Ericf said:
With all the comments about IMS failure etc, how safe, relatively speaking, is a low mile C4 (44,000) which has recently had a new clutch and IMS bearing upgrade?
Cheers
Relative to other models/mileages, or relative to how it was before?
Have a read of the sticky IMSB thread to follow lines of reasoning, but in summary, it seems likely that premature failure of the bearing is down to a dodgy batch of bearings, blocks or installation. The bearing is too tight in the block, and wears prematurely. Some fail early (before 40-60k), some never fail.
Depending on the age of your car it may or may not have the 'dual row" bearing (used on earlier cars). Lots of people claim the dual row is the better bet, but there's no way to tell what's fitted without taking things apart. Of course there's a counter theory that dual row are more prone to being over stressed if they're not fitted square (because each row then takes a different load at different points instead of an even load all the way round) and the ball bearings and bearing surfaces are smaller.
When it comes to 'upgrade", what does that mean? Was a roller bearing fitted? Better in some applications but not necessarily this one; was an oil fed bearing fitted? Where does the oil feed come from and does that affect the oil feed to anything else?; Was a ceramic bearing fitted (eg LN) and is it lifed? Some of these have a stated service life of 4 years. Is that an upgrade?
As you can see, the only answer to your question is 'it depends"!
The short answer is probably that if your original bearing was in need of replacement, then an 'upgrade" is safer. There is a risk to doing it in situ (ie during a clutch change with the engine in the car) because unlike, say a wheel bearing, IMS bearings are not designed to be replaced without stripping the engine down. Despite this, techniques have been developed and people seem to get away with it.
On the other hand if your original bearing was ok, my view and many others is that it's safer to leave well alone. If it ain't broke...