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Brake Disc and Drum Thermocouple Installation: SAE J79-2009 Guide
This guide details the two methods from SAE J79-2009 for installing thermocouples in automotive brake discs or drums to measure bulk temperature during dynamometer and vehicle road tests. Although the standard was cancelled in February 2009, the procedures remain useful for historical reference and general guidance.
Note: SAE J79 was cancelled in 2009. Verify current standards before applying these methods.
Overview of Installation Methods
| Method | Equipment | Process | Considerations |
|---|---|---|---|
| Method A (Resistance Welding) | Resistance welder | Each thermocouple wire is welded directly to the disc or drum. | Strong mechanical bond; requires specialized welding equipment. |
| Method B (Drilling and Staking) | General shop tools | Two holes are drilled; wires are inserted and staked with a center punch. | Accessible with typical shop tools; ensure secure staking. |
Both methods specify 20 gage (0.032 in. diameter) thermocouple wire with glass braid insulation.
Installation Location and Protection
- For ribbed or finned drums: place the thermocouple between the ribs or fins.
- All installations must be protected from water, dirt, salt, and oxidation.
- Use high temperature silicone adhesive sealant (or equivalent) to prevent fatigue breakage.
🛠️ Design insight: The choice between welding and staking depends on available equipment and required durability. Welding offers superior strength but requires a resistance welder, while staking can be done with basic tools.
⚠️ Protection is critical: Without proper sealant, thermocouples are vulnerable to environmental damage and mechanical fatigue, leading to inaccurate temperature readings.
Frequently Asked Questions
- What type of thermocouple wire is required?
- 20 gage (0.032 in.) diameter wire with glass braid insulation.
- Where should the thermocouple be installed on a ribbed drum?
- Between the ribs or fins.
- Is SAE J79 still in effect?
- No, it was cancelled in February 2009 and is considered obsolete. It may still serve as a reference.
- Why is sealant important?
- It protects the junction from moisture, debris, and oxidation, which can cause failure or inaccurate readings.
