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Driving FJ in 4 L


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Thanks for your response...there another school that says that it absolutely does nothing to the FJ gear box as long as you keep  shifting gear 4 and 3 on a 4 Low amd use for short burst. I have used  it  for short climb and it does wonders to the power. I would love to invite more comments there is another club which encourages this.

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4 hours ago, Zed said:

Hi @Ashok chaturvedi, this is not an FJ-specific thingy, I have a marshal friend who drives his Jeep in 4L 3rd gear consistently and some Nissan buddies also drive in 4L 3rd gear. I will get into the general stuff first, and at the end dive specific to A750F transmission which is used by FJ Cruiser to answer your question mathematically 😁

1. Generally for older 4-speed & 5-speed automatic, people drive in 4H 2nd gear and downshift to 4H 1st gear when climbing or need more torque. In contrast for modern 6-speed & 7-speed automatic, some I've noticed drive in 4L 3rd or 4th gear. They're pretty similar, and I'll prove it mathematically at the end of this post...

2. My Nissan buddies drive in 4L 3rd gear because driving in 4L allows them to turn off VDC (Vehicle Dynamics Control - computer will try to brake to fix understeer & oversteer), TCS (Traction Control System - brakes spinning wheel + cut-off fuel to engine and/or close throttle valve to reduce torque) and ABLS (Active Brake Limited Slip - Nissan's version of Toyota A-TRAC), as can be seen from this manual section:

842089487_Drivemodes.jpg.76b9924299e2f2e55698a0bbdf9d594f.jpg

 

3. If you're already in 4L, during stucks you don't need to shift from 4H > Neutral > 4L > 1st gear 'cos you're already in 4L, which sounds like an excuse a lazy driver would make 😂

 

FJ Cruiser A750F transmission: 4H or 4L?

These are the Gear Ratios for FJ Cruiser / any car with Toyota A750F transmission: 

FJCruiserTransRatio.png.a518545dbbe800d86e3a4c8a9dda64a6.png

Now I'll probably do a deeper dive with diagram what these different gear ratios mean, but for now I will use a cheat calculator to produce the numbers:

Problem Question: I want to drive 50 km/h (31 mph) in sand, what do I use? *The 50km/h is intentional as some manuals recommend this speed when driving in 4L, and also on average we usually drive below this speed for Newbie to FewbiePlus

Putting the A750 Gear Ratio numbers above, you can easily reach 50km/h in 4H 1st Gear after around 4000 rpm, which is what you'll probably do when climbing a steep dune... then shift to 2nd gear to keep RPM below 3000 for noise & fuel-efficiency.

  • 3.727 : Differential Ratio / Final Axle Gear Ratio
  • 31.6" Tire Diameter,  FJ stock is 265/70R17
  • 31 mph : Desired Speed (50km/h) 
  • 3.520 : 1st Gear Ratio

FJ_4H_1st.png.da1bf671f9c7831be18ad631c6891287.png

4L and Gear Reduction

Transfer Case in 4H is 1:1 (mentioned in A750F spec as High 1.000 above), but when you switch to 4L, it becomes 2.566:1 , this is why 4L in 1st Gear is slower and useful for crawling (but still with torque). But for the sake of fun, how much engine RPM do we need to make 31 MPH in 4LO 1st Gear ?

  • Transmission Ratio now becomes = 2.566 (4LO) x 3.520 (1st Gear) = 9.032

FJ_4L_1st.png.f8c27473a9e5db692309147b0122cfc0.png

Your Tachometer is usually maximum 7000 rpm, so this 4LO 1st gear will not do, let's skip to 4LO 3rd gear:

  • Transmission Ratio now becomes = 2.566 (4LO) x 1.400 (3rd Gear) = 3.592

FJ_4L_3rd.png.f50abf2477b877b76e4750fc6f6a4455.png

And there you have it, using 4LO in 3rd Gear, you will reach 50 km/h (31 mph) after about 4000 rpm engine speed... very similar to 4H in 1st Gear...

To recap:  If you trust the factory's book recommendation and will not go above 50 km/h in sand, then 4LO sounds safe as it disables all those pesky electronics (VDC, TCS, ABLS, ABS) without pulling any fuse. Otherwise if you're driving long-range dunes and flats and will go beyond 50 km/h in sand, you may want to use 4HI + kill-switch to ensure ABS, TCS, VSC are off.

 

Wonderful post @Zed

 

My only thing to add is my assumption that when using 4L, there are more gears involved (used) in the transfer case, leading to more heat, hence the much higher risk of destroying your transfer case. Is that correct ?

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1 hour ago, Ashok chaturvedi said:

Thanks for your response...there another school that says that it absolutely does nothing to the FJ gear box as long as you keep  shifting gear 4 and 3 on a 4 Low amd use for short burst. I have used  it  for short climb and it does wonders to the power. I would love to invite more comments there is another club which encourages this.

Your FJ Cruiser has VF2A model Transfer Case, which is Chain-Driven, similar to the Jeep's one that my marshal friend (another club) drives for 4 years in 4LOW 3rd Gear all the time... I'd say if it's going to stretch the chain / decrease lifespan of transfer case, by now he would have gone through a transfer case rebuild, but he hasn't, so yeah no issue with driving 4LO 3rd Gear for a long time every weekend 😁

If you mean the Gear Box as in Transmission, then again nothing to worry much. I have rebuilt the torque converter & transmission for my Toyota and also replaced the Transfer Case gears (my LC is gear-driven not chain-driven) and the front-differential, so I get to see how these parts work as shown by the mechanics in the garage. Simplified in text it goes like this:

Engine (rpm) >> Torque Converter >> Transmission (Gear Box) >> Transfer Case >> split into 2 in 4WD: rear propeller shaft to Rear Pumpkin/Diff + front propeller shaft to Front Pumpkin/Diff >> Finally, WHEELS!

Though your FJ Cruiser's A750F transmission remains 5-speed with 5-gear ratios, the VF2A with gear reduction (4LO) makes your FJ to have "12 gears", here are the ratio table again if you missed it in my prev post:

FJ Cruiser A750F “12-Gears” Transmission:

4High 1:1 ratio

1st Gear

2nd  Gear

3rd  Gear

4th  Gear

5th  Gear

Reverse

3.520

2.042

1.400

1

0.716

3.224

 

 

 

 

4LOW 2.566:1 ratio (basically multiply above numbers x 2.566)

1st Gear

2nd  Gear

3rd  Gear

4th  Gear

5th  Gear

Reverse

3.520 x 2.566 = 9.03

2.042 x 2.566 = 5.24

1.400 x 2.566 = 3.592

1 x 2.566 = 2.566

0.716 x 2.566 = 1.837

3.224 x 2.566 = 8.273

 

 

 

 

 

From these table you can see that driving 4H 1st Gear = 4LO 3rd Gear and driving 4LO 4th Gear feels like between 1st and 2nd gear (this is what people feel "more torquey")....  and because the Transmission / Gear Box is before your Transfer Case that does the reduction, if any should fail it should be the Transfer Case first...  

Keep on experimenting @Ashok chaturvedi, only you can tell how to drive your car best, we here are just giving you more encouragement to do trial-and-error (hopefully with a bit of sound reasonings behind it to make you more confident in approaching whatever you choose best) 😉

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Great illustration of how 4H & 4L works! Wish I could have the math for my raptor to do a trial & error. Will do some research and try to replicate your calculations @Zed. Thank you 👍 

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6 hours ago, Frederic said:

Wonderful post @Zed

My only thing to add is my assumption that when using 4L, there are more gears involved (used) in the transfer case, leading to more heat, hence the much higher risk of destroying your transfer case. Is that correct ?

Hi @Frederic fellow tech fan 🙂,

In the case of FJ Cruiser that uses VF2A Transfer Case, it's Chain-Driven and uses Planetary Gear, which is better explained through a diagram and a video below:

1. Planetary Gear: there's only 1 Gear involved in Gear Reduction from 4H to 4LO, highlighted in Yellow in this Service Manual Diagram of FJ Cruiser Transfer Case:

FJ_TCase_4LGearReduce.png.69de591b5051e38b0d61a52d3117843b.png

 

2. Chain-Driven: When FJ Driver switches from 2WD to 4WD, it already engages the Chain Belt, so even in 4H the Chain is rotating and passing power to the front & rear diffs... Changing it to 4LO doesn't change the belt reaction, it simply moves the fork down so that 1 Gear from point #1 above is in-place and changes the ratio, thus spinning the belt slower (providing slower output to front & rear diffs). This is best explained in the video below starting at minute 13:55 👇

 

The beauty of Chain-Driven mechanism is that it will still work with no oil or little oil... this is why in our bicycle you rarely need to lubricate the chain between the "pedal gear" and the "wheel gear"... Gear-Driven Transfer Case like my LandCruiser is such a maintenance hassle requiring full lubrication to work, and a hard lesson learned for me who got a broken Transfer Case + broken front diff due to no gear oil inside the transfer case 😂😂😂   

Source: http://www.differencebox.com/engineering/difference-between-chain-drive-and-gear-drive/ 

Edited by Zed
typo
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14 minutes ago, Zed said:

Hi @Frederic fellow tech fan 🙂,

In the case of FJ Cruiser that uses VF2A Transfer Case, it's Chain-Driven and uses Planetary Gear, which is better explained through a diagram and a video below:

1. Planetary Gear: there's only 1 Gear involved in Gear Reduction from 4H to 4LO, highlighted in Yellow in this Service Manual Diagram of FJ Cruiser Transfer Case:

FJ_TCase_4LGearReduce.png.69de591b5051e38b0d61a52d3117843b.png

 

2. Chain-Driven: When FJ Driver switches from 2WD to 4WD, it already engages the Chain Belt, so even in 4H the Chain is rotating and passing power to the front & rear diffs... Changing it to 4LO doesn't change the belt reaction, it simply moves the fork down so that 1 Gear from point #1 above is in-place and changes the ratio, thus spinning the belt slower (providing slower output to front & rear diffs). This is best explained in the video below starting at minute 13:55 👇

 

The beauty of Chain-Driven mechanism is that it will still work with no oil or little oil... this is why in our bicycle you rarely need to lubricate the chain between the "pedal gear" and the "wheel gear"... Gear-Driven Transfer Case like my LandCruiser is such a maintenance hassle requiring full lubrication to work, and a hard lesson learned for me who got a broken Transfer Case + broken front diff due to no gear oil inside the transfer case 😂😂😂   

Source: http://www.differencebox.com/engineering/difference-between-chain-drive-and-gear-drive/ 

I've rebuilt my chain-driven transfer case (looks very similar to the video) twice now, and i can tell you without any doubt that if it would run without oil, it would not last long.

I remember looking at the operating temperatures of a transfer case during offroading, and temperatures of 80-100 degrees Celsius seemed to be common.

Rotation generates friction, which in turn generates heat...

So should we be assuming that the stories of so many offroaders driving in 4L and overheating their transfer cases are all fake news ? I fail to believe so.

@Gaurav his encyclopedic brain might come in handy here on how many offroader he has encountered that busted their transfer cases from driving in low gear all the time.

 

 

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2 minutes ago, Frederic said:

Rotation generates friction, which in turn generates heat...

So should we be assuming that the stories of so many offroaders driving in 4L and overheating their transfer cases are all fake news ? I fail to believe so.

No I think you're right, it will largely depend on the car... when my Jeep friends with their 8-speed transmission drives in 4L 3rd or 4th and asked me to do the same, I'd say "I found my sweet spot and you found yours, doesn't matter as long as we get over the dunes just fine" 😁   I wouldn't dare drive in 4L just because another car with a different configuration does so, the same with transfer cases blowing up, probably best to check Transfer Case Temperature via ScanGauge/OBD PID during every break.... and fluids maintenance include transmission fluid & transfer case oil & diff gear oil.

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45 minutes ago, Zed said:

Temperature via ScanGauge/OBD PID during every break.... and fluids maintenance include transmission fluid & transfer case oil & diff gear oil.

Thanks to your previous advise Zed- I have been tracking the AT oil temp in real time during drives using an android device and an OBD2..  I also have gone through the service manual to keep in mind the range the AT should work within … not a single drive it’s gone over 126c including the recent Liwa trip and driving in summer  (… during a break I put into neutral and keep the car running which I read brings the temp down (and proven to for me).  I haven’t tried a sustained 4L drive … Ashok if you do experiment with 4L then def leverage OBD2 to observe the AT temp and have this as a backdrop for a decision/review.  

Edited by Niki
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1 hour ago, Frederic said:

 

@Gaurav his encyclopedic brain might come in handy here on how many offroader he has encountered that busted their transfer cases from driving in low gear all the time.

Sorry Fredy no comments for me on this topic.

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