71 TH425: Found in pan...

[wbdeford]

I removed my transmission pan and found these in it...what are they?

[The Tassie Devil(le)]

They look like links from the Morse Drive Chain that transmits power from the Torque Converter to the Transmission.

I was once told that these chains were indestructible, but maybe this is not true.

Bruce.

[The Tassie Devil(le)]

Here is a picture of said chain.

Looks like the engine/Transmission will be coming out sooner that later.

Bruce.

[bcroe]

Those are from the chain all right.  Usually when I see something like that, the cover has
been dented against the chain.  Bruce Roe

[wbdeford]

Not what I wanted to hear....but it is what it is...

Does this mean failure is imminent?  Will failure just mean the car won't go anywhere, or will it mean further destruction?

[bcroe]

Does this mean failure is imminent?  Will failure just mean the car won't go anywhere,
or will it mean further destruction? 

I would call it "ominous".  Hard to say how long that chain might last, but that means the end has
come off a couple pins, and the pins may start working their way out.  Hard to imagine what a
failure might do, with a 500 turning things.  Bruce Roe

[wbdeford]

My problem right now is lack of space to pull the engine out.  Is there a way I can lift it just enough to move it forward enough to replace the chain?

[bcroe]

My problem right now is lack of space to pull the engine out.  Is there a
way I can lift it just enough to move it forward enough to replace the chain?   

The only way to replace that chain is to pull the 2 sprockets, and to do that you will need
the trans out.  Instructions are in the factory manual.  Its possible to drop the trans from
the bottom (engine must be supported & rocked forward).  Most of us just pull the engine
& trans, which of course means you first need to get rid of that huge hood.  Bruce Roe

[wbdeford]

Even though I am short on space, I am long on time, so if it takes me extra time do things, I am OK with that.  I have no place to put the hood (even hanging it from the ceiling won't work).  I also tend to think outside the box (though 90% of the time, I return to the box).  I read the shop manual procedure for removing the transmission while still in the car and don't like that prospect at all.   So....

Compressor is off the car, so I can easily just remove the condenser too, along with the radiator..  If I remove the cross bar and grille, will I have enough clearance to lift the power train up enough to move it forward, then up and over the bumper to get it out with the hood still on?  If not, what if the bumper is off the car, too?  I could live with the power train being outside under tarps for a while.  This would also make it easier for me to work on the suspension.

[savemy67]

Hello William,

Even though you do not have enough room to store the hood, would it take about the same amount of time to remove the hood, lift the engine and transmission out of the engine bay - without removing radiator, condenser, grille, bumper, etc, and then put the hood back on the car while you work on the chain and sprockets, and the front suspension?

Christopher Winter

[wbdeford]

Guessing 2 hood removals and 2 hood installations would still take a bit less time than removing and reinstalling those other things once.  But I might remove the grille anyway as it has some damage to the mount points.  Radiator is coming out anyway.  Right now, just trying to figure out all my options.

[bcroe]

My first priority would be finding replacement parts.  Those chains, with a low failure rate, are
not so easy to find.  I read the factory actually graded the sprockets & chains into matched
sets for a tighter fit; hope that isn't necessary.  Another way is get a donor chain & sprocket
set from a lower mileage trans. 

My Eldo has a reversed version of a GMC POWER DRIVE which has a 57:65 ratio to turn the
motor slower and save me some gas, at some loss of performance.  These are all new parts. 
good luck, Bruce Roe

[The Tassie Devil(le)]

Thinking outside the box, why don't you simply remove the hood, and place it on top of the back of the car, with the roof down that is, and place a lot of blankets on top of the interior and trunk so that there cannot be any damage done by the hood resting on the blankets.   It will take two people to position it, but it will be out of the way.

Bruce.

[savemy67]

Hello William,

If I recall correctly, some of the early to mid '70s GMC motorhomes used the TH425, so if you are looking for a donor transmission, and a Cadillac or Toronado is not available, you might try looking for a motorhome graveyard.

Christopher Winter

[bcroe]

If I recall correctly, some of the early to mid '70s GMC motorhomes used the TH425, so if you are looking for a donor transmission, and a Cadillac or Toronado is not available, you might try looking for a motorhome graveyard.      Christopher Winter   

The GMC 73-78 used the Toronado drive train.  There is a lot of support for them, including
rebuilt transmissions.  I think complete TH425s are not especially hard to find.  Bruce Roe