5 Speed

[Lang]

Harry,

You are right.

GMC Box First 6.06 to 1
Second 3,50 to 1
Third 1.80 to 1
Fourth 1 to 1
Fifth .799 to 1
Reverse 6.00 to 1

All this is still just a moot point because you have transfer case ratios
(on all multi drive vehicles but below is for 6X6 GMC)
High 1.16 to 1
Low 2.63 to 1

Axle ratios 6.6 to 1

And tyre diameter which can easily change the on-road total ratio by 10%

When you are considering dropping down the engine revs during cruise (to make it quieter and less engine stress plus better fuel consumption) there are several ways. You can change any of the above to achieve the aim.

In order of ease and cost:

1. Easiest is to put on bigger tyres, but may not suit originality appearance requirements.

2. Higher ratio crown wheel and pinion in diff.


3. Overdrive gearbox.

4. Fit a 235 engine which will still scream and use fuel but can be safely run at higher rpm for long periods to give you the extra cruise speed.

Lang