Changing gear without clutch?

KTRIC

RicardoSmith wrote:

If you are referring to me. No. Heard it from people I know who remember when there wasn't such a thing as sychromesh gearboxs. Nothing special about not using the clutch. Double declutching, dogleg gear boxes, Straight cut gears were all boringly normal.

Done it myself in cars, vans and trucks when the clutch cables gone, or the clutch lining is worn out. Hill starts are a bugger. Remember having to do it going up ChristChurch Hill. (used to be the other direction with lights at the top) Stillorgan car park is also no fun without a clutch. Even no handbrake is tricky on a hill. No handbrake and no clutch, that would be tough.

No , i was refering to fjon and the website he /she read this crap on. I used to work for Hertz and I heard all the stories about cars coming back with the clutches burnt out after 5 days rental because some American can't use a "stick shift".

RicardoSmith

Banta Fodder wrote:

No , i was refering to fjon and the website he /she read this crap on. I used to work for Hertz and I heard all the stories about cars coming back with the clutches burnt out after 5 days rental because some American can't use a "stick shift".

ah..my bad.

I can only imagine. I remember trying to hire a manual in the States they didn't have any. had to get the guy show me how to use an automatic. He thought I was taking the p.

Capt'n Midnight

Citroen's logo is based on synchromesh gears, that's how proud they were about them. Or in other words they've been around a long time and as others have posted synchromesh are much easier to use with a clutch than the straight cut one, and much harder to use without a clutch.

Yeah my car that could change up without using the clutch, but I since had the gearbox changed.

ds20prefecture

All a clutch does is match the speed of the flywheel to the particular gear selected. If the revs are right on the flywheel, there is no problem meshing the gear without using the clutch.

Obviously there is some skill to matching the speed of the engine to the appropriate gear being selected. Changing up is easier as the engine revs are slowing to match the rotation of the higher gear. If downshifting, you need to blip the throttle to match the engine speed to the higher rotation speed of the lower gear.

AMurphy

RicardoSmith wrote:

Done properly ... The sync and the clutch are there so you don't have to match the speeds before making the change, and that clumsy oafs can drive a car. Syncho Mesh gears are less efficent at transferring power than square cut gears. Which is why racing cars used to use them. Dunno if that still applies these days.

"Done properly", there is the problem, 99% of the driving public couldn't. And just lile PS, soft clutches, Power windows, ABS, etc it makes the task easier and more comfortable, hence get more (sub standard) drivers behind the wheel.

Straight cut gears are stronger I believe and have non of the sidethrust problems associated with Helical cut gears and may be slightly more efficient.
However, Heli cut gears make less noise, are smoother, etc. Can you imagine is all your forward gears engaged and sounded like reverse?.
Synchro does not add or subtrace to the efficiency, the only time they are active/used is when changing gears, then it becomes part of the rotating mass, that all. They may add length and weight to the overall construction, which has some associated efficiency penalty, as would the constant meshing.

Lord Nikon

Clutch is your friend.

Scruff

The Atheist wrote:

I've heard you can stop without using the brake pedal.
You just need to be able to open your door and also to have a good pair of shoes.

no no no. the way to do it is drop 2 gears like from 4th direct to 2nd. slows the car fantastically without loosing revs and inducing a kind of handbrake turn. excellent for slingshotting around a tight corner.

fjon

My my, what a controversial subject. As mentioned before, I *do not* drive without the clutch. I did do it for a while as a DIY remedy for a problem I was having. Problem was solved; I started using the clutch again like a normal person.
For the record, it was a UK site, and not American.

Hotblack Desiato

AMurphy wrote:

Sure you can do it, tractors with non-synchro straight cut gears are better for the job though.

A motorcycle has the same sort of gearbox

If you're using a good bit of throttle on a bike you can change up very very smoothly by pushing the gear lever and partially closing then re-opening the throttle very quickly.

Drag racing motorcycles usually have a "quick shifter" - a pushbutton to cut the ignition - so they keep the throttle fully wound on and just quickly press the button to shift up - takes a fraction of a second.

xtrac

ds20prefecture wrote:

All a clutch does is match the speed of the flywheel to the particular gear selected. If the revs are right on the flywheel, there is no problem meshing the gear without using the clutch.

Ah, no :-). The clutch dis-engages the gearbox from the engine, in doing so takes the pressure off the gears to make changing easier(possible?)

There are specific gearbox types that allow clutchless gear changes, these are called dog boxes. Kersh was correct in saying Hewland make them, so do Quaife, Xtrac and numerous others. These mostly have straight-cut gears (for less powerloss, as mentioned by another poster) and have dog-rings. These are similar, (but different :-)) to synchromesh rings. A synchro ring has teeth on it like triangles, and these (on both gears) "mesh" with each other to make the gears rotate at the same speed and enable a smooth change. The dog rings on the other hand, have teeth (4,6 or 8 usually) like you would see on the tops of castles (not sure what these are called, look abit like lego bricks), you need to lift from throttle and then with speed and power ram it into the desired gear. Given that these mesh realy quick with each other, very fast gear changes are possible, if you try to change a synchro box this quick, you will either beat the synchros and damage them, or the box just wont change until it has corrected it speed enough, some toyota boxes are like this, and some subarus are like the former, hence the necessity to examine 2,3,4 and 5th gear in scoobys for notchy changes. I've used dogboxes for about 6 years now, and love them :-)

You can also get sequential, full throttle dog-boxes, but these mostly have electronics to cut power to engine when it senses a change coming and then the box acts like a standard dogbox.

A point of note is that dogboxes are by design, destined to wear out, hence you dont see them on road cars, and by wear out, I mean the dog teeth themselves wear and refuse to hold the car in gear, i.e. it just keeps popping out.

For me, the main benefit of a dogbox is that it allows me to left foot brake and change gear at the same time, hence my right foot never leaves the throttle position, allowing me superior reaction times than if I kept having to move my right foot from brake to throttle position all the time. (plus its faster imho :-))

Regards

-Roy

Chalk

ninja900 wrote:

A motorcycle has the same sort of gearbox

If you're using a good bit of throttle on a bike you can change up very very smoothly by pushing the gear lever and partially closing then re-opening the throttle very quickly.

Drag racing motorcycles usually have a "quick shifter" - a pushbutton to cut the ignition - so they keep the throttle fully wound on and just quickly press the button to shift up - takes a fraction of a second.

was just gonna say something like that,

i upshiift without the clutch regularly,
so much handier.
usually on motorways as the constant accelaration is more suitable