Overdrive

[Ian Anderson]

When re-building my "spare parts" Jupiter many years ago, I found that it had been built with a Javelin back axle. At the time I could not obtain a Jupiter axle, so it was suggested that I fit an overdrive to overcome the ratio difference. I acquired a Laycock-de-Normanville unit and an adapter plate from Dennis Sparrow which meant the overdrive replaced the gearbox tail unit. This meant that the overdrive shares the gearbox oil as it had in the Rootes group donor car.
Some time ago, the overdrive stopped working, and I have eventually decided to investigate. It turns out that there was insufficient oil in the overdrive. As there were no leaks, and the gearbox level was at max, I assume that the overdrive oil had transferred to the gearbox and was lost at the clutch end. (I do sometimes get clutch judder) When the overdrive is not operating, the whole planet wheel assembly rotates at prop shaft speed, and I assume that this splashes the oil into the gearbox making the oil level too high.
I believe that later systems fit the overdrive in the prop shaft, but wondered if anybody knew of a fix for this problem (assuming that I have actually identified the problem!)

Ian Anderson

[Keith Clements]

My overdrives use red ATF transmission oil not EP30 gearbox oil.
Overdrives have an oil pump inside them.
I would think the overdrive could be filled separatly.
viewtopic.php?p=45429#p45429 has workshop manual.

[Ian Anderson]

Hi Keith

I believe that the overdrive was from a 1960's Rootes vehicle (Hillman Superminx, Singer Vogue, Humber Sceptre Etc.) My father had a 1962 Sceptre and I am sure it shared the 30 grade oil from the gearbox (it was 60 odd years ago!). Certainly the adapter plate - more of an adapter ring -supplied by Dennis makes it unavoidable. In this set up, the gearbox tailpipe is removed and replaced by the overdrive, the speedo cable screwing into the overdrive. It requires the gearbox mounting to be cut from the chassis and welded back facing backwards to clamp the end of the overdrive. If your unit is between the gearbox tailpipe and the midship bearing, then it can have its own oil. If it bolts directly onto the back of the gearbox and still has its own oil, then the adapter plate design must have been changed to block the oil transfer since I fitted mine (1980s?), which it what I am trying to find out.

[Keith Clements]

Probably worth calling Overdrive Spares They are THE experts.

[PJGD]

I think, Ian, that you are right that on the Rootes cars using the Laycock D-type overdrive that the gearbox and O/D oil was shared. I have a manual from a mid-50's Sunbeam Rapier and here is the section on the overdrive. Elsewhere in the manual, it states that the combined oil volume for both gearbox and O/D is 4 pints.

Sunbeam Rapier Manual-Overdrive Section.pdf