Gearbox noise; could it be the clutch?

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adamskibx
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Gearbox noise; could it be the clutch?

Post by adamskibx » Thu Aug 03, 2006 11:25 pm

Right. Im totally confused. Im was going to change the gearbox in my car, but cant work out whether it is the gearbox or the clutch, or worn crankshaft bearings. I have had a good look around on the internet to try and diagnose it, but the symptoms are almost unheard of, but it does exactly what my last BX did.

I thought it only happened when the car is in motion, but I can get it to do it when parked, but only when it is in gear. If its in neutral, I can do anything with the clutch pedal and the sound wont happen. Basically, the noise sounds like a shot dry bearing and the sound resonates with the interior of the car; ie you cant hear it outside the car. For example, parked in the drive, I can engage any gear, take the engine to about 2300 RPM with the clutch pressed and the noise is only evident between 2300 RPM and 3000 RPM. If I push the clutch really hard into the carpet, the sound almost goes away, and if I start to engage the clutch very slightly, the noise goes away, but I cant get it to do this in neutral. However, the noise happens when driving along in low gears with my foot completely off the pedal. I cant get the sound to happen in neutral, but if I push on the gear lever slightly from neutral into any gear (ie put some load on the gearbox without pressing the clutch in) the sound happens too. It cant be the gears in the gearbox then, as the car isnt going anywhere.....? So that leaves: The input shaft bearing? Clutch release bearing? Crankshaft bearing possibly? Im inclined to think its the clutch release bearing but surely that would be noisy in neatral too. It really doesnt make sense to me. Im going to buy a complete clutch kit in any case, but cant decide which gearbox to use. I can risk using the cutrrent one, which would leave reverse in the right place, and it is only a 48,000 mile box, or I could use the 105,000 mile box from the donor car. I have got a TD gearbox that I was going to use the 5th gear from, but installing the whole thing would ruin the ratio's that are suited to a petrol engine so thats not an option.

I know ive moaned about this before, but as im about to change the clutch, any advice would be appreciated etc.

Cheers, Adam

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docchevron
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Post by docchevron » Fri Aug 04, 2006 1:40 am

Blimey, thats hard to diagnose without seeing the car... Are you anywhere near Bristol??
Could be the thrust bearings in the engine? My diesel had a noisy release bearing that was similar to the symptoms you describe but it was intermittant.
On that low a mileage box I wouldn't expext the input shaft bearings to be cream crackered..... Is there sufficiant quality oil in the box???
Maybe it would be worth draining the box and seeing what colour the oil is and if any metallic bits come out.
Also are the engine / gearbox mounts in good condition?
Cheers
Chris G
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Post by roscoe » Fri Aug 04, 2006 8:51 am

Sounds like the clutch release bearing to me as well - mine on the TZD was making strange noises and when the clutch finally gave out and I replaced it with the bearing, noise disappeared. Also check to see if any of the gear change rods are touching anything when moved - might be vibrations from them on something like the exhaust? Other than that - like Chris said - dump the gearbox oil, check the colour, quantity - and refill with the correct quantiy plus Nulon G70 additive if you can get it over there - it does work!
cheers,
Roscoe
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Post by jeremy » Fri Aug 04, 2006 2:00 pm

A severely worn engine mounting would rumble all the time, and as the crank could move around, would probably have destroyed the rear seal.

Engine thrust bearings seldom fail now - and when they wear usually the clutch adjustment disappears. You can probably check by levering the front oulley in and out.

The crank bearing setup is massive - large shell bearings with a pressure fed lubrication system - and has to be made that way to stand up to the use they get.

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Post by adamskibx » Fri Sep 08, 2006 7:14 pm

Right. Im getting to the bottom of this tomorrow. Ive got a new clutch ready, so I had a play about with the current one to try and diagnose this further. The sound is definately engine speed dependent, but only when a gear is selected. It is slower and louder sounding when in a gear, traveling along at a constant speed, and seems louder when delelerating than accelerating. Ive also noticed that with the clutch fully pressed, engine at 2500 RPM, there is no sound until you move the gear lever into a gear, and then there is a brief attack of this sound, which implies that the clutch is not fully disengaging, and that the sound happens as the syncros mesh together. Ive also found that if you slip the clutchat 2500 RPM, car still, then you get the same sound, but with a roaddrill type rythm instead of a slower on/off woosh. This is also engine speed dependant, yet the input shaft cant actually be physically turning. Im putting it down to either worn input shaft bearings (shaft shaking about due to clutch irregularity, causing the road drill like sound when the car is still), or some sort of freak clutch/release bearing problem. Hopefully the latter.

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Post by adamskibx » Sat Sep 09, 2006 11:05 pm

Yippee the noise has now gone. I replaced the clutch, and took the clutch release bearing guide tube off and cleaned it all and heavily greased it. The clutch is amazingly light now.

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docchevron
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Post by docchevron » Sun Sep 10, 2006 2:07 am

Well done dude, its always good when you do a job and theres a marked improvement after.

Cheers
Chris G
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Far too many BX's, a bus, an ambulance a few trucks, not enough time and never enough cash...

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Post by m_2975 » Sun Sep 10, 2006 10:08 am

That's definately the clutch release bearing. Mine's doing it too. Will get around to fixing it when I change the clutch. Noting too serious but needs to be greased well and the clutch needs to be adjusted correctly.
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adamskibx
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Post by adamskibx » Sun Sep 10, 2006 10:36 am

Cheers guys. I was releaved when I first drove it down the road, past 3000 rpm, no horrid sound.