Here in the US the 131 gearboxes are getting hard to find, and the shifter extension was never brought here, so that would have to be bought overseas.fiatfactory wrote:131 gearbox has a good 5th ratio, swap gearboxes...SteveC
Also, at least here in the US, up to 1978 the 131 had similar 5th gear ratio to the 124, I think 0.87:1 vs the 124's 0.88:1.
The 1979-on 131 (Brava here in the US) had a 0.83:1 ratio, but even that is only about 6% different from the 124. That's a lot of work to get 6% longer gearing.
Unfortunately there is no easy solution.