Thread: Maxi drive reduction gears

Originally Posted by rick130

I think Lowranger/Wayne has an underdrive, hopefully he chimes in, or one of us can direct him here....

I've got one too. Fantastic bit of kit.

Biggest advantage is that you dont lose the normal low range (as you do with lower range transfer gears) or mess up all ranges (as you do with 4.11's for example)

Using entirely std ratios, my 4 ranges are

1.4:1 high
3.77:1 high with underdrive
3.32:1 stock low
8.93:1 low with underdrive

total reduction is about 117:1 on mine

Disadvantages.. nothing particually serious, heavy.. another 25kgs or so on the car. more heat coming through the seat box, and cost, although the best option is rarely the cheapest!

Yep,I entirely agree with Pete

I am glad I went down the road I did,and fitted the underdrive.

In a 110 you don't notice the weight,and on a Tdi the heat through the floor is about the same.
I run 35's and 4.11's as well as the underdrive and love it.My total reduction is 135:1 a bit more that Pete,due to the changed diff ratios,but I don't have the power of a TD5 to turn the big wheels and find the 4.11/12s to be great in the Tdi.One thing though,once you have driven with an underdrive,there is no going back You are addicted,they are that good and that much fun.They give you that much more control.
On a trip that Pete and I did,Pete was being held up on one particular section of track,and was making no progress,I suggested he engage the underdrive,and he was able to proceed without spinning a wheel
The great advantage of the underdrive,is as Pete said,that you keep your original Low/Hi range for just normal driving,and then at the flick of a lever,you have very low gearing available.The underdrive is fabulous particularly in very steep rocky terrain.I can travel over terrain,and not even need to touch the brakes,where others are having to heavily apply brakes and run the risk of loss of control,as well as vehicle damage.
The cost is the major factor,I know I saw one for sale brand new last week for $2900.But I would happily spend that again.

I was running an lt95 with 4.11 gears and had endless hassles with the gears not lasting and costing heaps, I then swapped to zf,1.4 high range and 30% low with 35's. By the time I boughjt an lt230,rebuilt it put in 1.4 high and 30% the cost was about the same as an underdrive which in hind sight would have been better,I have had a few scary moments going down hill with the auto have shifted into reverse a couple of times to pull up.

The underdrive is definetly a good thing, I personally would have thought that on only 35's or under you would not have the tyre traction to make use of such a low ratio, but I stand corrected by Pete and Wayne. The one thing they did not mention is you loose the ability for a pto on the LT230. I have the 49% MD gear set. I am very happy with it. The only time it seems a little to low is in sand, and this only very occasionally...I do think that for work and 4x4 the stock defender Tdi gearing could be a touch lower in High range...like 3.8's instead of 3.54 R&P, but Ashcoft dont make a Sals 3.8. The trade off would be more RPM at HWY speed...then again this may help when not traveling on falt ground at 100km/hr

My low range has been invaluable for manoeuvring my trailer numerous times....

while there MAY be a slight difference in strength from 30%-49%, I highly doubt it an issue. These gears are made from EN39B, and are being used in comp rigs. I know Tony AKA Ruff did some very hard work on a LT230 and broke some internals...the gear set was untouched.

Originally Posted by uninformed

The underdrive is definetly a good thing, I personally would have thought that on only 35's or under you would not have the tyre traction to make use of such a low ratio, but I stand corrected by Pete and Wayne. The one thing they did not mention is you loose the ability for a pto on the LT230. I have the 49% MD gear set. I am very happy with it. The only time it seems a little to low is in sand, and this only very occasionally...I do think that for work and 4x4 the stock defender Tdi gearing could be a touch lower in High range...like 3.8's instead of 3.54 R&P, but Ashcoft dont make a Sals 3.8. The trade off would be more RPM at HWY speed...then again this may help when not traveling on falt ground at 100km/hr

My low range has been invaluable for manoeuvring my trailer numerous times....

while there MAY be a slight difference in strength from 30%-49%, I highly doubt it an issue. These gears are made from EN39B, and may are being used in comp rigs. I know Tony AKA Ruff did some very hard work on a LT230 and broke some internals...the gear set was untouched.

Serg
Both Pete and I run fairly agressive tyres,and I run fairly low pressures when offroad,so get a fairly high degree of traction.The thing with the underdrive is that with the gearing as low as it is,you have a lot more possibilities to choose from,including High range with the underdrive engaged,so there is a gear for all occassions.
You are correct in the fact that you loose out on the option of a PTO or overdrive for that matter,but these are the choices we have to make for the chosen way we use our vehicles.

Originally Posted by Psimpson7

I've got one too. Fantastic bit of kit.

Pete,Wayne, Although the components are different, the design and principal of your crawler units is the same as my cobbled together crawler unit, made from parts of an old Fairey overdrive grafted to a planetary low range reduction box (Borg Warner 1339) from an early Jeep Quadratrac transfercase. Underneath the tin cover at the back of the reduction unit is a short length of splined shaft to which I was able to graft a modified Thomas winch PTO. Seeing as most of the Ashcroft crawler box internals are also made by Borg Warner,is there any chance that there is also a shaft or dog hidden behind that 6 bolt cover plate at the back?

Bill.

Hi Bill,

Here are a couple more pics for you.





cheers
Pete

Thanks Pete. I also concur with you and Wayne that once spoilt by having a crawler unit with a wide selection of ratio choices, there is no going back.
My normal low 1st gear ratio is over 100:1 without crawler, and when I removed the unit recently to attend to some oil feed modifications, I felt almost naked without it.
$2900 for an Ashcroft unit seems quite respectable considering how much it expands the vehicles overall extreme terrain capabilities.
Bill.