I counted the driveshaft turns & came up with about 3.5 to 1. I seem to tach out at about 2600 rpm at 60 mph. Since that's not a very low rear end ratio, I wondered if the trans gearing was somehow changed.

Is that possible?

Thanks,

Your rmps seem to be about right for your rear gear. I don't t hink anyhting is unusual.

To wnaswer your question about 4th being changeable.... yes and no. Mostly no.

If it's using stock parts, its 1:1, and there's no changing it. Autogear does make an aftermarket gearset to give you 1:1 in 3rd, and an overdrive in 4th. So, 4th can be different than 1:1, but it would give you lower rpms, and it've very unlikely your trans has been changed. Most likely your 4th gear is 1:1 like it should be.

The speedometer gear in the trans can be changed however. So you might not be doing the speed you think you are.

The speedometer gear in the trans can be changed however. So you might not be doing the speed you think you are.

That may be. My next step was to drive behind another car at a known 60mph & check.

It just seemed that I wasn't going very fast and the rpm seemed very high. It made me think I had a 4:56 rear in there.

My Durango is at 1400 rpm @ 60mph & I know it an overdrive trans but it just seems a big block doesn't need that.

I also have a 66 Stingray stock small block 4 speed & it doesn't tach near that either.