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downshifting

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Old 04-15-2010, 12:49 PM   #1
luis05gt
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Default downshifting

well most of the time i only downshift at a stop but today my buddy wanted to run them from a roll so i tried downshifting into 1st going 15 mph and it didn't want to go in it just grinded like there something wrong with the synchro could it be something is wrong or is 15 mph too fast to drop it in
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Old 04-15-2010, 09:28 PM   #2
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Hard to say if 15 is too fast. Depends on the car. Some cars will slip into a lower gear at a pretty high speed. I drove a Passat turbo 6 speed. It seemed to be able to engage any gear at any speed.

Some cars will not. Generally steep geared cars and cars with big clutches. Big clutch means heavy disc. So the synchronizer is forcing the disc to ramp up to speed and it doesn't feel like ramping up.

Try throwing a few revs in and see if it goes in.
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Old 04-15-2010, 09:38 PM   #3
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first gear with stock gears is good to like 30 or 35 i forget what, 15 is by no means too fast for it. when i downshift to first i give it a good rev to just about redline and it goes in fine. it will have trouble going in if you don't rev it high enough though.
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Old 04-15-2010, 09:55 PM   #4
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first gear with stock gears is good to like 30 or 35 i forget what, 15 is by no means too fast for it. when i downshift to first i give it a good rev to just about redline and it goes in fine. it will have trouble going in if you don't rev it high enough though.
so do you think my syncrho is broke it used to go in at 20 before i had it replaced or could it be anything with my clutch every other gear is fine
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Old 04-16-2010, 06:16 AM   #5
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Mine wont do it, but I dont care its nice to know that if I screw up it wont let me.
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Old 04-16-2010, 04:07 PM   #6
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Quote:
Originally Posted by luis05gt View Post
so do you think my syncrho is broke it used to go in at 20 before i had it replaced or could it be anything with my clutch every other gear is fine
Just try reving it a little. If everything else with the tranny is working fine don't worry about it.
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Old 04-18-2010, 02:22 AM   #7
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Downshifting can be hard, and trying to downshift into 1st can be very difficult on most transmissions because the ratio requires very rapid changes in gear cluster speed which the synchro can't compensate for fast enough. You either have to slowly downshift into first or learn to heel and toe and rev match going into first.

My TKO 600 will downshift into 1st, though it's a fair bit notchy and hard doing it, but I usually rev match when I downshift most of the time anyway, so that makes it easy.
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Old 04-18-2010, 04:21 AM   #8
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No problems here and no revving for me
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Old 04-19-2010, 04:05 PM   #9
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I've never "downshifted' into 1st, I've always been under the impression you weren't suppose to put it down into 1st until you've stopped...
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Old 04-19-2010, 04:09 PM   #10
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At least with the 2010 v6 manual transmission the book said never downshift into first when above 15mph, could do transmission damage!
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Old 04-19-2010, 08:40 PM   #11
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Most transmissions aren't set up for it, the cluster speed is too high and it abuses the synchros.
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Old 04-21-2010, 02:23 PM   #12
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thanks for all the info guys
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Old 04-22-2010, 12:39 AM   #13
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when im going into first and im already moving..i just tap the gas alittle..and works fine.
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Old 04-22-2010, 10:28 AM   #14
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1st gear doesn't have synchro on it, it's straight cut. That's why it's always harder than the others to go into if the car is rolling [or sometimes even not]. Have you ever tried to put the car into first with the motor off, to stop it rolling when you're working on it for example, it often won't go in at all and you end up putting it in second. It's because the synchro allows the cluster to move when you push for 2nd but with 1st you stand a good chance of the teeth clashing but not rotating into place because there is no chamfer on them.

Changing down into 1st on the roll is considered to be at the very least unnecessary and normally a bad driving technique. In most countries where manual cars are the 'norm', switching into first on the roll is a formal taboo and a test failure point. This is where the nuances and tricks of driving manual in N America are largely overlooked, folk mostly pass their tests in auto's and end up learning manual on their own later.

1st is a gear used for when the most torque is needed, so starting off, hill starts, etc. The gear has to be strong which is why they don't compromise their strength by cutting a synchro into it.
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Old 04-22-2010, 02:34 PM   #15
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Huh? 1st on most transmissions is not straight cut, it's helical cut. And the gear cluster cut has nothing to do with synchronization. And in most transmissions 1st IS synchronized, otherwise it would clash every time you went into first from any speed other than stop without double clutching. Reverse is often a straight cut that's unsynchronized though.

And as far as shifting into 1st, it completely depends on the transmission and gearing. In most production cars 1st is a start out gear and not needed once you're moving over 5-10mph, but on some cars the way the trans and final drive are geared, 1st is used. If you race on a street course in something with a 5 speed set up for racing you'll find in turns where you go less than 20-30mph you may need to be in 1st. Lamborghinis used to run 5 speed manual boxes with TALL 1st gears and tall final drives, and would top 1st gear at around 60mph.
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Old 04-22-2010, 03:46 PM   #16
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I have a 2004 GT and I downshift into first all the time( comming to a stop or slowing down to a crawl in traffic). I downshift to first even at 30 mph. It's all in the right foot. You don't have to rev to 5000. I usually stomp it to about 3400 and let out the clutch.
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Old 05-02-2010, 11:08 PM   #17
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i never understood why people downshift to stop why not just pull it out of gear then use your brakes to stop that's what they are there for. i feel that downshiftng to stop puts extra strain on the tranny that isn't necessary

its all about rev matching
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Old 05-03-2010, 01:31 PM   #18
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Because the engine will provide braking force to the drive wheels. Depending on how a car is set up, if the brake bias is accounting for hard downshifting and you brake in N then you have slightly reduced stopping ability. Conversely if the bias is set for braking in N and you downshift hard under heavy braking, you could lock the drive wheels. Besides, you have more control of a car in gear than in N.
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Old 05-03-2010, 01:31 PM
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