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Discussion Starter · #41 ·
What does this? Is it rocks in the bell housing? Loose ball bearings from a failed input shaft bearing? Pieces of friction material from a failed clutch friction disc?

Michael
The diff carrier pin falls out, and along the way around it rips up the casing around it. Mine came out almost completely, hence the destroyed bellhousing.
 

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So you think I can fix this with JB Weld? :D
Probably! ;) Or fibre-reinforced filler...

But you'd have to fix the diff as well. That would need welding.
I guess anything can be repaired given the time and inclination...

-Alex
 

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Discussion Starter · #45 ·
Is this the "typical" failure mode on these boxes? Any thoughts on what can be done preventatively to avoid this occurring?
You would either have to weld the carrier pin in (probably what I will do on the replacement 'box), or replace the pin with a grade 12 or so bolt and and be sure everything is lined up and balanced and also clears the casing.

It would be possible to weld the pin in with the 'box in the car, just remove the rear diff cover (drain the box first!) and weld the pin in.

I wouldn't hesitate to weld in the pin, maybe just a couple of spot welds on each end. Dean Russell at Trail Alfa didn't express concern either when I inquired about it - sort of along the lines of, "well, you couldn't service it as easily but I've never had to service one [diff carrier]..."
 

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And here is a photo of the missing pin. Everything else seems to be ok except for the hole in the casing and pieces of aluminum everywhere. I'd bet that if the case could be fixed, this transmission could be saved. I'm definately going to look into having the pin welded into place on my replacement transmission.
 

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Any suggestions as to just what is happening here? Did Alfa not quite spec enough interference on the pin diameter? What would be the Right Thing To Do? Welding seems excessive and hard to undo. Maybe staking the pin in place? Just trying to understand here.....

I realize that the crank pins were re-spec'd as threaded and thread-locked in place instead of simple staking. But I don't see how staking (properly) could fail.

Michael
 

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I'm open to suggestions on how best to prevent this from happening, but I don't think welding is all that excessive. This box got me 180K miles, so if the replacement gets me another 100k, I don't care so much if the diff can't be rebuilt.
 

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As is generally the case with me, I was asking for technical reasons rather than practical ones. Your targeted service life is a good reason for welding. I just wanted to know why the problem exists and whether other solutions at manufacture would have been better.

I never did understand why staking the crank pins wasn't sufficient. That they fell out was a given, but is there some deficiency in staking, or were the pins that came out just not quite staked properly? Only someone who has looked at examples would know, and that isn't me.

Michael
 

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On a related note!

Just for your interest, please take a look at the following thread:
Failed driveshaft housing / gearbox - The FIAT Forum

No really, humour me - I used to own a Stilo 2.4 and I know that had the same C530 gearbox that my 164 has :eek: My Stilo had the robotised Selespeed shift (and clutch) but the gearbox itself was the same, easily identified by the dipstick in the diff housing.

HOWEVER the gearbox pictured in the thread is different (smaller engined-model) but I'm sure that the pictures and problem description will be VERY familiar - and I'd just like to point out that this is on 2002-2007 models - a good ten years newer than our 164s and the problem is STILL there!

For those that can't be bothered reading the thread, the solution was to tap and thread a hole and add a grub screw ;)

-Alex
 

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That was an interesting thread to read.
 

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Cheers guys. I've since remembered another case where the diff pin came loose in a FIAT 128 'box and made strange noises, but didn't quite make a bid for freedom. I still have that diff somewhere in my garage.

I think when I get the engine and gearbox out of my 164, some indeterminate time in the next year, I might take the diff out and add a grub screw. If my memory serves, you guys have a different term for 'grub screw', I can't remember what you call it. Basically a small headless screw, often with an recessed hex (Allen key) drive.

-Alex
 

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Does the pin under discussion here have a through hole (can be driven through to remove), or is the hole a one-way-only path, smaller or bottomed-out at the other side? If it is through, then one would expect to have to block both sides. If not, then one end is enough. U-joint bearings are retained with internal snap rings, as are some of the other transmission pieces. Why not have the part machined to accept an internal snap ring as a pin retainer? This makes removal a "snap" and there's no possibility of the grub screw backing out. (nor do you have to work hard to break a threadlocker secured joint.) The factory could add such an internal groove for (I _think_) nearly nothing in the fabrication process.

Michael
 

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Alex, I think we would call it a "set screw." I have been thinking about this problem a bit myself. I think the factory should have used internal circle clips to hold the diff pin in, as well. This is what VW has done in the past. VW Self Machine Syndrome What would be wrong with tack welding the pin in as a fix? Other than, you can't get the pin out again, which is OK with me if it insures my diff pin.
Charles
 

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Apparently some other cars have had this problem as well Pontiac Sunfire and Saturns I have found doing a web search.
But DON'T do this
How to check it on your Saturn
Charles
 

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Upon further though ;) welding the diff pin doesn't insure it against breakage nor does it insure it against spider gear breakage. Only thing it does is insure it doesn't back out which we don't know for sure is what is going on, is it backing out and then busting against the case, or is it breaking and then coming apart and busting the case?
Charles
 

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I would think that internal circlips (if there is room) would be a satisfactory backup failsafe solution to pin migration, in addition to an interference press fit.

I would imagine a good machine shop could cut the required grooves in the housing.
 

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So I took the two diffs up to a transmission shop today. The one with the broken roll pin from my 91B and the good one from the replacement 92S gearbox. The shop claims they rebuild the alfa transaxles for Ferrari of Seattle. OK.

A couple of hours later the owner called back. He said the roll pin broke or disintegrated. He was wondering if this was due to racing. The roll pin did not work its way out so welding would not be a solution, just weaken the pin. He is going to show me tomorrow a fix using clamps for Dodge Caravans that keep the pinion shaft in place in case the roll pin breaks. A google search shows its quite common on those minivans. Perhaps the clamps can be adapted to the 164.

Does anyone know if the differential on a 94-95 LS can be fitted to a 92 box? Did alfa change the roll pin or make another mod?

Thanks
David
 
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