Changing gear with overdrive engaged?

[storeyn]

Hi All

I have always been of the opinion from what people have told me never to change gear with overdrive engaged...which is what I have always done over my 20 plus years of Dolomite ownership.

I have recently been watching some YouTube videos of dolomites on track days...and it seemed to me that some of the gear changes were completed with o/d engaged. It may have been that it was dis-engaged just prior to the change..but listening to the engine note it didn’t seem that way... but I have been wrong before...

I just thought i would canvas opinion....

[yorkshire_spam]

If I want to go from 3+OD to 4+OD I just change and leave the OD engaged.
If I want to go from 3+OD to 4th I just change and flick the OD out as I shift the stick through the gate. I don't disengage the OD and then change up.

[xvivalve]

Look at the gear ratios and then consider the 25% effect overdrive has.

Changing from overdrive third to non overdrive fourth is wasted effort.

There is no issue with changing gear whilst overdrive is engaged (unless to inadvertently select and use reverse if the overdrive has failed to disengage!)

[GTS290N]

1850. If in a hurry, third to overdrive to fourth overdrive.
If pootling, third to fourth to overdrive.
Had this box for around 8 - 9 years although it doesn't do a lot of mileage, as a 19 year old late 70s early 80s I wrecked 3 boxes in 55,000 miles. More to do with youthful enthusiasm and ignorance than any overdrive non-switching.

[Carledo]

I too killed a good few overdrive gearboxes back in the day! BUT it was the (mostly 3 rail) gearboxes I killed, not the overdrive units. I became quite adept at rebuilding my GT6 gearbox and rebuilt the same box 2-3 times whilst retaining the same D type o/d unit untouched save for a swarf rinse!

Although the factory handbook has always recommended not shifting with o/d engaged (early 60s even recommended declutching!) I've ALWAYS gone up the box 1-2-3-3o/d-4o/d and missed out direct top, since as Alun has pointed out, the difference between o/d 3rd and direct top is negligible! However i've always downshifted the "correct" way, disengaging the o/d first then going down the box as needed. I think the shock load I can feel, coming out of o/d 3rd into direct 3rd under heavy braking and a trailing throttle, just made me wince a bit too much!

Steve

[soe8m]

I also go directly form 3od to 4od but the solenoid is shortly switched off and on again in between the movement from 3 to 4.

I think a J type will be fine but an A type can have a difficulty with this. The J type has a constant oilflow and when operated the relief pressure is set higher so the overdrive engages. There is always oil pumped through the system for fast engagement. An A type has no constant oilflow and when opererated a valve opens and oil is pumped to the operating pistons so it takes a little longer to engage. Switching off and on in between from 3od to 4od with a A type probably cause the od slip a little during gearlever movement.

That's why there are two different way's advised how to shift I think. Leave in od and switch it off before gearchange.

Jeroen