Transmission won't shift from first to second

RF_Burns

RF_Burns

Super Moderator
Staff member
Sep 7, 2008
5,148
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Ontario Canada
So I've had this issue randomly for over 10 years now. I've had the Murray out for a couple of short runs this year and the transmission shifter fine
every time. Today we left to go for the first weekend trip and right out of the driveway it would not shift on its own from first to second.

I can always shift it manually by putting it into second and then back to Drive it will goto third.

The modulator and governor have been changed along with the tubing and hoses to the modulator. I changed the tranny fluid and filter this spring. I
checked the filter diameter and put 2 o-rings on it.

It may not do this now for the rest of the season or it might do it for the next thousand miles.

Driving me crazy!

Its been doing this on and off since the spring after I bought it rebuilt when I got the engine rebuilt.

Amsoil HD synthetic.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
I had the same problem. Check the modulator vacuum line for leaks.
--
Patti & Jerry Burt Fresno, CA.
73 Gmc 26' Canyon Lands
77 Palm Beach - Parts Coach - SOLD
Members: FMCA - GMCMI - GMCWS
A truly happy person is one who can enjoy the scenery on a detour.
 
The modulator steel line is partially plugged up where it narrows down at
the top. What I have successfully done to unplug those crimped lines is to
heat them quite hot, whack them against the work bench to dislodge whatever
is plugging them, and blowing them out with compressed air. Repeat as many
times as necessary until the blockage is cleared. That should fix your on
again/off again problem. Make sure to inspect the lower vacuum line as well.
Jim Hupy
Salem, Oregon

On Sat, Jun 13, 2020 at 1:01 PM Bruce Hislop via Gmclist <

> Forgot to add, speedometer works fine, governor gear is fine.
>
> Fluid level is fine.
>
> Plunger valve that the modulator works against moves freely.
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Mine ended up being an old, hardened lower vacuum line.

> The modulator steel line is partially plugged up where it narrows down at
> the top. What I have successfully done to unplug those crimped lines is to
> heat them quite hot, whack them against the work bench to dislodge whatever
> is plugging them, and blowing them out with compressed air. Repeat as many
> times as necessary until the blockage is cleared. That should fix your on
> again/off again problem. Make sure to inspect the lower vacuum line as well.
> Jim Hupy
> Salem, Oregon
>
> On Sat, Jun 13, 2020 at 1:01 PM Bruce Hislop via Gmclist <

>
> > Forgot to add, speedometer works fine, governor gear is fine.
> >
> > Fluid level is fine.
> >
> > Plunger valve that the modulator works against moves freely.
> >
> > --
> > Bruce Hislop
> > ON Canada
> > 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> > http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> > My Staff says I never listen to them, or something like that
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
Patti & Jerry Burt Fresno, CA.
73 Gmc 26' Canyon Lands
77 Palm Beach - Parts Coach - SOLD
Members: FMCA - GMCMI - GMCWS
A truly happy person is one who can enjoy the scenery on a detour.
 
Sorry guys, more info on repairs I've done.

2 years ago after we aborted a Maritimes holiday because of this issue. When we returned I replaced the upper and lower rubber hoses and the steel
tube. I replaced the steel tube with a 3/16" tube so it would match with the new modulator vacuum tube size. I also added spring type hose clamps to
both ends of the rubber hoses to ensure they are sealed. After that it only gave me issues a couple of times until now.

I'm trying to understand the voodoo that goes on in the transmission that makes it shift gears.

Several times I varied the throttle to change the vacuum level. I thought this might cause the transmission to change gears but no go.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Make sure transmission vacuum line goes to manifold vacuum source. Might try teeing in a gauge to watch that signal when problem occurs. Possible
sticking valve or small piece of trash making one stick once in awhile and it can't escape the valve chamber.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
Well, You might r get a cheap vacuum gauge and Tee it in to the modulator to see what happens when it fails.

My other thought is the kick down switch might be sticking. Unplug it at the trans and see if you get any failures. You can always get by without the
kick down (passing Gear) switch. You can always pull the trans down a gear if needed with the gear shift.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Kick-down has been disconnected for years.

I'll T into the vacuum line at the modulator and see what I can read there.

Is it supposed to shift at a set vacuum level or how does that work?
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Have you given any thought to your speedometer cable or governor? Try
lubing that lower cable and see if that helps.
Jim Hupy
Salem, Oregon

On Sun, Jun 14, 2020, 7:21 AM Bruce Hislop via Gmclist <

> Kick-down has been disconnected for years.
>
> I'll T into the vacuum line at the modulator and see what I can read
> there.
>
> Is it supposed to shift at a set vacuum level or how does that work?
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
The lower the vacuum the later the shift. Double check your vacuum hose type. Some is soft and sucks flat especially if curved. Sorry I don’t
have the SAE numbers but I do know that the GM engineering cut sheet for each type vacuum hose is about 4 pages. I know this because my friend is
reproducing GM vacuum hose to be licensed. I also know that soft vacuum hose caused the same issue on my 77 E2
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
I do not know the shift points. I thought they were variable based on engine or governor speed and vacuum level. What I am hoping is that you will
see what is normal and then see any anomaly / difference when it is failing.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
The 1-2 shift point is about 14mph with throttle part way open. Quite a bit
faster than that when fully on the floor. Maybe, 25 -30. 2-3 shift normally
occurs around 30 mph. But as high as 50 at wide open throttle. I am talking
about stock transmissions, and stock final drive gearing.
Jim Hupy
Salem, Oregon

On Sun, Jun 14, 2020, 12:09 PM Ken Burton via Gmclist <

> I do not know the shift points. I thought they were variable based on
> engine or governor speed and vacuum level. What I am hoping is that you
> will
> see what is normal and then see any anomaly / difference when it is
> failing.
> --
> 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
>
 
Jim Hupy, so the shift is dependent on modulator for engine load (light throttle is high vacuum and WOT is low vacuum). And the govenor for road
speed.... That is what I understand. So it could be a govenor issue even though I have changed it and still had issues afterwards.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
I suggested the speedometer cable lube because that happened to me. My
cable was routed too close to the headers, and the heat carbonized the lube
and rubber covering on the outer cable. My fault. I had changed final drive
gearing, and installed the speedometer reduction gearbox up instead of down
and away from the header heat. When I do one of those today, I insulate the
cable with that bright orange nomex aircraft slip tubing. Good stuff,
spendy, but effective. Never had shifting problems since I did that.
Jim Hupy
Salem, Oregon

On Sun, Jun 14, 2020, 5:32 PM Bruce Hislop via Gmclist <

> Jim Hupy, so the shift is dependent on modulator for engine load (light
> throttle is high vacuum and WOT is low vacuum). And the govenor for road
> speed.... That is what I understand. So it could be a govenor issue even
> though I have changed it and still had issues afterwards.
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I made an aluminum heat shield to fit 1/2" or so off of the speedometer
cable so that the air flow protected it. Now that I've eliminated that
cable with a digital speedometer, the heat shield protects the Vehicle
Speed Sensor (VSS).

Ken H.

On Sun, Jun 14, 2020 at 8:43 PM James Hupy via Gmclist <

> I suggested the speedometer cable lube because that happened to me. My
> cable was routed too close to the headers, and the heat carbonized the lube
> and rubber covering on the outer cable. My fault. I had changed final drive
> gearing, and installed the speedometer reduction gearbox up instead of down
> and away from the header heat. When I do one of those today, I insulate the
> cable with that bright orange nomex aircraft slip tubing. Good stuff,
> spendy, but effective. Never had shifting problems since I did that.
> Jim Hupy
> Salem, Oregon
>
> On Sun, Jun 14, 2020, 5:32 PM Bruce Hislop via Gmclist <

>
> > Jim Hupy, so the shift is dependent on modulator for engine load (light
> > throttle is high vacuum and WOT is low vacuum). And the govenor for road
> > speed.... That is what I understand. So it could be a govenor issue even
> > though I have changed it and still had issues afterwards.
> > --
> > Bruce Hislop
> > ON Canada
> > 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> > http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> > My Staff says I never listen to them, or something like that
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
A few years back Dan Gregg had a similar problem. I kept telling him it was modulator associated. He would not listen to me. He replaced the
governor a second time with one rebuilt by Wally and fixed the problem.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
We just got back from our weekend getaway to the bush. I can type a message now on a real computer and not a silly little smart phone.

On the way here it did not shift right out of the driveway from a cold startup. And today it shifted fine through 5 stop signs in about 10 miles. On
the 6th stop it would not shift and had to manually shift to the balance of the trip (about 20 more miles and 6 more stop signs). So not sure that it
is heat related.

Before we left I checked the hose at the modulator (was new in 2018 with the modulator) and the hose to the manifold also new in 2018. Both seemed to
be sufficiently thick to resist collapse by the vacuum.

I'll T in a hose from the modulator and connect it to a vacuum gauge and see if I can find anything. If I had a spare MAP sensor, then I could log
the vacuum readings on the EBL.

KenB, I'm wondering about the governor. The speedo reads fine, no jumping so the governor must be spinning. I got this one from Al Hamilton who took
it off a spare tranny he had. It did the same thing after changing it so we assumed it was not a governor problem, but it could have been sticky as
well.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
> We just got back from our weekend getaway to the bush. I can type a message now on a real computer and not a silly little smart phone.
>
> On the way here it did not shift right out of the driveway from a cold startup. And today it shifted fine through 5 stop signs in about 10 miles.
> On the 6th stop it would not shift and had to manually shift to the balance of the trip (about 20 more miles and 6 more stop signs). So not sure
> that it is heat related.
>
> Before we left I checked the hose at the modulator (was new in 2018 with the modulator) and the hose to the manifold also new in 2018. Both seemed
> to be sufficiently thick to resist collapse by the vacuum.
>
> I'll T in a hose from the modulator and connect it to a vacuum gauge and see if I can find anything. If I had a spare MAP sensor, then I could
> log the vacuum readings on the EBL.
>
> KenB, I'm wondering about the governor. The speedo reads fine, no jumping so the governor must be spinning. I got this one from Al Hamilton who
> took it off a spare tranny he had. It did the same thing after changing it so we assumed it was not a governor problem, but it could have been
> sticky as well.

Bruce, I had this same discussion with Dan a few years ago. In the end I was wrong with my diagnosis. I was not there, so I did not see the fix.
Dan just told me that replacing the governor a second time took care of the problem. Unfortunately Dan died a few years back so we can not ask for
more details. Wally, if he is around, might know more.

Ken
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Does not the governor push the valve down as the weights spin outward? What this will do if the valve is sticking a bit is slow the shift a bit. Or
in the one we first put in my current coach stick such that nit never shifts. I'd replace it with a rebuild at this point. Smooth speedo operation
says it's rotating correctly, but says nothing about that valve.

--johnny

--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
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