This is a sentence from John le Carre's novel 'The Honourable Schoolboy'.
"Luke drove as if they were in a jeep, in high gear with hammer changes on the corners."
Does anyone know what 'hammer changes' mean?
We looked up "hammer changes gear shift Jeep" and got this;
For me one of the clues was "Luke drove as if they were in a Jeep, in high gear with hammer changes..."
See Jeep Forum Do you float your gears?"
So "hammer changes" may be another way to describe "banging through the gears", also known as float shifting.
... the process of changing gears, in typically a non-synchronous transmission, without depressing the clutch.
How it works: While driving at the top range of the non-synchronous gear, remove foot from accelerator pedal, wait for RPMs to come down to sync with the drive shaft, and then jam the stick into the next gear change without touching the clutch pedal. This needs to be coordinated with the steering (i.e. over, under, etc.
I used to race my MG back in the day, and my father showed me how to do this. Later on, my brother-in-law used to race in the 1/4 mile in Jersey, and he used to use his right foot to kick his '69 Camaro into 3rd gear while working the accelerator with his left foot.
The process of changing gears in a non-synchronous transmission —also known as floating gears, dead sticking, or bang shifting —usually occurs without depressing the clutch. When they work correctly, floating gears will allow your car to shift gears faster and more easily. However, they can damage the gears if they are not properly engaged. Therefore, it is important to know what floating gears are, how they work, and how to prevent them from wearing out.
Tabsnation "What is floating gears?"
This is likely related to the phrase put the hammer down, defined by TFD as:
To press down the accelerator (of an automobile) as far as possible; to accelerate to or travel at an automobile's maximum speed. Primarily heard in US.
In this case it seems likely that "hammer changes" refers to speeding up or slowing down by pressing or releasing the car's accelerator.
