Drive shaft turns in neutral

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timwilks13
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Drive shaft turns in neutral

Post by timwilks13 » Mon Mar 11, 2019 5:48 pm

As per the title, the drive shaft rotates even when I neutral, I only noticed it because I have a funny knocking noise coming from below and can't work out what it is (don't think it's the release bearing).

Is it normal for the drive shaft to spin even out of gear? It stops if you grab it but takes a fair bit of force to stop it.
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Jordi
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Re: Drive shaft turns in neutral

Post by Jordi » Mon Mar 11, 2019 8:53 pm

Which shaft?

G/box to t/box?
T/box to axle?

Surely if they were moving the SJ would be moving?

I’m gonna say it’s not normal. In neutral nothing visible underneath should spin, other wise you would be moving.

If there is no resistance the intermediate shaft may spin, if the t/box was in neutral or had no output shafts fitted.

Not sure how it works but because the gearbox input is always spinning some of that energy is transferred by magic to the output, it will spin if resistance is low enough.
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Anton
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Re: Drive shaft turns in neutral

Post by Anton » Tue Mar 12, 2019 1:59 am

Jordi wrote:
Mon Mar 11, 2019 8:53 pm
Not sure how it works but because the gearbox input is always spinning some of that energy is transferred by magic to the output, it will spin if resistance is low enough.
The output shaft has gears around it on bearings, none of which are connected directly to the output shaft (they just "float" on the output shaft) and they're all meshed to the input shaft gears, so if the input shaft is spinning, the gears that "float" around the output shaft will also be spinning (at different speeds). When you select a gear, a fork pushes one of the synchros into the gear, which forces the output shaft to spin at the speed of that particular gear. The rest are still spinning at whatever speed they want, they're just not connected to anything.

In neutral, the output shaft will have a tiny amount of power going through it - it'll want to spin at the average of gears 1-5, minus reverse. Basically the drag of the bearings transfers a *tiny* amount of power.

If the t-case is in neutral the gearbox has nothing to stop the output shaft from spinning with the tiny amount of power getting to it through the drag caused by the bearings.
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mike harris
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Re: Drive shaft turns in neutral

Post by mike harris » Tue Mar 12, 2019 7:46 am

Yeh mine does this too

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timwilks13
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Re: Drive shaft turns in neutral

Post by timwilks13 » Tue Mar 12, 2019 2:42 pm

Thats all I needed to know thanks guys! Yes the tbox was in neutral so I know realise with no resistance the output shaft will get residual energy from the input shaft.

The funny knocking noise I had was a bent heatshield from when I removed the gearbox fowling on the silencer. All is well and good!
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Ju
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Re: Drive shaft turns in neutral

Post by Ju » Sat Apr 13, 2019 7:36 pm

timwilks13 wrote:
Tue Mar 12, 2019 2:42 pm
Thats all I needed to know thanks guys! Yes the tbox was in neutral so I know realise with no resistance the output shaft will get residual energy from the input shaft.

The funny knocking noise I had was a bent heatshield from when I removed the gearbox fowling on the silencer. All is well and good!
Bent heatshield or you forgot to re fit all the bolts back for it?
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Re: Drive shaft turns in neutral

Post by timwilks13 » Tue Apr 16, 2019 1:11 pm

No its was bent, hadn't removed it and the exhaust had bent it backwards.
1986 SJ410 - Furry dice, new window winder.

10 kinds of people in this world, those who understand binary and those who dont.

if you can read this you're too close to the monitor, sit back and save your eyes!!

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