Rear Differential

[lenore]

Well just changed the rear differential fluid (second time) Made my own tool for easy access by cutting a 10mm allen off to fit inside a 10mm socket so I could use a socket wrachet wrench. This made it real easy to manuever the allen into the plugs on the differential with extensions. Put in 75-90 GL5 synthetic. the rear fluid looked much better than the front differential. Held 1.9 pints (1 quart approximately) by the way I drove in the snow up at Lake Tahoe today, could have sworn I smelled burning bands. Good God I just change the fluid with filters for the third time in less than 15K total miles on the new tranny which was installed just a little over a year ago. Boy I love the AWD. Lexus sucks bigtime not fixing this weakness or at least reprogramming the shift points for the over drive. I Drove on the ice and snow with the Snow ECT position on. IS this not good? Anybody else use that switch. Car seemed to do fine without it switched on. I guess I will change the fluid again this week. ARGGGGGGG. Just no excuse for this. Should have bought a Honda.

[jbarhorst2]

The snow switch starts you out in second gear so that you do not spin the tires.

I know it's little consolation, but Honda is not perfect either. Their largest warranty item from the past several years has been automatic transmissions. I have family in the Engineering group for American Honda and even he was affected. The tranny in his Acura died and he had to get it replaced. I guess it is a big problem. There are facilites dedicated to rebuilding and modifying these transmissions sent back from the dealerships. Ugly situation.

I bought a small pump that you hook up to a drill to run. I plan to use this soon to replace my gear oils as well. Hopefully it makes replacing the fluid easier.

Tom

[cnynctry]

I Drove on the ice and snow with the Snow ECT position on. IS this not good? Anybody else use that switch. Car seemed to do fine without it switched on.

I use the ECT switch a couple of times. After each use I could smell hot trany fluid. I stopped using it.

[wwest]

It is a lot more likely you were smelling the brake pads being overheated due to Trac activity. Since the VC mostly remains flaccid almost all of the engine torque remains at the front resulting in continuous slipping of the front wheels versus the rear on a slippery roadbed. Also remember that Trac braking is used to simulate a real, mechanical, LSD at both the front and the rear, not that it ever really has need to do that at the rear.

The only way the system can overcome front wheelslip/spin and allow you some simplance of directional control is via the Trac system's use of PWM, Pulse Width Moduation, of the front brakes. I'm surprised you didn't also encounter engine dethrottling along with the Trac system activation.

Edited January 16, 2006 by wwest

[bluestu]

You're saying that the front differential uses gear oil??? I was told that the front differential and transmission shared the same fluid, and the transfer case uses gear oil. If this is true, could it be possible that you've been mixing gear oil in with your transmission fluid? That would explain your frequent transmission failures. Just a thought.

[wwest]

Yes, it's only the PTO/transfer case that uses gear oil. I don't think you can "refill" the center/front diff'l except via the ATF fill tube.

[lenore]

The transfer case shares the tranny fluid, this provides drive to the front differential that provides drive to the rear differential through the drive shafts. I do not have trac lock, the 1999 RX300 only has ECT and another position which holds each gear longer on shifts.

[wwest]

The transfer case shares the tranny fluid, this provides drive to the front differential that provides drive to the rear differential through the drive shafts. I do not have trac lock, the 1999 RX300 only has ECT and another position which holds each gear longer on shifts.

No, the transaxle output drives the center diff'l directly. The center diff'l then drives the front diff'l and the PTO. The PTO is driven via a hollow shaft surrounding the right front half shaft.

At least that's the "case" according to the Lexus shop manuals for the 2000, 2001, and 2004 Rx AWD systems. Don't have the manuals for others.

I Drove on the ice and snow with the Snow ECT position on. IS this not good? Anybody else use that switch. Car seemed to do fine without it switched on.

I use the ECT switch a couple of times. After each use I could smell hot trany fluid. I stopped using it.

If you use ECT and accelerate aggressively you're asking more of the transaxle's 2nd gear clutches than they can provide without slipping and overheating.

[lenore]

The transfer case shares the tranny fluid, this provides drive to the front differential that provides drive to the rear differential through the drive shafts. I do not have trac lock, the 1999 RX300 only has ECT and another position which holds each gear longer on shifts.

No, the transaxle output drives the center diff'l directly. The center diff'l then drives the front diff'l and the PTO. The PTO is driven via a hollow shaft surrounding the right front half shaft.

At least that's the "case" according to the Lexus shop manuals for the 2000, 2001, and 2004 Rx AWD systems. Don't have the manuals for others.

I Drove on the ice and snow with the Snow ECT position on. IS this not good? Anybody else use that switch. Car seemed to do fine without it switched on.

I use the ECT switch a couple of times. After each use I could smell hot trany fluid. I stopped using it.

If you use ECT and accelerate aggressively you're asking more of the transaxle's 2nd gear clutches than they can provide without slipping and overheating.

The transfer case drives the left drive shaft, it also drives the front differential directly which has the right drive shaft and the PTO drive shaft coming out of it. The PTO drives the rear differential through the drive shaft.

[wwest]

First, the following information is being taken from the Lexus Repair Manual, titled:

U140F

AUTOMATIC TRANSAXLE

Jan., 1998

Pub. No. RM632U

For clarification, within these manuals of various years Toyota often uses the terms "transfer" as in transfer case/components, interchangeably with PTO, Power Take-Off. Prior to 2004 the PTO contained a viscous clutch/coupling, and as of 2004 this component is simply left out.

Things can be a bit confusing in trying to analize just what drives what as both the center and front differentials are contained with a single "casing". The best pictorial is on page AX-1 but I had to blow it up by a factor of 4 to really see how things were coupled.

Bolted to the center diff'l case/carrier is a ring gear which mates with the final drive output gear of the transaxle. So the transaxle output drives the center diff'l directly. One output side of the center diff'l drives the case/carrier of the front diff'l and the other output side drives PTO/transfer case ring gear which in turn drives the rear drive shaft via a pinion gear.

Prior to 2004 there were three drive couplings from the transaxle case into the PTO. First, a solid inner shaft to couple one side of the front diff'l to the US passenger side front drive half-shaft. A hollow drive shaft immediately surrounding the inner solid shaft to couple the front drive line to one side of the VC. And then yet another hollow shaft outside the first one to drive the other side of the VC and the rear drive shaft via the ring/pinion arrangement in the PTO.

As of 2004 the VC and the "Middle" hollow drive line were dropped.

Although the VC was mounted, fully contained within the PTO case, it was effectively mounted between the front drive line and the rear drive line so when it activated, stiffened, the effect was to partially "lock" the otherwise fully "open" center diff'l.

Edited January 17, 2006 by wwest

[monarch]

I know it's little consolation, but Honda is not perfect either.

According to Consumer Reports, American 4WD SUV's like the Jeep Grand Cherokee have had major transmission problems as well:

http://i5.photobucket.com/albums/y189/mastertech/cr.jpg

[Grumpa72]

I use the ECT switch a couple of times. After each use I could smell hot trany fluid. I stopped using it.

According to the dealer and others on this board, all the ECT (electronically controlled transmission) does is to start you out in second gear while in snow to avoid spinning the tires. After you reach the normal shift point, your transmission acts normal and you can accelerate all the way to redline with the ECT button illuminated. I can't say that using the ECT button and the smell you are experiencing but it might be related to the stability function, meaning brakes.

Gary