The case of the rattly 300GD gearbox………

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John Green
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The case of the rattly 300GD gearbox………

Post by John Green » Mon 22 Jun, 2009 12:27 pm

My turn to ask for help, I have a problem that to date has beaten me and all the other experts that I have discussed it with. Have a read of this and see if you have any brain waves:

Chassis number: WDB460 333 27 05481 300GD LWB wagon

- Vehicle’s original specification was OM617 engine, naturally aspirated and 4 speed auto.
- Engine wore out and owner wanted more power as well as a manual transmission.
- Around the same time as the engine died, we purchased another 300GD with an aftermarket Turbo and 5 speed Getrag Manual gearbox (717 422), The body was very rusty as it was imported from the United Kingdom, but the engine had been recently fully overhauled.
- As deal was struck to fit this engine and manual transmission as well as carry out the modifications to convert from Auto to Manual.
- The work was carried and when the engine was started a rattle was heard coming from the gear box. Very quickly it was realised that this rattle must have been there when the engine/gearbox was fitted to the rusty 300GD. How this happened was that the rusty vehicle had a loose exhaust system and worn engine mounts so everything rattled masking the rattle coming from the gearbox.
- Diagnosis of the noise revealed that it would go away when the clutch pedal was pushed down. It was there in neutral and in all forward and reverse gears. The noise level did not change between gears.
- Gearbox was removed and the input shaft bearing was found to be very badly pitted. This bearing was replaced and the gearbox reinstalled, only to find the noise was exactly the same. Spend some time listening to the noise. Find that it will go away if you put it in gear (on the hoist, wheels hanging free) and very lightly apply the foot brake. Take you foot off and the noise comes straight back. So quite obviously some kind of free play in the gear sets.
- Gearbox was removed again and all roller bearings replaced including those in the sandwich plate. Gearbox was reinstalled with no improvement in the noise. Very frustrating.
- Priced new gearbox and nearly had a fit! Found a new 230GE gearbox (717 420) that we could buy for 1500Euro. Spent 2 hours looking at the parts books to see what the difference is. The only difference I could find was the bell housing. So ordered the 230GE gearbox and had it air freighted out from Germany.
- Very carefully removed the 230GE bell housing and fitted the 300GD bell housing, double checked all the clearances and installed the NEW gearbox and NEW throw out bearing. Same noise!
- Removed gearbox again and tried a new clutch plate, the old plate had done around 30000kms and appears to be perfect, reinstall gearbox, noise still there.
- Spend hours thinking about it and cruising the net. Find plenty of stuff but none like this. Listen to noise in gearbox. Remove the shifter plate and drain out 50% of the oil. Put a listening probe into the gearbox with the engine running. Do the trick of putting it in gear and then light pressure on the brakes. Find noise is at the loudest near the input shaft gear. So theory is that the noise is the input shaft gear rattling against the lay shaft gear. Theory is that the rattle is caused by the vibration of the 5 cylinder engine.
- Discuss problem with a MB tech who has worked on these for years. He says there is a MB service bulletin that recommends SAE30 engine oil. Replace shifter plate and fill with SAE30 engine oil, start engine and let clutch out. No noise, go for a drive, oil gets hot and the noise comes back.
- Vehicle drives perfectly, gear changes are OK (but a little stiff when cold with the SAE30 oil) and there are no other noises. When you drive the vehicle you never hear it. Pull up at some traffic lights and so long as you have your foot on the clutch no noise. Take you foot off the clutch and it starts.
- End result is 12 months work, lots of money that we will never recover as the job was done to a quote and an upset but somewhat sympathetic customer. Customer does not want to take delivery of the vehicle unless we can fix the noise.
- Many people tell me that these are all like this; I have trouble believing this as if they were MB would either never have sold one or had the most horrendous trouble with warranty claims. The noise is terrible, especially when the gearbox is hot and has the correct specification oil in it.

Some theories that we have come up with from brain storming it are:

- Engine out of balance, but it runs very smooth and produces good power.
- 300GD bell housing incorrectly machined so the two shafts are too far apart.
- Turbo back pressure on the exhaust system creates the imbalance.

Someone somewhere around the world must have had this problem before all I have to do is find that person? If say there were a set of bell housings that were machined incorrectly this problem will have happened before.
Any help very much appreciated.
M.B Spares & Service 14-16 Lyell St, Fyshwick ACT. Ph 02 6239 1099

http://mbspares.com.au - Supporting Australia's Mercedes-Benz Enthusiasts.

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Hendrik
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Re: The case of the rattly 300GD gearbox………

Post by Hendrik » Sun 28 Jun, 2009 9:59 am

Have you tried removing the propeller shaft to eliminate it from the list?
Have you tried installing the box without a clutch assembly/throw out bearing,clutch release fork?

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