Jaguar XK150 Overdrive


(Kim Rutherford) #1

Did all the XK 150 models have overdrive or was it an option ?.
From any owners experience Is there a huge downside to not having it on this model .
Does the gearing in the Moss box without overdrive make for super high revs at cruising speed at say 70/75 mph .
Kim R.


(Lee140FHC) #2

Doubt O/D was standard on all 150s…IF present, the rear end gear would have been a 4.09, which is quite a bit “shorter” than a non-O/D car, which is in the 3.54 range, IIRC.


(Rob Reilly) #3

No, overdrive was an option, not standard. Look at the 150 listings on xkdata.com and those with JLE or JLS gearbox numbers are overdrive, while JL or M is non-overdrive. Automatics were not overdrive.
The Service Manual page A18 gives speed per rev as 22 mph per 1000 rpm with the standard 3.64 axle, so 70 mph is 3182 rpm and 75 mph is 3409 rpm.
There were other optional axles, which can be identified by the tooth ratio on a little brass tag on one of the rear cover bolts.
There seems to be conflicting information as to the OD ratio, perhaps because Laycock DeNormanville made several models, but .78 seems to be the prevailing opinion so lets try that.
So with .78 and a 4.09 axle, it is 25.1 mph at 1000 rpm or 75.3 mph at 3000 rpm.


(Morris Barnett) #4

The revs drop by about 500 while in O/D.


(Bob Curran) #5

Kim, Its not clear from your post whether your car originally had overdrive or not. If it was built with overdrive you likely have a 4:09 rear end ratio. If the overdrive is removed, this may be too low a rear end for comfortable driving. I am not an expert, but when rebuilding my rear end I was told that it could not be converted to a lower ratio such as a 3:64 without replacing just about everything including the drive shaft. I would determine what your rear end ratio is and your options for altering it before removing the overdrive. The opposite does not necessarily hold true if you are thinking of adding an overdrive unit to a non-overdrive car. Many people prefer matching an overdrive with a 3:64 rear end for more relaxed freeway cruising.