What This Slack Adjuster Fits
This is a universal automatic slack adjuster - 1-1/2" diameter clamp, 28-spline, with a 5-1/2" arm length. That combo shows up all over the trailer and tractor world on S-cam drum brake setups, Meritor, Eaton, Rockwell axles, and a pile of trailer manufacturers who all used the same basic geometry.
Because it's a universal fit by spline/arm-length spec rather than a single-application part, it can end up on straight trucks, tractors, and trailers alike. The spline count and arm length are what matter here, not the make of axle.
Don't just go by wheelbase or axle brand. Pull the old slack adjuster and check the spline count (count the teeth if there's no stamp) and measure arm length center-to-center. That's your fit confirmation, every time.
How These Cross Numbers Line Up
AS1172 is the number that ties this whole group together - Alliance's N42AS and BorgWarner's K043197 both cross to it because they're built to the same spline/arm spec. These aren't identical castings from one factory, but they're built to the same working dimensions, which is why they interchange.
Watch three things when you're matching a slack adjuster: spline count (28 here), arm length (5-1/2"), and the clamp/collar diameter (1-1/2"). Get any one of those wrong and the slack either won't seat on the camshaft or the pushrod geometry will be off, which throws your stroke adjustment out.
If your old part number doesn't show up in our cross list, don't assume it doesn't fit - slack adjusters get relabeled by a dozen different brands. Match the physical specs first, then use the number on the old part or your VIN to confirm before you order.
Ordering From PartStop
We're in Tacoma and keep these in stock for same-day pickup or will to get it on a truck same day if you're local. Ship nationwide if you're not close enough to walk in.
This R801075 comes with our standard 6+ month warranty. It's an aftermarket part - we don't claim it's identical to any OEM casting, just that it's built to the same working spec and will do the job if it matches your application.
Bottom line: confirm spline, arm length, and clamp diameter against your old unit or VIN before you order. A slack adjuster is cheap compared to a brake job done wrong, so take the two minutes to measure.
AS1172 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to AS1172. 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 |
|---|---|
| Alliance | N42AS AS1172 |
| BorgWarner | K043197 |
Frequently asked questions
Does AS1172 fit my Freightliner Cascadia trailer axle?
Maybe - AS1172's spec (1-1/2" clamp, 28 spline, 5-1/2" arm) shows up on a lot of trailer axles including ones paired with Cascadias, but it's not exclusive to that truck. Pull your old slack adjuster, count the splines, and measure the arm before you order. That's the only way to know for sure.
Is this the same as the Alliance N42AS?
They cross to each other because they share the same spline count, arm length, and clamp diameter - but they're not the same manufacturer's casting. Functionally they do the same job on the same application. Confirm by matching the numbers on your old part or checking your VIN if you're not sure.
How do I know if my slack adjuster is automatic or manual?
Automatic slacks self-adjust as the brake shoes wear, so you shouldn't need to manually crank them during routine service - if yours needs regular manual adjustment to keep proper stroke, it's probably a manual unit or the auto adjuster mechanism has failed. Check for a manual adjustment hex on the end; automatics typically won't need it turned in normal operation.
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.