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Shouldn't the speedometer halt for a second while switching gears?

oiprocs

oiprocs

Diamond Member
In a manual transmission, I notice that when I shift gears, the speedometer will freeze for a second at whatever speed I'm traveling, and then continue moving after I've completed the shift.

Today I was driving my current car, an automatic, and I noticed that when the car shifts gears, the speedometer does not freeze. It keeps moving with absolutely no hesitation at all.

What gives?
 
An auto when shifting gears is still accelerating a little even through the shift usually. Even if it isn't, the shift is quick enough to keep the momentum going.
 
Try accelerating with the manual a lot faster and try to shift as quickly as possible, proceeding with the same rate of acceleration.
 
When you shift with a manual transmission, you are disengaging the drivetrain completely. Automatics don't - hence the difference. 🙂

Originally posted by: fleabag
Try accelerating with the manual a lot faster and try to shift as quickly as possible, proceeding with the same rate of acceleration.
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But that will waste fuel.
 
Originally posted by: JLee
When you shift with a manual transmission, you are disengaging the drivetrain completely. Automatics don't - hence the difference. 🙂

Originally posted by: fleabag
Try accelerating with the manual a lot faster and try to shift as quickly as possible, proceeding with the same rate of acceleration.
Click to expand...

But that will waste fuel.
Click to expand...

Troll
 
Originally posted by: fleabag
Troll
Click to expand...

Bwahahahahahaa....

You have no idea how ridiculous it is for you to call anyone else a troll.

Sparky is correct.

Also, an automatic transmission transmits power by fluid when the torque converter isn't locked up, like during a gear shift. I wouldn't be surprised if the fluid is still moving enough to keep up the acceleration for the split second during the gear shift.
 
in old school automatics (3 speeds) there is a delay in shifting causing the rpm to drop between shifts. This was done to make shifting smoother. This delay causes unnecessary wear and tear on the transmission.

This is why a shift-kit is a great idea, but the shifts can be pretty harsh depending on how its set up.
 
Originally posted by: SparkyJJO
An auto when shifting gears is still accelerating a little even through the shift usually. Even if it isn't, the shift is quick enough to keep the momentum going.
Click to expand...

This.
 
The gear sets in an automatic are always enabled; the act of switching gears is merely releasing or stopping a section of the gear set while they are still moving. Nothing is ever disconnected as with a manual.

And an auto by nature of it's purpose can always shift at full throttle and under constant load, while you usually lift off the throttle while shifting a manual, hence the pause in acceleration. It takes skill and practice and a good mechanical setup to shift a manual fast enough to shift at full throttle and under load, and even then it can cause accelerated wear due to the drive line shock inherent in a mechanically rigid coupling.
 
What kind of car are you driving? On my car, the speedometer decreases but mostly because I shift slower than most people.
 
Speedometer input is derived from the speed of the traction wheels.

If a vehicle breaks traction under acceleration and the wheels spin the reading will be higher than the speed over ground. In braking if the wheel locks the reading will drop to zero.
 
Originally posted by: fleabag
Try accelerating with the manual a lot faster and try to shift as quickly as possible, proceeding with the same rate of acceleration.
Click to expand...

An automatic shifts faster than any manual.


For the OP: It really depends on how hard you're accelerating and how quickly you shift if you're driving a stick.

If you're accelerating slowly and taking forever between shifts, you might see the speedo at least stall....but even when you disengage a manual for a second, the inertia you have built up keeps accelerating you long enough for you to get to the next gear.
 
Originally posted by: Pacfanweb
Originally posted by: fleabag
Try accelerating with the manual a lot faster and try to shift as quickly as possible, proceeding with the same rate of acceleration.
Click to expand...

An automatic shifts faster than any manual.


For the OP: It really depends on how hard you're accelerating and how quickly you shift if you're driving a stick.

If you're accelerating slowly and taking forever between shifts, you might see the speedo at least stall....but even when you disengage a manual for a second, the inertia you have built up keeps accelerating you long enough for you to get to the next gear.
Click to expand...

Huh. The instant the clutch loses contact with the flywheel, all acceleration is lost. There will always be a blip, no matter how small, in the speedometer reading when you shift with a manual.

As others have said, an automatic doesn't actually disengage the drivetrain while shifting. That's why you'll often feel a surge of acceleration as an automatic shifts and the clutch band initially slips, but then brings RPM down.
 
Originally posted by: nkgreen
Just don't take your foot off the accelerator when you change gears. 😛
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Yea pretty stupid to recommend to anyone as they are probably going to mess up their tranny.
 
Originally posted by: zerocool84
Originally posted by: nkgreen
Just don't take your foot off the accelerator when you change gears. 😛
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Yea pretty stupid to recommend to anyone as they are probably going to mess up their tranny.
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Wait, so powershifting at 7k rpm every time could possibly have an adverse effect on my clutch and synchros? :shocked:
 
Originally posted by: nkgreen
Originally posted by: zerocool84
Originally posted by: nkgreen
Just don't take your foot off the accelerator when you change gears. 😛
Click to expand...

Yea pretty stupid to recommend to anyone as they are probably going to mess up their tranny.
Click to expand...

Wait, so powershifting at 7k rpm every time could possibly have an adverse effect on my clutch and synchros? :shocked:
Click to expand...

Well to someone who's clueless about cars like the OP obviously is, it's not that smart cus they won't know what it does to their car.
 
I bet what you are seeing is a digital speedometer that doesn't keep up well. For example, when stopping, you may be at complete stop, but the neddle will still be moving down. Even my 6spd GTO had a digital speedometer that would also lag by 3-4mph when stopping or accelerating quickly.
 
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