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I'm the new owner of a Black 2002 Tundra AC 3.4L RWD. It has 94,000 miles on it and I don't think the differential fluid was ever changed. I do not have an owners manual and have done some searches on the site, but I'm confused. Some recomend 75w-90 and others say 75w-140. I have also seen posts saying I should not use synthetics because of leaking seals. Any information on the correct oil and if can use synthetics would be appreciated.
 

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2015 Toyota Tundra DC SR5 5.7L
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You live in the NE. You should not put a viscosity higher than the 90W called for in your rear diff. Any quality dino changed every 25K-30K miles will do you fine.

If you like the idea of and want to invest in the superior protection factors provided by a synthetic, the Mobil-1 75W-90 will also be fine in your diff. You should not have problems with leaking as the newer seals are designed to work wth both petroleum-based and fully-synthetic fluid formulations.
 

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I have a 2000 3.4 4x4 5 speed and have run the Mobil 75-90 for the past 10 years with no problems. I know Toyota changed the recommended fluid in later years but not for the 2000 so I don't know what yours needs, check the owners manual if you were lucky to get one with your truck. All I can say is don't over fill the rear.
 

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I have an '02 Tundra 3.4 L & 5 speed manual gearbox. I changed my gearbox and rear dif oil at 30k. I put Red Line in both and have had zero issues. No leaks, no noise, & very smooth shifting, 113k now, just my experience.
 

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I'm the new owner of a Black 2002 Tundra AC 3.4L RWD. It has 94,000 miles on it and I don't think the differential fluid was ever changed. I do not have an owners manual and have done some searches on the site, but I'm confused. Some recomend 75w-90 and others say 75w-140. I have also seen posts saying I should not use synthetics because of leaking seals. Any information on the correct oil and if can use synthetics would be appreciated.
Go to the link below and join the site and it will let you download your owners manual plus it will give you all the documented service that Toyota has providied for your VIN#, this is a great site and it will let you manage all your wehicles!
Toyota Owners Online | Official Toyota Owners Website
Then you can go to the section in the back of the manual where it tells you what fluids YOUR truck needs!
Also some good downloads here http://www.ncttora.com/fsm/
 

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75w-90 should suit you just fine. And regular oil will also work just fine.

I know people say that synthetic will work just fine with the seals, but unless you replace them.....it won't. I don't know why, but within a week of putting synthetic in my rear diff both axle seals started leaking. I'm sorry, but that just doesn't happen unless there is a cause.

Now with new axle seals I'm not worried about it.....but the stock ones leaked. Still don't know why exactly....but I can guess ;)
 

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Go to the link below and join the site and it will let you download your owners manual plus it will give you all the documented service that Toyota has providied for your VIN#, this is a great site and it will let you manage all your wehicles!
Toyota Owners Online | Official Toyota Owners Website
Then you can go to the section in the back of the manual where it tells you what fluids YOUR truck needs!
Also some good downloads here Toyota Tacoma/ 4Runner/ Tundra/ FJ Cruiser Factory Service Manual Page

HOGWILD!!!

You Da Man when it comes to finding useful information. I was just wondering yesterday if there was a way to find out what has been done for my truck by Toyota before I owned it. Tried to send you points but was not allowed to.
 

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Less than 5K miles after putting syn in my diff, I was replacing two axle bearings and all of the associated hardware. And I was in Pueblo, Co. Cost over $700. Seals leaked washing down the bearings.

I may have the "new" seals now, but I won't be using syn. If it ain't broke, don't fix it.
 

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Less than 5K miles after putting syn in my diff, I was replacing two axle bearings and all of the associated hardware. And I was in Pueblo, Co. Cost over $700. Seals leaked washing down the bearings.

I may have the "new" seals now, but I won't be using syn. If it ain't broke, don't fix it.

Replaced my seals and bearings, and then ultimately the rear end within a few hundred miles of changing out the fluids. Rear differential fluid should be changed every 30,000 miles (15,000 if towing or severe duty). The seals went because the differential breather was nonexistent and the open hole on top of the differential was clogged. In motion the fluids heated up and the air inside the differential heated up and expanded. This ruptured the seals and caused unbelievable headache.

The leaks are more than likely a result of the required maintenance not having been done and not as a result of synthetic gear oil. I run synthetic with no problems since I started doing my maintenance per the schedule.
 

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The leaks are more than likely a result of the required maintenance not having been done and not as a result of synthetic gear oil. I run synthetic with no problems since I started doing my maintenance per the schedule.
That makes sense, but it was not the same for my case. I have always changed all of my fluids in a timely manner since I have owned my truck with 34K on it. I ran regular fluids in everything, except the motor, until I tried synthetic in the rear. My only guess as to why it leaked, was because of its better lubricating abilities. It simply may have worked into the old seals better than the regular dino oil did. Honestly, both started leaking within a week of the new oil. That just doesn't happen :confused:

Now that I have new seals I could probably run synthetic oil, but I just put regular back in to be safe.
 

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Go to the link below and join the site and it will let you download your owners manual plus it will give you all the documented service that Toyota has providied for your VIN#, this is a great site and it will let you manage all your wehicles!
Toyota Owners Online | Official Toyota Owners Website
Then you can go to the section in the back of the manual where it tells you what fluids YOUR truck needs!
Also some good downloads here Toyota Tacoma/ 4Runner/ Tundra/ FJ Cruiser Factory Service Manual Page

Great post HOGWILD! Thank you so much for all the info. From the post I will stick with regular dino oil for the differential. I would love to run synthetics but don't feel like shelling out $700 on a repair.
 

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I just did mine and I used Royal Purple in the rear.
 

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I have a 2001 4.7 Tundra and have had Royal Purple in Engine, Transmission, Rear End, for over 5 years ! I have pulled trailers, made a couple of trips to west coast and so far no leaks and everthing is running very smooth.
Very happy with Royal Purple products!
 

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Less than 5K miles after putting syn in my diff, I was replacing two axle bearings and all of the associated hardware. And I was in Pueblo, Co. Cost over $700. Seals leaked washing down the bearings.

I may have the "new" seals now, but I won't be using syn. If it ain't broke, don't fix it.
Just curious: what brand of synthetic gear oil did you use?
 
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