## Facts

- Michael Rix was driving a 1968 GMC pickup in Yellowstone County, Montana, when it was rear-ended by a 1978 GMC two-ton chassis-cab truck.
- The 1978 truck was sold as a chassis-cab; after sale, an authorized dealer installed a water tank on the vehicle.
- The parties stipulated that failure of a hydraulic brake line caused the brake failure at the time of the collision.
- The brake line/tube separated at the Hydrovac unit, causing loss of hydraulic braking.
- Rix sued General Motors Corporation in strict products liability alleging (1) a manufacturing defect in the brake tube/line and (2) a design defect because GMC used a single-circuit braking system rather than a safer dual-circuit system for a truck foreseeably used with heavy loads.
- GMC stipulated the brake tube was defective but contended the defect resulted from post-manufacture alteration, and denied the single-system design was unreasonably dangerous.

## Issues

1. Whether the strict-liability jury instructions, including the “without substantial change” requirement, incorrectly framed the plaintiff’s design-defect theory and prejudiced the verdict.
2. Whether Montana Rule of Evidence 407 bars evidence of subsequent design changes in a strict products liability case.
3. Whether res ipsa loquitur applies to strict products liability claims in Montana.
4. Whether the trial court abused its discretion in excluding adjuster conversations, permitting cross-examination about brake-line alteration, and denying a motion to compel further discovery supplementation.

## Decision

- The Montana Supreme Court reversed the judgment and remanded for a new trial.
- The court held the strict-liability instructions were erroneous and prejudicial as applied to the design-defect claim because they failed to adequately present that theory and improperly tied liability to the product reaching the user without substantial change.
- The court held Rule 407 applies to strict products liability; subsequent design changes were inadmissible to prove defect or culpable conduct.
- The court held res ipsa loquitur does not apply to strict products liability under Montana law.
- The court affirmed the challenged evidentiary and discovery rulings as within the trial court’s discretion.

## Legal Principles

- In strict products liability, manufacturing-defect claims properly focus on whether the product was defective when it left the manufacturer and whether post-sale changes caused the defect.
- Design-defect claims focus on whether the product line’s design was unreasonably dangerous in light of foreseeable use; instructions that make “no substantial change” dispositive can misstate the design-defect inquiry.
- A party is entitled to jury instructions that fairly and adequately present its theory of liability; instructional error is reversible when it prevents the jury from considering a central theory.
- Montana Rule of Evidence 407 excludes evidence of subsequent remedial measures, including subsequent design changes, when offered to prove defect or culpable conduct in strict products liability.
- Res ipsa loquitur is not a separate doctrine available to establish strict products liability in Montana.
- Trial courts have broad discretion over evidentiary rulings and discovery management; appellate review is for abuse of discretion.

## Conclusion

The court ordered a new trial because the jury instructions improperly constrained the design-defect theory by emphasizing “no substantial change” and failing to present whether the single-circuit brake design was unreasonably dangerous for foreseeable heavy-use configurations, while also holding that subsequent design changes are inadmissible under Rule 407 and that res ipsa loquitur does not apply in Montana strict products liability cases.


Rix v. Gen. Motors Corp., 222 Mont. 318, 723 P.2d 195 (Mont. 1986)