I've been following the Lexus scheduled maintenance book. At 60 months it says the automatic transmission fluid needs to be replaced. At 72 months it says rear differential oil needs replacing.
My car has only done about 45,000km. It's a late 2017 build.

I try to DIY everything. Has anyone ever replaced the above 2 fluids? I don't intend on keeping the car for 10 years. Maybe 5 more years.

Any advice would be appreciated

 

I've done the gearbox. It's nothing magical, but it's also not exactly simple. You need to get the car in the air and level to do anything with the gearbox. You'll need 4 or 5 liters of WS ATF unless you open up the pan and remove the valve body (not recommended). This will replace about half the fluid. System volume is 11.2 liters.

The diff is a question mark - do you have a TVD model? Diff oil is dead simple, just drain and fill. The TVD has two wet clutches that use WS ATF (same stuff in the gearbox) and have a drain and fill each, so if you have the TVD, you'll need standard gear oil for the diff and WS ATF for the wet clutches. Diff volume is 1.4 liters, clutches are 0.7 liters each.

 

I've recently changed the rear torque converters(uses ATF fluid), rear diff, and ATF with filter and pan gasket. Not difficult at all. Make the job easier with fluid pumps for the gear oil and ATF and use a Scan Gauge or instant read thermometer to measure the ATF fluid to drain the excess (drain from 113F to 133F). Yes, I know the thermometer isn't the correct way but I ran them side by side and it's just as accurate. Buy more fluid than you need to account for spillage.

 

Yea I'm in Australia - all GSF here come with TVD.

Im a bit worried about draining and filling the transmission though. I've heard stories of the transmission slipping etc. I plan to follow the process on a few YouTube videos.

Is it recommended that I drop the pan to get more fluid out?

Also I saw you commented on Bullet Garage's video saying 'If you jack up the front of the car and drain you'll get more than 6 quarts out of the system. That's a 50+% change on a system with 11.8 quarts total volume. Besides, if you jack the front up, the cooler will drain by itself, same as the air/oil cooler for the engine does.'

What do I need to do to ensure I get pretty much 100% of the old fluid out? Is it as simple as doing a drain and fill twice using the same method?

One more thing: is it necessary to replace the transmission filter like he did in that video?

 

You know what's strange?

I have been servicing my car at the Lexus dealership it's whole life. My car has 140k kms (75k miles). I take it in every 10k kms (6k miles) as per their instructions.

I am looking at my service history and not once have they carried out a transmission or diff fluid change.

Recently, I have been noticing a slight thump when downshifting, and the shifts have been ever slightly rough. I am worried it might be a shaft or diff mount issue, or even worse, a transmission issue. I don't know.

Would a fluid change help? Seems I need to instruct the dealer to do it. My next visit is due in 7k kms ( 4k miles )

 

There's no way short of fully rebuilding the unit and putting in a new torque converter to get all the fluid out. It's not that big a deal. I have 215,000 miles on my IS F and I've only done a few drain and fills over the entire life of the unit. I sent used fluid to Blackstone and at 150,000+ miles, it was still in good shape. There are places with machines that do as full a swap as you can without rebuilding, and they typically connect to the oil cooler lines to extract the old fluid as they feed in the new fluid. The machine to do this is not economical for the home mechanic to buy.

Lexus does not recommend changing the filter ever. They claim in the new car features it never needs to be replaced (at least in the US market where the EPA has made "lifetime" fill the norm for all manufacturers). I replaced the one in my IS F when I did my first fluid change at the same time I took the sample and sent it to Blackstone. I also cleaned out the oil pan and put in a new (rather pricey) oil pan gasket.




The IS F drops 5.5 US quarts if you lift the front of the car alone to drain. The GS F only dropped 4 US quarts when I did the same thing. I'm not sure why that is, but that's my experience. It might be that the GS F is longer and doesn't get the same angle when raised to the same height. Regardless, if you're really worried about the volume swap, just over load the gearbox to get the best possible ratio of used to new, and drain out the excess. You'll spend a lot more money on ATF doing this, but you'll achieve the goal of more new fluid than used fluid.

FYI - the TVD uses two wet clutches, not torque converters. ATF is made specifically for wet clutches, because your automatic transmission is built on them. See #6 below.




FYI 2 - If your gearbox shifts abruptly or flares when cold or sticks in gear after a hard turn, the fluid level is low, AMHIK.

 

I'm no expert, as you can see why I started this thread, but it does sound like it's a problem with your transmission. Having said that, from my own research a lot of people have noticed much smoother shifts after doing a transmission fluid change so it might be as simple as doing one.

 

I flushed the transmission fluid myself on my gsf and sienna. Both around 70k. I used Amsoil atf and drained and fill 3x. The gsf does shift quicker after change. The vehicle engine MUST be running and at appropriate temp when you are removing the excess fluid. I pinned the obd as shown by carcarenut to make sure it is at correct trans temp. For me the hardest item was installing the overfill bolt but with a good wrench you are able to get it in.