Out of habit, I double clutch when down shifting. If I want to accelerate or slow down, say from 50 mph and 5th gear, I'll hit the clutch and take the shifter out of 5th. Then rev match, hit the clutch again and stick the shifter into 3rd or 4th depending on what I want to do.

In older cars, you had to do this because they either didn't have synchros or didn't have good synchros. Now you can just hit the clutch once, rev match and down shift.

Does anyone still use the double clutching technique for down shifting or up shifting?

 

NO
Rev match donwshifts, Yes.

 

I double clutch sometimes on downshifting, its an old 'hang-up', I know its not needed.

I recall driving a truck some years ago that I had to double clutch every shift. But those days are over with.

 

I double clutch most of the time. My understanding is that blipping the throttle matches the speed of the engine and the rear axle, while double clutching matches the speed of the intermediate shaft in the transmission with the engine speed.

I understand that the intermediate shaft slows down when you press in the clutch, and the job of the snycros is to increase the speed of the intermediate shaft to match the speed of the next lower gears. The The teeth of the differnet shafts cant connect until the speed of the two shafts match. Double clutching relieves this syncros of the job and makes for smoother easier on quicker shifts.

Typically, i dont use the clutch when I shift from a gear to neutral. The tranny can easily slide into neutral while the gears are floating in the region of gear lash after I take my foot off the throttle. Then while in neutral I blip the throttle and use the clutch to go to the lower gear.

 

Any particular reason why you do this?

 

Sure. I don't know where people got the idea that modern synchros can't be made to wear out. They certainly can.

With smooth double-clutch/rev-match downshifts, you can go from 6th to 3rd without encountering any resistance at all from the gear selector, because the synchro has nothing to do.

Rev-matching without double-clutching is pointless. The gearbox must be in neutral with the clutch engaged so you can accelerate the transmission input shaft.

 

The job of the synchros is to stop the rotating assembly in the tranny enought to line up the teeth on the synchros for the gear change. Thats why people put in the older trannys thicker gear oil to stop the old synchros faster so it didnt grind. Double clutching is mostly meant for ollllllddddd transmissions that didnt have synchros.

 

A gear synchronizer (synchro) doesn't serve to stop rotation, it's there to match -- or synchronize -- rotational speed. When downshifting, the synchro has to speed up the input shaft.

Double-clutching/rev-matching when downshifting a synchronized transmission isn't the necessity it once was, but it still has advantages: 1) smoother shifts, 2) less wear, and 3) it's fun.

On upshifts, it doesn't buy you much unless the gear oil is really cold.

 

I double clutch it on colder mornings when the fluid is cold, and sometimes on the downshifts. Otherwise I usually don't bother.

 

I double clutch consistently on downshifts. Lots of fun and sounds great. I do not do it when I upshift.

 

I do. I learned to drive in a 1910 Hupmobile. No synchros. The good habit is now engrained in my driving.

 

Its all about control. When you match engine speed to rear wheel speed, you avoid any drag on traction that could cause a loss of adhesion and control in turns. Assume that you are driving a tire at 100% of its capable traction, and when you downshift, you use the rear tires to speed the engine up, the additional traction demand caused by the compression of the engine will exceed the capability of the tire to adhere to the road and then you are relying on the cars traction control to control your turn.

Match the speeds of the engine and tires, there is very little additional demand on the traction capability of the tire when you downshift, and you go fast. 100% traction equals maximum adhesion which equals maximu tire performance. There is no 101% of traction because once the tire loses adhesion, traction falls to nearly 0% very quickly and goodbye to performance.

The pros heal and toe the accelerator and brake so that they can drive hard into a turn, brake with the right foot to bring the traction demand toward the 100% mark, and while braking blip the throttle with the right foot, double clutch with the left foot to a lower gear, and accelerate out of the turn using engine torgue to maintain near 100% traction. This is the fastest way through any turn

 

Even faster way through is to select the proper gear **before ** turn in. Anyone shifting gears in the middle of a turn does not know what they are doing.

 

All the time. It's also a habit I learned a long time ago.

 

I don't think that's true. And I KNOW that statement isn't universally true.

 

Seems like a slow waste of time and cumbersome. Are'nt you also potentialy putting more wear on a clutch.

 

If you haven't noticed the modern transmissions with syncromess cones have elimited the need to double clutch since the 1960's. And the T56's are even better than the old muncies. (M-21 &M22 rock crushers.) If you have to double clutch to disengage or engage a gear you've got major transmission problems. Take it to a dealer.

 

Not so. Imagine you are doing 80mph on the freeway and you are getting ready to take a very tight clover leaf off ramp. Assume the max speed you can maintain on the ramp is 25 - 30 mph. Best gear to exit the ramp is probably second because it puts you dead center in the power band so you can accelerate out of the turn.

Your options are either 1. slow down early before you get to the turn so you wont cause the rev limiter to engage when you go to second gear at 80 mph, or 2. attack the ramp at 80 mph in third or forth gear, maximize braking so that you carry as much energy into the start of the turn for as long as possible, which will bring tire adhesion up to close to 100%, and then double clutch into second at the neck of the ramp as your speed drops to 25-30. Your tires are operating at near 100% adhesion from the braking, and remain at 100% adhesion through the turn (as long as you stop braking and start accelerating to maintain 25-30) and adhesion unwinds from 100% as you accelerate out of the turn.

Double your money back guarantee that there is no quicker way around the corner. (which is why the pros use this technique). If you do it right, you can set up a neutral drift on the car and then you go through the turn without sterring inputs with the front wheels facing straight.

Oh yes, this is the fastest way to get yourself in trouble too. Exceed 100% for an instant, traction falls to near 0%,the wheels stop turnng and the car will start sliding on a tangent that will take you places you dont want to go as in off the road or another lane (and no - anti lock brakes wont prevent the wheels from stopping and sliding - anti lock brakes only work if the tire is operating within the limits of adhesion).

 

If it's slow and cumbersome you aren't doing it right. To regular practitioners of these techniques (those of us used to non-synchronized or poorly-synchronized gearboxes), it's second nature. The increase in clutch wear should be very small, because the first re-engagement occurs when the driveline is in neutral.

Major problems too often caused by habitually not double-clutching and matching revs on downshifts. On upshifts, double-clutching is generally unnecessary.

The T-56 synchromesh will accomodate huge rev mismatches (i.e. 6th-to-2nd), but these will cause premature wear, and they won't go as quickly or as smoothly as a proper double-clutched gearchange, which places no wear on the synchros at all.

 

And since the spped of the clutch, the engine, intermediate shaft and rear axle are nearly matched after you double clutch, there is much less wear on the clutch because the clutch is not being drug across the flywheel because the engine is going slower than the rear wheels. Also, a double clutch makes shifts many times easier because the intermediate shaft in the tranny matches the speed of the engine and rear axle, so there is no syncro lag time.