Triumph Repair: diff qstion, vintage triumph, register website

Question
i have a 77 spitfire and i have to change the differential
, i just get a used diff. in good shape. but i just find out the my diff has a prefix FH... and ratio 3:89:1 rigth??
but the one i buy it has a FK.... and i investigate from what car and year is coming from...it seems belong to Mk4 with a ratio 3:89:1 or maybe 4:11:1... i dont know witch one i have .. the qst? is , in the case is a 4:11:1 im gonna have a problem with my 77 (org 3:89:1) .. and how is gonna work on higher gears..more or less speed ,more rpm ..whats gonna happend... best case is a 3:89, and no probleam at all.....thanks jim

Answer
Manuel,

You're correct, the FK differential is a 4.11 ratio and your car should have a 3.89.

The main problem is that your speedometer will now read high, and on the highway the engine will run faster for the same speed.

Depending upon where you are located you might be able to trade the FK differential to someone for the proper one for your car.

Try putting an ad on the Vintage Triumph Register website (www.VTR.org) and see if someone might want to swap.


Cheers,

Jim