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Thread: 63% Reduction Gears To Suit GQ GU Patrol

  1. #21
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    I think what you will find is the vehicle will be basically speed limited if you don't exceed the redline mark. The RPM of the gearbox gears is unaffected by the downstream reduction, so its automatic. For example, if i drove on the redline in high range in 5th gear, the gearbox would be spinning at the same rpm as in low range but the transfer reduction will limit the final speed, hence the sticker on the door is more to get people to concentrate on speed rather than RPM as its probably safer that way, I am guessing now.

    So for us, in the bush, fitted with reduction gears, its more about rpm than speed as you are going to be crawling around like a slug anyway, even if you are revving its head off.

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    MB (8th December 2018)

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  4. #22
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    I think that’s what I was worried or advised against mate. Pinging 4th & 5th LR gear regardless of speed. Had assumed it was an oil heat thingy from heaps of spinning maybe?


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    Quote Originally Posted by MB View Post
    I think that’s what I was worried or advised against mate. Pinging 4th & 5th LR gear regardless of speed. Had assumed it was an oil heat thingy from heaps of spinning maybe?


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    Only thing you are not getting is the increased heat transfer from air at 100kph against 40kph. The radiation energy will be the same, however the lower speed will affect what gets transferred into the surrounding metal and then makes that hotter - which in turn can re-radiate back towards the gearbox, as against the surrounding areas getting hit with the same radiated heat, but the air velocity acts in an erosion effect to strip the heat away. I guess simply, you cant destroy energy, only transfer it, and heat is energy. Inversely, if you put a fan under the vehicle and replicated the air velocity at 100kph, you would have greater cooling effect. This probably why earthmoving equipment and the like have cooling circuits for gearboxes, transmissions, differentials etc as they are pottering around, sometimes in the same position and airflow is poor. I am going to bed now, this is too difficult for my old head to think about, good night and sweet dreams my friend.

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    Cheers mate, learning is good!


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    Morning Philstar mate!
    One last honest quandary bugging me on our GU stock sticker warning.

    Transfer case is safely engaged say stationary from 2WD to 4WD High Range (no ongoing drivable max warning listed, speed and or rpm)
    Snot along Fraser Island beaches as you choose? (80kmph max open beach legal limit IIRC in the day)

    Transfer case is then safely engaged to Low Range and a definite warning is listed.
    There must be something in that mate, almost has to be LR stuff spinning harder and to take greater care of mate?



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    OK, I think I understand what you are concerned about.
    There are a couple of fundamental parameters that affect gear life and strength, rotational gear speed, tooth size, tooth width, material of construction, engagement width, hardness, lubrication and tooth finish. The gearbox gears are sized predominantly against torque rating, so the first gear is designed to transmit the greatest torque at lowest speed to get moving, within the applied power and is the largest gear. As you move up in gears the torque is reduced on the gear set itself until you get to the 5th or overdrive where the vehicle has greatly reduced requirements because it is already now moving quite quickly and has inertia and kinetic energy as well. It is then apparent that this 5th gear is the 'weakest' gear in the drive train. (you might recall the failures within the Toyota 60 series gearbox when they moved from a 4 speed to a 5 speed - predominantly caused by a 5th gear being sized to fit within a preexisting gearbox instead of modifying the gearbox size to allow for correct gear design sizing)

    Then if you take that gear train and stick it into the back of essentially another reduction gearbox, being the transfer case, what happens in the situation of driving in 4th and 5th? So, the warning no doubt is related to how much hp is being transmiited, and torque from the motor thru the weakest gearset. So 4th being 1:1 and 5th O/D being say 0.85, I can see potential for gear set overload in the gearbox as a reaction to the vehicle drivetrain now increasing torque on the output shaft of the transfer case, especially in say a deceleration condition or jolting. Imagine this picture. 100kw motor, running thru a final 5th gear inside the gearbox, that is 1mm wide, then driving into a transfer case that is designed for high torque and has 50mm wide gears. You are cruising along at 50knhr on the sand in 5th low and hit some deep sand, which puts an instant load on the vehicle because its kinetic energy is now being strongly resisted by the sand, however your motor is trying to work against that at full torque because thats why you are in low range, for max torque output, so your hard locked up drive, assuming there is no clutch or automatic transmission involved where you can shear/absorb the change in energy, transfers through the drive and where the forces exceed the mechanical design capacity of the element, you will break something, in this example the 1mm gear will get damaged.

    I think this is perhaps the limiting rational. I could pull the books out and work this through but its been 30 years since i designed a gearbox from scratch and it would take a bit of a headscratch to be honest. In summary, the designers want you to preserve the drive train by not exceeding your gearing design parameters, not only from a motive power perspective but also a resistive load from what you are driving in. (you have generated torque and resistive torque or reaction taking place) Logically you would not select the weakest gear to drive into a reduction gearbox and expect it to last, as opposed to a high torque capacity gear into a high torque condition - this will last, but relates to a reduction in physical speed and generated energy or inertia. Pretty heavy at 3.50 am MB, I think thats correct.

    Pls, no more thinking from you for the rest of the DAY!

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    Ah ha, thanks mate, I got now finally!
    So to clarify my mates warning too must have been about the gearbox gears and not transfer gears.
    Appreciate your efforts heaps here, top stuff mate!!


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  13. #28
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    Are these reduction gears still available???
    04 ST 3lt auto, not enough Mods to keep me happy, but getting there

  14. #29
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    Threedogs, did mudski sort you out with the gearset?

    I still have them in stock if Mudski has sold his now.

    I dont get on here much, so shoot me a text or call.

    Cheers, Andy
    0433 108 569
    97 patrol coilcab ute. 4" lift, snorkel, 315/75R16 cooper S/T's. and about 200rwhp and some expensive bits and pieces

    Organising a group buy for 63% transfer reduction gears, check the link here

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    Hey guys, I'm still looking for a set if someone has one for sale let me know, I'll take them...

    Thanks

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