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Author Topic: Manual gearbox makes knocking sounds  (Read 387 times)

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mandula

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Manual gearbox makes knocking sounds
« on: 20 September 2017, 17:26:31 »

My manual gearbox (R25 ?) makes this knocking sound when changing gear and/or when I press clutch while driving. Also at low speed at 1st and 2nd gear I can hear whining that I believe comes also from gearbox.

Gears go in easily without any unwanted sounds.

I know knocking is coming from gearbox, because I can reply it by turning the output shaft of gearbox when cardan is disconnected.

Earlier I have replaced dual mass flywheel to solid one (with suspensed clutch disk of course) and brand new differential. DMF was defected and I believe because of that my dif and gearbox got some banging that caused dif and gearbox to damage.

Ok, my question is:
Is it worth/easy to repair my gearbox or should I just change it?
I think it cannot be so bad defect, because gears go in easily without trouble..  ::)

Edit. Gearbox oils been changed twice in a year, no change to problem.
« Last Edit: 20 September 2017, 17:28:45 by mandula »
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Chazza12

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Re: Manual gearbox makes knocking sounds
« Reply #1 on: 21 September 2017, 05:46:50 »

it could be the shaft bearing at both ends, excess torque or twist would damage the bearings can also warp the shaft. its more easier just to swap out the gearbox. it could be warn bearings it could be a stripped cog etc. gear changing is no real indicator of the problem, just means the mesh is in line.
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Doctor Gollum

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Re: Manual gearbox makes knocking sounds
« Reply #2 on: 21 September 2017, 06:32:26 »

2.2 shouldn't stress the gearbox, although it is designed to have a dmf...

A bit of backlash is normal from new so shouldn't be a concern. A decent gearbox specialist should be able to overhaul it easily enough.

Is the oil correct type and at the correct level? Could be than it has previously run low, causing the bearings to wear prematurely.

Not on an Omega, but have had the lay shaft snap on an otherwise good gearbox due to previous abuse/neglect.

Even a hard driven 3.2 manual will see at least 480k km from the gearbox... a 2.2 one should at least match that without trying :-\
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mandula

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Re: Manual gearbox makes knocking sounds
« Reply #3 on: 21 September 2017, 06:47:40 »

I tried two different oils, one from Castrol and now GM transimission oil (I think its just ATF..).

But the knocking sound remained, no matter what oil.

There is really very much play when I turn that output shaft, its like 10 mm free play before it hits something and makes that same sound what I hear when I change gear.
It's hard to explain, but there is this free play somewhere inside gearbox and when pull is on and then off and on again for example when changing gear, that free play causes the knocking sound.

Maybe I just try to find some cheap used gearbox and swap that in place, because I need car almost daily.. But will try to fix the problem anyway from old gearbox, just for interest to see whats the problem  8)

And yeah, car has now 310 000 km and I think DMF was loose for at least 20 000 km before I realised it was making all the weird noises I was hunting down for awhile  ::)
« Last Edit: 21 September 2017, 06:53:33 by mandula »
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Doctor Gollum

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Re: Manual gearbox makes knocking sounds
« Reply #4 on: 21 September 2017, 06:56:19 »

Most definitely should NOT be atf :o
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mandula

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Re: Manual gearbox makes knocking sounds
« Reply #5 on: 21 September 2017, 07:19:34 »

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Andy A

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Re: Manual gearbox makes knocking sounds
« Reply #6 on: 21 September 2017, 11:26:38 »

Most definitely should NOT be atf :o

Well, it seemed like ATF but it's MTF  :)

http://www.motonet.fi/fi/tuote/590044/GM-vaihteistooljy-1l-194018293165290

Can it be confirmed that this is the right manual gearbox oil for a Desmond?

I need to replace mine. Just did a trip to Yorkshire plus site seeing 1000 miles and now I'm getting a slight wine from the gearbox mainly in third.

Thanks
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Fuse 19

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Re: Manual gearbox makes knocking sounds
« Reply #7 on: 21 September 2017, 12:08:54 »

Pop the filler bung out and use a screwdriver to move the aux shaft and get an idea of how much play there is (should be small at around .2mm (ie not a lot!)

The bearings are not hugely hard to get and the play is adjusted using shims, its not a complex gearbox by any means
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mandula

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Re: Manual gearbox makes knocking sounds
« Reply #8 on: 21 September 2017, 17:36:14 »

Ok, thanks so far for all replys!

I found used unit for 100 euros, so I go with that to solve this problem.

Anyways, I think this gearbox is good practice unit to dig in to gearbox insides.  8)
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