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Diff Ratrios/Gearing


Les Brock
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Hi All,

Gears confuse me :blink:

Plan is -

200Tdi Big Alisport intercooler and boost upped to about as far as you can go with a Taxi Engine roflmao.gif

4 speed Auto – with 22D 1.4 Transfer box

Under drive

Will need Drive it everywhere.....no where for a tow truck and trailer in the box I now live in :rolleyes:

Two set of Tyres these are:

235/85/16

35/10.5/16

Used to have 3.54 diff on my old truck, is it best to stick with these, as its used on motorway to get to and from events, so I would like decent motorway manners ( Motorway manners and Simex in the same sentance :huh: ), need your advice really ?

I've ordered a nice pair of Mr Ashcrofts pegged Diff Locks, so its decision time as to what to do......

What HD ring and pinions to have fitted :blink:

Thanks for looking

Regards

Les

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Les

Give me a speed you would like to be doing, say cruising at say

X RPM In 4th (being an auto) doing Y MPH - using which set of tyres

each will be different - do you have a preferance - and I'll work it out for yer :)

Also it would be useful if anyone can post up what a STANDARD

200TDi 90 factory fresh does at D RPM and E MPH in 5th :)

And then I run me calculator and put graphs up with choices for yer

:)

Nige

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Use the gear calculator in the tech archive, it works it all out for you.

The issue with keeping 3.54's is that although you can run a "slower" transfer box to correct the high range on the road, low range is always the same so you can't do much about the loss in low-box. Depending on your preference & setup this may or may not be acceptable.

As an example, my axles are 6:1 overall gearing, way low, but I have a 1:1 LT230 which means my high-range speeds are similar to a stock defender but my low range is actually lower, even with 37's.

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always start with wat you in want to achieve in low box, using the diff ratios (3.5, 4.1 or 4.7) and than choose the transferbox to get the correct high ratio (1.0, 1.2, 1.4 0r 1.6)with this. On 35s with a manual box, I found 4.7 diff ratio with 1.2 Transfer box ratio ideal for my needs. I suppose you know what your hybrid had, so work from there I would say.

Daan

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If you have got underdrive stick with the 3.54 as they are definitely stronger and easier to get hold of in an emergency.

I have run 4.75 kam in the past(pre underdrive) and unless your truck is seriously light or you are a very mechanically sympathetic driver I wouldn't recomend them sorry.

I broke 2 x 3.54 diffs at mamby and managed to get spares at a market stall to be able to carry on.

You wont be able to do that with any other diff ratio.

I would try your truck on the road with the 1.4 ratio transfer and see if you want to go 1.6 or 1.2 slower or faster on the road.

I used to run a 1.6 as I thought it gave me the largest choice of different gears, I since found that being auto I didn't need as much choice anyway.

I didn't do hardly any road miles but if I did I would have been looking for a 1.2 or 1.0 transfer box.

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Well, if you have broken 2 x 3.54 diffs on one event, that doesnt sound like a good recomendation either dont you think? I bought 3 of these from kam in 2003, and the spare has not been used yet. My truck is light, but has been loaded to about 2.5 tons on the RFC, no problems. The Kam r&p is seriously beefy, if you compare this with the standard 3.54, I choose the kam option any day. I do run pegging in my diffs as well.

Daan

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Les - have a play with the ratio calculators, but also think carefully about what it tells you. 70mph @ 2250rpm doesn't sound too far from 70mph @ 2000rpm, but that's the difference going from a 1.6 to a 1.4 box (depending on your diffs, tyres etc) - and it can be a big difference if it means the engine will bog down and drop off boost when it clunks into top gear.

I went from a 1.6 t-box to a 1.2 and it's miles apart, 3rd gear now is where 4th gear was. With 32" tyres it's sensible (volume-wise) cruising at 70mph now, but it's only good for 80mph in top, or revving out at 75mph in 3rd. With the 1.6 t-box it would drop into top at 30mph and then carry the same gear all the way up to 85mph or so - plenty of power but it was a bit 'revvy'.

I'm happy with 1.2 and 3.54 diffs as a "relaxed" drive (I've got faster cars if I want to step out a bit) but it would be better with lower diffs / 1.4 t-b / smaller tyres if it was for towing or hilly work.

You're welcome to a drive in mine if you like, I'm only in the next valley as you know.

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I know HFH runs KAM 4.75's in his truck - it's not light and has big power, the only gear he broke was when his axle casing split and let sand in, and then it was the bearings that let it all go! The later KAM gears are defo alot better though than older generation ones that required the spacer ring.

Les i run KAM 3.8 ratio with 35's and a 1.4 transfer box 5 speed r380 though not auto and i find them perfect in every aspect and they are far superior in strength than the other ratio's. I used to get through a ring and pinion every time i went out - not any more. (i do keep a spare though)

You may struggle to get KAM 3.8's at the moment but Ashcroft does 3.75's i believe.

And HFH Does superior diff pegging ;)

Steve

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Daan is 100% right about the approach to sorting your gearing. Use diff ratio changes to lower your speed at tick over in low 1st - the std gearing is good, or go slightly lower. Faster than standard just means that you go down steep hills to fast - fine until you need to stop for a pumch half way, etc. Then correct your road speed with transfer box ratio's.

I'm another KAM user that has had no issues with 4.75's. Allthough pegged, ring gear glued on, schnor washers and KAM 12.9 ring gear bolts.

Adrian

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Well, if you have broken 2 x 3.54 diffs on one event, that doesnt sound like a good recomendation either dont you think? I bought 3 of these from kam in 2003, and the spare has not been used yet. My truck is light, but has been loaded to about 2.5 tons on the RFC, no problems. The Kam r&p is seriously beefy, if you compare this with the standard 3.54, I choose the kam option any day. I do run pegging in my diffs as well.

Daan

but I have broken Kam 4.75,(it allso broke the bearing hub on the arb, couldn't tell which broke first) none in stock when I was desperate for a replacement, I have never had an issue with crown wheel bolts coming loose on 3.54 but have on 4.75.

ashcroft can't peg 4.75, as the crown wheel takes up too much space.my 3.54 are now pegged.

Les wants to use his vehicle on the road I would still recommend 3.54.

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I have ashcroft pegging on mine, it does go, although the mounting flanges on the diff need turning down. The coming undone thing is solvable, so I cant see 4.75 r&ps being a problem from the reasons you are giving me. Supply used to be a problem, which is why I bought 3 at the time. Maybe nigel (HFH) can tell us more on this and the current situation?

Daan

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Confused.com..... :blink:

Dont forget I have the underdrive as a extra low as well :unsure:

Will have a scan at ratio calculator

Asked Dave for advise as well but i'm not back in the office till friday so wont know what he had to say, might just ring him tomorrow!

Might have a trip over to Turbo's :)

Cheers Chaps

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3.54s, auto, high and a 1.4 work ok on mine for road miles on Fedimas (36"). a 1.6 would be better but i am not doing the motorway miles.

3.54s, auto, low and a 1.4(well all lows are the same) works well but box gets hot when winching (36"s)

3.54s, auto, low and u/d perfect on mine on the 36"s

3.54s, low and an underdrive will be perfect on 35s too i would of thought. no need for 4.11s etc.

keep an eye on the box temp, 36s and low on mine with 3.54s and she gets hot - same cooling system as you. put her in underdrive/low and temp is fine.

on road temp again box gets warmer than it should really with the fedimas on it. sits about 110.

If i were you with an underdrive i would stick with 3.54s as low is then covered.

for on road i would expect a 35 with a 1.6 box would be about the same as a 33" (255.85) with a 1.4 box.

but the 1.6 will rev its nuts off on the 235s.

change the 235s(31) to 255.85s (33) and stick a 1.6 box in it gets my vote.

where is the gear calculator? link please?

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3.54s, auto, high and a 1.4 work ok on mine for road miles on Fedimas (36"). a 1.6 would be better but i am not doing the motorway miles.

3.54s, auto, low and a 1.4(well all lows are the same) works well but box gets hot when winching (36"s)

3.54s, auto, low and u/d perfect on mine on the 36"s

3.54s, low and an underdrive will be perfect on 35s too i would of thought. no need for 4.11s etc.

keep an eye on the box temp, 36s and low on mine with 3.54s and she gets hot - same cooling system as you. put her in underdrive/low and temp is fine.

on road temp again box gets warmer than it should really with the fedimas on it. sits about 110.

If i were you with an underdrive i would stick with 3.54s as low is then covered.

for on road i would expect a 35 with a 1.6 box would be about the same as a 33" (255.85) with a 1.4 box.

but the 1.6 will rev its nuts off on the 235s.

change the 235s(31) to 255.85s (33) and stick a 1.6 box in it gets my vote.

where is the gear calculator? link please?

I second this, I think this is spot on :)

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