Gearbox Fluid Change

The gearbox fluid should be changed regularly (owners manual calls out at least every 2 years).

In my case, it wasn’t clear when the last change had taken place so I decided to do it immediately.

To begin, choose a appropriate oil.  This is actually the hardest part of the entire process as there are a few challenges with this:

1. This is a trans-axle and the transmission and differential are sharing the same fluid

  • We need to identify a lubricant that suits the needs of both systems simultaneously 

2. The tranaxle makes use of helical gears

  • This necessitates the use of a GL-5 lubricant to deal with the high pressures experienced by the helical gear set.  Some say that the offset is minimal so the amount of pressure isn’t actually that high as far as helical gears go.

3.The syncros are brass

  • Because of the copper content, they are prone to corrosion.  The additives used to make a lubricant GL-5 can also attack the copper (and hence our brass syncros are at risk of damage)

4. The LSD in the diff wants some form of friction modifier

  • Friction modifiers make the lubricant more ‘slippery’.  This is great for the LSD, but the syncros can’t work if it’s too slippery (e.g. they want none of these friction modifiers).

The manual calls for 75W/90 over the GL4-GL5C API MT1-PG2 Standards. Recommended Rota LSX.

As you can see, there are a conflicting set of requirements.  I spent a lot of time researching options, but nothing seemed like a great solution.  Some people have reportedly moved to a GL-4 lubricant in order to protect the syncros, but at the risk of damage to the helical gear-set.  As a note, if there was a failure, syncros are generally cheaper to replace.


You should go strictly with what the manufacturer recommds. I ultimately decided to go with for myself was a Redline 75W90NS for quick availability and because this fill would soon be changed.  This is a GL-5 lubricant and so should be good for the helical.  The NS designation is important (there’s a version without the NS) in that it has no friction modifiers added.  This is good for the operation of the syncros.  Redline also claims that their formulation is compatible with copper/reduced corrosion.  Whether it completely prevents it is to be seen.  The Redline also carries a mention of being popular in Ferrari (in which the gearboxes are built somewhat similarly).  Redline sells a separate friction modifier in a bottle such that if you end up with issues of a chattering LSD, the idea is to SLOWLY add more and more of this to your gearbox mix to find the minimum amount to make the LSD happy, while keeping the slipperiness down to keep the syncros happy.  Most people report not needing to add any of this modifier.

Again, that all said, you should be going with the factory recommended fluid. Rota LSX doesn’t seem readily available in North America but can be ordered online.

You require around 3 bottles of fluid (just under 3 quarts).  Cost is generally about $25/bottle regardless of brand/etc.

When doing this change, it is recommended to replace both crush washers, as well as the o-ring on the filter.  These parts are just a few dollars each.  You require 2x 10263460 copper crush washers and 1x 182119 o-ring.  I usually look at both the Ferrari and Maserati part catalog as often one is in stock vs the other. Oddly enough, I find the Ferrari version of the part is actually usually cheaper too!

You will need a transfer pump.  I picked this simple Quart one up at the parts store as well.  Unfortunately the Redline bottles are not standard quart bottle (like you’d say find motor oil in).  I ended up having to cut the tops of the bottles off to use this pump. I may find an alternate one in the future.  Cost was only around $7.

This reference drawing shows the items of interest.  Use it as a reference for the steps below.

The first step is to remove the fill plug as well as the two bolts holding on the exhaust hanger to the gearbox.  I usually start with the fill bolt just in case I can’t remove it for some reason after I’ve drained the box of all fluid.  This is simply a 22mm wrench.  The two exhaust hanger nuts & washer need to be removed to make clearance for removing the filter.  Once the nuts are removed, pull the hanger off the studs and rotate it out of the way.  Discard the crush washer on the fill plug, inspect the threads and clean it off.

Next, remove the drain plug with a 14mm hex.  Depending on how cold, and how old the fluid is, you want to leave some time for it to drain thoroughly.  Because I needed to wait for parts to arrive (see info on filter below), I ended up just letting it drain for a few days.  Discard the old crush wash and inspect the magnetic drain plug for any metal debris, and then clean.

Next we want to remove the filter.  To do so, remove the one small 8mm bolt (careful not to loose the washer).  The filter can be difficult to remove depending on how long it has been in there.  I found the best way is to rotate it back and forth while gently pulling on it to make its way out.  

To rotate, I gripped onto it using adjusting pliers with a microfiber cloth in-between to prevent damaging the filter. Be patient and go slow working it out.  Eventually it will pop out.  You will need to do some maneuvering around the exhaust hanger to get it all the way out.  Once out, you will want to thoroughly clean the part.  I used warm water and Simple Green to get all the old fluid, sludge and other nastiness off it.  The filter was DIRTY and had a few SMALL metal flakes on it.  I understand from others this is expected/normal (as long as you aren’t finding larger pieces).  The sludge also indicates the fluid probably hasn’t been changed in some time.  Get it all off, make sure nothing is on the inside and thoroughly dry the filter.  At this stage, you should also remove the old o-ring, discard, and slip the new ring onto the filter.

The fluid that came out was pretty dark and nasty.  Again it likely hadn’t been changed in a long time.  You want to ensure there are no weird burnt odors, or large chunks of metal/etc. I did find quite a few strands of the case sealant the factory must have used.

During my extraction, I ran into a problem in that the filter came apart.  The front housing separated from the mesh housing.  This isn’t intended to happen (I could see the remnants of some adhesive the factory had used to hold the two pieces together).  I was able to fish the mesh half out by sticking my pinky into the gear box and pulling it out.  Although I could have probably cleaned and glued this one back together, I thought it was safer to just order a new one.

The part number for the new filter is 182416. I ordered it online and had it in a few days at a cost of around $55+shipping.

Although the replacement filter is the same part number, the design seems to have been modified. Notably, the rubber o-ring has been moved further to the face presumably to assist in easier removals in the future.

Now that everything is drained, the next step is to start putting everything back.  Start with the main drain plug, with a new washer. I had troubles finding specific torque specs so snugged it up until I could see the copper washer starting to yield.

Then reinstall the filter.  I would recommend applying a bit of gear oil to the o-ring to allow it to insert easier.  I needed to use a small rubber mallet to gently tap it in.  Reinstall the 8mm bolt.

Next, use your transfer pump to start pumping fluid back into the gearbox via the fill plug.  You want to keep adding fluid until it overfills and starts pouring back out of the opening.  You should get in just under 3L of fluid.  After the first “overflow”, let it sit for 5 minutes as you can usually squirt a little bit more in. Since the oil is so thick, it’s probably slowly finding its way into all the crevices.Once filled, reinstall the fill plug, again with a new washer.

Finally, rotate the exhaust hanger back and reinstall the two nuts securing it.

At this point, you should be good for another couple years.

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2 thoughts on “Gearbox Fluid Change

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    1. Hi. See the photo showing the two exhaust hanger bolts and the fill plug. Fill the case up slowly through that until it overflows on level ground. There’s not many photos but described in the text.

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