425 transmission chain

["Cadillac Kid" Greg Surfas 15364]

I was just lookin at the 76 Eldo transmission/final drive I picked up a decade or so again and was amazed by the apparent physical strength of the transfer chain connecting the converter and the transmission. It got me curious. Has anyone out there had or heard of those chains failing, and what might have been the cause.
Greg Surfas

[Dr. John T. Welch]

From when they were first specified for use in the 1966 Oldsmobile Toronado and later the Eldorados, I have never seen, heard of, or experienced a primary failure of the chain.  This was the critical power transfer component in what GM called the  “Unitized Power Package”,  a revolutionary new combination of a longitudinally mounted V-8 mated to the parallel side -by- side Turbo Hydramatic 425.  GM was not going to suffer the public embarrassment of this iconic engineering feat  simply due to a broken power transfer chain.  The reputational damage to these halo products and their brands was unthinkable.

Accordingly, the chain was manufactured by the renowned Link Belt Corp. to extraordinary specifications of alloy composition, hardness, link tolerances and dimensional accuracy. They were very expensive as an OEM part.  There was no stretch wear tolerance service specification for these chains because there was no stretch.

[Cadman-iac]

Just curious,  can you still get one of these if it was needed? I never had the occasion to get one for a customer in either the aftermarket or as a dealership employee. You never heard of one going out that I know of.
Impressive indeed.

Rick

["Cadillac Kid" Greg Surfas 15364]

It DOES look like the chain on the jacking motor of the Queen Mary. Just curious if ANYONE has had one fail.
Greg Surfas

[The Tassie Devil(le)]

From looking back into my memory box (Brain), I remember that when these were first introduced, somewhere it was mentioned that these Morse chains were guaranteed for life.   Not like a normal lifetime guarantee in the Auto industry, but actually for life.   Never to break.

As an aside, has anyone ever heard of a simple Mores Link Timing chain break?   It is usually the Cam Gear that destroys itself, but in all my years, I have never heard of one breaking.

Bruce.

PS.   If they didn't require lubrication, and weren't as heavy, it is a wonder that nobody in Top Fuel would have tried to replace the Gilmer Blower Belts for driving the Superchager with one.   That would really test their strength.

[bcroe]

Those chains are very strong, pulling a 5 ton motorhome with a 500
engine is no problem.  It has been done with both superchargers and
turbo chargers.  At the time I think there were thoughts of V12s
and 600 engines for the Eldos.  If you look at the TH325s and the
later 4 speeds, you will note they steadily reduced the size of the
chain, still with no issues. 

The chains were actually fitted with selected sprockets to make sure
they were tight.  Many miles later they were not so tight, but I have
not seen one worn enough to be unusable.  Yes owners have damaged
the covers so things were rubbing, causing fatal damage. 

Some new chains were made up to fit a 65:57 sprocket set for the
motorhomes, gearing down to help the engines pull.  But it is
doubtful there are any more new parts available for this.  I
dodged the problem (for my lifetime) by getting one of these built
IN REVERSE to make my 2.73:1 final drive appear like a 2.40:1
overall.  That may sound slow, but a big engine and switch pitch
in a downsized car can manage quarter miles over 90mph. 
Bruce Roe

[Dr. John T. Welch]

The first generation "Unitized Power Package" was one of the most clever, over engineered and overbuilt power trains ever to be offered for passenger car use by General Motors.  Look at the size and look at the sheer mass. The WWII  GM power train tank engineers were still around and active in swan song mode when the "Unitized Power Package" was developed in the early 60's.  Compare it to the Turbo Hydramatic 125 FWD "X" cars (Chevy Citation) and you have a feel for how rapidly FWD design and engineering progressed at GM and evolved to the "transaxle "concept from the classic "differential axle" of the "Unitized Power Package". 

[MulletMachine67]

I know this is an old thread but I broke my chain over the past weekend although I'm not using my TH425 in the conventional way. lol    Link to video below.

TH425 chain broke

[The Tassie Devil(le)]

Now, that is what I would call a "Fusible Link"

So, from the look of it, there is no need for a Scatter Shield around the cover, as the cover appears to be in one piece, even though it is slightly out of shape in many areas.

Thanks for posting the picture, and the story.

Bruce.