over revving 420 (wrong box,dif)

[simon4253]

my friend has recently imported a 66 420 auto which is now looking very cool but is doing 4000rpm at 70mph which seems rather high. It has an lsd and is running 205/70/15 tyres. Does anyone know how to spot a wrong box or diff and would a series xj auto box be a suitable swop? The rear main is leaking so the box has to come off so would be happy to swop then to retrieve it,s cruisability as the xj is generally doing at least 1000rpm less. Thanks simon

[stuarthardy]

Simon

Did you get my reply to your private message? I've just looked through my inbox and sent messages and can't find either your message or my reply.

Are you making any progress? If I remember correctly, your friends car had BW35 gearbox instead of the Model 8, is that correct?

Regards
Stuart

[simon4253]

hi stuart I didn,t get a reply but I have been away until today and membership expired during holiday so not long redone it! It seems to be a borgwarner box but can,t read all of id tag.I may have been rebuilt in america as it was there for 25yrs or so! I do have a series2 xj engine and autobox which I may have to try if I can,t find an easier answer! thanks for any help simon