Punto gearbox - some useful information

Information some may find useful.
If your Punto MK 1 gearbox is making a rumbling/whirring noise during idling then it is almost certainly a bearing fault. If you press the
clutch pedal in and the noise is still present, then suspect the thrust bearing. If you do the same and the noise disappears, then it is almost certainly the bearings supporting the input shaft. Pushing in the clutch allows this shaft to slow down and stop, thus the cessation of the noise.
This was the case with my Punto and I have just replaced the input shaft bearings. Thankfully, the box now sounds like new. If you are able to remove the box itself, then stripping the box should present no difficulties. You will need a bearing puller - cheap on eBay.
Once the box is removed, drain the oil and remove the selector mechanism casing. Then, remove the fifth gear end cover which exposes the two nuts on the end of both gearbox shafts. To remove the nuts, you need to lock the box, which is done by selecting third and first at the same time. This can be done once the selector cover is removed. You need a large socket (32 mm I think) to remove both nuts. Remove the 5th gear syncho and the other cog (extract using wedges - careful of the teeth) which will expose both end bearings. There is a circlip around both - remove and take off the heavy plate. Remove the 13 mm nut from the side of the box - this holds the reverse shaft - and now the casing can come away. The whole internal assembly can be lifted out.
What I found interesting was that the secondary shaft bearings had integral seals and they ran smooth. The main shaft bearings did not and had become rough thus giving the noise. The bearings on this shaft are of different sizes. The front bearing is smaller and is a standard bearing you can get in any bearing supplier - make sure it has plastic spacers and not metal ones. The rear bearing is larger and has a groove cut in the outer race for the circlip. You can also get these in bearing suppliers, but they may need to order them. It was this larger bearing causing the noise. To remove this bearing, put the circlip on again and pull the selector ring up against it - watch out for the three springs that may pop out. This allows you to put a bearing puller onto it and extract the bearing. I obtained a replacement from Fiat (20) and have noticed that it has been modified - you guessed it - to contain side seals. So obviously there have been some problems with this earlier exposed design.
The box goes together in the reverse order. It is a long job but the parts are not that expensive even from Fiat.
Hopefully, somebody may find this of some use.
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[Snip useful description of input shaft bearing repair]

Now there's a thing. Just had the input shaft bearing on my Marea JTD replaced (57K miles) - I wonder if this is a generic weakness across several Fiat 'boxes?
What function do you reckon these seals provide? - after all isn't the bearing submersed in the oil in the box for lubrication.

--
steve

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Steven Briggs wrote:

If you remove the magnet from the bottom of the differential housing, you will notice that it is covered in metal fragments. If you run these between your fingers, they are noticeably rough. So at some stage, these particles must have been floating around in the oil before the magnet got a hold of them. You can only but guess where they spent some of their life.
IT is possible to take the bearing apart. Punch out the centre of the bearing, move all the balls to one side and use a level to wedge the inner race away. You can then inspect the running surfaces. The bearing I removed, without seals, was pitted and the balls had a matt appearance. Obviously, some large debris had gained easy access and done this. Where it came from, who knows? In the newer bearings, the seals run very tightly against the races so that all, but microscopic particles, are unable to enter the bearing, thus extending its life.
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Paul wrote:

I suspect they are sealed bearings and not even oil gets in there. Also I don't think the open bearing will have worn its case hardening as you describe as a result of debris. It is more likely to be from lack of lubrication or just coming to the end of its life. Many gearboxes now use sealed bearings but I have no idea whether this leads to a longer service life.
Huw
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in article snipped-for-privacy@o13g2000cwo.googlegroups.com, Paul at snipped-for-privacy@qub.ac.uk wrote on 02/01/2006 13:18:

It'll always be useful for the knowledge base - thanks Paul.
Paul
1999 Fiat Punto Sporting 16V (Mk1) ... and some SAABs :)
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