Took my Fiat Punto in for a clutch repair, and the garage said that there
was also a problem with the gearbox.

What they said was 'the crown wheel has sheared off the pinion' because of a
sheared weld.

Speaking to the transmission specialist where they sent the gearbox to
investigate the problem, he said that the crown wheel was supposed to be a
tight fit on the shaft. He thought it was heated up then forced onto its
shaft. He said it was now loose. Possibly, this was because of incorrect
tolerances in the design/manufacture stage.

I understand how differentials work in principle, but not how they are
implemented on a transverse engine FWD car. Does a crown wheel have a
pinion, and does this take any significant amount of torque from the engine?

The car is 4 years old and has only done 20k miles. I am therefore a bit
surprised at having to fork out for a major gearbox rebuild, and I wonder if
this is likely to be a problem that was inherent at the time of manufacture?
Alternatively, what are the likely causes?

I am inspecting the gearbox tomorrow morning, at the same time as a
representative from the Fiat garage that sold me the car (new). Any
advice/help would be appreciated before we turn up.

"GB" <NOTsomeone (AT) microsoft (DOT) com> wrote

Are they sure?
The last Fiat gearbox I worked on had an interesting design feature in that
the inner CV boot housing bolts onto the gearbox, in so doing it holds the
taper roller bearing that supports the crown wheel, so with the drive shaft
out the crown wheel flops about.!! That sounds rather similar to your
description. It catches you out the first one you see !!

Mrcheerful

"GB" <NOTsomeone (AT) microsoft (DOT) com> wrote

made properly so you should not be liable for any costs. This should be
especially true as you bought the car from new and if you have had it
serviced by the garage at the correct intervals.

The act covers up to 6 years so they cannot use the excuse that you are out
of your 3 year warranty. Given the low milage you should have a good case.
Also the fact that the garage is also comming down indicates they know they
have some liability.

In practice they may admit some liability and pay part of the costs. It is
probably down to how hard you argue your corner. A solicitors letter may
work wonders.

I would think it is worth spending a few quid on a solicitor to find your
exact position.

This is only my personal view though.

Good luck and let us all know the outcome.

"Paul Edwards" <paul_edwards (AT) nospam (DOT) talktalk.net>

Thanks. I am aware of the legal point. I am more concerned at this stage
with understanding what I should be looking for tomorrow.

In article <460ac0a2$0$27103$db0fefd9 (AT) news (DOT) zen.co.uk>,
GB <NOTsomeone (AT) microsoft (DOT) com> wrote:
The crown wheel is attached to the diff cage. The pinion is the gear wot
drives it - ie on the output of the gearbox. In other words, they are a
gear set.

--
*Would a fly without wings be called a walk?

Dave Plowman dave (AT) davenoise (DOT) co.uk London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" <dave (AT) davenoise (DOT) co.uk> wrote


Thanks for the input guys. I have now been to see the gearbox in bits, and
it is clear what happened.

The crown wheel is manufactured in two parts, the diff cage looks like a
hub, and it has the planetary gears inside. The crown wheel gear teeth are
made separately as a ring and then pressed onto the outside of the hub,
probably with the teeth part being heated up so that it contracts onto the
hub and grips it well. The gear teeth part came loose from the hub, so that
I lost drive, which is the same symptoms as a slipping clutch.

The question is what caused that to happen? One explanation would be
tolerances, ie the gear teeth were a bit too big, and the hub was a bit too
small, so when they were pressed together the bond was not strong enough.
(That's my view.) The alternative is that the car has been misused in some
way. (That's Fiat's view.)

As far as I know, the car has been driven reasonably sensibly. It is only a
1.2 litre 8v engine, so there is not a huge amount of power going through
the gearbox. The car is 4 years old and it's only done 20k miles, although
this particular join in the assembly is not an item that would be expected
to wear out. The gearbox engineer said that he has seen this sort of failure
before, nearly always where the car has been modified with wider wheels than
it was designed for. My car has not been modified.

Any ideas? I can't see any obvious way of telling why the item failed after
20k miles.

On Thu, 29 Mar 2007 12:54:26 +0100, GB <NOTsomeone (AT) microsoft (DOT) com> wrote:

Ask fiat for goodwill, if not forthcomimh then go to watchdog, local
papers etc., however badly treated it was 2ok is inadequate!

"Duncan Wood" <newsto (AT) dmx512 (DOT) co.uk> wrote


I got the brush-off I expected, so I'm issuing proceedings.

"GB" <NOTsomeone (AT) microsoft (DOT) com> wrote

It should not fail in that manner, even with abuse. If you were to drop in
an engine of vastly greater power I might expect it. And I dont see how
wheel width has any effect whatsoever on such a diff failure? Wide wheels
can only stress the suspension components (and it will) - the diff has no
clue what width wheels it is driving. Even larger diameter wheels cannot put
more torque through the diff than the engine can produce - and since you
might use the engines max torque to overtake someone in 5th 10 times a
day...

The only abuse you might find that could overload the join is snap-loading
the transmission - 5000rpm, step off the clutch sorta thing. Dynamic loading
would be massive, but I'd expect the clutch to be shredded first unless
there was an inherent weakness....but then you ARE having a clutch replaced
at 20K miles...which isnt very normal for an underpowered tin box unless its
had its nads thrashed off ...

"Coyoteboy" <coyoteboyuk (AT) hotmail (DOT) com> wrote


Ahh sorry, slight adjustment, i re-read your post - i see the clutch is OK
and the gearbox was the cause of the slipping, in that case (and looking at
your clutch and flywheel should prove whether it was driven hard - i.e. if
it looks like mine did after i drove it hard
http://www.alltrac.hobby-site.com/index.php/Flywheel) it is unacceptable for
a gearbox to fail in that time.

J