Rear Differential Question

Hey guys, new to the forum.

Just scooped up a 2006 V8 4x4 DC Tundra about a week ago and have been going through it to see what it needs and changing fluids. Today, while changing the rear diff fluid I noticed my differential fill plug was not OEM. I also noticed the rear diff cover does not appear to be original either. I cannot find a picture online of one that looks like mine, I'm not sure if it was custom fabricated after the old one rusted through or something like that. I could also be wrong.

The print out the parts guy at Toyota gave me says for my rear diff (Double cab with LSD) it should take 3.5qts to fill. About 5.5qts just came out. Although some was coming out of the fill plug when I pulled it so it was overfilled. Not sure how, I did add maybe half a quart after buying it to get the fluid up to the fill hole so I knew it was safe to drive until the gear oil I ordered came in. I drove the truck around for a little before draining the rear diff today.

Just looking for some help so I know exactly what I'm looking at and if I should just fill it with 3.5qts or fill it up to the drain plug like I usually would with a differential. Totally new to the 1st gen Tundra, but not new to working on vehicles. I have 4qts of Amsoil 80w-90 to go in, not even sure if that will be enough at this point. Any help is greatly appreciated.

Here's a few pics of what I'm talking about:

 

Definitely an interesting diff design.

I can't imagine the Brake Proportioning Valve working correctly or at all with it coated in bedliner though

 

Someone definitely fabricated that after the original rusted out imo. I would fill it to the bottom of the fill plug if it was mine.

 

That's definitely not the stock diff cover or fill hole in the rear. It looks like it has more room then the stock cover does so 3.5 quarts might be too low. Agree to go up to the fill plug.

Also check the breather vent on the driver's side of the axle, consider doing a relocation mod for that while you're at it.

 

Looks like someone made a high capacity diff cover.

 

I was told that the frame was sprayed in 2015 by Toyota with a corrosion inhibitor. Whoever sprayed it obviously didn't really care and just coated everything. A lot of stuff I personally wouldn't have coated. I didn't know what that thing was, now I do. Thank you. I'll strip the paint off the brake valve.

I also just checked that breather before making this thread, I'll be sure changing or modifying it is on my to-do list. I'll do a search to figure out exactly what I need to do.

Does anyone see an issue with filling it with some

$39 75w-90 GL-5 Limited Slip, Ultra Long Drain 500k Miles, Manual Transmission, Gear/Differential Lubricant (1 Gallon)

75w-90 if the 4qts of 80w-90 are not enough? Both are Amsoil severe gear.

 

I think you'd be fine mixing in a little

$39 75w-90 GL-5 Limited Slip, Ultra Long Drain 500k Miles, Manual Transmission, Gear/Differential Lubricant (1 Gallon)

75w-90. If your truck is equipped with an LSD, you might need to use LSD additive if you experience some chatter, but I think the AMSoil has some in it.

Here's a link to the breather mod, pretty straight forward. https://www.tundras.com/threads/diy-rear-differential-breather-mod.5253/

 

Thanks man, looks super easy. Thank you to everyone that replied. Love to get answers so fast so I can go finish this up today.

Got fluid back in and it took right around 5.5qts to fill. I guess the design must hold more fluid, I just hope they didn't put the fill hole up too high. Thanks again guys.

 

I noticed it was coated, that had me worried.

Be careful with the coating situation, tread lightly. Not only did that action invalidate your ability to ever have the frame replaced, but the frame continues to rust under the coating, and if it was bad enough to coat, the inside of the framerails are potentially fucked - the coating is just an external cover-up and does nothing for the rust inside the rails.

Do you have a borescope you can look inside the framerails with? How do the stiffeners look? What about the spots where the x-shaped crossmember meet the frame above the spare tire?

 

I tried to the best of my abilities to look the frame over before I purchased the truck. Wasn't thrilled about the coating, but the guy before me had it done. I'm actually going up to a local guy that is known for working on toyota frames tomorrow morning and having him take a professional look at it. Depending on how that goes, I do plan to have him strip all that off and put on Eastwood rust encapsulator paint on everything instead. We'll see tomorrow.

 

Interesting. Definitely not the stock diff cover based on the shape and hole location. My concern with filling it until it spills out the fill hole is if this is some type of homemade replacement then they might have just placed the fill hole wherever they thought was good and it doesn't necessarily indicate that its filled to the correct level as the OEM cover would. Maybe do some research as to what aftermarket cover that is and see if they give any insight on their website.