Transmission won't shift from first, can shift it manually

RF_Burns

RF_Burns

Super Moderator
Staff member
Sep 7, 2008
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Ontario Canada
So we have started out on a 2 week vacation and the transmission will sometimes not shift from first gear. However I can shift it manually by pulling
from Drive to second. Shifting back to Drive it will shift to 3rd.

Checked modulator and tubing and that's Ok. Checked the valve the modulator works against and it moves freely. Although I thought I might have felt a
slight interference.

Installed a spare governor, but the existing one seems fine.

Seems to be fine when cold, but acts up when it gets up to operating temperature.

Hopefully it will work fine tomorrow, otherwise we will need to decide wether or not to continue.

Will I do any damage to the transmission shifting manually?

Thanks
--
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
 
This sounds like vacuum loss to the modulator to me. Several things could cause it like a cracked / leaking vacuum hose or the steel line that run
along top right side of the intake manifold being plugged or partially plugged.

My non-conventional way to diagnose this would be to install a TEE in the vacuum line at the modulator and run a hose from there up and into the
passenger side cockpit window. Then install a vacuum gauge and you can see if you are missing vacuum when the failure occurs.

If you already have a vacuum gauge then move it to the newly installed TEE. If it is not a vacuum to the modulator problem then we need to start
looking at the governor or modulator itself
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Hi Ken,

I checked the modulator by first pulling the hose from the modulator and looked for transmission fluid, it was clean.

Then I put my manual vacuum pump at the manifold connection and wasn't able to hold a vacuum so the tubing is clear. Then I plugged the hose back on
the modulator and pulled a vacuum again. So this showed the tube was clear and the modulator holds vacuum.
--
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
 
Hi Bruce, was the governor that you took out scored at all or was it smooth? I have seen the case bores get scored and cause this problem. The bore in the case should not have any grooving and be very smooth. I don't believe it will hurt to shift it manually.

________________________________
From: Gmclist on behalf of Bruce Hislop
Sent: Monday, July 16, 2018 10:34 PM
To: gmclist
Subject: Re: [GMCnet] Transmission won't shift from first, can shift it manually

Hi Ken,

I checked the modulator by first pulling the hose from the modulator and looked for transmission fluid, it was clean.

Then I put my manual vacuum pump at the manifold connection and wasn't able to hold a vacuum so the tubing is clear. Then I plugged the hose back on
the modulator and pulled a vacuum again. So this showed the tube was clear and the modulator holds vacuum.
--
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
[http://www.gmcmhphotos.com/photos/data/20/IMGP2540-small.jpg]http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001

Murray's looking spiffyhttp://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
www.gmcmhphotos.com
New wheel flares, Ramco mirrors and square headlights!

My Staff says I never listen to them, or something like that

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Bruce, the steel line, if it is still factory, has a crimped section at the
top, behind the engine block, and it sometimes becomes partially plugged
and restricted. Sometimes it is a problem for the modulator. I would check
that first.
Jim Hupy
Salem, Or

> Hi Ken,
>
> I checked the modulator by first pulling the hose from the modulator and
> looked for transmission fluid, it was clean.
>
> Then I put my manual vacuum pump at the manifold connection and wasn't
> able to hold a vacuum so the tubing is clear. Then I plugged the hose back
> on
> the modulator and pulled a vacuum again. So this showed the tube was clear
> and the modulator holds vacuum.
> --
> 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
>
 
Bruce, It sounds like you are one step ahead of me in your diagnosis.

I would still like to know exactly how much vacuum is being applied to the modulator when it fails.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Brian, the bore on the existing governor is very smooth and so was the spare I installed. Valve spool Inside both seems to move freely.

Jim, I tested the metal tubing by pulling a vacuum on it from the top with the modulator disconnected. It pulled air freely through the tube, so I
assume the tubing and the restriction is clear. I then plugged the modulator and pulled vacuum again using the hand pump. I held vacuum, so I assumed
the tubing and modulator is good.

Ken, my Tach-Vac is Tee'd into the same hose as goes to the modulator, except at the top. It reads a range of vacuum while accelerating of about
5-12". I can't say exactly as I am usually I traffic which requires my attention. I'm not sure if I have fittings and hoses to move the tach vacuum
connection down to the modulator.

Maybe the additional hose going to be Tach-Vac is upsetting the modulator operation? Y could plug that, but it's been connected like the for years.

We are about 350 miles from home, but it's freeway the whole way. Except for one gas stop, there is only two stop signs and one traffic light between
here and home.
--
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
 
So, we continued on this morning. stopped several times to test it and it shifted each time. Then we had to stop for a light and it did not shift.
Tried a couple more times and it did not shift on its own.

We decided to cut our loses and come home. Because of a traffic jam in Toronto we ended up on city streets and lots of top lights at rush hour. It
worked perfectly every time. 5 hour trip home and no issues.

Not sure what to do now, hard to troubleshoot and fix something that works. Until I know the cause and repair it, I have no confidence to go anywhere
in it.

--
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
 
That is a real problem. Without it failing, it is very difficult to guess what the culprit is. I, like Jim Hupy, am still thinking a restriction at
the crimp in the steel line is a good possibility. When mine became restricted years ago it failed similar to yours. I ended up removing the line
and tried to blow it out. That did not work. So I attached shop air pressure to the bottom end of the steel line (out of the coach) and started
heating the other end with an acetylene torch. When the end got red from heat it all of a sudden opened up from the air pressure applied to the
opposite end. I painted the line gray and reinstalled it again with the factory installed crimp intact.

Before I did all of this I did have some air or vacuum flow but it was not enough to keep the modulator happy. After I cleaned it the modulator
never failed to shift properly again. I am just guessing here.

Because this is intermittent, you might go get 6 feet or so of vacuum line. Run it direct from the carb port all the way to the modulator. This
would eliminate the steel line and all of the existing vacuum hose. Now go run the coach normally on your next trip(s). If it doesn't fail again,
I'm right. If it does fail again I guessed wrong and you are out the cost of 6 feet of hose.

Ken B.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Easy stuff and cheap stuff first. Replace vac hose top and bottom with the heavier wall type. Oil had softened the lower line enough it looked good
but was bad and sucking flat. Also if you have pulled modulator you will be at "stick scribe off level" but below "running in park level" so you will
need to top off ir it will be low, but you knew that.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
I learned in my younger time that it is worth pending few dollars on a new
hose and toppig of fluids.
John is very correct. When we have a coach in for handling issues, our guys
know we start with air pressure. Took over a year to convince them that we
need to start from the very basic.

On Wed, Jul 18, 2018 at 5:39 AM, John R. Lebetski
wrote:

> Easy stuff and cheap stuff first. Replace vac hose top and bottom with
> the heavier wall type. Oil had softened the lower line enough it looked good
> but was bad and sucking flat. Also if you have pulled modulator you will
> be at "stick scribe off level" but below "running in park level" so you will
> need to top off ir it will be low, but you knew that.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Ken,
I checked my steel line with a hand vacuum pump at the top, and the modulator disconnected. By the movement of the pump gauge I could tell there was
a slight restriction but not much. Just pumping the pump itself( nothing connected), the gauge need barely moves with each pump. Connected to the tube
the gauge will jump to 7" or so with each pump, then immediately drop to zero.

JohnL,
I've always found it near impossible to read a transmission fluid dipstick on any vehicle I've owned. The dipstick comes out with fluid from the side
of the tube. There is no contrast between the fluid and the stick. I've drilled a couple of tiny holes at the ADD and FULL marks and that helps.

We had stopped at Al Hamilton's place, so I pulled the modulator and made sure the valve it works against was free. The coach was parked on a
downhill slope and I pumped up the passenger side airbag so the modulator was on the high side of the pan. After running the engine for about a minute
to pump up the convertor, I still had fluid come out when I removed the modulator, that would indicate the level was too high. I had measured the
fluid level multiple times and thought it was just below the FULL mark. So I lost about 1 cup of fluid during my testing and though, well maybe I
have too much, so I didn't add anymore.

Then while testing it I felt a shutter a couple of times, so we pulled into a level parking lot and pulled the dipstick a dozen times or so. Paula
and I came to the conclusion it was low, so I added back the amount we lost. Then it "appeared" to be just below the full mark. The engine did
stumble a couple times in the next 15 miles of driving. But I did have my computer connected to my EBL system and that showed I was losing electrical
power (either battery or ignition) to the EFI system. We turned around at that point to go home and stopped at Al's again. It ran fine the 20 miles
back to Al's house. I could not find any electrical issue. We continued home with no more electrical or transmission issue.

Can you elaborate on your statement " Also if you have pulled modulator you will be at "stick scribe off level" but below "running in park level". My
understanding was with a hot transmission in Park, engine OFF, pull the modulator and the fluid should be at the level of the modulator. Let any
excess drain, or fill it till it comes out the modulator and mark that as FULL. I had done this when I drilled the holes in the dip stick. The fluid
seemed to be coming from above or around the valve as I moved it. I don't think I'm understanding this measurement. I've kept the fluid at the
levels I've marked on my dipstick since 2010 when I installed a rebuilt transmission a the same time Dick Paterson rebuilt my engine.

Thanks

--
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
 
So, I believe I have found my transmission shifting issue. I had checked the vacuum hose to be sure it had no blockage it was holding vacuum with
the modulator attached.

Today I checked it again, but this time I went under while my wife pumped up the manual vacuum pump on it and watched the gauge. Suddenly it quickly
lost vacuum when I touched the metal tube at the hose connection. I had Paula pump the vacuum up again and sure enough moving the hose connection
cause it to lose vacuum. The hose is a 4" (or less) piece of 1/4" 30R7 fuse hose. The tube is 0.19" OD and the sealing bump on the tube and the
modulator connection is 0.3" The hose looks great on the outside, no cracks anywhere. However the tube's sealing bump is very narrow. I expect it
has relaxed around this bump in the tube and when it gets hot (exhaust is not far away) it softens and leaks.

Anyway, off to get a new hose and some tiny clamps!

--
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
 
Good to hear you found the issue!
--
JD Lisenby- USAF Ret
1978 Royale-455
MacDash, Manny Tranny, FI-tech, 3.70 etc etc

Navarre, FL
 
I used the next smaller ID hose on mine and forced it on. Moved the shift points it did.

--johnny
--
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" - ol Andy, paraphrased
 
On the stick cal it's simpler than people make it. With modulator out the fluid will waterfall out the hole. Doesn''t matter hot (difficult) or cold
all you are looking for is that liquid level even with bottom of hole to scribe stick as full. Then when you reassemble, you run it in park and add
fluid to that new mark. The level will drop running as pump is opperating and require you to add. That is my understanding. Looks like I was on right
track with lower vac hose, same place mine was bad.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Johnny,
I'm thinking the OEM modulator valve had the same size connection as the metal tube coming down to it so a smaller (5/32") hose was likely OEM. But
the new modulator is 0.3" was likely too much for the 5/32" hose so the fleet garage that installed it used 1/4" fuel line. The "sealing bump" on
the metal tube was likely a stop to prevent the proper size hose from sliding up further, but it was also 0.3" diameter so the 1/4" hose fit snugly
over it. But then the hose relaxed over time and the heat allowed it to start leaking.

I've now used a 7/32" vacuum hose with a clamp at each end and it fits nice and snug. I got 16" so enough to make 4 replacements. :)
--
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 forced the smaller hose - new piece - on the modulator and the pipe. It didn't split so I skipped the clamps. Works fine so far.

--johnny
--
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" - ol Andy, paraphrased
 
Good job Bruce. Any time left for the trip?
--
Deb McWade
Logan Lake, BC, CAN
"Li'l Sister"
'77 Kingsley, 403, EBL EFI;
TZE167V101404
It's Bigger on the Inside!
 
Deb,
Gave up on that trip. We will need to make a few local trips before Paula will have confidence to go further again. Might be able to do some day
trips to start, but she is pretty busy with her furniture refinishing.

--
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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