Reduction gears for the mighty 2.8

[patrol2.8]

Just got permission from the finace department for the go a head for a set of reduction gears for the mighty 2.8 now what size reduction should i go for biggest part of my 4wding is a day out in the bush (Wombats / Tallarook etc)

[nissannewby]

Can you give us a little more info like tyre size. Generally the 85% are the pick but these help a great deal when running 35"+ tyres and a petrol engine or auto.

[patrol2.8]

Nissannewby Im running 33s 5 speed box (2.8s dont have an auto option ?) diffs are 4.6s

[nissannewby]

If you dont intend running any larger tyres or going to extreme then I think marks adaptors do some around the 60% mark

[Bigrig]

With 4.6 ratios and a manual, I'd be going the 43% gears that Marks do ... that'll still be crawling - any lower and you'll find first gear becomes obsolete (even down hill) as its simply to slow ... my 85% gears in an auto box petrol engine have near rendered first gear obsolete.

[macca]

Got a set of 43% gears in the shed to go into my 4.2TDI manual, guys in our club with the 80% gears dont like them as they can not get enough momentum in some cases like sand.

The gearing affects all the low range gears and they can not pick one that suits the terrain which drives them nuts.

To watch them very slowly idle up a steep rocky track is quite a sight to see though.

1st low is fantastic for crawling over a very difficult rock climb but nothing else they reckon, its just so low.

They are talking of swapping them for 43% gears, hence why I got a set of them.

[patrol2.8]

Thanks Guys will look into the 43%

[P4trol]

Silly question:

85% means 85% slower than the speed you would be travelling in standard low range?

How much effort is it to fit reduction gears?

[nissannewby]

Yep 85% reduction. Not to much mate can be done in a day quite easily.

[macca]

Attached are ratios in my ute, and with the various reduction gears, gives you a bit of an idea to help make your mind up.

[Outrage]

The reduction is the transfer case gearing, so 85% means 85% more teeth, as seen in Macca's pdf, original ratio of 2.02, 85% reduction gives 3.743 ratio. It ends up around 54% of original speed. From the pdf, standard, 35.4 rotations from the motor gives 1 at the wheels, with 85% reduction, it now takes 65.6 (1.85 times more) rotations to make 1 turn of the wheels. You're close to doubling (1.85 times) how many rotations it takes, thus you're close to halving the speed.

That's my understanding, correct me if I'm wrong.

Same process, 43% reduction leads to 70.6% of original speed. 24% reduction leads to 81.3% of original speed.

[macca]

Something else to consider is the final drive ratio in reverse as that changes in low range as well.

Backing out of a bog might get a whole lot more interesting!!!

Macca

[Winnie]

Same process, 43% reduction leads to 70.6% slower at the wheels. 24% reduction leads to 81.3% slower.

Think you mean 70.6% and 81.3% of the original speed, not that percentage slower.

[Outrage]

definately misworded that, thanks kristoffa, edited my post.

[patrol2.8]

Thanks Macca and thanks outrage for explaining it gives mr more to think about

[gu4500]

I have the 3.743 ratio in my GU - one of the first batch Marks ever made for Patrols, back in Oct/Nov 2002. Awesome if you want to go slow, and rock crawl, but most normal offroad use requires 3rd gear takeoffs, even on 35" Centipedes.

Was funny seeing my boss trying to drive it when I left it in L4 though....

[buderimlad]

I have 85% with 33's. Wouldnt go the 43% because it still wouldnt be low enough to crawl. If you want to go faster user a higher gear.

[Outrage]

I done an excel spread sheet comparing different transmission/dif/transfer combinations, will try and find it and post it up. I do remember my 4.5 petrol auto was shocking compared to the manual, manual runs at 65% of original speed (of the auto) in first (no reduction gears), 85% gears in the auto bring it to the 54% of original making it a bit slower than the manual.

Ended up, 24% reduction in the manual was equivalent to 85% reduction in the auto...

[Outrage]

Delayed response, finally remembered it. Couldn't actually put the spreadsheet up, but gives an idea of some engine/transmission combos (only some of them).

[mfw]

I have the 43% in a gu td with 33, Made it a really nice 4WD go down the steepest hill in first full control with no brakes, crawl up in 1st or 2nd and will still do 40-50 in low 5th, withy the 80% you will have to change between high and low range more often

[Winnie]

will still do 40-50 in low 5th

Why would you want to do that?

[Bigrig]

Why would you want to do that?

Beach driving ... easier on the gearbox, and easier on fuel as the reduction keeps the power/torque to the wheels (as it were) up, and the revs down ...

but even so, it'd be a rare event in my thinking ...

[patrol2.8]

Ok ive been doing some resaerch on the net and have really totally confused myself about wether to go 43% or 85 so when time comes to get them hopefully soon im just going to toss a coin heads 43% tails 85%will let you all know how it pans out but as for the finance department though she rekons the slower the better

[patrol2.8]

Come on tax man bet if i owed you you wouldnt wait this long for your money:frown::blowup:

[macca]

Ok ive been doing some resaerch on the net and have really totally confused myself about wether to go 43% or 85 so when time comes to get them hopefully soon im just going to toss a coin heads 43% tails 85%will let you all know how it pans out but as for the finance department though she rekons the slower the better

Mine were fitted last weekend, they are 43%. On 33' tyres.
Used them over the weekend in what would be considered a hard trip, not extreme.

I am glad I didnt get the 85%, basically went up 1 gear. Idling in low/low the GPS doesnt register a speed sits on zero, but able to slowly walk over the really hard bits.
What was done in 1st before was done in 2nd and sometimes 3rd low. and downhill control was amazing, stock boxes were braking all the way down 1 hill, mine sat on 1500 rpm with no brakes at all.

I am very happy with the result.

A mate with us has 85%, they are too low, he said if you went to the Wattagans all the time and crawl rocks then they are good. He did most climbs yesterday in 3 or 4 low on 36" tyres.

Happy to talk to you if you like, PM your number and I'll call you.

[patrol2.8]

Thanks Macca might take you up on the offer a chat just waiting on Mr taxman now so got a bit of time to sort out my mind 43% is the way to go just more im thinking if i didnt go the 85% would i be wondering for a while why didnt i

[macca]

When your ready mate.

The bloke with the 85's is going to change to 43% after seeing how mine went over the weekend.

Another thing to consider is reverse is changed as well, backing out of something is different as I found out on a slippry clay hill.

[patrol2.8]

OK heres the update finally after talking to about 8 different places and jumping in my mates 3.0ltr with 85% reduction and him recently fitting the same size diffs as mine 4.6s ive gone and had the 85s fitted i figure the easier i can make it on the 2.8 the better i was absolutley rapted with the way his went up and down the hills and the control he had and im giving them their maiden voyage this weekend in the wombats so hopefully all will go well

[patrol2.8]

Well had a good day out in the wombats trying out the reduction gears and am absolutly rapt cannot believe the difference they make to the car most hills used to be tackled in low first were done with ease in low 3rd i have no regrets going with 85% now they really seem to suit the 2.8

[patrol2.8]

Just got back from 4 days in the high country and have to say that these gears are by far the best modification ive done to the car the way they have transformed the car is unbeleivable nobody could beleive the control i had driving a really rocky section normally i would need a lot of revs and need to ride the clutch etc but i was just able to crawl and steover them with such ease and no riding of the clutch at all