 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / June 2005How a manual transmission works... a question
Trying to understand more about manual's, and came across this excellent article: http://auto.howstuffworks.com/transmission5.htm However, here's the part I don't get: What is preventing the driver from shifting into reverse while going 60 miles an hour? >From the colored diagram.... Please correct me if I have this wrong: The purple collars are always spinning when the car is moving. The blue, red, and green STOP spinning when the clutch is in neutral and the clutch is pushed in, or at least, spinning slowly from the friction of the output shaft (yellow) rubbing on the bearings that the blue gears ride on. TIA! > Trying to understand more about manual's, and came across this > excellent article: [quoted text clipped - 3 lines] > However, here's the part I don't get: What is preventing the driver > from shifting into reverse while going 60 miles an hour? Nothing whatsoever, beyond the difficulty likely to be encountred in trying to get the involved gears to mesh at those speeds. (never mind the fact that the tranny is likely to actively fight you due to the fact that the reverse gear is being driven "the wrong way" by the forward-turning wheels/driveline) Muscle it hard enough, and/or play with the throttle right, and you could indeed do it - Although you'll almost certainly wish you'd failed within a second or so of your "achievement". A grenaded clutch disk (spun apart by way too many RPMs) would be the most likely outcome, I would think, with other parts possibly "going south" on you as well - Perhaps with great noise and violence...  SignatureDon Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004. Short form: I'm trashing EVERY E-mail that doesn't contain a password in the subject unless it comes from a "whitelisted" (pre-approved by me) address. See <http://www.sonic.net/~dakidd/main/contact.html> for full details. > > Trying to understand more about manual's, and came across this > > excellent article: [quoted text clipped - 9 lines] > that the reverse gear is being driven "the wrong way" by the > forward-turning wheels/driveline) I understand that if the clutch is engaged, but why would it be turning if the clutch is pressed in? If you look at the 2nd diagram on that page above, but input shaft (green), layshaft (red) and blue gears should NOT be turning when the clutch is pressed in and the tranny in neutral, right? If I'm incorrect in this, please explain why. > > > Trying to understand more about manual's, and came across this > > > excellent article: [quoted text clipped - 17 lines] > clutch is pressed in and the tranny in neutral, right? If I'm > incorrect in this, please explain why. The reverse gear is still being driven "backwards" by the rear wheels so even if the input shaft and layshaft have completely spun down, you'll have quite a bit of speed mismatch. Now some modern vehicles have synchros on reverse so you theoretically *could* engage reverse at speed if you wanted to; not that that wouldn't be a spectacularly bad idea... nate > > > > Trying to understand more about manual's, and came across this > > > > excellent article: [quoted text clipped - 21 lines] > so even if the input shaft and layshaft have completely spun down, > you'll have quite a bit of speed mismatch. How is it driven backwards if the tranny is in neutral? The reverse gear isn't engaged, is it? IOW, on that diagram, the blue gears are riding on bearings, are they not? They'not not connected to the differential, only the purple dogs are, right? > > > > > Trying to understand more about manual's, and came across this > > > > > excellent article: [quoted text clipped - 26 lines] > riding on bearings, are they not? They'not not connected to the > differential, only the purple dogs are, right? Sorry, I mis-spoke. The reverse *dog* is being driven by the wheels, and the reverse *gear* will be driven by the input shaft/layshaft. There's going to be a speed differential between the two at any speed. Even if the clutch is held disengaged long enough for the clutch/input shaft/layshaft/reverse gear assembly to spin down to 0 RPM the reverse dog will still be spinning with the output shaft at whatever RPM the driveshaft is turning. Thus if there is no synchronizer at any speed above a couple MPH you will get a lot of metal on metal noises and nothing much will happen when attempting to shift into reverse. If there *is* a synchronizer, when you try to engage the dog the synchro will spin up the gear/layshaft/input shaft/clutch etc. *in the opposite of normal direction* which will allow engagement of reverse but probably wouldn't yield very desirable results should you release the clutch after doing so. nate > > > > > > Trying to understand more about manual's, and came across this > > > > > > excellent article: [quoted text clipped - 36 lines] > above a couple MPH you will get a lot of metal on metal noises and > nothing much will happen when attempting to shift into reverse. Ok, now we're getting somewhere... Is there no reverse synchronizer in transmissions? larrybud2...@yahoo.com wrote: > > > > > > > Trying to understand more about manual's, and came across this > > > > > > > excellent article: [quoted text clipped - 39 lines] > Ok, now we're getting somewhere... Is there no reverse synchronizer in > transmissions? Traditionally no, but some newer transmissions do have one. nate > Ok, now we're getting somewhere... Is there no reverse synchronizer in > transmissions? Most didn't in years past. In theory there shouldn't be a need for it... since its not intended to be shifted into while moving. I think some newer trannies have reverse synchros just to stop the clutch plate from spinning when people jump in, punch the pedal, and slam the lever into reverse without waiting for the clutch plate to stop spinning. Lots of older vehicles had unsynchronized first gear, for the same reason- no need to shift into first when moving (except when dowhshifting, and a quick double-clutch fixes that problem). > > Ok, now we're getting somewhere... Is there no reverse synchronizer in > > transmissions? [quoted text clipped - 8 lines] > reason- no need to shift into first when moving (except when > dowhshifting, and a quick double-clutch fixes that problem). A simplistic explanation of what happens when trying to exit a slow corner in an old American car with the 3-on-the-tree "suggestion lever" :) Unless you have that mechanical sympathy and a certain level of understanding between you and your car, you usually end up at a dead stop before you find first gear, which I guess, does solve the problem... nate > Trying to understand more about manual's, and came across this > excellent article: [quoted text clipped - 3 lines] > However, here's the part I don't get: What is preventing the driver > from shifting into reverse while going 60 miles an hour? Absolutely nothing, I have done it. I hit reverse in a car once and only locked the rear wheels into a chirp when I realized it. Nothing blew up.... I was lucky.... Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's > > Trying to understand more about manual's, and came across this > > excellent article: [quoted text clipped - 7 lines] > only locked the rear wheels into a chirp when I realized it. Nothing > blew up.... I was lucky.... Yep, that would make two of us - Although I accomplished mine in a car with an automatic. Had this "hit the lights all green" strategy that seemed to do *WAY* better than 75% - Come off the the north/south freeway onto the east/west freeway leading into town, and mash the throttle for all it could give me/all traffic allowed in the space between the end of the off-ramp and the "Freeway ends 1 mile" sign. Usually that meant I'd be hitting somewhere between 70 and 80 as I blew past the sign. Bump the shifter into neutral, and coast in to the first light, which would (more often than not) change green just as I rolled up at about 40-ish. If I caught the first one, bumping it back into gear and holding at 40 would put me through the entire ten light sequence with every one of them green my way. One day I did this for probably the 100th time, if not more, only my "bump" was a bit too energetic, and I went through neutral and into reverse... <SHREEEEEIIIIIIIIK!> Smoking rubber, a.s-end juddering around like it was about to go into bucking bronco mode, and me grabbing wildly at the gearshift with one hand while trying to keep the car pointed straight with the other, and the engine stalling out. It was a rather "interesting" ride that I don't have any wish to go on again! Didn't do any damage (that was evident right then, anyway... Strongly suspect that it WAS the death-stroke for the tranny, though, since it was only a couple months later that the thing went completely tango-uniform) but by all rights, that transmission should have gone off like a bomb... Manual or automatic, they just aren't made for being punched into reverse at 70+! SignatureDon Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004. Short form: I'm trashing EVERY E-mail that doesn't contain a password in the subject unless it comes from a "whitelisted" (pre-approved by me) address. See <http://www.sonic.net/~dakidd/main/contact.html> for full details. Shifted into reverse once while driving a automatic Ford Crown Victoria. It was a rental car I had just picked up at the airport and I hadn't taken the time to "adjust" everything before I left the lot. Decided to adjust the height of the steering wheel while hitting about 60 mph. Only the "steering wheel adjustment lever" I grabbed was actually the gear shifter. Car came to a complete dead stop with as mentioned a horrrific screeching of tires. Started right up however and I drove it some 25 hours with no problem before returning it to Hertz. Don't know what happened to it a month down the line, however..... >> > Trying to understand more about manual's, and came across this >> > excellent article: [quoted text clipped - 35 lines] >like a bomb... Manual or automatic, they just aren't made for being >punched into reverse at 70+! Yea, other than burning the CRAP out of the reverse/high clutch pack (reverse/low if GMC, don't know Mopar trans too well, ) and the band, there's probably not too much else you could screw up. Of course, all that clutch material that's suddenly been given a permanent vacation from the disks (and the band!) would probably have contributed to the death of that trans... but, sh.t happens. :) -LMB > Trying to understand more about manual's, and came across this > excellent article: [quoted text clipped - 12 lines] > > TIA! Nothing. Just like most transmissions you can shift into reverse from a forward gear. If your REALLY lucky the only thing that happens is that the rear tires lock up and the engine quits and you slide to a stop. If your unlucky, the trans will go into gear and then grenade the weakest part in the driveline. What that part is depends on the vehicle. Anything from U-Joints to the clutch disc or even the crankshaft in the engine. Something will give. SignatureSteve Williams Some cars used to have a reverse lockout which helped to prevent disaster when overvigorously shifting. It isnt likely you would get it completely into reverse while moving forward, but even to snag a little bit of the gear could, would, cause splinters to fly. > Some cars used to have a reverse lockout which helped to prevent disaster > when overvigorously [quoted text clipped - 3 lines] > forward, but even to snag a little > bit of the gear could, would, cause splinters to fly. The percentage that had that lockout was small, in my experience. None of my cars had it. I have driven ones that did, however. Usually it required an upward 'lifting' of the lever when going into reverse. > > Some cars used to have a reverse lockout which helped to prevent > > disaster when overvigorously [quoted text clipped - 8 lines] > Usually it required an upward 'lifting' of the lever when going into > reverse. Most of the (new-ish) cars I've driven have had a reverse lockout of some kind on the lever mechanism. Several kinds come to mind: Push down on lever whilst moving to reverse Pull up on lever whilst moving to reverse Pause in the centre of the pattern (neutral) first, then to reverse Two-fingered handle to pull up whilst moving to reverse > However, here's the part I don't get: What is preventing the driver > from shifting into reverse while going 60 miles an hour? Depends on what gear you are shifting from. If you stick it in neutral, you can go straight into reverse. If you have a trans that's a 5 speed with reverse directly below 5th gear, these will have a reverse lockout that prevents you going directly from 5th to reverse. On other types of patterns, there is often a reverse "gate" that you have to go through to get to reverse. Under normal conditions it's unlikely that you will go thru the gate while shifting gears, it takes a bit more effort to go thru the gate and into reverse. Ian > However, here's the part I don't get: What is preventing the driver > from shifting into reverse while going 60 miles an hour? A greyish organ with lots of lumps and folds, located between the driver's ears. > > However, here's the part I don't get: What is preventing the driver > > > from shifting into reverse while going 60 miles an hour? > > A greyish organ with lots of lumps and folds, located between the > driver's ears. Plus a *very* pronounced grinding noise when he attempts to do it. "What is preventing the driver from shifting into reverse while going 60 miles an hour?" JS> Aside from the fact that it would take a real effort to grind those gears together I suspect the overriding reason would be cost. A boneyard gearbox on most cars will set you back $2k. If you can't find one a new one may exceed the value of a used car. > Trying to understand more about manual's, and came across this > excellent article: [quoted text clipped - 7 lines] > of the output shaft (yellow) rubbing on the bearings that the blue > gears ride on. Something I hadn't considered before: this diagram shows that when you're in gear, ALL of the blue and red gears are moving. Now I understand why people quote such high figures for power loss in the transmission! (eg. 300hp at engine = 220hp at wheels). > Trying to understand more about manual's, and came across this > excellent article: [quoted text clipped - 3 lines] > However, here's the part I don't get: What is preventing the driver > from shifting into reverse while going 60 miles an hour? The damage deposit you left with the auto rental agency. SignaturePaul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ definition: recursion; see recursion. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.