Driving without the clutch

[Bob]

Well my clutch gave out yesterday. I should have known something was wrong because it was getting very hard to shift and kept grinding when i put it into reverse, but its my first car and I didn't know any better. Anyway my dad came up and drove me home without the clutch. I double clutch and i know how matching engine speed and tranny speed works but I was wondering if anyone could tell me more about it or give me a link. My dad told me that truck drivers shift without the clutch all the time is that bad for the tranny if its done right?

[HSVLVR]

I couldn't say that it's impossible to drive without one.

[Bob]

Its clearly not impossible to drive without one since I did so for about 20 minutes yesterday. I was asking for some technical information about it. I know that when upshifting you need to pull out of the gear and then push into the next gear just as the engine matches speeds with the transmission. Downshifting is like double clutching, you pull out of the gear and goose the engine to match revs, then shift into the new gear, all without the clutch. I want to know whether this is a faster/better way to shift on a drag run, if its bad for the tranny when done wrong, if its bad for the tranny when done right, how it affects the gears/collars etc.

[2ndclasscitizen]

Most racing gearboxes have dog-engage, straight cut gears. Now, I don't know the specific technical aspects of how they work, but what that basically means is you can get them into gear without disenganging drive via a clutch or converter, or sychro. However, you will need to lift to upshift to lessen the old just enough to engage, though often today on EFI cars this is done by a shift-cut built into the engine ECU which momentairly cuts spark just enough for the shift to happen. On downshift, some drivers use the clutch and heel-and-toe the throttle and brake, whilst others while just bang it down a gear, giving it a rev. To downshift sans clutch you will need to rev and match revs.

Truckies don't use the clucth cause their gearboxes don't have synchro so they need to match revs to engage the next gear.

[Bob]

Originally Posted by 2ndclasscitizen

Most racing gearboxes have dog-engage, straight cut gears. Now, I don't know the specific technical aspects of how they work, but what that basically means is you can get them into gear without disenganging drive via a clutch or converter, or sychro. However, you will need to lift to upshift to lessen the old just enough to engage, though often today on EFI cars this is done by a shift-cut built into the engine ECU which momentairly cuts spark just enough for the shift to happen. On downshift, some drivers use the clutch and heel-and-toe the throttle and brake, whilst others while just bang it down a gear, giving it a rev. To downshift sans clutch you will need to rev and match revs.

Truckies don't use the clucth cause their gearboxes don't have synchro so they need to match revs to engage the next gear.

I've done a little bit of research myself so I'll put it up here for anyone whose interested. Straight cut gears mesh more easily but also more abruptly and roughly. The reverse gear in manuals is straight cut. Rev matching and clutchless shifting are not the same thing. I rev match all the time, with the clutch. To shift cluthlessly however, you need to rev match perfectly and also use proper technique going into neutral. Truckies rev match because they dont have synchros, but they don't use the clutch because the massive torque of those trucks burns out the clutch very fast.

Clutchless shifting doesn't hurt the tranny much if done perfectly, and the clutch is not involved, but the less perfect you are the more wear you put on the gears and syncros. For starting from a stop, you do need the clutch unless you start in gear.

Next post for technique.

[Bob]

Heres the technique for a hypothetical car at around 20 mph from 1st to second gear.

1. start in first at 20 mph
2. let off the throttle and gently nudge the shifter to neutral
3. wait until engine speed drops to ~1500 rpm (actually the exact rpm for 20mph in 2nd gear, that numbers just a guess)
4. again, gently nudge the shifter into the gear, if it does not go in easily, don't jam it, tap the throttle and try again at the right engine speed

Downshifts 2nd to 1st

1. cruising at 20 mph
2. let off the throttle and tap into neutral, just like before
3. rev to ~2200 rpm (whatever the exact engine rpm is for first gear at 20 mph)
4. nudge the shifter into 1st



The key to the whole technique is to know the exact engine speed for any given gear and speed. This technique isn't extremely useful unless you're in a situation like mine where you don't have a clutch. For starting out, you need to start in gear, or use the clutch, because you would need to shift from neutral to first at 0 rpm. If you want to learn how to do this, try part of it; ie double clutch and rev match on downshift or shift to neutral and then upshift without the clutch.

[coolieman1220]

how do u pull off without a clutch? is that possible? wouldn't u cut off esp on a hill

[nota]

Originally Posted by Bob

Its clearly not impossible to drive without one since I did so for about 20 minutes yesterday.

I want to know whether this is a faster/better way to shift on a drag run, if its bad for the tranny when done wrong, if its bad for the tranny when done right, how it affects the gears/collars etc.

When shifting (up or down) the trick is to 'float' off the throttle when you go from being in-gear, into neutral, to reduce the load on the cogs as much as possible. This makes for easier gear dis-engagement, and greatly reduces the chance of chipping the cogs

As you say, to 'find' and engage another gear without using the clutch you need to be really precise about matching the revs exactly to what the new gear demands - because there's no slop and no cushioning and no room for error

As mentioned, the big risk is chipping teeth off the gears, and likewise giving the synchros a hard time. When dis-engaging, slide it out promptly. But be gentle when attempting to re-engage from neutral. Never force the gearlever - use your fingertips rather than your fist. If you muscle the shift, or have to force the shift -which indicates poor rev-matching, this greatly increases the chance of causing damage - including simply bending the gear linkages if your car has those

So the key imo is being gentle. If you have to force it you're doing it 'rong'

Doing rapid drag upshifts in a conventional gearbox without using the clutch would pose the worst of risks imho

Btw I've driven big trucks with Spicer/Road-Ranger non-syncro gearboxes, and could shift those with only two fingers resting on the top of the gear-knob

[ballast]

don't do it with a synco box because all of the load from the engine and the drive wheel's is on the syncro's and although you can't hear it you will be damageing the synco dog's,as for dog boxes tes you can do clutchless changes because that's what there designed to but after about 1000km's in one of these boxes it will have to be pulled apart and have the dog's replaced

[h00t_h00t]

If you can still accelerate and climb hills then it isn't the clutch that is knackered, if the clutch slips when doing either then I would only drive it when I absolutly needed to because it will only get worse and finally won't work at all and the car won't move. Fix it.

[KnifeEdge_2K1]

Originally Posted by Bob

Its clearly not impossible to drive without one since I did so for about 20 minutes yesterday. I was asking for some technical information about it. I know that when upshifting you need to pull out of the gear and then push into the next gear just as the engine matches speeds with the transmission. Downshifting is like double clutching, you pull out of the gear and goose the engine to match revs, then shift into the new gear, all without the clutch. I want to know whether this is a faster/better way to shift on a drag run, if its bad for the tranny when done wrong, if its bad for the tranny when done right, how it affects the gears/collars etc.

it's bad for the tranny, just think about it

from purely logical point of view, if you could safetly shift without the clutch ... why's it there

from a mechanical point of view, if you're going to shift while the tranny and engine is still hooked up, you're doing one of two things, either forcing the engine down/up to the new revs, or forcing the gears/syncromeshes against each other, all this friction increases heat and wear

while powershifting (shifting up without clutch) is possible and often done in race cars it's not feasible to do this with your road car since race cars can afford to rebuild their tranny every couple races, you dont have that luxury, if you're talking about a drag race then yes power shifting will be faster since by forcing the engine down to the lower revs for the next gear some of that energy is transfered to pulling your car forward. it's a slight difference but a noticible one, hardcore drag racers use sequential strait cut dog gear trannies, a regular helical syncro'd tranny wouldnt provide the same oomph in the same situation

all in all, the clutch is there, use it

[Rockefella]

Originally Posted by KnifeEdge_2K1

it's bad for the tranny, just think about it

from purely logical point of view, if you could safetly shift without the clutch ... why's it there

from a mechanical point of view, if you're going to shift while the tranny and engine is still hooked up, you're doing one of two things, either forcing the engine down/up to the new revs, or forcing the gears/syncromeshes against each other, all this friction increases heat and wear

while powershifting (shifting up without clutch) is possible and often done in race cars it's not feasible to do this with your road car since race cars can afford to rebuild their tranny every couple races, you dont have that luxury, if you're talking about a drag race then yes power shifting will be faster since by forcing the engine down to the lower revs for the next gear some of that energy is transfered to pulling your car forward. it's a slight difference but a noticible one, hardcore drag racers use sequential strait cut dog gear trannies, a regular helical syncro'd tranny wouldnt provide the same oomph in the same situation

all in all, the clutch is there, use it

In his case, it's not there.

[ballast]

what sort of car is it and is the clutch hydraulic or cable if it's not slipping it maybe the spiget bearing in the flywheel has seized

[jcp123]

Go to some old-skool hot rodders' websites, there's probably plenty of guys with un-synchro'd trannies on there who have learned to skip the otherwise requisite double-clutching on those. In fact, the rev-matching is required on those trannies on a downshift. They'd probably be able to give you a pretty good lesson.

[Bob]

Originally Posted by Rockefella

In his case, it's not there.

Exactly. This isn't something I'd do every day, but its a nice skill to have when your stuck like I was. I was actually at a football game with insane traffic (it just ended) and a tow wouldn't have come until the next day. Also, it depends on the strength of the transmission and clutch. Like I said truck drivers do it all the time because they're very good at it and they have strong trannies and weak clutches.

Anyway what went wrong for me wasn't simply the clutch that went bad, it looks like it was the slave cylinder (hydraulic clutch). The clutch started to burn while i was driving it but it might still be alright. Hopefully this bill won't be too big I've already spent a ton of money on this car.