Home » Public Forums » GMCnet » Transmission won't shift from first to second
| Re: [GMCnet] Transmission won't shift from first to second [message #355725 is a reply to message #355723] |
Mon, 15 June 2020 18:30   |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Reason I mentioned the speedometer cable, is, if it seizes up, one of two
things is going to happen. The nylon gear on the end of the cable strips
out, OR, the pin that locks the governor gear to the shaft shears off, or
that gear strips out, or some combination of all 3 happens. If you have
headers, pulling the governor requires removing the header on that side.
With iron manifolds, the governor will clear. Just saying.
Jim Hupy
Salem, Oregon
On Mon, Jun 15, 2020, 4:17 PM Johnny Bridges via Gmclist <
gmclist@list.gmcnet.org> wrote:
> 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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| Re: Transmission won't shift from first to second [message #355727 is a reply to message #355641] |
Mon, 15 June 2020 19:45 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I’ve fixed 2 coaches with vacuum to modulator issues. Mine a 77 where there was excess hose length forming an S by the modulator and pinching. Simple cut and reinstall hose in restaurant parking lot. The second one was a 75 that had your shifting issues. The problem was not in either main line vacuum hose but a hidden 1” piece under the air cleaner that had chafed and rubbed through. Still part of same vacuum circuit and was open to atmosphere
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Transmission won't shift from first to second [message #355771 is a reply to message #355641] |
Tue, 16 June 2020 12:33 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Actually fluid is new... Amsoil AFT. I changed the filter and the fluid this spring. First change fluid/filter change in 11 years and about 30K miles. Old fluid looked good.
Amsoil AFT is what the rebuilder put in after it started doing this the first time out the next spring (2010) after getting the rebuilt transmission and engine installed in 2009. After that it was Ok for a few years, then started doing it again. Usually the first time out it would do this, then clear itself for the rest of the season. I had it out a couple of times this spring (short test run, then to town for gas) and had no issues.
If this wasn't a random occurrence, I would have thought that I likely messed something up changing the fluid and filter.
There wasn't much debris in the pan, just a little bit of fine black stuff which I suspect is a bit of worn clutch material.
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: Transmission won't shift from first to second [message #355783 is a reply to message #355776] |
Wed, 17 June 2020 05:35 |
6cuda6
Messages: 975
Registered: June 2019
Karma: -6
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Senior Member |
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Bruce few questions:
- Did you back up out of the garage then go or into drive only?
- When you turned around did you reverse then go or just drive only?
- Did you give the trans time warm up before you left?
- Did you put the trans in neutral before you left for a few minutes to allow the pump to circulate fluid threw the trans or did you just drop and go?
Trying to see if their is a pattern to the problem [so cold or hot, fluid threw trans or not etc ]
RF_Burns wrote on Tue, 16 June 2020 18:28So I T'd a hose off at the modulator and ran it up to a vacuum gauge so I could compare it to my TachVac. Pulled out on the road and it would not shift with about 12" of vacuum at the modulator. I used the throttle to vary the vacuum from about 8" to 18" and still no shift. No difference in readings between the two vacuum gauges.
Turned around about 1/2 mile down the road and it shifted fine coming home.
Rich Mondor,
Brockville, ON
77 Hughes 2600
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| Re: Transmission won't shift from first to second [message #355784 is a reply to message #355776] |
Wed, 17 June 2020 05:59 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I think that says it is not a vacuum problem. Looks like governor is next.
Another thought. About 8 or 10 years ago Manny was having problems with some of the kick down solenoids causing shift problems due to leakage. He sent me a replacement and told me to install it even though I was not having problems. You might ask Manny about that. I just did what I was told and installed it.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Transmission won't shift from first to second [message #355787 is a reply to message #355641] |
Wed, 17 June 2020 07:49 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Rich,
The coach was sitting by the house, so I pulled it over into the shop to get under and add the T'd off vacuum line. Its not a straight run into the shop so I had to go forward and back several times to line up. run time about 5 minutes.
About an hour later I backed it out of the shop for the road test. Again back and forth several times to maneuver out so it was running for several minutes before I got on the road. Also in drive and reverse several times to maneuver out of the shop driveway area.
So it was not hot, but was not stone cold either.
When I got on the road and up to about 20mph I knew it was not going to shift, so I varied the throttle position to vary the vacuum as I noted above, but no shift. Then I manually pulled into second and it shifted fine, then back to drive and it shifted up to 3rd gear. Got up to about 40mph.
I knew then I had vacuum at the modulator so I decided to turn around. There is a turn around where 2 sideroads meet the main road. Left turn onto sideroad about 200ft the left onto another sideroad for about 300ft then stop at the main road again.
Coming back on the main road from a dead stop, it shifted to second and 3rd on its own just fine. it would have been much warmer then.
Going to the bush on Saturday, just started up and were on the road within one minute and it did not shift right out of the driveway. However 2 miles down the road in a small town we have to stop twice and it shifted both times, plus at a stop sign in a village another 5 miles further it was fine. After that for another 20+ miles and a dozen stop signs/lights I believe it may have shifted once automatically.
However coming home from the bush on Monday morning, that was started from stone cold. Put into Drive, no other gears and it shifted fine.
-drove out of bush, up laneway about 1/8 mile (not sure if I went fast enough to shift)
-Pulled onto road (not from dead stop, but close to it) shifted fine.
-drove about 1/2 mile @40mph then stop sign and pulled onto main road, shifted fine.
-Drove 2.5 miles @50mph and stop sign and turned onto another main road, shifted fine.
-Drove 1.25 miles @50mph and stop sign, then turned onto main hyway, shifted fine.
-Drove 1.25 miles @35mph (in a village), then stop light and turned on to another main road, shifted fine.
-Drove 5 miles @50-55mph then stop sign, then turned onto another main road... did not shift automatically
The remaining 20 miles home there were 3 round-abouts, one stop sign and one stop light. Each time I needed to shift manually.
So it doesn't seem to matter whether it is hot or cold, but tends to act up more when hot.
History:
I got this rebuilt transmission from Dick Paterson when he rebuilt my engine in 2009. The next spring on the way to the first rally, it did not shift out of the driveway on the road. Turned around and went home. I called Dick the next Monday and he put in contact with the guy who rebuilds transmissions for him. He asked me if I tried manually shifting by pulling into second. I had not thought of this so I tested it and it worked. So I drove the 175 miles to his transmission guy... sometimes it would shift, sometimes not.
Transmission guy said the valve the modulator was working was sticking and he freed it up and installed a new modulator. He also drained and filled it with Amsoil ATF synthetic. He said he highly recommended it in HD service like the motorhome. After that it worked pretty good. Sometimes in the spring it might act up a couple times on the first trip but after that it was good for the rest of the season.
In 2018 we were heading to the Maritimes. When we got into Toronto we found ourselves on a detour through city streets and it started to act up. We pressed on and stopped at Al Hamilton's near Kingston. We talked with the transmission guy that Al had used. He thought it might be the governor which Al had a spare. We put Al's spare governor in and I pulled the modulator and checked the valve spool behind it... it seemed to move freely. Took a test drive and it shifted fine.
So we left the next morning saying if it acted up we would be back. About 20 miles down the road it did not shift again from a stop. We turned around and went back to Al's. Of course it shifted Ok on the way back.
The next morning we cancelled our trip and went back home. Of course it shifted fine all the way home if I recall.
Back home I put a hand vacuum pump on the line at the manifold and had Paula pump the vacuum up while I went under to see if I could find a leak. Well I found it... the newer modulators have a larger port so the larger hose did not fit the metal tube coming down. It did fit over a crimp in the tube which I believe was a stop for the OEM smaller tube. The modulator hose had relaxed over time, and heat would make it worse, but the hose was now slightly loose on the tube crimp.
So I made a new tube from 1/4" brake line, installed a new modulator (for good luck) and I also installed spring type hose clamps on the vacuum hose. At some point I put my original governor back on as well. This seem to fix it... the next year we did our maritime trip and I think it acted up maybe twice.
So now this year.. I changed the transmission fluid and filter. Once again used Amsoil ATF, but my problem is back. BTW I used a Wix filter and measured the tube diameter 0.75" and installed 2 O-rings.
The vacuum lines are fine to the modulator and I measured the vacuum at the modulator and it is good when it wasn't shifting. Used the hand pump to confirm no intermittent vacuum leaks.
So I'm thinking the modulator valve must be sticking again... maybe changing the fluid stirred up some crud in the valves. So I'll check that next.
Not today though... Honey-do list first.
Sorry for long post
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: Transmission won't shift from first to second [message #355791 is a reply to message #355641] |
Wed, 17 June 2020 08:22 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Sounds like you can rule out Amzoil vs Dex/Merc, the modulator and the governor. That puts us at the valve body which could have a burr or chip in it. Had same thing happen on a friends 57 Chevy with Glide, but never on a THM400/425. I’d say time for a THM expert who should be able to say “ I know what’s wrong” Hopefully bench exam of valve body with trans in coach
John Lebetski
Woodstock, IL
77 Eleganza II
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