Sudden Transmission Failure

A

andrew stopoulos

New member
Nov 10, 2016
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Hello fellow GMCers,
This is my first ever post. I bought my 1973 Painted Desert 260 6 months ago. I was excited for the prospect of a work-in-progress, but boy, I am not
sure I was ready for the stress of breaking down. So I am arriving at my brothers house in Portland, Oregon and it's a narrow residential city street.
I menuever the GMC across the width of the street so I can begin carefully backing into his driveway. I then put the selector in Reverse, press the
gas, AND... the engine revs and goes nowhere. what the...? Back to drive... nothing? What about S and L. Still Nothing. It seems like my choices are
Park and Neutral. I am now blocking the whole street from ever being used again. My wife and child and dog are all barking at me and if I can't fix it
I'll have to push this sweet dream machine into the Willamette. With the help of my He-Man brother we actually pushed GMC (we call it The Gator) into
a parallel parking position (the driveway is uphill, so there is no way we can push it into the driveway). And now I am here at 11 pm to make my
petition before the GMC Parliament: How do I begin to tackle this problem? What is wrong? Please help me!

Cheers!
Andrew

A little helpful background on me. I am a city boy, but I am not entirely un-handy. However, I am 28 and I got my drivers license just to buy this
machine, so let's just say I am a fresh face on the scene.
 
G'day,

I've sent the pages out of MM X-7525 showing how to check the trans fluid and adjust the linkage directly to his email address as
the email system does not allow attaching files or pictures.

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Andrew Stopoulos
Sent: Thursday, November 10, 2016 6:04 PM
To: gmclist
Subject: [GMCnet] Sudden Transmission Failure

Hello fellow GMCers,
This is my first ever post. I bought my 1973 Painted Desert 260 6 months ago. I was excited for the prospect of a work-in-progress,
but boy, I am not
sure I was ready for the stress of breaking down. So I am arriving at my brothers house in Portland, Oregon and it's a narrow
residential city street.
I menuever the GMC across the width of the street so I can begin carefully backing into his driveway. I then put the selector in
Reverse, press the
gas, AND... the engine revs and goes nowhere. what the...? Back to drive... nothing? What about S and L. Still Nothing. It seems
like my choices are
Park and Neutral. I am now blocking the whole street from ever being used again. My wife and child and dog are all barking at me and
if I can't fix it
I'll have to push this sweet dream machine into the Willamette. With the help of my He-Man brother we actually pushed GMC (we call
it The Gator) into
a parallel parking position (the driveway is uphill, so there is no way we can push it into the driveway). And now I am here at 11
pm to make my
petition before the GMC Parliament: How do I begin to tackle this problem? What is wrong? Please help me!

Cheers!
Andrew

A little helpful background on me. I am a city boy, but I am not entirely un-handy. However, I am 28 and I got my drivers license
just to buy this
machine, so let's just say I am a fresh face on the scene.

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Well, the first thing to do is to determine if it is really the transmission failing.

The first thing I would do is check the trans fluid level.

The the second thing I would look at are the 6 bolts (per side) that hold the drive shafts to the final drive still there. Those things are heavier
than grade 8 and if they are not torqued to 70 Pounds or so they will fall out leaving you stranded. I have been out on two different Black List call
over the years that when I arrived I found all of the bolts on one side missing. So start it and put it in nay gear and go look underneath to see if
one 1/2 of the axle shaft (on both sides) is turning and the other side is sitting still.

The third thing I would look at is to see if the problem is in the shift linkage. Without the engine running and the wheels blocked so it will not
roll, have someone shift the gear shift through various gears while you watch to see if the shift linkage is indeed moving the shift lever on the
trans.

If all three of the above are good, come back here and we will give you some more ideas.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Here is the trouble shooting manual for the THM 425 transmission

http://www.bdub.net/manuals/THM_425_Trouble_Shooting.pdf

My transmission filter intake pipe had fallen out causing the symptoms you
described.

> Well, the first thing to do is to determine if it is really the
> transmission failing.
>
> The first thing I would do is check the trans fluid level.
>
> The the second thing I would look at are the 6 bolts (per side) that hold
> the drive shafts to the final drive still there. Those things are heavier
> than grade 8 and if they are not torqued to 70 Pounds or so they will fall
> out leaving you stranded. I have been out on two different Black List call
> over the years that when I arrived I found all of the bolts on one side
> missing. So start it and put it in nay gear and go look underneath to see
> if
> one 1/2 of the axle shaft (on both sides) is turning and the other side is
> sitting still.
>
> The third thing I would look at is to see if the problem is in the shift
> linkage. Without the engine running and the wheels blocked so it will not
> roll, have someone shift the gear shift through various gears while you
> watch to see if the shift linkage is indeed moving the shift lever on the
> trans.
>
> If all three of the above are good, come back here and we will give you
> some more ideas.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
 
Keep us posted on what you find out. I'm betting it's something fairly simple. A transmission doesn't go from running to doing completely nothing in
all gears including reverse in just a second. I think the above recommendations are on target.

It could also be broken shift cable.
 
Or the bolts holding shift cable ends or the adjustment bolt on the trans linkage loosened up. That is why I suggested that he have someone move the
gear shift while he watched the linkage move at the trans. I'm thinking he will easily see the linkage move or not move.

He can also easily see if the final drive is turning and the axle is not.

I also agree with you. It probably is not a trans problem unless he ran it out of ATF.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
good suggestions here. Hope it is something simple, as usually the transmission will do a little more then what you are describing as it goes bad.

Keep us posted as to what you find out or what other help can be needed. I am in portland next Monday-sunday, so if you would like, we can meet up
and go over the coach a little bit one evening next week.(class during the day). give you an idea on some thing to watch out for.

--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
It only takes a quart+ of tranny fluid low to cause the symptoms that you suggest. Check it cold to see if you have any fluid on the dip stick. Add fluid a little bit at a time. Over fill is just as bad as under fill.

JR Wright
Michigan

>
> good suggestions here. Hope it is something simple, as usually the transmission will do a little more then what you are describing as it goes bad.
>
>
> Keep us posted as to what you find out or what other help can be needed. I am in portland next Monday-sunday, so if you would like, we can meet up
> and go over the coach a little bit one evening next week.(class during the day). give you an idea on some thing to watch out for.
>
>
> --
> Jon Roche
> 75 palm beach
> St. Cloud, MN
> http://lqqkatjon.blogspot.com/
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Does the shifter feel the same with detents, or different? If different or loose sloppy you may have a broken cable or linkage. Rob sent you the GM
service pages which great info, are over most peoples heads. To check your Dexron fluid level, remove the hatch and idle the engine in park. Use (
pull wipe and replace and read) the trans dipstick and be sure it is at the full hot level. It should be clear bright red in color. You may have a
slight leak and now are below working level. Hope that's it.
--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First
 
Check that shift cable. Ours has broken twice--once every 10 years. If
that's broken, order one from Jim Kanomata. We did last year when we were
in Portland and we received it in less than 20 hours.

Hope that's all it is.

Bob Price

> Does the shifter feel the same with detents, or different? If different
> or loose sloppy you may have a broken cable or linkage. Rob sent you the GM
> service pages which great info, are over most peoples heads. To check
> your Dexron fluid level, remove the hatch and idle the engine in park. Use (
> pull wipe and replace and read) the trans dipstick and be sure it is at
> the full hot level. It should be clear bright red in color. You may have a
> slight leak and now are below working level. Hope that's it.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I think if you had a broken shift cable, that you would be unable to get the transmission physically into park...that is short of crawling under the
coach and by hand moving the shift arm to the park position. If you can move the lever through the gears, back to park and the transmission holds the
coach in position, i think it is obvious that the cable is intact. If the cable is OK, I would go with low fluid first. As others have said, 1 qt
low will give the symptoms you describe. With the engine running and trans in park, check it cold. Then add to about 1/2 pint low. (between add and
full). Drive it until it is warm, then add more as needed. If trans operates as expected, you need to go out and find the reason for it being low.
If none of the above works, my guess is that you have an internal transmission problem. I'm not versed enough to advise on how to diagnose that.
Others may pipe in here. Good luck, been there....
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Hello Rob [USAussie]

Would you kindly send me the same to david.del.rio >at< live.com

Your private message option is turned off, so that's why I posted here.

Thanks much,
Dave

> G'day,
>
> I've sent the pages out of MM X-7525 showing how to check the trans fluid and adjust the linkage directly to his email address as
> the email system does not allow attaching files or pictures.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> USAussie - Downunder
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
> USA '77 Kingsley - TZE 267V100808

--
David del Rio - 75 Avion - Raymond, CA
 
David,

Done.

The private messages function on the forum is turned off because I use the email system. I discovered that people were sending me
pm's asking questions and I never saw them.

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of David Horowitz
Sent: Friday, November 11, 2016 7:13 AM
To: gmclist
Subject: Re: [GMCnet] Sudden Transmission Failure

Hello Rob [USAussie]

Would you kindly send me the same to david.del.rio >at< live.com

Your private message option is turned off, so that's why I posted here.

Thanks much,
Dave
 
If you still have park and neutral, then your able should be good.
Check your trans fluid level. What we do in time of crises, we dump in a
quart of fluid and see if it does anything. should it not then there is
something internally wrong.

On Thu, Nov 10, 2016 at 12:13 PM, David Horowitz
wrote:

> Hello Rob [USAussie]
>
> Would you kindly send me the same to david.del.rio >at< live.com
>
> Your private message option is turned off, so that's why I posted here.
>
> Thanks much,
> Dave
>

> > G'day,
> >
> > I've sent the pages out of MM X-7525 showing how to check the trans
> fluid and adjust the linkage directly to his email address as
> > the email system does not allow attaching files or pictures.
> >
> > Regards,
> > Rob M.
> > The Pedantic Mechanic
> > USAussie - Downunder
> > AUS '75 Avion - The Blue Streak TZE365V100428
> > USA '75 Avion - Double Trouble TZE365V100426
> > USA '77 Kingsley - TZE 267V100808
>
>
> --
> David del Rio - 75 Avion - Raymond, CA
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Thanks everybody!

We spent the morning trying to tow the Gator into the driveway with my brothers minivan and a couple of (dinky, light duty) ratchet straps. But it
worked! So at least I am not blocking the road. Phew!

Here is what I have found:

1)Transmission fluid appears to be fine. I had checked it a month ago, and while I cannot check it properly now (because I can't drive the beast to
warm up the ATF) a basic cold check reveals that there is quite a bit of nice clear pink/red fluid.

2)The cable, and the selector, still seem to be attached correctly. The cable is clearly not broken and it moves a lever on the drivers side of the
transmission oil pan with a satisfying click sound. The detents/indexing seems to be identical to before I had the problem, except I can't get the
selector to settle/lock in the Reverse position. Normally you have to pull the selector toward you before moving it left or right. Not the case with
Reverse. But it may have always been like that and perhaps I am only noticing it now.

3) I know the transmission is in neutral because we pushed and towed it into my brothers driveway. What I don't know is if it is shifting into park.
It may be still in neutral as I sit here typing because, while I am not rolling away, my wheels are chocked and the parking brake is on. I don't wanna
test it because then I gotta pull the beast back up the driveway. The only thing I know for sure is R,D,S,&L are no-go.

4) I tried to have a look at the drive axles coming out of either side of the final drive but all efforts were inconclusive. I still need to jack her
up so I can really get under there, now that I am in the driveway. The idea of putting it in gear and seeing if they spin resulted no spinning on
either side. I could see at least some of the bolts that were mentioned. They look more like stars then your typical grade 8 hex cap. Assuming I am
looking at the right thing.

5) Normally when I shift into drive or reverse I get a host of differing engine noises. Idle speed changes a bit, I get some funny growling noises
sometimes, these noises always even out once we get underway. Right now I am getting non of that. Just the nice clean sound big 455 in neutral. That
seems to tell me the torque from the motor is not even getting far enough down the drivetrain to affect the axle.

I am going peruse that THM troubleshooting manual (thanks for posting that) and jack this thing up once I get my son to take a nap, but any additional
input is always welcome. You all have already helped my drop my gas tanks and reconnect my vapor canisters and fix my alternator squeal and you don't
even know it. And now this! I couldn't be more grateful.

Cheers!
Andrew

P.S. It's nice to know there is a list of GMCers ready to help. Now that I am not stuck in the road I will try not make sure its not something obvious
and simple before I ask someone to come out of there way to my aid. Never a dull moment with this machine!
 
I wonder if part of the linkage that's inside the pan could have lost
a connection or something? Maybe a call to Manny Travao 408-937-1583
would be helpful. He's a TH 425 transmission expert.

> Thanks everybody!
>
> We spent the morning trying to tow the Gator into the driveway with my brothers minivan and a couple of (dinky, light duty) ratchet straps. But it
> worked! So at least I am not blocking the road. Phew!
>
> Here is what I have found:
>
> 1)Transmission fluid appears to be fine. I had checked it a month ago, and while I cannot check it properly now (because I can't drive the beast to
> warm up the ATF) a basic cold check reveals that there is quite a bit of nice clear pink/red fluid.
>
> 2)The cable, and the selector, still seem to be attached correctly. The cable is clearly not broken and it moves a lever on the drivers side of the
> transmission oil pan with a satisfying click sound. The detents/indexing seems to be identical to before I had the problem, except I can't get the
> selector to settle/lock in the Reverse position. Normally you have to pull the selector toward you before moving it left or right. Not the case with
> Reverse. But it may have always been like that and perhaps I am only noticing it now.
>
> 3) I know the transmission is in neutral because we pushed and towed it into my brothers driveway. What I don't know is if it is shifting into park.
> It may be still in neutral as I sit here typing because, while I am not rolling away, my wheels are chocked and the parking brake is on. I don't wanna
> test it because then I gotta pull the beast back up the driveway. The only thing I know for sure is R,D,S,&L are no-go.
>
> 4) I tried to have a look at the drive axles coming out of either side of the final drive but all efforts were inconclusive. I still need to jack her
> up so I can really get under there, now that I am in the driveway. The idea of putting it in gear and seeing if they spin resulted no spinning on
> either side. I could see at least some of the bolts that were mentioned. They look more like stars then your typical grade 8 hex cap. Assuming I am
> looking at the right thing.
>
> 5) Normally when I shift into drive or reverse I get a host of differing engine noises. Idle speed changes a bit, I get some funny growling noises
> sometimes, these noises always even out once we get underway. Right now I am getting non of that. Just the nice clean sound big 455 in neutral. That
> seems to tell me the torque from the motor is not even getting far enough down the drivetrain to affect the axle.
>
> I am going peruse that THM troubleshooting manual (thanks for posting that) and jack this thing up once I get my son to take a nap, but any additional
> input is always welcome. You all have already helped my drop my gas tanks and reconnect my vapor canisters and fix my alternator squeal and you don't
> even know it. And now this! I couldn't be more grateful.
>
> Cheers!
> Andrew
>
> P.S. It's nice to know there is a list of GMCers ready to help. Now that I am not stuck in the road I will try not make sure its not something obvious
> and simple before I ask someone to come out of there way to my aid. Never a dull moment with this machine!
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
Ray Erspamer
78 Royale - "The Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMCRoyale
414-484-9431
Web Site: http://ray-lisa.page.tl/
 
> ...The private messages function on the forum is turned off because I use the email system. I discovered that people were sending me pm's asking
> questions and I never saw them. ...
Log in to the forum. Click on "Control Panel". Click on "Account Settings". Scroll down to the "Preferences" section. Click the "Yes" radio button to
the right of "Private Message Notification:" You will then be notified by email whenever a private message is sent to you.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
Those are the correct bolts. They are 12 point rather than the 6 point that you are use to seeing. Although you should have 6 per side. For now,
just check to see if you have any number per side. When it fails to move because of missing bolts, ALL of the bolts will be missing on one side.

If the bolts are there then you need to start looking at the fluid level and the possibility that the shift mechanism is not working inside the trans.
I'm not good with the internals of the trans and Manny is our go to person on that. I also believe Jim Hupy is in your neighborhood. (I could be
wrong on this) Look on the Black List and get his phone number.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
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