Overdrive switch ?

About the Granvia or about whatever....
ibex32
Posts: 5
Joined: 18 Dec 2017, 17:35

Re: Overdrive switch ?

Postby ibex32 » 29 Jan 2018, 21:52

Really appreciate those responses Jarmmo & 72 degrees. I'm getting the hang of the beast.
Cheers, ibex32

Richard
Posts: 463
Joined: 28 Oct 2008, 16:48
Location: S.E. London

Re: Overdrive switch ?

Postby Richard » 24 Feb 2018, 17:36

jarmmo wrote:It is illegal to freewheel in the UK as this will affect things like power steering and brake servo vacuum....

Hmmm, I don't think so! We're talking about freewheeling, the equivalent of slipping the gearbox into neutral. If the engine is still idling then power assistance for the steering and vacuum for the brake servo will still be available. Switching the engine off whilst coasting in neutral is much more problematical because, as you say, all power assistance will be lost quite quickly (and trying to apply the brakes on a Granvia without power assistance can be frightening - the brake pedal seems immoveable!) There's also the risk when switching off the ignition key that turning the key a fraction too far will engage the steering wheel lock!

72degrees wrote:I assume it's also a good idea to flick the overdrive off and unlock the torque convertor if faced with a long, steep, downhill stretch (particularly if signed with an "engage low gear now" warning).

Toyota have created some confusion over labelling this button as "overdrive". Yes, technically it is an overdrive in that the ratio is less than 1:1, but it's simpler to just think of it as "top gear" or "4th" gear**. By switching "Overdrive Off", you prevent the gearbox from engaging top (4th) gear, so you'll do most of your driving in 3rd gear! I've been driving my Granvia for 11 years now and I've never seen a need to switch "overdrive" off - just let the automatic gearbox do its business. Only if you're pulling a very heavy load can I think that restricting the gearbox to the lowest three gears would make any sense.

You can get engine braking only in 1st and 2nd gear, so you have to move the gear lever. The freewheel function, which precludes any engine braking, will operate in 3rd gear too.

ibex32 wrote:3) I can't control the torque converter.

The speed at which the torque converter locks is set by the ECU, so if you're prepared to modify your Granvia you can change the lockup speed. See the discussion here: http://www.toyota-granvia.co.uk/viewtopic.php?t=2155
I'd love to reduce the lock-up speed to 50mph (when stuck in motorway roadworks with speed limits) but the slight savings in fuel I'd make don't really match the cost and potential for creating a reliability problem.

** Technical note: In the traditional design of automobile gearboxes, "top" gear is a direct drive - the output shaft is rotating at the same speed of the input shaft with a 1:1 gear ratio. In direct drive, the gearbox runs quietest, with least energy loss and least wear; since a car spends most driving time in top gear, that's the one which usually has direct drive. The traditional "overdrive" was usually an *extra* bolted-on gearbox for luxury or sports cars, which allowed lower engine revolutions at high speeds. For some reason, Toyota designed the gearbox for the Granvia to use direct drive for third gear, not top (4th) gear. (Perhaps Toyota found that it was cheaper to modify a three-speed gearbox just by adding another set of gears and layshafts for the 4th gear.)

jarmmo
Posts: 68
Joined: 30 Apr 2011, 06:43

Re: Overdrive switch ?

Postby jarmmo » 24 Feb 2018, 18:36

Slipping into neutral is not good practice and I think that you may find coasting is illegal on British roads because you do not have full control of the vehicle, the engine is on tickover thus not providing enough vacuum for the brakes if you use them too often which you are more likely to do when coasting. I learnt this when I was learning to drive by my driving instructor and my Father who used to be a traffic policeman at an earlier stage in his life but the highway code states that:-

122. Coasting.​This term describes a vehicle travelling in neutral or
with the clutch pressed down. It can reduce driver control because
● engine braking is eliminated
● vehicle speed downhill will increase quickly
● increased use of the footbrake can reduce its effectiveness
● steering response will be affected, particularly on bends and
corners
● it may be more difficult to select the appropriate gear when
needed.

Regards
Jarmmo

User avatar
72degrees
Posts: 22
Joined: 19 Jan 2012, 20:52

Re: Overdrive switch ?

Postby 72degrees » 24 Feb 2018, 19:12

Richard wrote:
72degrees wrote:I assume it's also a good idea to flick the overdrive off and unlock the torque convertor if faced with a long, steep, downhill stretch (particularly if signed with an "engage low gear now" warning).

Toyota have created some confusion over labelling this button as "overdrive". Yes, technically it is an overdrive in that the ratio is less than 1:1, but it's simpler to just think of it as "top gear" or "4th" gear**. By switching "Overdrive Off", you prevent the gearbox from engaging top (4th) gear, so you'll do most of your driving in 3rd gear! I've been driving my Granvia for 11 years now and I've never seen a need to switch "overdrive" off - just let the automatic gearbox do its business. Only if you're pulling a very heavy load can I think that restricting the gearbox to the lowest three gears would make any sense.

You can get engine braking only in 1st and 2nd gear, so you have to move the gear lever. The freewheel function, which precludes any engine braking, will operate in 3rd gear too.


** Technical note: In the traditional design of automobile gearboxes, "top" gear is a direct drive - the output shaft is rotating at the same speed of the input shaft with a 1:1 gear ratio. In direct drive, the gearbox runs quietest, with least energy loss and least wear; since a car spends most driving time in top gear, that's the one which usually has direct drive. The traditional "overdrive" was usually an *extra* bolted-on gearbox for luxury or sports cars, which allowed lower engine revolutions at high speeds. For some reason, Toyota designed the gearbox for the Granvia to use direct drive for third gear, not top (4th) gear. (Perhaps Toyota found that it was cheaper to modify a three-speed gearbox just by adding another set of gears and layshafts for the 4th gear.)


Thanks for that explanation. Most of my Granvia trips are made while pulling a trailer carrying two motorcycles. Not that heavy, but makes a difference on a steep hill (for example some of the gradients on the North Devon link road (A361). I suppose I could also 'kick down' to continue to 'make progress'. Sometimes the short stretches of two lanes are the only way to get past the cars and caravans going even slower (than 50 mph).

I've thought about going down to '2' a couple of times going down steep passes in the Pyrenees. Fortunately the brakes on Granvias are pretty good and they are so twisty that you aren't going at much of a road speed between the hairpins.
Granvia 3.0TD 4WD Camper
"Do not adjust your mind there is a fault in the reality"

Richard
Posts: 463
Joined: 28 Oct 2008, 16:48
Location: S.E. London

Re: Overdrive switch ?

Postby Richard » 25 Feb 2018, 10:48

72degrees wrote:Sometimes the short stretches of two lanes are the only way to get past the cars and caravans going even slower (than 50 mph).

While towing a trailer on narrow hilly sections in rural Devon? I can understand why you would find the overdrive/3rd-gear button useful and it shows how radically different are our driving styles - I'm the guy you're trying to overtake!

User avatar
72degrees
Posts: 22
Joined: 19 Jan 2012, 20:52

Re: Overdrive switch ?

Postby 72degrees » 25 Feb 2018, 11:05

Richard wrote:
72degrees wrote:Sometimes the short stretches of two lanes are the only way to get past the cars and caravans going even slower (than 50 mph).

While towing a trailer on narrow hilly sections in rural Devon? I can understand why you would find the overdrive/3rd-gear button useful and it shows how radically different are our driving styles - I'm the guy you're trying to overtake!


To clarify, the two lanes on the A361 are both on 'my side' going up a straight steep hill, with a solid white line between them and one lane coming down the hill. They are signed in advance as passing opportunities.
Granvia 3.0TD 4WD Camper
"Do not adjust your mind there is a fault in the reality"

Pdjm43
Posts: 19
Joined: 22 Jun 2017, 14:06

Re: Overdrive switch ?

Postby Pdjm43 » 12 Mar 2018, 18:37

The link to the other discussion is about my van.
I made a lock-up controller, have used it for about a year now, prior to that I just used to switch on a simple circuit to lock when ever the van went into 4th gear. Now it locks up at 30mph, but could be set to anything dynamically.
My last tankful 60 litres did 410 miles, that sounds like 31MPG. Van is a diesel 4x4 converted to 2WD, I did a 250 mile round trip (half with roof rack on) on that tank before using the rest for my commute. My MPG had been worrying me during winter, but that's because I have an Eberspacher cab heater that I've used a lot. When I go on summer holiday, I take 3 sot kayaks on the roof rack and four adults with lugggage and get 28MPG ish.


Return to “general chit chat”

Who is online

Users browsing this forum: No registered users and 1 guest