What This Cover Is and Where It Goes
This is the driver side arm cover for the mirror assembly, not the mirror head itself and not the whole arm — just the outer shell that bolts/clips over the arm casting. On a lot of Freightliner Cascadia and Columbia trucks this cover takes a beating from ice scrapers, tree branches, and guys leaning on it to wipe the glass off in winter.
It's a direct replacement piece, meaning it's built to bolt into the same mounting points as the original 22-78606-517. Doesn't change your mirror function, doesn't add or remove adjustment points — it's cosmetic and protective, but on a truck running down I-5 at 65 mph with debris flying, protective matters.
Comes in the driver side (LH) version only — don't order this thinking it covers both sides, the passenger side has its own part number and usually a different bracket layout.
How the Cross Numbers Line Up
The Freightliner 2278606508 shows up as a running change or minor revision — same physical mounting, sometimes slightly different clip material or paint match, but it interchanges with the 517 for practical purposes. The 563.46104C and FRCA-1401-2-LS32 are the aftermarket manufacturer numbers you'll see stamped on the box from different suppliers who make this same cover to fit the same arm casting.
TRM310500BL is another cross you'll run into from parts jobbers — same story, different label on the box, same cover underneath.
Where this can go sideways: Freightliner changed mirror arm castings across model years and depending on whether the truck has heated mirrors, power mirrors, or manual — the arm casting shape can differ enough that a cover for one won't seat right on another. Always pull your old cover's number off the part itself or check your VIN before ordering. Don't go by memory of 'it's a Cascadia' — there's enough variation year to year that assuming gets you a return shipment.
Ordering From PartStop
We're out of Tacoma, WA — if you're local and need this same day, call ahead and we'll have it on the counter. Ship nationwide too, usually next-day if you're on the west coast.
At $39 this isn't a part worth agonizing over, but it's still worth confirming fit before you buy so you're not shipping it back. Give us the number off your old cover or your VIN and we'll match it up.
Backed by our standard 6+ month warranty — if it cracks prematurely or doesn't seat right, we'll sort it out.
2278606517 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 2278606517. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| OE/Cross-Ref | 563.46104C, FRCA-1401-2-LS32 |
| Freightliner | 2278606508 |
| Cross-Reference | TRM310500BL |
Frequently asked questions
Does 2278606517 fit my 2015 Cascadia?
Probably, but confirm with your VIN or the number stamped on your current mirror arm cover before ordering — Freightliner changed arm castings across model years and options like heated or power mirrors can affect fit.
Is this the same as the TRM310500BL cover?
Functionally yes, it crosses to the same mounting and covers the same arm casting. Different label, same part underneath — but still confirm against your old cover's number since packaging changes hands between suppliers.
Does this include the mirror glass or motor?
No — this is just the outer arm cover, the plastic housing. Mirror glass, motor, and the arm casting itself are separate parts.
Not sure it fits? We check before you pay.
Run your VIN and we’ll match parts to your exact truck, or call the counter — a person who knows trucks verifies fitment by OEM number before the order ships. No wrong-box returns.
More cross-reference guides
Need the part, not just the reading?
Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.