jzc28

I have had my 964 for 2 years now and, sorry to say, my upshifting while going uphill could use some improvement. It seems as though I can shift more smoothly from 2nd to 3rd if I boost the rpms to around 5k rather than 4k+ and and throttle up very slightly. I do know that I'm punished with the scent of clutch plate burn if I'm slow to reengage the clutch. Since my mechanic informs me an '89 clutch replacement is approaching $4k, I'm anxious to improve my skills.

KaiB

Think momentum loss...a slow uphill shift is somewhat like starting off from zero on an uphill grade.

If that's what you mean from yer post...

Makmov

sounds like if you have to do all that you are not running 2nd out far enough there is no reason for a 4-5k rpm shift into 3rd.

braol

Two things: A clutch job should NOT cost 4k. That's ridiculous! I had clutch install, all new plugs and wires, degrease of my engine, and all new firewall material replaced for around 2k. For 4k you could buy the porsche engine stand, engine lift, jack, all the parts, do it yourself, plus put in new shocks a windshield, and get your dings touched up! Or get some engine work done....

Second thing: Switching from the Dual-mass FW will result in quicker "spin-down" of the engine...especially in the morning when the oil is cold and you're driving up that first hill in your neighborhood. I know this because I have a slightly more circuitious route I take on the way to work to avoid just this issue. Who wants to spin 4-5ooo RPM on a cold engine???

Harry Apps

You need to learn to double de-clutch or use a constant-throttle technique. If you pay for my flights and hotel, I'll come across and teach you.

KaiB

You need to learn to double de-clutch or use a constant-throttle technique. If you pay for my flights and hotel, I'll come across and teach you.

Yer going to have to explain this one, please...

jzc28

Yes, momentum loss is the issue. When this problem arises it's like when I throttle up too much and release the clutch pedal too slowly from a stop on an uphill road. Braol is correct - the burning is more likely to occur before the oil cooler kicks in. Like you, I would like to know what double de-clutching is.

KaiB

I'm quite familiar with it, but fail to figgr out why on earth double clutching would apply to uphill upshifts...

Had hoped my sarcasm would have been a bit more obvious.

braol

Kind of like heel-toe shifting in the opposite direction. When heel-toe shifting you are trying to get the transmission to downshift smoothly at a rate of speed that would result in the engine turning at a high RPM when engaging the lower gear. When upshifting on the hill and the trans is cold the internal gears and synchros immediately slow down when lifting the throttle (the momentum of the gears isn't enough to overcome the cold oil). Essentially there is a mismatch between the internal rotational speed of the transmission and the rate at which the wheels are turning (given the gear you selected).

What the trans/synchros want is to be spinning at the relatively same speed as the wheels. By letting off the clutch pedal in neutral and blipping the gas pedal you are goading the transmission into spinning faster to better match it's speed to the rate the wheels are spinning the axleshafts in relation to the higher gear. Semi-trucks do this all the time to avoid dropping their trannys all over the road.

mark kibort

the main difference between upshifting and downshifting, is that the layshaft speed, tied to the rear wheel speed, when in gear. out of gear, gong to the next gear, there is a speed differnetial of the mass of the layshaft, clutch discs and drive shaft, vs the wheel speed in the next gear, UP OR DOWN. down, a double clutch can release the clutch to take engine rpm and speed up the layshaft, but the sychrs have enough friction to slow ths mass easily to match the hopefully matched engine RPM. (pre blib of the engine).

However, on upshift, going up hill, THE ONLY THING that is changing, is that the wheel speed ,would decay at a faster rate than shfting on level ground, and not much at all going down hill. the reason you should see no issue, is that when you press in the clutch and go for the upshift, the sycnhros are trying to SLOW down the rotating layshaft mass, which already is slowing down due to friction (as opposed to having to be sped up to meet a downshift)this means very very litle time and force is needed to do this. the ownus, is on the operator to really know the next rpm of the next gear to match engine speed to drive speed. double clutching will not help this really at all.

think of the shift timing going uphill as if you were shifting a wider spaced gear box. that is it in a nutshell. (shift timing, engine matching, rpm, transmisson, etc)

Mark

PS to further the point, if you wait too long, you may as well put it back in the same exact gear you were shifting out of. so timing is slghtly different to have the same smooth shiftig as you would have on level ground. going downhill, your rpm matchng becomes (timing wise) more like a closer ratio gear box.


a slow upshift will alow the transmission layshaft and driveline, to slow down and use the frictional forces, to match those compoents for a upshift. Opposite to those when downshifting. It has nothing to do with being relatng to startng off from 0 mph on an uphill grade.

ever notice when you upshift , and you wait too long, its a messy hard, notchy shift. why, because if you are good, you time your shift to be real quick, because revs go down real quick. if you have shift timing based on a close ratio gear box, going uphill, that shift timing would have to be delayed to have the same effect as the ONLY difference would be the appearance of wider spaced geas with respect to timed-matche rpm shifts.