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gsg2013 · 08-04-2022, 07:40 AM

Good morning. My wife and I went to British Columbia, BC Canada in our 2004 Landyacht, towing our car. I have been using my transmission as a brake on the 9, 10, and 12% downhill grades there. At the bottom of the last 12 per center the transmission started shifting rapidly from 4th to 3rd back and forth by itself. We are now in Burlington, Wa headed home and the transmission will not shift into OD. I have tried manually upshifting thru the gears and it still will not go into OD. I checked fluid level, it is ok. Fluid color looks ok. Fluid does not have an off smell to it. I am stumped. We are still 1000+ miles from home and I am a little stressed right now. Searched forums but could not find an answer that matched my issue. Looking to the experts for help please. gsg

civeng99 · 08-04-2022, 08:30 AM

Before I panicked I’d check to see if there is a solenoid issue or a pressure issue. Might prevent that last up shift.

Quote:

Originally Posted by gsg2013

Good morning. My wife and I went to British Columbia, BC Canada in our 2004 Landyacht, towing our car. I have been using my transmission as a brake on the 9, 10, and 12% downhill grades there. At the bottom of the last 12 per center the transmission started shifting rapidly from 4th to 3rd back and forth by itself. We are now in Burlington, Wa headed home and the transmission will not shift into OD. I have tried manually upshifting thru the gears and it still will not go into OD. I checked fluid level, it is ok. Fluid color looks ok. Fluid does not have an off smell to it. I am stumped. We are still 1000+ miles from home and I am a little stressed right now. Searched forums but could not find an answer that matched my issue. Looking to the experts for help please. gsg

gsg2013 · 08-04-2022, 11:39 AM

I crawled around under rv at transmission. Can’t find a solenoid. Electrical connections, yes. They are tight. Would not have a clue where to look for vacuum lines.

**richard5933** · 08-04-2022, 01:00 PM

Might sound like a silly suggestion, but it might be a good idea to confirm that any ground straps or cables to the transmission and/or the transmission controls are solid, clean, and corrosion free.

I've heard of poor grounds causing all sorts of problems with electrically controlled transmissions, and if yours has electrical connections it likely also needs a solid ground connection.

gsg2013 · 08-04-2022, 02:51 PM

I checked all the connections while crawling around under the rv this morning. I also disconnected all 3 batteries, waited 30 minutes, and reconnected them to see if the computer would clear and re-boot. Running out of wild ••• ideas.

TerraYacht · 08-05-2022, 10:47 AM

The symptoms suggest that there is an internal issue. My 2005 has the GM tranny but I know they used Allison's also and I have no Allison experience. If you can find a GMC truck service garage they can probably help with it. There are still Workhorse service garages around too since they built many trucks on the same chassis. Maybe a fluid change and drive with fresh fluid will break things loose.
When we bought our 2005 with the P32 Chassis the PO qwas doind a demo drive, exited the freeway and downshifted to slow the RV down, proudly telling me he was "saving the brakes." Saving them for what? Brakes are made to slow/stop the vehicle and that is NOT the primary task of a transmission. However, on these long down slopes early downshifting, not at high rev's, can provide supplement to the brakes.

Professional assessment can help

davidz71 · 08-05-2022, 06:07 PM

I had a 700R4 transmission that did that. I took it to a dealer and they suggested I not worry about it. I drove the van home and talked with a friend I could not reach before. I had 100,000 miles on that transmission and not changed fluid because it always looked fresh. I had plans to change it then anyway so I pulled the pan and filter to find a dirty filter. I cleaned the underside transmission area, replaced the filter and put in new fluid. Lol and behold the OD came back on line. We drove that van another 100,000 before we sold it. You might have the same luck.

PeterH-350LE · 08-05-2022, 08:00 PM

Quote:

Originally Posted by gsg2013

Good morning. My wife and I went to British Columbia, BC Canada in our 2004 Landyacht, towing our car. I have been using my transmission as a brake on the 9, 10, and 12% downhill grades there. At the bottom of the last 12 per center the transmission started shifting rapidly from 4th to 3rd back and forth by itself. We are now in Burlington, Wa headed home and the transmission will not shift into OD. I have tried manually upshifting thru the gears and it still will not go into OD. I checked fluid level, it is ok. Fluid color looks ok. Fluid does not have an off smell to it. I am stumped. We are still 1000+ miles from home and I am a little stressed right now. Searched forums but could not find an answer that matched my issue. Looking to the experts for help please. gsg

TPS (Throttle position sensor) can cause the transmission to not shift into OD. Its a very easy replacement and the part should readily available. It is typically located at the throttle body, assuming you have TBI

Por Sonia · 08-06-2022, 12:46 AM

FYI there is a sub-forum for Land Yacht motor homes, where you might find a more refined audience for your question IMO:

https://www.airforums.com/forums/f312/

Good luck,

Peter

gsg2013 · 08-06-2022, 07:22 AM

Good morning everyone. Thank you for the responses. Here is an update to my situation. Yesterday the rv started the up down shifting again and finally quit completely leaving us stranded on the side of the interstate. The only gear that worked was park. On a whim after 15 minutes sitting there, I restarted the engine and the transmission worked! For 10 miles. Then quit again. Managed to limp my wAy into Ellensburg, WA and here we sit. Called 9 different rv and workhorse repair places yesterday and no one will touch it. Out of frustration, I called my workhorse mechanic in Albuquerque for possible suggestions. I learned that my transmission is actually a 4L80 GMC/Chevy transmission. There is a Chevy dealership in Yakima about 1 hour from here. They are closed until Monday. Will see Monday how long it takes me to make that 1 hour trip Monday morning. My fluid and filter were changed less than 20k miles ago.

PeterH-350LE · 08-06-2022, 09:26 AM

Quote:

Originally Posted by gsg2013

Good morning everyone. Thank you for the responses. Here is an update to my situation. Yesterday the rv started the up down shifting again and finally quit completely leaving us stranded on the side of the interstate. The only gear that worked was park. On a whim after 15 minutes sitting there, I restarted the engine and the transmission worked! For 10 miles. Then quit again. Managed to limp my wAy into Ellensburg, WA and here we sit. Called 9 different rv and workhorse repair places yesterday and no one will touch it. Out of frustration, I called my workhorse mechanic in Albuquerque for possible suggestions. I learned that my transmission is actually a 4L80 GMC/Chevy transmission. There is a Chevy dealership in Yakima about 1 hour from here. They are closed until Monday. Will see Monday how long it takes me to make that 1 hour trip Monday morning. My fluid and filter were changed less than 20k miles ago.

Its unfortunate, that you ask for advise, but do not listen to it. I had exactly the same problem with a 4l80e. This may be the one for your year https://www.rockauto.com/en/moreinfo...=5136&jsn=1041

Good Luck!

Quote:

Originally Posted by PeterH-350LE

TPS (Throttle position sensor) can cause the transmission to not shift into OD. Its a very easy replacement and the part should readily available. It is typically located at the throttle body, assuming you have TBI

gsg2013 · 08-06-2022, 09:42 AM

Hmmm. Can’t follow advice that I get while I am broken down on side of road. All I have posted is what my situation is and what I am going thru looking for a mechanic so I am not sure what advice I am not following. My wife has been on the phone for the past hour trying to find parts based on all the suggestions.

PeterH-350LE · 08-06-2022, 09:48 AM

Quote:

Originally Posted by gsg2013

Hmmm. Can’t follow advice that I get while I am broken down on side of road. All I have posted is what my situation is and what I am going thru looking for a mechanic so I am not sure what advice I am not following. My wife has been on the phone for the past hour trying to find parts based on all the suggestions.

Are these not your own words?

Quote:

Originally Posted by gsg2013

...... Searched forums but could not find an answer that matched my issue. Looking to the experts for help please. gsg

PeterH-350LE · 08-06-2022, 09:57 AM

The TCI (Transmission control Unit) gets the signal from the TPS (throttle position sensor) to control the shifting of the 4l80E. Its not a mechanical issue or fluid issue or or or. So, good chance its the TPS, unless your Transmission Control unit itself is defective.
Its a $40.- part and real easy to replace. Call some autopart stores and see if they have it. They want to know chevy, year, engine size and transmission type, nothing else. Workhouse is not getting you anywhere at the autopart store.

gsg2013 · 08-06-2022, 11:03 AM

We are calling around looking for one. Thank you.

gsg2013 · 08-06-2022, 05:25 PM

At the expense of opening a new can of worms, the attached photo (I hope) is of my TBS. it is 5” x 3” and pop riveted to the throttle body. No one in town sells the complete unit.

gsg2013 · 08-06-2022, 05:27 PM

Forgot to add that two mechanics have verified this is my throttle body sensor.

gsg2013 · 08-06-2022, 05:28 PM

Sorry. TPS. Throttle Position Sensor. Is it obvious yet I don’t do these types of repairs every day?

PeterH-350LE · 08-06-2022, 07:35 PM

Quote:

Originally Posted by gsg2013

Forgot to add that two mechanics have verified this is my throttle body sensor.

That does correspond with the Rockauto TPS.
https://www.rockauto.com/en/catalog/...sor+(tps),5136
and here on Amazon
https://smile.amazon.com/WVE-5S13583...s%2C141&sr=8-1
the other option per Rockauto, shipped to my house on Monday via amazon

https://smile.amazon.com/nobrandname...7-93deae8f9840

Oreilly autoparts

https://www.oreillyauto.com/detail/c...+TH0009&pos=21

It is unusual that it was riveted to the throttle body. Did the 2 mechanics agree that it could be the culprit?

gsg2013 · 08-06-2022, 09:11 PM

That is it! If you zoom in on my picture, you can see mine is riveted onto the throttle body. All the places we called said I had to purchase the entire unit, which was unavailable. The two mechanics were not sure if that was the culprit but were willing to replace it if I could find one. (The entire throttle body that is). Thanks! I have an Amazon account and now I have hope and a project! Again, thank you thank you thank you!!!