Jupiter Gearbox lubrication

[Brian Cole]

The gearbox on my car is quite noisy except in top. Has anyone had experience of using STP or Molyslip type additives and would addition of such additives help to quieten the gear noise? I seem to remember reading somewhere that such additives can damage the internals. Some guidance on this will be much appreciated.
Brian Cole

[Srenner]

Hello Brian:

You didn't describe the noises, so I will shoot from the lip. The additives you suggested might quiet things down, but it is likely you have worn internals. The additives might be "stickier" or "slicker", but generally things get noisy when the clearances get too big. Some oils and additives have compounds that can erode bronze/brass parts. Increasing the viscosity of the oil adds to the strain put on the moving parts.

I am not schooled in the oils you mentioned, but would advise looking at a rebuild. Things only wear out more the longer one waits.

[Forumadmin]

Agree with Scott on rebuild. It is likely a washer or bearing is shot and could do much damage if not replaced. Molyslip was used on rallies and proved very valuable when oil runs out. I have used various additives in the gearbox as they should help improve high load conditions experienced in racing and rallying. No idea if they work as you have no controillled way of testing and observing results. Sawdust used to be used when selling cars in the 60s to quieten gearboxes!

[Brian Cole]

Thanks for the advice. I'm happy rebuilding engines but have always shied away from gearboxes, quite complicated devices not to be trusted to the ill equipped! Have you ever stripped and rebuilt a Jupiter box? To qualify my post the noise is in the form of a very noticeable whine which increases in pitch with speed. Top is quiet. Selection is not too bad in third, second is slow, and first is traffic lights only. Reverse is OK. Lots of oil leaks of course. As top is quiet I assume that the mainshaft and bearings are OK? Any further thoughts appreciated.

[Forumadmin]

There are some good notes on rebuilding gearboxes by Harry Brierley. Searching the Gallery gave me that link.
And the answer to your question yes, many many times once even on the side of a mountain in a forest in France on the way to Le Mans. They are really satisfying and interesting to rebuild.

[Leo Bolter]

Hello Brian.
You said:

Lots of oil leaks of course.

For anyone concerned with gearbox oil leaks, I suggest looking at this modification "conversation": http://jowett.net/forum/viewtopic.php?f ... eaks#p3451

(NOTE: the next paragraph has been edited in light of further reading I have done )
Regarding gearbox overhaul.
The following suggestion has been documented in Harry Brierley's Paper (which was mentioned previously at section 5. 7 Layshaft), but I give my picture here anyway.
When the gearbox has been stripped and the layshaft has been examined for wear where the bearings run, it will often be seen that the shaft surface shows slight wear or the hardening is failing. If this is very minor the shaft could be reused and should be quite "satisfactory" for many more miles if the following is done.
I note that mention is made in that section of "penny pinching" and I agree that if new is available then new is best . . . but sometimes a "cunning plan" (as Baldrick would have said) is necessary

As illustrated in the image below, make a new layshaft locating peg hole in the case at 180° to the original. When this location is used on assembly the old "pressure point" will be on the opposite side of the shaft.



The next image shows a very useful bit of kit . . . it does require the sacrifice of a side plate and also having the mechanism up to scratch, but it's great to be able to see what's going on inside the box when trouble shooting, setting up and trial changing gear whilst assembling.