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Discussion Starter #1
I have a question that I don't have the math brain to calculate:
How much will the difference in gear ratio of the ZD30 (4.3:1) vs TD42 (3.9:1) effect the final gear ratio.
Or more interessting: How well will 35's work on a stock 50B on a TD42 vs. the ZD30 I am used to?

Cheers

Dane
 

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Not sure of your question? Will try and read between the lines.

Gearbox's are the same between 3.0 and 4.2
3.9 versus 4.375 is a around 12% increase which will roughly equate to how much more revs you will have at the same speed.

A general rule of thumb is go up a ratio for every tyre size.
3.9 = 31 inch tyres
4.11 = 33 inch tyre
4.375 = 35 inch tyres
4.6x = 36/37 inch tyres

for a 4.2 wagon runs 3.9's, ute is 4.11 standard:
Since 3.9's are way to sluggish to start with most opt for 4.6's on 35's.

Since a Di3.0 runs 4.375 with 31's I would assume you would need to run 4.6's or higher to keep the same level of power & torque.

If you have a common rail I believe the ratio is 4.11 not 4.375 as per the older model.

Not sure if this helps?
 

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Discussion Starter #3
Since a Di3.0 runs 4.375 with 31's I would assume you would need to run 4.6's or higher to keep the same level of power & torque.
This is the info I was looking for... thanks.

Already with the 4.3 ratio of the ZD30 combined with the 50B makes the car go too fast when you want to "crawl" slowly trough difficult terrain - At least when 35" are fitted.
So with the TD42 3.9 ratio, I will need to change something to make the car go slower. And of course a side effect is more torque, but the speed is really the biggest problem.

What is the best way to go about it (besides a crawler box)?

Cheers

Dane
 

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Learned the hard way - RD28t out TD42 in
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4.1s are standard ratio on the TD42 - I thought ? 3.9s are found on the petrol versions. Certainly in the Y60s anyhow.
 

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Discussion Starter #5
4.1s are standard ratio on the TD42 - I thought ? 3.9s are found on the petrol versions. Certainly in the Y60s anyhow.
Ok - Got the data from the reference thread on this forum for td42??
 

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Naturally aspirated GU 4.2D are usually 4.11.
Factory Turbo GU 4.2D are usually 3.9's.

4.2D GQ's are different, Tracteur Tom is correct in that petrols are 3.9's and diesels are 4.11's.
 

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So Dane,
I assume what you are doing is changing the ZD30 for a TD42T but keeping the gearbox and diffs (from ZD30) un-changed?

So what you will end up with is the TD42T but the ratios in the diff to suit the ZDs higher reving nature. Remembering that the higher the ratio, the higher the engine revolutions for each wheel revolution. I.e. the 4.375:1 means you motor will be doing 4.375revs for one wheel rev (at final 1:1 drive from gearbox in top gear that is). The 3.9:1 diffs will make the car faster for the same revs. Ie at 100km/h your motor will be reving lower with the 3.9 than with the 4.3 or 4.6. Bigger wheels will be taking the ratio back to other way so will suit having a higher diff ratio.

Effectively you are making the car slower but making the new TD42T motor rev higher (for the same actual road speed say 100km/h) than it would have normally with its standard ratios.

By fitting bigger tyres in combination with the higher ratio diffs from the ZD you should effectively be bring the final ratio back closer to what the factory TD42T would have been running with standard tyres and 3.9diffs.

To make it Crawl you would be having to fit higher ratio diffs 4.6:1 but then it is affecting your road speed making it rev higher (maybee too much) for the same real road speed.


Personaly, I would be leaving the diff ratios (for the time being), fitting 35" tyres to get a good combination of road speed, power and revs then if you need good low range crawling off road, go for reduction gears in low range only.
 

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Discussion Starter #9
Thank you very much all for great input. And for a thorough description - I now have a good picture of what to expect. It seems like I will end up with an ok solution at the end of the day.
Damn I look forward to that first spin after the transplant :)
Cheers

Dane
 
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