Frequently Asked Questions

Custom Trim Option (Code 554)

Short answer: The 1968 Custom Trim option (554) included: Custom seat covers (Morrokide + stitched knit vinyl), custom molded door and quarter trim panels, the assist bar above the glovebox, dual horns, deluxe wheel covers, deluxe steering wheel, custom pedal trim, front & rear wheel-opening moldings, drip-rail moldings (coupes), and windshield-pillar garnish moldings.

The RH sideview mirror was not part of the option. Everything in the package could be ordered separately on a Standard-trim car except the custom seats/trim panels and the assist bar. (And contrary to a common claim, the etched “Bird” front-side glass was not tied to Custom Trim — many original Standard-trim cars have it.) More on FGF.

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Content last modified: June 13, 2026 at 10:06 am

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Speed-o Cable Lube

Short answer: Pull the cable from the housing, clean the cable with solvent and flush the housing (brake cleaner), then re-grease the cable with white assembly grease (or a good graphite lube) as you slide it back in. That stops the minor needle jumping.

Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.

Content last modified: June 13, 2026 at 10:06 am

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Speedometer Off

Short answer: A speedo that reads off after a rear-end swap or a tire-size change usually just needs the correct speedo driven gear (the colored plastic gear on the cable at the transmission) to match the new ratio/tire size. It’s an easy, ~$8 part at a GM dealer (Classic Industries sells them too — give your trans type and rear ratio), or a shop can recalibrate. If originality matters, fitting reproduction original-size tires is the other route.

Why it’s off: a rear-axle swap changes the gear ratio, or a taller/shorter tire changes the rolling distance, but the trans speedo drive gear wasn’t changed to match. Quick tire-diameter estimate: error = 1 − (new dia ÷ old dia). Going 225/70-15 (27.4″) to 245/50-16 (25.6″): error ≈ 6.6%, and the speedo reads faster than you’re going (shows ~70 at ~65.5). Tire-size decode: 225/70-15 = 225 mm tread width, 70 = sidewall as % of width, 15 = rim diameter.

Original tire size was E70-14 or F70-14 (probably F70-14). Comparable sizes:

Comparable Tire Sizes
Size	Diameter
E70-14	25.8″
F70-14	26.2″
195/75R14	25.5″ (5.1″ tread)
205/75R14	26.1″ (5.3″ tread)
215/70R14	25.9″ (6.0″ tread)
225/70R14	26.4″ (6.3″ tread)

Since 215/70-14 is close to original, a ~5% over-read more likely reflects a ratio mismatch (e.g., 3.23 vs 3.08). To dial it in: measure the actual error over a 10-mile measured stretch, then compute the needed gear, or use the formulas: Drive Gear = (.0495835 × Tire Dia × Driven Gear) ÷ Gear Ratio; Driven Gear = (20.168 × Gear Ratio × Drive Gear) ÷ Tire Dia. A GM parts supplier can give the gear/housing part numbers from your ratio, tire size, and trans.

Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.

Content last modified: June 13, 2026 at 10:06 am

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Wheels, Brakes, and Axle - Speedometer