The Triumph Dolomite Club - Discussion Forum

With my 1850HL, since getting the overdrive connected up I have noticed that 3rd gear + overdrive is about the same as 4th gear without overdrive.
So, I reckon for best acceleration down the slip road and upto motorway cruising speed is to go 1st, 2nd, 3rd, 3rd+od, 4th+od. That means to completely miss out 4th gear without overdrive.

So it seams that 4th gear is pointless, but then I was on the dual carriageway and I wanted to cruise at 60, but was being held back by a dawdler doing 45-50 mph. From 4th+OD I floored the accelerator and dropped out of OD, that gave me the right range in revs to get past the dawdler and on to 60mph without letting off the power, nice move.

Although there seems to be overlap there are definitely various situations where the OD is spot on in the additional ranges it provides, what are your favoured uses of it and what moves have you made with yours?

I tend to use overdrive in 4th as soon as I reach an indicated 40mph. That's closer to 45mph.
I do switch out of od to get acceleration when overtaking, but I am mindful of the stresses on the chocolate 1850 gearboxes. Has to be done though.

I try to use o/d as aften as is suitable but sometimes 'forget' to come out of o/d when changing down to 2nd or even 1st. Is this a big no-no?

Tim

In normal driving I usually go through the normal 1, 2, 3, 4 and use 4/OD as a cruising gear once I'm up to speed.

Overdrive 3rd only really gets used in London instead of 4th as its one less gearchange to do in terrible stop/start traffic!

If it hasn't been modified, there's no overdrive in 1st and 2nd gears.

Does the Sprint have a similar overlap of "3rd+OD = 4th"?

Yes, they are very similar but slightly different. I have the ratios written down somewhere.

I've had many Triumphs with overdrive and in every case direct top and o/d 3rd are almost the same.
My tecnique has aways been 1, 2, 3, 3o/d, 4o/d going up but going down I shift out of o/d first, then go down the box as needed. this method tends to ensure that I don't forget to disengage the o/d (which shouldn't operate in 1st and 2nd anyway) but saves the embarassment of a botched upshift to 3rd with the o/d engaged and coming in immediately which drops the revs too low, too soon!
Incidentally, I read in several original handbooks that one should use the clutch when engaging and disengaging the o/d, something i've never done and don't seem to have suffered for, my attrition rate for o/d units is tiny (though electrical faults and failures are all too common) even though i've never been exactly kind to my gearboxes!

Steve

When my own dolly was 1500 powered I used to go through 1st,2nd,3rd,4th then go for OD,,but tbh as you point out its basically the same as going 3rd,,od 3rd then 4th

the main good thing I used to find was in reasonably free flowing urban driving I would leave it in third and basically just auto shift the OD in and out which gave a nice easy 2 speed auto effect for sheer luxury laziness

I think as the mechanism is basically akin to an auto its ratio changing ability under load is very good certainly by the sounds of it more problems occur due to the hydraulic actuation going to pot than slipping

Yes it can and does engage under high throttle loads but trust me when I say the
cone clutch will wear and eventually slip if you do this a lot.

Best to switch it in when you've reached cruising speed.

You can use it when overtaking in 3rd so you dont run out of revs but I wouldnt make a habit of this.

Jonners

http://www.mintylamb.co.uk/gearspeed/ will show you the ratios, my 1850HL box: 3rd OD had a 0.01 of a ratio higher than 4th or so the manual dictated, so there was no noticeable difference at all!

The sprint gearbox however, 3rd OD is noticeably different to 4th

30mph in 3rd OD is around 1700rpm and 4th is around 1550rpm to give you an idea, however I personally just go 1st, 2nd, 3rd, 4th, 4OD as 30 in 4th seems the most efficient for the engine, on track changing from 3rd OD to 4th is a much more useful option as it is much more noticeable at higher speeds, it also allows for a faster acceleration towards the standard top speed and when you change into 4th you won't have drifted too far out of the peak power band to continue accelerating, but this is at engine speeds of around 6000rpm which I'm sure you don't drag the dear 1850 engine to and, being an 1850 it will be no different at any engine speed

Another bonus of a sprint box is that it is impeccably easy to wire in OD for 2nd which is fantastic for slow moving traffic of around 15-20mph!

Just be careful if you do switch out of OD whilst changing gear, as if it is mistimed, you'll feel it!

It's good to know how other people drive and use their cars. I took a drive from to Southampton the other week. A bit of a brave outing TBH. Furthest run I had been in it was 12 miles. Steady 60 in 4th OD on the dual carriageway way fine, occasionally dropping out of OD for the hills. A few times while slowing down for round-abouts the drive train would emit a dull squawking/high pitched humming sound when dropping out of O/D or dropping down the gears. It all held together on a 120 mile round trip, but my shoulders did ache as I am used to left and right arm rests in my other cars.