My speedometer is now accurate

[SeventyOne]

Originally Posted by DeadheadNM

Absolutely!!

I needed about a 13% bump in speed at the speedo. This box has a ratio of about 1.13. Cost $108 with shipping and I got a pen from the business too. Most of you probably are aware but these K5s had a ratio adapter as standard from GM. I had a stock 1.3 or so adapter lying around and that turned out to be exactly what I needed for my k20.

On that note do you know if all the stock K5 adapters were the same ratio?

[DeadheadNM]

Originally Posted by SeventyOne

On that note do you know if all the stock K5 adapters were the same ratio?

These were not. I believe the gear ratio in the rear axle was a big discriminator but I'll need to research that in the parts manual. I suspect there are two ratios one near 0.97 the other near 1.3 but these are a guess. I'll try to firm up the knowledge and repost. There are gear drives in the transmission that come into play as well and I suspect it's because of these that there are only two ratio adapters.

EDIT: this chart from the parts manual lists two adapters for a 3.73 rear end and several for 3.07. The chart is for four speed manual transmission equipped trucks. There are other charts for auto and three speed manual.

[SeventyOne]

Originally Posted by DeadheadNM

These were not. I believe the gear ratio in the rear axle was a big discriminator but I'll need to research that in the parts manual. I suspect there are two ratios one near 0.97 the other near 1.3 but these are a guess. I'll try to firm up the knowledge and repost. There are gear drives in the transmission that come into play as well and I suspect it's because of these that there are only two ratio adapters.

EDIT: this chart from the parts manual lists two adapters for a 3.73 rear end and several for 3.07. The chart is for four speed manual transmission equipped trucks. There are other charts for auto and three speed manual.

Interesting. I just emailed speedocableUSA to get a correct adaptor as I think I'm running about 22% too fast. But I have 4.56 gears and 37'" tires so