Double De Clutch?

[AlanBartlett]

Can someone explain to me the principle of it the proper techinque, Ive got the jest of it but when I do get the engine running I'd like to be able to reverse it into the garage for once instead of pushing it. I know its something like clutch down - 1st, then its 1st-clutch down, neutral - clutch up, clutch down - 2nd and so on for changing up a gear. I just want to check if thats the right way

[AlanBartlett]

No it doesnt

[george garside]

Alan
would not expect it to have a freewheel as I believe its a 1934 model & the free wheel only came in with the x braces 1935 model year. Ass to double declutching should not be needed when changing up provided you pause in neutral to allow the revs to die down a bit rather than puching the leaver sraight through as on a modern vehicle.
changing sown the sequence is much as you have said
- 4 simultaneous actions - throttle off- clutch down & leaver into neutral - clutch up
followed by
- blip throttle whilst in neutral ( the faster the road speed at the point of changing down the more it needs to be reved up)
follwed by
- 4 simultaneous actions - clutch down - lever into lower gear - clutch up - throttle down

The skill comes in guaging how much to rev up in neutral and this varies with both road speed and which gear you are changing into. The Jowett 4 speed box is very forgiving and is one of the nicest 4 speed non cyncho boxes around having a particularly easy change between top & third due to its , I believe. unique design.

To quote from the Autocar road test of a 1934 Kestrel --- ' Gear changing is at all times easy . The four speed box has double helical gears for the third speed and the constant- mesh wheels , but there are no special devices to facilitate gear changing; nor do these appear to be necessary, for the downwardchange from third to top can be made without doubledeclutching, at low speeds, wilst upwards changes do not call for double - declutching - it is merely necessary to declutch and move the leaver with a slight pause in neutral'.

In sep 1937 The Motor made a similar comment on testing an Eight. 'A word about gear changing. This must be another feature of the Jowett that is unique, for there is neither synchromesh nor any other form of modern convenience. Yet the astounding thing is -- and, believe us, it really is true,-- one can change these gears perfectly easily despite the abcence of mechanical aids.'

Hoepfully this should set your mind at rest!
george

[Tony Fearn]

Alan,

Take note of all that has been said, especially from George, but on re-reading your original post, believe me, you won't need to double de-clutch whilst trying to reverse your car into the garage!

George has it right. Pausing (not posing!!) between gear changing will obviate crunching sounds. Waiting a bit between gear changes on the way up through the box from 1st to top will give relatively noiseless changes. I usually count, in seconds, clutch in, - one, out of the gear through neutral - two, and then three before engaging the next higher gear. In fact once you get used to the notes of the engine revs, you can actually change gear up or down without using the clutch pedal, but I wouldn't recommend it for the first few years of pre-war driving.

Changing down is more difficult but follow the instructions from George and in time you will become a master of the 'throttle blip'.

Tony.

[Keith Andrews]

Can someone explain to me the principle of it the proper techinque,

Generation gap..well couple generations now...

A niece , asked how to use a dial phone, I wounder how long before we a generation that cant wund windows up and down lol

Double D was explained to me like this many yrs ago in very basic terms

Clutch in and gear stick in neural
let clutch out in neutral
and give it a rev, a a rev a bit more than u at 1st think will be enough.
This rev then spins up the next gear to approx the same speed of the car
Then before the revs die off, clutch in put into gear and let the clutch out.

Then when u have it down pat, get a driving instructor or licience inspector to do it, chance are they dont have a clue lol.

Most manual boxes, one can change gear without a clutch...
If u drop into neutral, get the revs spot on for the next gear, the gear stick will slide into the next gear smooth, get it wrong to often and you will change the gear ratios to nothing to nothing, and need a new gearbox lol
NOT a good practice to do.

[AlanBartlett]

So it would not be a good idea to normal gear change then?, Is there any classic car instructors out there ha ha. (Gotta pass my proper test first) August 7th lets pray I pass

[Keith Clements]

Getting into reverse.

If you are having trouble getting into reverse then it is either adjustment outside the box or wear inside the box. Sure, putting the clutch in and out, or trying in first, then back into reverse, may coax the gears together.

Good idea to understand the mechanism, from your hand to the gears and figure out what is wrong. It may be locking system on the gate, rods to the box or levers in the box, or wear on bearings in the box.

Double de-clutching.
I usually do DDC in order to 'save' the synchro in the box. It is really not necessary except when going down to first when moving as there is no synchro on the 1st on a Javbox. Would not recomemend using first at any time on a Jav box anyway! The teeth are very weak!

The syncho is essentially a clutch that gradually feeds the power from the wheels back to the engine via the layshaft and synchronises the speed of rotation of all the components. If you know the difference in engine revs between two gears at the same road speed, you can try to make up that difference by revving the engine in neutral (but clutch out) when changing gear. This raises the rotational speed of not only the engine but also the layshaft giving the syncho mechanism little to do. Many pre-war cars did not have synchro so you had to do this.

An opposite principle is used when making a racing change going up the gears. The aim here is to keep the power on the engine and not loose any speed in the gear change. I do not recommend doing this on a Jowett box! An overdrive is an excellent device for this.

[george garside]

as the pre war box lacks external rods, balls & other pivoty bits I presume the 'outside the box' adjustments must be limited to the arm
george

[AlanBartlett]

All the gears and clutch are fine(recently set them up) I was just wondering what exactly the motions are with the double clutch to change up and down the gears. Thank you for your contributions

[TedAllen]

On my last two advanced driving courses with the old Manchester City Police driving school in the late 60s we were instructed to double declutch at all times, even though we were well in to the synchromesh era by then.
I am not sure now of the reasoning but I think it was to do with not being able to brake when changing gear.
I continued this practice for many years afterwards...habit.....now the family car changes irs own gears for me. We were also taught never to use the gears for braking, that's what the brakes were for. I never have done to this day.
Ted

[PAUL BEAUMONT]

Alan, I find that these sort of things are more easily understood when you understand a bit about what is actually happening, so here goes!
Effectively within the gearbox there are 2 sets of gears. One set is connected permanently to the rear axle (unless a free wheel is fitted) the other is connected through the clutch to the engine. You can only change gear quietly when the cogs in each set are turning at the same speed. Whenever your car is moving the cogs connected to the driving wheels are turning. If it is in gear the engine drives them, but if it is not in gear the road wheels turn them.
When you drive your car, as you start off the engine speed increases as does the speed of the car. When you want to change up, you take your foot off the throttle and push in the clutch. The driven cogs continue to be driven by the road wheels, but once the engine is separated the driving cogs start to slow down naturally. Changing gear to a higher ratio (slower engine speed) is therefore appropriate to what the gearbox wants to do naturally. Going the other way presents the problem as the gear box input gears need speeding up to match a faster engine.
What happens is:
clutch down, gearbox into neutral: driving wheels drive the gearbox, input gears slow down
Gearbox in neutral clutch out, blip the throttle: input gears speed up, but because the box is in neutral the driven part is still being driven by the road wheels they are unaffected.
Clutch in again, gear change down, links the speeded up input gears to the output ones at a lower ratio. The trick, as Tony says is to match the speeds fairly accurately. It also helps to not let the gearbox oil get too old or it increases drag and everything takes longer to match up. Does that help - feel free to say no!

[David Morris]

Hi there,

This post has set me thinking. Keith Clements has mentioned that he uses DDC to 'save' the syncro in the Javbox. I certainly do as well, especially from second into third, probably due to a worn syncro. He also mentions that you don't need to use first gear.

Recently, I have had the opportunity to drive several different Javelins which have been fitted with Meadows and Jowett gearboxes, and have noticed the considerable difference in second gear ratios between the two types of gearboxes.

On the Meadows box, as fitted to my Javelin, you can easily pull away in second. However, the Javelins with a Jowett box makes this a real struggle and first gear has to be used much more often.

I think the biggest difference in driving a 50 year old car when you are perhaps more used to modern boxes is to allow plenty of time for things to happen. It was perhaps a less hectic world when they were made!

My first car was a Ford 8, with a three speed box and no syncro on first. You had to use DDC and my driving instructor insisted I got the hang of going from 2nd back into 1st at 30mph! This was a tall order and I was relieved when my next car was my first Javelin!

I certainly wouldn't like to try it now and on the Javelin it would probably spell the end of the gearbox!

All the best,

David

[Keith Clements]

I have just provided a couple of layshafts to Bill Lock for refurbishment. He can get new 1st gears fitted; but don't let that encourage you to try DDC into first at 30mph!

[Mike Allfrey]

Dear Alan,

This has turned into a lengthy discussion topic. I learnt to drive (under age!) in a Dodge Kew lorry with a crash box. The very first instruction I was given was to not have a tight grip on the gear lever. The Dodge's gear lever always rattled while the lorry was in motion. I was told that my grip should allow it to keep on rattling while changing gear.

My instructor was Sid Hendy, a lovable character who drove tank transporters during WW II. Sid told me that, when his instructor was teaching him to change gear, he should "take a walk around the cabin while the engine revs come down". It has always stuck with me!

Good luck in August,

Mike Allfrey.

[Keith Andrews]

I was told that my grip should allow it to keep on rattling while changing gear.

Isint it funny that things are forgotten over the yrs....
As soon as I read that, I could see my grandfather saying the same thing when I was very young...My memory says we where in a large round shaped Austin???...thu I dont think so, because I can still visulise a column change???? We must have been in something else..
We where feeding out (winter) on the farm from a trailer behind

Regardless, the comment is very clear, I can still see him pionting with his pipe.
If my Gramdfather was still alive he would be well over 110yrs now.