Product Details
S2550-15, S2550-16 Tachometer Cable
FAA-PMA Approved Direct Replacement Tach Cable for Various Cessna 172 and 182 Aircraft
Replace your worn or binding OEM S2550-15 / S2550-16 tach cables with McFarlane FAA-PMA MCS2550-15. This captive tach cable assembly delivers improved torsional strength, smoother operation, and long-term reliability compared to the original OEM configuration.
All McFarlane PMA tachometer cable assemblies are manufactured as captive assemblies, meaning the inner core is secured with swaged terminals at both ends to prevent the core from being pulled out of the conduit. This design helps protect tachometers from damage and supports long-term reliability.
- Improved design over OEM
- Core withstands up to 3x the torsional load compared to OEM
- Thrust washers on both ends for longer life and smoother operation
- Captive assembly design prevents core pullout and tachometer damage
- Polymer-jacketed casing protects the core and improves durability
- McFarlane proprietary lubricant for smooth, consistent performance
- Left-lay core design matches OEM configuration
Common Tach Cable Failure Symptoms
Tach cables most commonly fail due to binding (seizing or jerking), caused by improper lubrication, contamination, sharp bends, kinks, conduit damage, or wear over time. Binding is often visible on the instrument panel as a jumpy or erratic tach needle and may worsen until the cable fails. There are specific instructions in the service manual for how to properly install the cable or troubleshoot any issues; visit our FAQs for more information or give our technical support team a phone call.
Why are the McFarlane Tach Cables Better? Our tach cable design has improved strength compared to the OEM. When testing torsional strength, our core exceeds the OEM core, which is exceptionally important with the functionality and reliability of the tach cable. Some may inquire about replacing the core of the tach cable only, rather than replacing the full assembly. When replacing the core only, your old casing will have wear, and sometimes the wear can be significant enough to prevent a brand-new core from rotating smoothly when used with the old casing. Because of this, we do not offer replacement cores, and we highly recommend replacing your full tach cable assembly instead. Our full assemblies are an affordable alternative with better strength and reliability than a simple core replacement or a full assembly from the OEM.
Specifications
- Captive, pre-lubricated assembly
- Male ends only
- One end: 0.102″ square
- Opposite end: keyed with 0.152″ diameter
- 7/8-18 internal thread on one end
- 5/8-18 internal thread on the other end
- Left-lay core design (matches OEM)
Related Products
McFarlane also offers magnetos, alternators, starters, and additional engine accessory components to support your maintenance needs.
Installation Notes
Proper installation is critical for long service life. Tach cables should be routed as straight as possible from the tachometer through the firewall to the tach drive housing, with no sharp bends or kinks. Avoid bend radii smaller than six inches and avoid bends within three inches of either terminal. The tach cable should also be installed with the oil drain hole oriented downward to allow oil drainage if the tach drive housing seal fails. Refer to your aircraft service manual for specific torque requirements and routing guidance.
Eligible Aircraft
| Make | Model | Start S/N | End S/N | Qty/Aircraft | Location | Comment | Eligibility Chart |
|---|---|---|---|---|---|---|---|
| Cessna | 172R | 17280001 | 17280951 | 1 | Behind Instrument Panel | 7866 | |
| Cessna | 172R | 17280952 | 17281074 | 1 | Behind Instrument Panel | See Note 4 | 7866 |
| Cessna | 172R | 17281075 | 17299999 | 1 | Behind Instrument Panel | 7866 | |
| Cessna | 172S | 172S08554 | 172S08907 | 1 | Behind Instrument Panel | See Note 4 | 7866 |
| Cessna | 172S | 172S08908 | 172S99999 | 1 | Behind Instrument Panel | 7866 | |
| Cessna | 172S | 172S8001 | 172S08553 | 1 | Behind Instrument Panel | 7866 | |
| Cessna | 182S | 18280004 | 18280944 | 1 | Behind Instrument Panel | 7866 | |
| Cessna | 182T | 18280945 | 182999999 | 1 | Behind Instrument Panel | 7866 | |
| Cessna | T182T | T18208001 | T182999999 | 1 | Behind Instrument Panel | 7866 |
Part Number Information
Supersedes Part Numbers
S2550-15 (Textron) | S2550-16 (Textron)
Cross-reference information
Cross Reference Reference only: Please verify the product is eligible for your aircraft before adding to your cart. OEM Part Number McFarlane Part Number Comment S2550-15 MCS2550-15 S2550-16 MCS2550-15
Additional product information
Approval: FAA PMA (DocumentNumber: PMA-MCA-219) SupersedesPartNumber: S2550-15 (Manufacturer: Textron) SupersedesPartNumber: S2550-16 (Manufacturer: Textron)
Frequently Asked Questions
Should I try replacing my tach cable core instead of purchasing a new assembly?
We recommend replacing the full tach cable assembly instead of only replacing the core. The old casing will have wear, and sometimes this wear will be enough to prevent a brand-new core from rotating smoothly when used with the old casing. We do not offer replacement cores; however, our full tach cable assemblies are an affordable alternative with better strength and reliability
What are some recommendations for installation?
1) Tach cable should be installed as straight as possible. The installed cable should be free of kinks, dents, and sharp bends, with no bends on a radius shorter than six inches and no bends within three inches of either terminal. Any deviation from these instructions is very likely to cause binding/jerking of the tach cable as it rotates, which will prevent the tachometer from reading accurately.2) It’s unlikely to be an issue but ensuring that the hole in the engine ferrule is pointed downward when installing may help with oil drainage if the oil seal in the tach drive housing ever fails for any reason. If that seal fails in flight, and the oil can’t drain out of the drainage hole in the ferrule, it may travel up the tach cable into the tachometer and leak out of the instrument panel into the cabin.
Why is my tach needle making a weird noise? Why is the needle moving abnormally
A noisy and/or inconsistent tach needle is a sign that something is likely wrong with the tach cable. If the cable is new, the problem is more than likely either in the installation or the lubrication of the assembly. In which case:1) check the housing for kinks, dents, or sharp bends. Ensure it is routed as straight as possible. The more bends in the assembly, the more likely the tach cable will have issues rotating smoothly, especially as those bends get sharper or get nearer to one or both ends.2) Disconnect your cable at the tach, hold it vertically by one end, and slowly rotate the core terminal by hand to check for smooth rotation. Any jerking may be an indication of wear spots, kinks, or breaks in either the core or conduit. Damaged spots on the core will snag on the inside of the conduit when rotating (or vice versa), causing the jerkiness in the tach needle.3) Re-lubricate the assembly. Re-install per the maintenance manual instructions. Check the tach needle for steady and accurate reading.4) If the problem persists, the cause is less clear. If the tach cable has been in service for some time, it may have become too worn to work correctly. Even if the core didn’t have obvious worn spots, kinks, or breaks during the earlier troubleshooting, the inside of the conduit/casing may have accumulated enough wear over time to prevent smooth rotation. A replacement will fix that. It may also be an issue with the tachometer itself if the normal troubleshooting steps don’t fix the issue.
