63% Reduction Gears To Suit GQ GU Patrol

[AB]

This is what I lifted off the Marks 4x4 website. I have 85% reduction in ,y manual, but they are recommended for auto's. Be aware though that 85% is a huge difference in top end speed in low range - could affect sand driving ease as you are putting a lot more torque down to ground instead of speed. I think mine is too low for sand to be honest.

The 85% reduction gears give you the biggest reduction we offer. These are mainly suited to rock crawling vehicles or vehicles that are prone to run away down hill (fitted with an automatic transmission). As an example this reduction gives a manual vehicle about two full gears below where the factory gearing sat. The maximum speed in low range will be approximately the same as third gear with standard gearing. High range is not altered when fitting our low range gears

Yeah 85% is huge Phill.

Awesome for the dedication of climbing etc but hard to still be an all rounder.

63 is perfect in my opinion. I've played a little bit on the soft sand with the 63% on the Murray 200m runs 1 foot soft as hell sand and it's awesome in 2nd and 3rd.

Still, a good set up rig should do first high with ease on sand flats moderately steep dunes too but that's another conversation...lol


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[Bloggsy]

I have these 63% reduction gears in my 4.8 auto (I'm running 3.9 diffs, not 3.5s that come standard). I would have to say they are one of the best mods I've done to this Patrol. 1st low down hill is brilliant, no runaway, sometimes a bit too slow if I'm running the 33" tyres, but a little throttle solves that. I can drive around the tracks in low range all day long, not a problem. So much better control over the lumpy stuff. I haven't actually tried them in sand as yet, but I can't really see a problem as top speed is around 50-60kmh without revving the guts out of the motor.

Cheers,
Darren

[PeeBee]

I would max out at around the 35klm mark with 3.9's and a manual, in 5th, redline is 3200rpm in chev

[MB]

Reduction gears in general I now agree are probably one of the newfound nuffy MB best mods I’ve ever done too.
Makes for such a more relaxed descent in the gnarly stuff and same same up those rocky tracks.
Sorry Philstar but will say your beast kindly allowed a putt putt drive prior is just too damn slow in between tracks on the flat ridges old mate.
IIRC we shouldn’t be running LR 4th&5th for too long up top and it’s a little annoying switching back to HR repetitively, your honest thoughts @PeeBee mate?


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[Winnie]

Reduction gears in general I now agree are probably one of the newfound nuffy MB best mods I’ve ever done too.
Makes for such a more relaxed descent in the gnarly stuff and same same up those rocky tracks.
Sorry Philstar but will say your beast kindly allowed a putt putt drive prior is just too damn slow in between tracks on the flat ridges old mate.
IIRC we shouldn’t be running LR 4th&5th for too long up top and it’s a little annoying switching back to HR repetitively, your honest thoughts @PeeBee mate?


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Why not use 4th and 5th? There are 5 gears available to use and I use them all!

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[MB]

For “too” long I was told, maybe a spinnie heaty thingy?
EDIT: Donk-Box-‘Transfer’-Diffs ?

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[PeeBee]

MB, its not a problem from a drive perspective. When I am in say 4th or even 5th, its easy coasting stuff, not any load, so in reality its basically using the gears as they are designed, but at a fraction of the speed. The 85% gears were installed to transform the vehicle when it had the original 2.8TD, and it absolutely did that, however with that engine there was too much gap between low and high range, so the middle ground flexibility was lost for stuff like sand. I would have struggled to get the barge across the Simpson in low with the 2.8 and it would not have made it over the first dune out of dalhousie in high.

With the Chev, and 85% reduction, its basically a third low all day in the high country, maybe 2nd on a climb, then if steep and ledgey and slippery, first low and its a doddle down as you know. It is a pain at times when 5th is ringing my ears off, but I can always stop, which i don't! Personally I think the 63's would be ideal for this engine/diff combination, but most of my driving is high country and its a conservative package. With this gearing it would pull anything up any hill it could drive itself, so thats another comforting thought. I think the 85% question arose regards the selection for a vehicle with an auto trans?

[MB]

Just noticed yesterday the warning sticker under the visor of our stock 2001 GU TD42T family wagon, yet to install these great reduction gears.



(4L) Must not exceed 50kmph it reckons so ran a few gear versus fully stock drivetrain tests on the old bus.

4L 3rd gear = 3,500rpm ish
4L 4th gear = 2,500rpm ish
4L 5th gear = 2,200rpm ish

I’m only assuming now it’s roughly those ‘TD42’ engine rpm’s per gearbox selection choice that we need to keep under for transfer case health and possibly not the 4th & 5th gear warnings I was once campfire Babbel given before?

Would this below be roughly speed calculated up @PeeBee mate or have I got it arse about upside down again mate. Maybe it doesn’t matter with the final drive reduction gears?

50kmph @ 85% reduction = 7.5kmph
50kmph @ 63% reduction = 18.5kmph
50kmph @ 43% reduction = 28.5kmph
50kmph @ 24% reduction = 38kmph

Either way, do love the 63% gears in my Chev ute too and reckon they’d be even better in the family TD42 wagon one day soon too.
Still reckon you should try if hopefully possible to hang onto them Mark mate if keeping your beautiful beast of a TD42Ti




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[PeeBee]

@MB, have a look here, its a spreadsheet on the Marks 4x4 website that will give you HOURS of joy!!! You had me a bit confused and I could not really make sense of where you started and ended up, however either way this table gives you all the max sppeds based on your inputs for tyre size, engine rpm, original transfer case, reduction fitted and diff ratios. Its a beauty and will arm you with everything you need for that next campfire discussion - enjoy!!!

https://www.marks4wd.com/gear-calculator.html

[MB]

That’s very cool, thanks Philstar!
Seems briefly to calculate speeds etc....
Any max warning speeds recommended built in for us?


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