Dog box

[marvmul]

I've bought a dog gearbox (or how do you call this?) for my race car.

Any idea's on how to use this type of gearbox to get the best of it, how to avoid damage?

Can changing gears really be done without use of the clutch?

[jonlar]

Any idea's on how to use this type of gearbox to get the best of it, how to avoid damage?

Can changing gears really be done without use of the clutch?

 

Hi Marv., have you never had to drive a car with knackered clutch cable or hydraulics? Worst part is pulling away. Changing up let revs drop slightly and increase if changing down, to synchronise engine output with transmission - takes practise, but yes it can be done. I assume you've bought a gear-box with straight-cut gears? tend to be a lot more transmision noise - get the ear defenders out - makes the crunches quiter as well!

[Rex Wyer]

Hi Marv., have you never had to drive a car with knackered clutch cable or hydraulics? Worst part is pulling away. Changing up let revs drop slightly and increase if changing down, to synchronise engine output with transmission - takes practise, but yes it can be done. I assume you've bought a gear-box with straight-cut gears? tend to be a lot more transmision noise - get the ear defenders out - makes the crunches quiter as well!

Jon, is that the same as the old double- de- clutch method used without synchro gears ?

[jonlar]

Jon, is that the same as the old double- de- clutch method used without synchro gears ?

 

Hi Rex, with a standard gearbox, the synchromesh rings get the lay-shaft spinning at the correct matching speed to the engine, this is what double de-clutching does with a 'crash' gearbox. If the hydraulics or cable are shot, matching the engine revs to the lay-shaft speed enables a gear change. With the box Marv. is referring to 'dog' box - I believe this is the straight-cut gears - only really used in competition - no de-clutching, therefore less time wasted in changes, the clutch only being used to pull away. A competition box, would not be my choice for a road car - tend to be very much noisier than a synchro. box. Give it a try going from second to third to fourth without using the clutch and back down again, matching the engine speed to the next gear at the road speed. If you don't fancy trying it in your TR, try it in your company car (or your wife's) or whatever else you've got access to! Perfecting no clutch changes is an acquired and practised art, but very useful if clutch disengaging mechanism fails. I find it more difficult with front-wheel drive (probably due to remote linkage) as opposed to more direct boxes. I've found Fords are usually easier to run through. For my PSV test (1978) I had to learn to pull away in 1st (opposite Reverse in double H, crawler gear - no synchro.) change up to 5th (in normal position of 4th) and then back down into 1st without using brakes, just engine deceleration. It was a 51 seater which would go at about 5 mph at max. revs in 1st - only used for pulling away on hills, otherwise you'd pull away in 2nd which is where 1st normally is.

[Cinnobar]

Car dog boxes can have helical gears but are unlikely too. Hewlands are a common race example of dog boxes, also all motorbikes are dog boxes. Reasons for dog box is that they take up less space for a given gear size, so given an existing gearcase the gears can be bigger thereby giving more power capability without having to make a bigger case. Also gearchanges are much easier without having synchro rings to fiddle with, so ratios can be changed easily.

They need a firm hand are really unsuitable for road use.

[marvmul]

Thanks for the replies so far. I'll report how a dogbox is doing in racing in comparison with the conventional box (and how I'll get accustomed to it).

Hewland has a website with useful tips : www.hewland.com/svga/help.