Last post on Aug 21, 2013 at 5:16 PM
You are in the Toyota Sequoia
What is this discussion about?
Toyota Sequoia, Toyota Highlander, Toyota 4Runner, Toyota Land Cruiser, Toyota RAV4, Toyota Tacoma, Truck, SUV
#1892 of 2493 Re: 2005 Highlander 4WD How? [2toyotas]
Dec 03, 2005 (11:00 pm)
From discussing this very issue with a lexus factory rep several years ago I was led to believe that the differing final drive ratios F/R was so that under acceleration the front wheels would initially receive the brunt of the engine torque. I was told that only at a constant speed with all four tires having roughly equal traction was the F/R torque distribution 50/50.
I don't see it myself, sound a bit like hocus-pocus, but I was also told, in writing, that the center and front diff'ls are "beefed up" beyond that of the rear diff'l in order to handle the additional drive torque.
And keep in mind that the instant Trac applies the brakes to simulate a partially locked diff'l, front, center, or rear, the engine will also be instantly dethrottled so the brake rotors don't overheat (and later warp) due to continuous use should the engine be left to produce high torque.
Personally I think Toyota and Lexus have now learned a hard lesson and the HL, Sienna, and RX will soon have the RAV4's new AWD system.
And by the way as of the 04 model year the drive ratios are 3.48:1 and 2.92:1 for what it's worth.
#1893 of 2493 Re: 2005 Highlander 4WD How? [wwest]
Dec 04, 2005 (7:04 pm)
The transfer unit drives the front axle and propeller shaft for the rear at .341:1, and that is what equals out the front and rear. If there was no transfer unit to do this, and just an open diff or VC the different ratios would send a lot more power to the front. The service departments in both toyota and lexus in my opinion, have not a clue how their vehicles work. Every time I take my sequoia in for service they take it out of 4WD and tell me it is bad for it. Don't they know it now has the same transfer case as the multi mode 4Runner with a torsen center diff?? I just laugh.
#1894 of 2493 Re: 2005 Highlander 4WD How? [2toyotas]
Dec 05, 2005 (11:41 am)
Pardon me, I may be wrong, but I believe your Sequoia has a full time AWD system that uses the brakes for torque apportioning if a wheel slips/spins and in 4WD mode actually locks the center diff'l in which case the service technicians are correct, as much as it really pains me to say so.
You seem to be saying that the transfer unit drives BOTH the front axle and rear drivelines with a common ratio and I don't see how that would "equal out" the differing F/R rear final drive rations.
And I assume by "transfer unit" you mean the gearset from the transmission section into the center diff'l.
#1895 of 2493 Re: 2005 Highlander 4WD How? [wwest]
Dec 05, 2005 (9:59 pm)
The Sequoia has a manual center lock which is not locked when they say this. When in 4WD unlocked mode the torsen center diff splits power same as on the 4Runner. Trac controls both axles.
On the Highlander power comes from the transmission to the center differential, then splits left to the front differential, and right to the transfer unit which is a gear unit which drives the front .341 to the rears 1 turn. The transfer unit is after the center differential, actually next to it. The transfer unit connects the front axle and the propeller shaft which drives the rear. It does not matter what the final ratios are because the wheels are turning at the same speed. This means that torque is delivered equal to each axle and wheel until there is wheel slip.This is when trac steps in and slows any spinning wheel. The ratios are different because they have to fit everything, while keeping it compact and lightweight. Three open differentials are used front, center, and rear. Open diffs always send power equal unless there is wheel slip, and then trac makes it equal once again.
#1896 of 2493 Re: 2005 Highlander 4WD How? [2toyotas]
Dec 05, 2005 (11:27 pm)
Then I guess you need to tell me why, with the right front tire and right rear tire off the ground, I can turn the front wheel one full turn and the rear wheel doesn't.
#1897 of 2493 Re: 2005 Highlander 4WD How? [wwest]
Dec 06, 2005 (8:45 pm)
If you are saying that when you turn the front wheel the rear wheel does not move, try turning the rear wheel and see if the front wheel turns. It won't because of the open differentials. Only the wheel you turn will spin.
#1898 of 2493 Re: 2005 Highlander 4WD How? [2toyotas]
Dec 07, 2005 (8:50 am)
Left to right testing in this way if you turn one wheel the opposite wheel will turn an equal distance, maybe in the opposite direction but an equal distance just the same.
Because the front to rear final drive ratios are not equal turning the front wheel exactly 360 degrees will result in the rear wheel turning, again possibly the opposite direction, but plus or minus the ratio difference.
#1899 of 2493 Re: 2005 Highlander 4WD How? [wwest]
Dec 07, 2005 (9:11 pm)
I believe they will turn exactly the same distance. In different directions but the same distance. The transfer unit evens it out. The pinion gear in the transfer unit is smaller than the ring gear, this is what turns the wheels the same speed no matter what the ratios are. Once again the transfer unit does a gear reduction of .341. The rear ratio is 2.929, and the front is 3.27. Add 2.929 and .341 and you get 3.27 the same as the front. The ring gear overdrives the pinion by .341 so they turn exactly the same, with 3 open differentials the power is split equal to each wheel.
#1900 of 2493 Re: 2005 Highlander 4WD How? [2toyotas]
Dec 07, 2005 (9:16 pm)
All I can say in response is that the difference in rotation distance of the front vs the rear in this test on my 2001 AWD RX300 relates directly to the documented difference in final drive ratios.
#1901 of 2493 Tacoma 4X4: to VSC or not to VSC?
Dec 13, 2005 (7:39 am)
Iím not a regular on this forum so I may be asking something fully covered previously; if so I apologize. Iím about to buy a Tacoma 4X4 access cab 4-cylinder (had a 1994 T-100 4X4 that just blew the head gasket.) Here in Texas, VSC comes only as a special order on such a truck, and would come with TRACS and limited slip differential. Iím willing to spend the money to get it, but is it really worth it (reliability, drawbacks)? Is the reduced reliability of a limited slip differential a major issue? Iíll use the vehicle both to commute and for long, often quite rugged and muddy trips in Mexico. Thanks very much for any pointers.