99 Rx300 Trans Failure

[artbuc]

My 99 rx has 60k miles. Have changed ATF every 15-17k miles. Since reading this forum, thought I better start changing every 10k. Until now, ATF coming out of both drains looked pretty good. This time however, ATF coming out of main pan (about 4 qts) looked slightly dark red but not bad. ATF coming out of housing drain (about 1 qt) was nasty- noticeably darker and the end of the drain plug was covered with a black sludge.

Why would the fluid look so different? I assumed the ATF would be well mixed and look the same from both drain locations. Doesn't sound good to me.

Any suggestions? I think I'll do another drain at 5k and see how things look.

[wwest]

First, I would recommend the next time drop the pan and clean the "debris" out. I had about 1/8 inch of clutch wear material in the bottom of the pan at ~40,000 miles.

My 2001 RX300 is AWD and I have become somewhat suspicious of the fact that the transfer/PTO case has lots of exterior cooling fins. Additionally I have come to believe that the VC, viscous clutch/coupling within the PTO is, has, been the source of an inordinant level of heat generation and has now failed, seemingly, in the (mostly) locked position.

That could put a lot of stress on the driveline resulting in further overheaing problems.

It goes into the shop to check that next month, the first time since 93 that I have had any Lexus in the shop for ANY reason.

[RX in NC]

wwest,

If your viscous coupling system has indeed failed, I assume you are planning to stand your ground and insist that Lexus cover all diagnostic and repair costs regardless of whether or not your original warranty has expired (I'm guessing that it has).

Please keep us posted on the results as to what Lexus diagnoses and whether Lexus covers all repairs of any failures discovered.

[lenore]

Wow, sure would like to know how you could diagnose that kind of failure in the Vsc coupling. I am also the nervous one now after two transmissions.

Actually would like to know how that coupling system works in laymans terms. And is it serviceable without replacing the tranny.

[wwest]

Wow, sure would like to know how you could diagnose that kind of failure in the Vsc coupling. I am also the nervous one now after two transmissions.

Actually would like to know how that coupling system works in laymans terms. And is it serviceable without replacing the tranny.

The center diff'l control coupling (viscous "clutch") is mounted entirely within the "transfer"/PTO case and can be replaced without opening the transaxle case itself. The purpose of the VC is to provide a variable level of locking between the two center diff'l output drives if/when those two drives do not have equal rotational rates, the front drive wheels (90% torque biasing) are slipping in relation to the rear wheels.

The VC is connected between/across the two drive outputs of the otherwise fully OPEN center diff'l. If those two output drivelines have a different rotational rate then the viscous fluid between the two very closely spaced VC clutch plate sets is "stirred" violently and the resultant turbulence heats the fluid. Were it not hermetically sealed within the VC casing it would expand dramatically due to specific formulation of the fluid. Since it cannot expand the EFFECTIVE fluid pressure rises, "thickening" the fluid, and thereby increasing the coupling coefficient between the closely spaced VC clutch plates.

Basically the VC will remain "flaccid", no significant locking of the two center diff'l outputs, unless those outputs have differing rotation rates. The longer and/or greater the rotation rate differs the higher the temperature of the fluid will rise and that results in stiffening the coupling across the center diffential.

Some VC designs will have a small bubble of air/gas injected during manufacturing to delay the onset of VC coupling. The gas itself must be fully compressed before the fluid begins to thicken enough to provide any significant level of locking. Other systems provide quicker VC coupling by having different final drive ratiosn front to rear such that the fluid is always heated up to some inital level of coupling. It appears that Lexus uses this latter method since the front and rear final drive ratios are different on the RX300.

Testing is relatively simple. With all four wheels off the ground and the parking brake applied the engine should drive the front wheels easily at a fairly low speed. The center diff'l is open and there should be no loading of the engine via the rear parking brakes until the VC begins to stiffen.

On a 4 wheel dyno my 2001 AWD RX300 at 40MPH simulated road speed there was no measureable engine torque at the rear wheels initially. It took almost 30 seconds at 40MPH simulated roadspeed before the rear wheels got up to ~25% of the engine torque delivered.

[jgr7]

I wonder if all the dyno testing trashed your VC?

Jeff

[wwest]

That was right after I purchased the RX, new, and if asking the VC to stiffen up and do its job for all of 30 seconds results in it failing then it is really a poor design.

But you make a really good point, maybe the VC didn't survive the work level it encountered during the two snow and ice storms it has had to endure in 50,000 miles.

[artbuc]

My 99 rx has 60k miles. Have changed ATF every 15-17k miles. Since reading this forum, thought I better start changing every 10k. Until now, ATF coming out of both drains looked pretty good. This time however, ATF coming out of main pan (about 4 qts) looked slightly dark red but not bad. ATF coming out of housing drain (about 1 qt) was nasty- noticeably darker and the end of the drain plug was covered with a black sludge.

Why would the fluid look so different? I assumed the ATF would be well mixed and look the same from both drain locations. Doesn't sound good to me.

Any suggestions? I think I'll do another drain at 5k and see how things look.

Quick update. 15 months and 13k miles later I have done another drain/refill. ATF looked noticeably different than new stuff, sort of a muddy brown/red color. Unlike the 60K drain, ATF from transfer case and drain pan looked the same.

The first ATF drain I did was at 27k miles. At that point I could not tell the difference between new and used ATF. That tells me that something bad is going on in my transmission. If the ATF itself was breaking down after 13k miles, I should have seen that on the first drain at 27k miles. I did the second drain at 50k miles, also not seeing too much difference between new and used.

I know there has been much discussion about what causes what. Does "brown" ATF cause the trans failure or does the trans failure (burned clutches, etc) cause the ATF to turn brown? Considering the bad state of my ATF, I will do another drain in a few weeks to get more fresh ATF in the system.

I think I'm on a collision course with the infamous trans failure.

[lenore]

Is your use of the vehicle mostly on street traffic or highway? My wifes is mostly street and in Sacramento during the summer gets quite hot. I have asked her to deactuate the overdrive while commuting unless she goes on the highway. I am 35k on my second tranny at present and have changed fluid 3 times. I want to move the tranny cooler to a place where it will receive more air flow. Good luck

[artbuc]

Is your use of the vehicle mostly on street traffic or highway? My wifes is mostly street and in Sacramento during the summer gets quite hot. I have asked her to deactuate the overdrive while commuting unless she goes on the highway. I am 35k on my second tranny at present and have changed fluid 3 times. I want to move the tranny cooler to a place where it will receive more air flow. Good luck

Thanks Lenore. Yes, my wife does almost all stop and go, around town driving. This is the first time I recall anyone suggesting to deactivate the O/D. How did you decide to take that step? Does it seem to be helping you?

Sounds like you are doing a drain/refill every 10-12k miles on your new tranny. How does the used ATF look? Any difference in appearance on the third drain/refill vs the first?

Thanks and good-luck to you also.

[lenore]

I have not experienced the Muddy brown look lately, but Someone mentioned to deselect the overdrive while in town so that the tranny is not searching for the highest gear in slower traffic. Last night she forgot and drove it home with overdrive deselected at highway speeds, bummer, ate more gas. I just try anything to make it go further, I have already added an external tranny filter, but would like to move or add a cooling fan to the external tranny radiator which is located in the right front fender well. I sure wish Lexus would step up to the plate and recall these darn things....wishful, but will never happen.

[MrEhden25]

When i bought my Lexus Rx300 1999, it had 86K miles on it. The transmission fluid was pretty dark. I had then drain the transmission fluid and put new one in. I then had my friend put an external transmission radiator, right in front of the main radiator. The cost for the transmission radiator was $38 (shipping included). Since then (1 year and 25K miles) the transmission fluid is still pink as the day i replaced it.

Get an external transmission radiator.

I have not experienced the Muddy brown look lately, but Someone mentioned to deselect the overdrive while in town so that the tranny is not searching for the highest gear in slower traffic. Last night she forgot and drove it home with overdrive deselected at highway speeds, bummer, ate more gas. I just try anything to make it go further, I have already added an external tranny filter, but would like to move or add a cooling fan to the external tranny radiator which is located in the right front fender well. I sure wish Lexus would step up to the plate and recall these darn things....wishful, but will never happen.

[artbuc]

MrEhden, can you give some more details? Make/model # of cooler, where purchased and installation tips?

[MrEhden25]

MrEhden, can you give some more details? Make/model # of cooler, where purchased and installation tips?

I am not sure about installation as my friend did it for free. The link below shows you different coolers you can buy, depends on the size of your car and how much you wish to spend.

http://www.usa-trailer-hitches.com/transmi...CFQkmZQodRkO61Q