 = 650.91, so; 650.91 tyre revolutions per mile which handily equals the tyre revolutions per minute at 60 mph.
Multiply this by the diff ratio gives 650.91 x 4.10 = 2668.73 engine rpm @ 60mph in direct. (just to gauge your highway revs.)
2668.73 / 0.86 = 2295 rpm in O/D.
It's a short jump to work out the rest.

A quick look at NP435 / T98 ratios gives 0.7 as (roughly) a good splitting ratio. Somewhere around 0.8 for the NP445. 0.86 would still be handy. You've put a lot more effort into this than I would ever get around to, my hat's off.

Jarrod.

Jarrod,
Thanks fir posting that detailed explanation of how you arrived at those figures. Makes a lot more sense now.
I'll save that for future reference.

As you said, around the 0.70:1 would be ideal, gears I have here should give me around the 0.86:1, which does tend to "crowd" some of the lower gear ratio's.

Cheers, Dave

Dave M80



https://lh3.googleusercontent.com/jrKURoypufA95md9toJJ15BvV9Jlfy0wM9ELkmczdUN-79kyj7Y=w802-h403-no

cya

You blokes have to much time :huh: :huh:

You blokes have to much [strike] time [/strike] phunn

:lol: