Which two pinions are likely to have worn dogs to cause jumping out of third gear?
G: Gearbox (Twin) Jumping out of third gear.
- Thread starter Len Matthews
- Start date
Always meant to sit down and write this out.....
Firstly G6 on the clutch shaft is always engaged with G7 on the layshaft. The constant mesh pinions.
For first gear G9 engages the dogs of G10 which is turning driven by the G6/G7 constant mesh pinions. G9 also engages the big end of the double gear G11 as it slides on the output shaft spline driving the output shaft and final drive sprocket.
For second gear G8/1 engages the dogs of G7 and also the teeth of the small end of G11 as it slides on the output shaft spline driving the output shaft and final drive sprocket.
For third gear G10 still turning through the engagement of the constant mesh pinions, and is also in constant mesh with G12 the third gear pinion, now has the large end of the double gear slide over the driving dogs which like first and second above Drive the output shaft and final drive sprocket.
For fourth gear, often referred to as direct drive as it really doesn't involve any speed change through gears, is obtained by the internal small end of the double gear G11 engaging the external dogs of the first constant mesh pinion G6. This makes the out put shaft turn the same speed as the clutch shaft so the final drive sprocket turns the same RPM as the clutch shaft.
All other gears are not engaged in each of the above scenarios, and also in neutral, should any issue occur to engage more gears, say for instance G8 becoming welded to the layshaft at around 100 MPH, disaster can ensue, don't ask how I know this except to say that a very wiggly black stripe measuring 208 feet (not stretched out but as the crow flies) and a trip to the haberdasher are occurrences to be dealt with.
So to answer Len, G12 and G 11 are likely the culprits!
Firstly G6 on the clutch shaft is always engaged with G7 on the layshaft. The constant mesh pinions.
For first gear G9 engages the dogs of G10 which is turning driven by the G6/G7 constant mesh pinions. G9 also engages the big end of the double gear G11 as it slides on the output shaft spline driving the output shaft and final drive sprocket.
For second gear G8/1 engages the dogs of G7 and also the teeth of the small end of G11 as it slides on the output shaft spline driving the output shaft and final drive sprocket.
For third gear G10 still turning through the engagement of the constant mesh pinions, and is also in constant mesh with G12 the third gear pinion, now has the large end of the double gear slide over the driving dogs which like first and second above Drive the output shaft and final drive sprocket.
For fourth gear, often referred to as direct drive as it really doesn't involve any speed change through gears, is obtained by the internal small end of the double gear G11 engaging the external dogs of the first constant mesh pinion G6. This makes the out put shaft turn the same speed as the clutch shaft so the final drive sprocket turns the same RPM as the clutch shaft.
All other gears are not engaged in each of the above scenarios, and also in neutral, should any issue occur to engage more gears, say for instance G8 becoming welded to the layshaft at around 100 MPH, disaster can ensue, don't ask how I know this except to say that a very wiggly black stripe measuring 208 feet (not stretched out but as the crow flies) and a trip to the haberdasher are occurrences to be dealt with.
So to answer Len, G12 and G 11 are likely the culprits!
Thanks Robert, that's very helpful.
Yes, I did the same as Robert, How I stayed on was pure luck,
Just passed many cars on a small road, Thought the engine locked up,
In with the clutch and thought it will be OK now !, But why am I still skidding ???.
When I worked on Mini Cars , To undo the gearbox nuts, We put the box in 2 gears at the same time.
Len, Is the detent spring strong enough on the camplate ?.
Good luck Bill.
Just passed many cars on a small road, Thought the engine locked up,
In with the clutch and thought it will be OK now !, But why am I still skidding ???.
When I worked on Mini Cars , To undo the gearbox nuts, We put the box in 2 gears at the same time.
Len, Is the detent spring strong enough on the camplate ?.
Good luck Bill.
I have never done it yet, But I like the idea of building the gears on the
two bearings in the plate behind the clutch, On the bench , To see how things work,
it was shown on here some time ago.
two bearings in the plate behind the clutch, On the bench , To see how things work,
it was shown on here some time ago.
G 12 and G 11 double gears equate to 3rd gear.........It is not uncommon to find either the G 19 or the G 20 shim washers missing, especially if the output shaft bearing is not fully home in the housing. This can happen if a new sprocket is installed and is too tight on the shaft, the resultant hammer blows will shift the bearing in the crank case. You might like to check first if the selector mechanism is the culprit, and for whatever reason the travel is not fully picking up that gear.
Its a bit of overkill......You can simply clamp the G2 cover plate in the soft jaws of the vice and assemble it all up and check it like that. Its only an issue if the cases have had any machining off the center faces, a few thou is ok but more can cause clearance problems.