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Old 06-13-2021, 09:15 PM   #1
Join Date: Jul 2011
Posts: 56
'93 Ford E350 with E40D - slips/bucks when downshifts from OD to 3rd

This problem just started on our way home from Ohio. I have a ‘93 E350 Class C motor home and I was in OD heading up an incline when the transmission downshifted in to 3rd it started bucking/slipping badly and stopped as soon as I turned the OD off. If I turn OD off on shifter - no problems - RV runs fine. If I turn on OD it runs fine UNTIL the tranny downshifts in to 3rd (up a hill). Then it will ‘slip’ or ‘bucks’ in 3rd until I turn the OD off and then it starts running fine again.

Couple of additional notes - just checked the fluid - it’s full, red and doesn’t smell burnt at all. I have a trans temp gauge and trans temp hardly ever goes above 180F. Transmission was rebuilt 3 years ago (<10k miles).

Just pulled back on interstate and shifts fine up through 3rd gear (I turned OD off).

But - if I do not turn the OD switch off on the shifter the Coach will not go in to gear when I shift (it will go in to Reverse). Turn the OD off and the coach shifts normally from 1st to 3rd gear.

Pulled codes and I got Code 512 and 553 - but I'm not sure these are related to this issue.

Any thoughts?

thanks, ryan
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Old 06-14-2021, 05:22 AM   #2
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Location: LA, Lower Alabama
Posts: 2,259
Just a thought but the E350 chassis was built with an OD transmission giving the user the opportunity to use OD in the appropriate situation. Appropriate meaning lightly loaded on flat ground. With the weight of a motorhome, it's no longer lightly loaded and OD shouldn't be used.
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Old 06-14-2021, 06:46 AM   #3
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Join Date: Aug 2019
Location: Meshoppen, PA
Posts: 1,007
have it looked at, ican be the plug in trans loose
A vacuum leak, defective transmission module, or bad throttle position sensor could cause this issue is talked about..

if you let it go, i can become a bigger issue..
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Old 06-15-2021, 05:08 AM   #4
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Location: Meshoppen, PA
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sorry for typing errors in last post.. . bad on my phone.. LOL

In my last 15 years of old ford iron..

in my 94, we had that issue intermitent came, go , came.. I changed fluids, changed brands as I found some oils way better, I toed a 7K trailer behing RV for many miles, I bought her with about 138K.. Around 160Kish.. That cut out, slap, surge from OD happened alot until one trip, it was nasty but also my speedo needle was jumping 3-5 mph..
To shorten my going grey on this one.. Trans shops, searched for a good rebuilder or a jasper... ready to pull plug..
I went to an event that idid twice a month..A local tech school teacher I knew was there. auto technologies/powersports etc.. he was teaching my son..
He said tranny seems strong as I had trailer on.. did you check the PSOM/VSS circuit, these trans are sensitive to vehicle speed.
Found a broken frayeed wire in the twisted pair coming from rear axle up frame rail near fuell tank. broken in harness with a few strands shorting each other.. I actually drove with a small snap on scope on wires , to watch the wave as I drove , and saw the drops and spikes etc.

I had few more twitches on the 94 and it was a bad PCM/ECM main computer.. it always had a idle stumble too . once i replaced it, trans shifted so much better, firmer and ran incredible, Sold it at 196K still going..

Fast forward, I updated, I am chaeap.. Found a 96 winnie 29RQ, 30K. sweet .
On my way home from NY to PA.. it ran great, then 30 miles from home the bang, clack, in / out of OD, then I saw the speedo twitch.

This one was a stinker,, ran a new VSS connecter at rear and sensor, and a new wire from there all the way to th dash speedo cluster . as the issue was at a splice in the dash area and i was not pulling it, I had it narrowed from ABS to cluster.. Any way, drove it first time this year yesterday for a couple hundred miles, and all is still working.. LOL

good luck,, just saying could be many things.. that trans was noted for that issue..
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Old 06-16-2021, 09:04 AM   #5
Join Date: Jul 2011
Posts: 56

Thanks for the replies - I was wondering about the possibility of this being electrical. I have noticed a 'dead spot' for years when I set the cruise right around 62-63 mph - a slight surging being noticed as the coach runs with the cruise on at that speed on level road. Speed up some, slow down some and the motorhome runs smoother (TPS??).

On this trip we got home just fine - turned the OD off, set the cruise at 58 mph and the coach ran great! Seems to be a 'sweet spot'...

The only question about it being electrical - I don't see how that effects the initial shifting in to gear. When you turn the RV off and restart it, the default is the OD is on (I have a button on the end of my shift stalk that turns the OD on/off). If I try to start out with the OD on (light off on the stalk), I can't get the tranny to shift in to gear - turn off the OD - no problems. And, if I turn off the OD with the RV in Drive, I can feel a noticeable lurch - as something is 'switching on/off??). Once the OD is off, RV shifts perfectly up through 3rd gear and runs fine.

I had the transmission rebuilt 3 years ago and I called the shop. They indicated that I could drive it indefinitely with no OD, but I'm going to have them look at it. Hopefully, they'll work with me in fixing it - I gotta believe a rebuild should last longer than 10-12K miles.

I am going to further explore the electrical issues though...just not sure how.

Thanks, ryan

I did develop ball joint issues on our last leg- really loud creaking...but I'm going to post another thread
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