Home » Public Forums » GMCnet » Transmission won't shift from first to second
| Transmission won't shift from first to second [message #355641] |
Sat, 13 June 2020 14:43  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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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
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| Re: [GMCnet] Transmission won't shift from first to second [message #355644 is a reply to message #355643] |
Sat, 13 June 2020 15:51  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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
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| Re: [GMCnet] Transmission won't shift from first to second [message #355645 is a reply to message #355644] |
Sat, 13 June 2020 17:56 |
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pjburt
Messages: 436
Registered: February 2016
Location: Fresno, California
Karma: 1
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Senior Member |
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Mine ended up being an old, hardened lower vacuum line.
James Hupy wrote on Sat, 13 June 2020 13:51The 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 <
gmclist@list.gmcnet.org> wrote:
> 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
>
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Jerry Burt Fresno, CA.
73 Gmc 26' Canyon Lands
Members: FMCA - GMCMI - GMCWS
A truly happy person is one who can enjoy the scenery on a detour.
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| Re: Transmission won't shift from first to second [message #355661 is a reply to message #355655] |
Sat, 13 June 2020 23:48 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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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.
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| Re: Transmission won't shift from first to second [message #355662 is a reply to message #355655] |
Sun, 14 June 2020 04:46 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Well, You might get a cheap vacuum gauge and tee it in to the modulator to see what happens with the vacuum level 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
[Updated on: Sun, 14 June 2020 04:48] Report message to a moderator |
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| Re: Transmission won't shift from first to second [message #355674 is a reply to message #355641] |
Sun, 14 June 2020 10:14 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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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
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| Re: Transmission won't shift from first to second [message #355676 is a reply to message #355670] |
Sun, 14 June 2020 14:08 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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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
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| Re: [GMCnet] Transmission won't shift from first to second [message #355688 is a reply to message #355687] |
Sun, 14 June 2020 19:49 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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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 <
gmclist@list.gmcnet.org> wrote:
> 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
>
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| Re: [GMCnet] Transmission won't shift from first to second [message #355689 is a reply to message #355688] |
Sun, 14 June 2020 20:02 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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 gmclist@list.gmcnet.org> wrote:
>
>> 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
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Transmission won't shift from first to second [message #355703 is a reply to message #355687] |
Mon, 15 June 2020 08:17 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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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
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| Re: Transmission won't shift from first to second [message #355715 is a reply to message #355710] |
Mon, 15 June 2020 11:17 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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RF_Burns wrote on Mon, 15 June 2020 10:14We 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
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| Re: Transmission won't shift from first to second [message #355723 is a reply to message #355641] |
Mon, 15 June 2020 18:17 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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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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