4th Gear Raio of 1.2

[2Types]

My series 2 FHC seems to have a non-standard gearbox. It has the filler plug on the right hand side and more annoyingly a 4th gear ratio of around 1.2 instead of 1:1. It has a 3.07 diff so at 3,000rpm I am only doing about 63mph which makes motorways quite a chore.

Does anyone what this box may have come from as I cannot find any numbers on it.

[LesterE]

Hi.
I can’t recall any manufacturer who makes a four speed box with an underdrive top gear.
63/64 mph is exactly what my U.S. spec does in in forth with the 3.5 : 1 rear axle ratio.
It may be worth marking the diff flange and wheel and physically checking the ratio.
Lester

[2Types]

Lester,

I have done the check on the diff at it is a 3.07 and I have then worked back from there to work out the 4th gear ratio.

[XJR308]

I would like to see a four speed box with an underdrive top!!
I would work on the assumption your box has a 1:1 fourth gear and calculate the theoretical diff ratio from there. It is possible you have the wrong speedo drive gear and you are actually going faster that 63MPH.
Bruce

[2Types]

Bruce

I have checked the speedo against the GPS speed on my Sat Nav at it is reading accurate. My only other though would be that the rev counter is reading incorrect. That seems unlikely as it does feel/sound about right compared to other e types I have been in, although any easy ways to check would be appreciated.

[XJR308]

Hi Lester
An unusual problem!
To have a 4th gear of 1.2 to 1.0 wouldn’t make engineering sense as 1:1 just connects the input shaft to the output shaft. A gear box with a 1.2 4th would make the gear box expensive and heavier.
So either the speedo is wrong, the revcounter is wrong or the diff ratio is wrong. Unless the clutch is slipping!
Bruce