Failing bearing in front drive unit, just diagnosed at 112,647 miles.

[MountainAlive]

Just catching up to this whole thread. I blurted out loud “holy sh*t” when I saw that fluid pan pic. I know you said you used your truck to its potential, yet I think we all hope this isn’t a common occurrence as these motors pass 100k miles. Looking forward to hearing how this all pans out (no pun intended).

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[StrikesTwice]

This reminds me of “lifetime” or long interval transmission fluids in ICE vehicles. There’s a lot of doubt around those recommendations. I’ve heard the theory that manufacturers are trying to appeal to buyers with a low maintenance vehicle knowing those same people will probably sell that vehicle before there’s a problem. Meanwhile, someone gets shorted later on with a transmission that fails early.

 

[21st Century Truck]

This reminds me of “lifetime” or long interval transmission fluids in ICE vehicles. There’s a lot of doubt around those recommendations. I’ve heard the theory that manufacturers are trying to appeal to buyers with a low maintenance vehicle knowing those same people will probably sell that vehicle before there’s a problem. Meanwhile, someone gets shorted later on with a transmission that fails early.

An emphatic "YES" to this post.

Nothing is "lifetime". It's really a question of these fluids' degradation rates.

As a former avid motorcyclist I became very conscious of the brake fluid and its ability to absorb tiny amounts of water over time. Brake fluid's one critical quality is its very high boiling point, even when in intermittent contact with highly heated disc brake components. Of course, the more percentage of H2O it absorbs over time, usually through the small vent hole in the brake fluid system, the lower is the boiling point of the whole system because the more H2O is in there the larger is the possibility of that dissolved H2O beginning to boil in tiny amounts... and there goes the brake fluid pressure when the system heats up under hard braking.

So now IMHO it is a really good idea to change out the cooling fluid of the huge traction battery, the front and rear motors' Mercon fluid, and also the brake fluid on our really heavy trucks. All these components heat up and then cool down during the truck's operations and it must incrementally affect all the fluids and all the seals. In our case, the December early January trip to Newfoundland Canada with that sub-Arctic island's temperature extremes might well have contributed to our front motor's failure.

I happened to have reached a high mileage within just about two years' ownership. The truck is an awesome well-built vehicle. No reason to junk it that I can see, so I'm swallowing the cost of the new front motor.

I had thought of changing the two motors' Mercon fluid before 100,000 miles and sending the samples for lab analysis. Unfortunately, life interfered.

Now I'm changing out all three fluids, so that the new motor and all three other fluid systems have the same mileage and time start point from now on. Since the truck has to be on the lift for the great majority of the needed work, I figure the pain is worth it to do it all at the same time.

For other owners here, I'd recommend having all this done in the three - to - six month window before the truck's 1000,000 mile warranty runs out.

 

[21st Century Truck]

UPDATE (14 July 2026): after replacing the front motor unit, the EV Technician repeatedly washed out the front motor's Mercon cooling radiator, basically a smaller radiator akin to a gas / diesel engine's transmission coolant radiator.

While washing the small coolant radiator out over and over, the tech found that metal shavings from the failed front motor kept coming out of the radiator (see my fluid pan picture in a post above). As a result, I approved changing out the front motor coolant radiator so as to not contaminate the new front motor. The part cost is not significant, less than $200. Of course, this means waiting for the new coolant radiator... sigh.

The EV Tech also found signs of really degraded coolant fluid after transmission-flushing the rear motor out.

Based on this I repeat my recommendation to transmission-flush BOTH front and rear motors before Your truck hits the magic 100,000 warranty limit miles on the odometer, or at the least soon after.

 

[Grumpy2]

sending the samples for lab analysis

Are the drive units constructed such that sampling of the fluid can be done easily without contamination by most any shop mechanic?

 

[21st Century Truck]

Are the drive units constructed such that sampling of the fluid can be done easily without contamination by most any shop mechanic?

Both front and rear motors do have a small spin-on fluid filter each. A filter exchange and then a lab analysis of the fluid trapped in the filter could provide such a sampling.

However, I cannot answer how easy or even feasible getting to these spin-on filters would be without unbolting the underbody armor or without access to a heavy vehicle lift.

There are many pictures out on the Internet of Lightning motors... they show these spin-on filters up on the motors' side.

 

[Heliian]

This reminds me of “lifetime” or long interval transmission fluids in ICE vehicles. There’s a lot of doubt around those recommendations. I’ve heard the theory that manufacturers are trying to appeal to buyers with a low maintenance vehicle knowing those same people will probably sell that vehicle before there’s a problem. Meanwhile, someone gets shorted later on with a transmission that fails early.

There shouldn't be much doubt about it. The manufacturers found that more contamination and damage was being caused by the filter and fluid replacements that have now been found to be unnecessary. These transmissions are lasting 100s of thousands of miles and the added bonus of not needing extra maintenance.

Are the drive units constructed such that sampling of the fluid can be done easily without contamination by most any shop mechanic?

Anyone can take an oil sample as long as they keep it clean.

Oil analysis looks for 2 main things. 1)the condition of the oil and 2)how many particles it contains. The particle analysis is only useful if you know what your component is made out of, it can help you in determining if it's wearing before it shows as large flakes.
In this case, it has failed and there isn't much to investigate.

 

[21st Century Truck]

There shouldn't be much doubt about it.

- it all really depends on how the vehicle is used.

Oil analysis looks for 2 main things. 1)the condition of the oil and 2)how many particles it contains. The particle analysis is only useful if you know what your component is made out of, it can help you in determining if it's wearing before it shows as large flakes.
In this case, it has failed and there isn't much to investigate.

- Oil analysis can also reveal trace metals of components which are microscopically beginning to approach failure, and which haven't yet begun to actually fail. Therefore, it can serve as a factual predictor. IMHO we aren't talking here about my failed motor, but about my other motor and others' motors which haven't begun their failure cycle.

- I've done this on my motorcycles and it can be useful when thinking through what the analysis can provide.

Yes I know my two replies are inside Hellian's post just above. Frankly, it's a bit too inconvenient to resend as imho they are clear enough.

 

[RocketGhost]

This reminds me of “lifetime” or long interval transmission fluids in ICE vehicles. There’s a lot of doubt around those recommendations. I’ve heard the theory that manufacturers are trying to appeal to buyers with a low maintenance vehicle knowing those same people will probably sell that vehicle before there’s a problem. Meanwhile, someone gets shorted later on with a transmission that fails early.

I really don't think that's a motivation. I bet 99+% of buyers don't know or even bother asking what the transmission fluid change interval is before buying a car. It's been awhile since I've seen anything regarding maintenance intervals being advertised by manufacturers.

They do have to be careful because they could be open to liability. If they say change fluid at 150k and the transmissions or drive motors or whatever commonly blow up on people before then due to poor fluid, the manufacturer is likely to get sued and may lose.

 

[Pioneer74]

Now I'm changing out all three fluids, so that the new motor and all three other fluid systems have the same mileage and time start point from now on.

Just curious what the quote is to change out the battery coolant and the rear motor fluid. I'm coming up on 95k miles and thinking of getting mine done.

 

[21st Century Truck]

Just curious what the quote is to change out the battery coolant and the rear motor fluid. I'm coming up on 95k miles and thinking of getting mine done.

I expect to pick up the truck later today and I'll report afterwards.

 

[AMB_Tremor]

My battery coolant should be good as I had two modules swapped out at 65K miles and I imagine the coolant was replaced.
I am at 112K miles and I am thinking of getting the fluid changed now in the motors as a preventive maintenance measure but I am just concerned the dealer does not have any experience doing this task.

 

[21st Century Truck]

So I picked up my Lightning. BTW it is amazing how much quieter it is now - is the 1st thing I noticed.

The tech said that the Mercon fluid in the rear motor was pretty clean. Pics are attached below. The 3d Pic is of the rear motor fluid pan. The black round thing in the center is the fluid pan magnet, with 115 thousand miles of residue on it.

The brake flush cost $200. The rear motor Mercon flush + filter change cost $174. The ER traction battery coolant flush & exchange cost $256.

The front motor unit weighs about 175 pounds or so. Pics of the failed unit, without the inverter on top (reused) are below.

The last pic is of the old coolant heat exchanger for the front motor, the one that was so full of metal shavings we changed it out as well.

 

[MountainAlive]

So I picked up my Lightning. BTW it is amazing how much quieter it is now - is the 1st thing I noticed.

The tech said that the Mercon fluid in the rear motor was pretty clean. Pics are attached below. The 3d Pic is of the rear motor fluid pan. The black round thing in the center is the fluid pan magnet, with 115 thousand miles of residue on it.

The brake flush cost $200. The rear motor Mercon flush + filter change cost $174. The ER traction battery coolant flush & exchange cost $256.

The front mirror unit weighs about 175 pounds or so. Pics of the failed unit, without the inverter on top (reused) are below.

The last pic is of the old coolant heat exchanger for the front motor, the one that was so full of metal shavings we changed it out as well.

This is great info and photos thanks! All in all, that’s not a bad price to replace all those fluids and get the peace of mind (or not) that the motors are ok. Definitely worth doing this just shy of the 8yr/100k mile warranty as you mentioned before.

 

[Pioneer74]

So I picked up my Lightning. BTW it is amazing how much quieter it is now - is the 1st thing I noticed.

The tech said that the Mercon fluid in the rear motor was pretty clean. Pics are attached below. The 3d Pic is of the rear motor fluid pan. The black round thing in the center is the fluid pan magnet, with 115 thousand miles of residue on it.

The brake flush cost $200. The rear motor Mercon flush + filter change cost $174. The ER traction battery coolant flush & exchange cost $256.

The front motor unit weighs about 175 pounds or so. Pics of the failed unit, without the inverter on top (reused) are below.

The last pic is of the old coolant heat exchanger for the front motor, the one that was so full of metal shavings we changed it out as well.

2 questions. Was this an independent shop or a dealer? And were there any problems with the truck recognizing the new drive motor, or was it just plug and play?

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