Overdrive Box and Speedo

[Rangi246]

So i'm all set to put in the new OD gearbox to replace a non overdrive unit but my gut is telling me i've overlooked something.

The new gearbox is a Dolomite 1850 3 rail with the J type overdrive.
The car is a 65 Vit 1600 running a beefed up 4.11 diff.

I have read a few posts on here that mention a change in the speedo is possible when the new gearbox is installed. Is there anything I need to do with the speedo angle drive or the speedo? Something is nagging me (its not my wife) and I can't quite put my finger on it.

Also, the new gearbox doesn't have its top cover and selector mechanism. I was hoping to swap over the one from the old box (also a Dolomite 3 rail but non OD). This should be a straight swap or am I missing something here too?

Any help would be very much appreciated as I want to have everything sorted before putting it into the car.

Mark

[Clive]

no need to swap speedo. However, there may (or may not!) be an issue with the speedo drive gear in the overdrive. My J type runs about 20% out.....
There are a few different gears that can be fitted, but I have no idea which one you (or I) need.

Top cover. Will work BUT and it is a huge, enormous but, you need an inhibitor switch that is part of the overdrive one. Without it you can engage overdrive n any gear and leave it engaged. OD in second is probably OK, in first, well, should live. In reverse (possibly just rolling backwards ) bye bye overdrive.
the inhibitor mechanism is there for a VERY good reason.
You may be able to fabricate something, a look in the parts book should give you an idea. Bear in mind the same gearbox (more or less) is used in vit/gt6/spit and I am pretty sure all are interchangable (except the single rail versions of course) but the parts are the hens teeth, hence making is a good path to follow. Some parts (inhibitor switch brackets etc) may even be available new, but simple enough to make if needed.

[garyf]

I've got an early 3 Rail Doly 1850 box with J Type Overdrive in my Vitesse, its got the standard 3.89 Ratio Diff, 13" Wheels with 175/70 tyres.

It's spot on whe you go past the 30 Limit warning signs that tell you your speed and to SLOW DOWN! ;D

I've not got a Sat Nav so don't know if it's really spot on though?

A mate who owned my car previously and fitted the O/D Box back in the mid 80's was told to use the Brown coloured drive gear with 18 teeth (NKC49 I think is the Part number?)

You can get other gears of different colours and teeth quantities, the Grey coloured one has 20 teeth, not sure which one you will need with a 4.11 Diff though? :-/

Gary  

[dar]

download gps speedo app to your phone, its good