Manual gearbox oil discussion.

[Dave2000]

I remember those days Frank....yeh I am that old as well! The only thing I see there is the BMC gears were submerged in the oil and the LC uses a pump, maintaining a viscosity to suit the pump may be hard when it is designed for a 80/90 weight oil? Much thinner than say the 75w I (we) have in there may result in a lower pressure to the gear train?

@Towpack I know nothing about motorbikes, but I am guessing the 'wet clutch' means exactly that 'wet'? If that is the case then that sort of goes 'against the grain' of thinking. Friction is needed for a clutch to work and no friction is needed where gears mesh, or have I got that wrong?

regards

Dave

 

[frank rabbets]

Lots of mbikes had their clutches submerged in an oil bath which also contained the primary chain running from the crankshaft to the gearbox. I don't really know the reason. The Nortons I had had 14 plate clutches and the linings were Ferodo but I used to throw away the bath and run the clutch dry as the racing Nortons did. I know some mbikes had cork inserts. Perhaps they needed an oil bath for cooling.

I don't think hot engine oil is much thinner than hot gearbox oil. Aren't the two types measured on different scales ? The oil pump in the LC box has a very close tolerance so it will cope with engine oil. I think my Morris Minor owners handbook said to use engine oil in the gearbox.

 

[frank rabbets]

Just checked...........20W50 engine oil in the Morris Minor gearbox. Synchros on 2,3+4. They were reliable boxes except when the teeth wore off the 1st+reverse gearwheel.

 

[Dave2000]

I will not comment on the motor bikes as I do not have a clue. I think you are correct Frank about the gearbox/engine oils being measured differently, I did see a comparison chart recently on my searches but do you think I can find it now...can I hell! The chart showed some rational about the oil comparisons, something to do with high speed/low torque and low speed and high torque sheer rates and so forth, gear oil formulation managing to lubricate at both ends of the scale and engine oil not so comfortably?

regards

Dave

 

[Dave2000]

Karl asked about the gearbox yesterday so here is an update, I have tried it around the village for about a week now and 'think' it is improving. You would think it would be easy to evaluate a vehicle and how it drives however, having driven literally hundreds of different vehicle types/marques, I realise that once I have driven it for say 20 or 30 minutes I 'adapt' my driving style without realising it, if there was a minor problem I would probably alter my driving style to work around it, difficult to explain if you are not mechanically minded. I can say with conviction that the reverse grating when cold has stopped so that is a plus, this was something that was never there until I changed to the synthetic gear oil. Why this has improved I am not sure, I did surmise the 75W synthetic oil was a little on the thin side allowing the cluster to spin more freely when cold? Now the weather has started to get colder (no shorts the last couple of days ), this may be the reason the grating has stopped? When cold 1st to 2nd changes are still a little reluctant when cold, the gears not quite smooth, this improves as the transmission warms, so nothing new there. 3rd to 2nd seems to have improved as well in fact, I did not notice it the last couple of trips out, again I may be altering my driving to accommodate it so this is a guarded comment. The car has stood in the garage for the last couple of days and as mentioned it has got colder, tonight as designated driver I will be the taxi for the party animals, I will try and be a bit more subjective when I next report, I will be changing the neutral bias springs as they so not 'feel' right, another of those bloody subjective things....perhaps a bit 'Mr Picky' with a gearbox design which must be approaching 30 years?

Have a Happy New Year.

regards

Dave

 

[Chris]

When I got mine, the gear change was pretty good. Not 100% but pretty good. I did an oil change on it and it was then awful. It was originally running with a mix of oil and ATF. I drained a bit of the new oil out and added some ATF back in. it improved. Still not happy and not having the time to swap the box over, I drained some more out and added another litre of ATF. An almost immediate change to the box. Quieter and smoother. I can hit 2nd from 3rd almost every time and get into 1st when still rolling. Sometimes I need to line it up a bit but it's genuinely transformed.

 

[frank rabbets]

Well done Chris. Goes to show the thinner the oil the quicker the bronze synchro teeth bite through to the steel cone on the gearwheel speeding up the change.

 

[clivehorridge]

Not intending to hijack this thread too much, but my manual "chinks" into 3rd, irrespective of going up or down the box. I always put it down to having 19 years and 360k kms on the clock, and all the other gears select just fine.

Do you think I would benefit from trying the ATF addition, like Chris?

I obviously don't want to do any damage and I don't know what oil is in it at the moment, it was changed not so long ago by my trusted Service workshop who are well familiar with 80's.

The staff there own 3 themselves...

I'm also surprised that none of the alleged oil guru's chip in on a thread like this, where's the expert advice that Opie are supposed to give freely? Even their thread queries seem to go unanswered

Happy New Year all!

 

[Chris]

When you say it liek that Frank it doesn't sound altogether good!!! But as you know I have a 100 box sitting here waiting to go in. I understand that Merc run their gear boxes on ATF as do some others. I certainly is noticeably different and that's in this freezing weather at the minute. With 100% correct gearbox oil in it was desperate. Even when hot. Mine doesn't crunch or grate or anything Clive, it simply baulks. It just won't go into gear. You can push and shout and it's like there is no gate there at all. You can DDC or even push forward to 1st then pull back quickly and it usually slides into 2nd. But with the ATF in, it's actually close to functioning correctly.

 

[clivehorridge]

I have to admit that mine is a pig when it's cold. It's about -11 at the moment and we've just been to the mall. The box was quite stiff for the first 2 kms, but it soon loosened up after that.

I might give this a go, can always go back to standard if it doesn't improve things...

 

[frank rabbets]

Mine has always chinked going in to 3rd Clive and it only had 30 k miles when I had it.

When I worked on a lot of cars years ago Chris it was common to have syncro failure as in stuck or grating gears as we get with ours but the cause was nearly always worn out bronze syncro cones with no teeth left, just a smooth surface which slid rather than gripped. So you can't really win, if the syncro works well the cones will wear out. The LC gearbox oil comes out very clean whereas with the old cars it looked like gold paint.

 

[Cptsideways]

Mine is now transformed on its mix of MT75 & ATF, from an unusable box to a lovely one.