Hope this is just one off - TVD fail!

[Pielight]

TVD failure, albeit at 138k miles. Hopefully one off and who knows how the cars been treated, e.g. regular track days.

Scary bit is price....every bit as bad as expected. What he eventually paid seemed very cheap relatively speaking, but in isolation not so cheap.

Glad I've been getting the scheduled diff oil changes (seems in states it's 'for life' so maybe is a factor). I don't know if a dealer diff oil change includes changing the oil in both TVD clutch units as well as in the main diff. 🤔

Glad to have relax!

[ColinBarber]

6 hours ago, Pielight said:

I don't know if a dealer diff oil change includes changing the oil in both TVD clutch units as well as in the main diff. 🤔

I highly doubt it, it's not listed in the service schedule. But it uses ATF WS fluid, if it can last a 'lifetime' in the gearbox then it should also be able to in the diff transfer module.

The diff oil itself should be changed every 20k (major) service.

[Jgtcracer]

I must admit, feeling pretty good about not having a TVD at this point…

Got to be something else going on with this example, with my reliability engineer’s hat on id suggest there isn’t a trend of these failing so what’s the root cause.

I do wonder sometimes whether manufacturers would like to have old units back even if for no other reason than to carry out root cause analysis and determine whether there is room to improve. I suppose it would be tiresome, but if I was the design engineer on such a low volume part Id be interested!

Toyota leads the way with kaisen continuous improvement so I bet they do it with certain warrantied parts…..

[Pielight]

Ive often wondered of the merits of TVD for road use. A load of extra complexity for little gain I would think.

[DamianLEX]

Similar when people having 471hp change the exhaust to gain 10-15hp extra. It is not a game changer itself but when you add all different mods together then a stock car has no chance… 

[GMB]

23 hours ago, ColinBarber said:

I highly doubt it, it's not listed in the service schedule. But it uses ATF WS fluid, if it can last a 'lifetime' in the gearbox then it should also be able to in the diff transfer module.

The diff oil itself should be changed every 20k (major) service.

When I had the big 60K service I noticed that the diff oil had not been changed although it was a fixed price major+ service ( about £750) and it was on the printed schedule. Lexus told me that it depended on the type of car. It had never been changed. I tried to research it but found confusion everywhere. At the next service I told them to change it anyway. They agreed and charged me accordingly.  Maybe I paid twice for the privilege?

So the big question: On an ISf does the diff oil and auto gearbox oil need changing or is it a lifetime "one fill" product?

I still don't know for sure.  BTW I asked what the condition of the old diff oil was like - gritty/dirty/ whatever.  They told me that it was perfectly fine and did not really need changing.   Confused.com or what?🙄

[ColinBarber]

10 hours ago, Jgtcracer said:

I do wonder sometimes whether manufacturers would like to have old units back even if for no other reason than to carry out root cause analysis and determine whether there is room to improve.

I imagine so. In the 90s I worked for Toshiba, back when they were a leading laptop manufacturer, and we had a customer's power supply fail which had melted a little bit. Japan were insistent they received it back rather than just being thrown away so they could perform a root cause analysis on it. Obviously it could have been a safety issue so it was more important to them to understand what happened but I was always impressed that they took the time and expense to understand the fault.

[ColinBarber]

15 minutes ago, GMB said:

So the big question: On an ISf does the diff oil and auto gearbox oil need changing or is it a lifetime "one fill" product?

Auto gearbox is lifetime (if you aren't on a severe service schedule (i.e. taxi, towing)), diff is every 20k miles.

The following is the European service schedule, the UK essentially follows this but the timing as slightly different as they count up in 15,000km and we in the UK have a 10,000 mile schedule:

 

[GMB]

15 minutes ago, ColinBarber said:

diff is every 20k miles

Thanks for that. I had this very same discussion with Lexus and they told me that the ISf has a different LSD and does not need it ( unless it has been raced maybe ). According to your attached file it seems to suggest every 4 or 5 yrs or 60K miles approx for "normal " use in the ISf. Although the schedule provided is a bit confusing at first glance. So I think it is OK now and will probably not need changing again for quite a while based on the low mileage that I do in it.

  --  Thanks again for the info.😉

[ColinBarber]

3 hours ago, GMB said:

According to your attached file it seems to suggest every 4 or 5 yrs or 60K miles approx for "normal " use in the ISf.

No, it has an R at 30k km/18k miles (which would be 20k miles in the UK) and then again at 60k km/36k miles (40k miles in the UK) etc. The 4 years would be if you aren't hitting the distance and therefore it is changed at 4 years instead.

 

There seems to be confusion/reluctance by UK dealers to change the rear diff oil no matter what model. There have been posts here for owners of IS300h and GS300h/450h where it hasn't been changed on a major service. The owners service schedule book is clear - every 20k miles/2 years for those.

[Jgtcracer]

5 hours ago, GMB said:

Thanks for that. I had this very same discussion with Lexus and they told me that the ISf has a different LSD and does not need it

It’s a real interesting one this, part of my role involves oil analysis and Tribology generally.  Oil degrades over time the Lexus will have had to input a ‘lifetime’ value into the calculations to determine whether they would need to replace.  I suggest that have deemed it be be ‘good enough’ in reality.

Also worth noting that oils degrade over time, as well as mileage so must have attributed a length of time, along with mileage into their calcs.

I think it’s all a risk assessment by them to determine that the benefits of not doing it outweigh the tolerable risk of failure…

[GMB]

I think I would rather change any lubricants too often rather than not often enough. In the days of Castrol GTX, Duckham's and the like it was probably even more important, but I suppose modern synthetic oils have a bit more tolerance.

After this advice I will insist on changing oils, esp diff oils, regularly and on time. I think it pays to do this for longevity's sake even though some manufacturers don't agree. Same as they tell you not to run the car in - Always run it in - better safe than sorry.

[Jgtcracer]

8 hours ago, Jgtcracer said:

It’s a real interesting one this, part of my role involves oil analysis and Tribology generally.  Oil degrades over time the Lexus will have had to input a ‘lifetime’ value into the calculations to determine whether they would need to replace.  I suggest that have deemed it be be ‘good enough’ in reality.

Also worth noting that oils degrade over time, as well as mileage so must have attributed a length of time, along with mileage into their calcs.

I think it’s all a risk assessment by them to determine that the benefits of not doing it outweigh the tolerable risk of failure…

It’s also worth noting that for an RC-F, they recommend a rear diff oil change, I think at 4years…..

[GMB]

10 hours ago, Jgtcracer said:

It’s also worth noting that for an RC-F, they recommend a rear diff oil change, I think at 4years

RCF probably has the same diff as the ISF?

I think this is the problem, depending who you ask, and what evidence they show you, you will get a different answer. The only solution I believe is change the oil every 20K miles, as suggested by Colin who seems to know these things, as a worst case scenario and insist that Lexus do it regardless of their opinion, if it is affordable. There are other factors that may extend the life of the oil but we just don't know for sure.

I don't fully understand the descriptions at the bottom of this spreadsheet relating to rear differential.

 

[GMB]

10 hours ago, Jgtcracer said:

It’s also worth noting that for an RC-F, they recommend a rear diff oil change, I think at 4years

RCF probably has the same diff as the ISF?

I think this is the problem, depending who you ask, and what evidence they show you, you will get a different answer. The only solution I believe is change the oil every 20K miles, as suggested by Colin who seems to know these things, as a worst case scenario and insist that Lexus do it regardless of their opinion, if it is affordable. There are other factors that may extend the life of the oil but we just don't know for sure.

I don't fully understand the descriptions at the bottom of this spreadsheet relating to rear differential.

 

 

Now here's  something to further confuse us all below:

Comparison Chart of Gear Oil and Transmission Fluid

Aspect	Gear Oil	Transmission Fluid
Purpose and Application	Designed for manual transmissions and differentials.	Primarily used in automatic transmissions. Provides lubrication and cooling for components within automatic transmissions.
Viscosity Variance	Thick and heavy consistency, typically with viscosity ratings like 70/80W-90 or even 140 weight.	Significantly lower viscosity, typically ranging from 0W-30/40, to enable smooth operation in automatic transmissions.
Additives	Contains corrosion inhibitors, antifoam agents, antioxidants, and suppressing additives such as viscosity index improvers and pour-point depressants.	Includes additives for preventing fluid loss, impurity control, temperature regulation, wear protection, and noise reduction during gear changes.
Color	Light brown when new, due to additives and base oils.	Translucent dark red color in its fresh state, distinguished by added dye.
Cost	Prices vary widely, ranging from less than $10 to over $500, influenced by formulation and performance levels.	Price range is typically between $80 and $250 for automatic transmissions. Manual transmissions have lower fluid costs but can increase with complete service.

[ColinBarber]

10 minutes ago, GMB said:

I don't fully understand the descriptions at the bottom of this spreadsheet relating to rear differential.

The schedule form is used for all Toyota/Lexus vehicles - the only line that applies to the IS-F has a black dot against it on the right hand side - it requires GL-5 gear oil

There are some vehicles that use ATF in the rear diff, hence the lines below but they aren't relevant to the IS-F. For the same reason there are lots of lines at the top of the page for the front diff - but there are no black dots because these are not relevant to any IS.

[GMB]

11 minutes ago, ColinBarber said:

The schedule form is used for all Toyota/Lexus vehicles - the only line that applies to the IS-F has a black dot against it on the right hand side - it requires GL-5 gear oil

Thanks for that. It was not knowing which type of fluid was the correct one that caused the confusion.

This helps:

API GL-5 – Intended for heavily loaded gear sets with high sliding forces such as hypoid differentials. GL-5 lubricants contain high levels of extreme-pressure additives to provide protection under boundary lubrication conditions. Common heavy duty applications include differentials in on-road and off-road trucks, differentials, final drives in Caterpillar scrapers, and differentials and planetaries in Euclid haul trucks. Some manual-shift transmissions can use GL-5, but typically should not be used in synchromesh-type transmissions, as the EP additives can be corrosive to yellow metals found in those transmission types. Limited-slip differentials also typically require a specific lubricant with a limited-slip additive.