Goes In and Out of Overdrive and burns up the Transmission!

We recently purchased a 1991 Minnie Winnie (Winnebago) which rests on a 1990 Ford E350 chassis. It only has 58k miles. While driving on the freeway or highway, the Overdrive starts to go in and out; downshifting and upshifting willy nilly. It has a manual button for turning off the Overdrive and when I do this, it stops jerking and drives smooth. But, of course, this effects the gas mileage significantly. I took the Minnie to a garage recommended by the company I purchased the Minnie from. They replaced the manual Overdrive switch and replaced the transmission with a rebuilt Ford transmission. We got it back and it was okay for one trip but by the second trip, it was doing the same thing again. I took it back to the garage and since it was under warranty, they put in a new rebuilt transmission, another new Overdrive switch, a new fuel sensor and checked the wiring but it still had the same problem. So they sent the onboard computer board to Ford who rebuilt it. The guys at the garage thought for sure this would resolve the problem. It didn’t. They have exhausted their ideas as to what is causing this problem. We love the Minnie Winnie and other than this problem it is in beautiful condition. What do we do now? HELP!

You need a new mechanic.

First clarify what you mean by “overdrive” - in an auto transmission it is typically 4th gear. But sometimes people mean the torque converter clutch (TCC). How far up and down are the RPMs going?

I don’t know this transmission or engine or its systems. But the transmission “decides” what to do based on what the engine is doing or what you are doing with it. E.g. a faulty brake light switch can make a transmission go in and out of TCC lockup. So too can a faulty throttle position sensor, or a vacuum issue or other things as well. These characters apparently know how to R&R a transmission, but are clueless as to how to diagnose one. Your problem is apparently in engine/trans management rather than in the transmission itself.

At what speed does this occur?? I’m betting 40-50 mph…What is the elevation where you live/travel…

Welll your Winnie is too heavy to be using overdrive, (in many conditiions), so it is normal to downshift and then to upshift when it gets back up to speed. That is why the “overdrive lockout button” is there. Yes you might use more gas but it could save the transmission. There probably wasn’t anything wrong with the overdrive switdh, and maybe nothing wrong with the transmission. A vehicle that large really has no business with an overdrive.

I’m with Elly and Caddy. Older vehicles use chassis that often were not designed to run in overdrive under load.The dump truck I use for deliveries has an overdrive you use only when unloaded. With the Winnie, I believe you are perpetually loaded. To me it’s that simple. You want to conserve fuel while in a lower gear? Your solution may be to just drive slower. Use OD only in conditions that it doesn’t hunt…level ground and slight down grades where speed build up is not an issue. I googled that the base engine is 5.8L with only 200 hp. That tells you that even the optional may still be whoefully under powered for your use and speeds you travel.

The issue here is not whether the vehicle should have an overdrive or not but whether the overdrive is working properly. This transmission can handle pulling this vehicle in overdrive. There are still questions that need to be answered such as: has the shop scanned for codes?? Has the shop checked cooler operation and flow ?? Is this an intermittent problem ??


Another thing to check…Low power output from the engine, low engine vacuum, will cause the transmission to “hunt”…

Even if the overdrive is working properly, it will downshift and upshift all day long, so overdrive should be locked out!!

Caddyman, You are so right. I can’t count how many times I have had people so sure that they have a bad transmission whether they have mis diagnosed it themselves or had a mechanic mis diagnose it, pull it, and bring it to me only for me to tear it down and find nothing wrong. It’s always wise to have a drivability guy give it a once over before condemning the transmission.

Ellis: Are you saying to lock out overdrive all the time?? Just forget about it?? Even on the highway??


That E-350 stripped chassis had one of the earliest iterations of the E40D and had aq non-repogrammable PCM (12A650). There were many program changes made such as line pressure control and default shifts, etc. I’d definitely recommend canning the original if it is still on there. It really needs to have an Aux ( air cooled) cooler in addition to the engine radiator heat exchanger. This chassis would also have a 7.5L with a notable reputation of melting the inner wall of the double-walled “Y” pipe shut. Catlysts were also frequently melted. Indofar as the transmission mechanicals… The original was E9TA-7000-XXX was completely upgradable to dependable levels. But, ake no mistake ablut it, that E9 level was absolutlely a POS. Most every componenet in ti would be replaced to bring it up to date costing far more than an already an update FMC rebuilt…so, good choice on that. f,I it is indeed upgaded completly including the PCM, you can let the O/D cycle as much as it wants…obnoxcious, but innocuous. The “real” problem is the torque converter clutch which like EVERY other American-engineered TC clucth is completely inadequate…anyhow, they aren’t that way any more…it took nearly 10 years for the US Mfgs to produce quality and durable autos… GM and Chrysler gave up on the HD (diesel) units and subbed them out. It was a pretty poor run in thiose years…maintenance pretty much niot required because the unit would never last long enough to warrant it… Enjoy.

You are in fact TOWING a loaded travel trailer with a van.
With a motor home configuration you can never unload and NOT be in towing mode.
If you were actually towing a trailer with a truck, it would be obvious and you would treat the transmission as such.
Don’t keep fooling yourself with this motorhome and correctly use towing practices.

Transman, no, one can use overdrive where it is not shifting in and out most of the time. But if it is shifting back and forth, lock it out. In my state there are too many hills.

When the transmission and engine are operating properly, it will downshift and upshift as driving conditions change, it’s when it doesn’t downshift, for instance and bogs the engine down is when you have a real problem. If you’re pulling weight and driving up and down Mont Eagle in tennessee for example, hit your tow-haul or o/d off button and ride it out. Use 3rd gear to get you back up to highway speed and apply O/D.


I was saying that the current and proper transmission design level can easily performing O/D cycling w/o any (and I do mean ANY) notiaible negative (wear) effects on the mechanicals… The original was an embarrassment addmintted to me by several design engineers of the day…theiy were told to “keep it cheap” and the E4OD 1989 through 1994 were really, really bad. They’s fine now. Heat rejection at highway speeds is negligible even from older, non-lockup trans… (e.g. C6). Almost all heat rejection occurs at <20MPH and comes directly from the torque converter stator redirect. Now, when you try to enguage meagerly thin, crack-prione friction material tio a 300deg F converter hub face, you can start the goodbye sequence soon because it will not last long I’ve done several case studies on these with plow trucks, airport shuttles, etc. With any of these, you can beat the crap out of them at highway speed (30+) and you will notice no temperature rise at all. T less than 20 mph it is a whole different story.

My thought was along Caddyman’s line of thinking. Maybe it’s an engine performance problem; horribly out of tune, clogged exhaust, or even a tired old engine.

I’m not familiar with details on these things but considering it’s a 1990 model this means that it’s in the middle of the TFI era. If the TFI module has been changed in the past and someone has not set the ignition timing correctly (or possibly during some other procedure) then maybe the timing is way retarded. That will make the engine as anemic as all get out and the transmission will be in a perpetual state of confusion.

What would I do? Stick a vacuum gauge on it and then follow it up with a compression test if there’s a vacuum anomaly. The gauge should show a timing or compression problem if one exists.

I used to have an anemic, non-turbocharged SAAB with a 2.0 4 cylinder and in the mountains of CO that car was pathetic at altitude due to lack of power. The auto trans did nothing but hunt for another gear…

Well, as I reread the original post, I believe the engine/transmission was operating normally. He should have locked the overdrive OUT and saved the tranny. I even doubt that he needed an overhaul. He said that with the overdrive off, it performed fine. Too many mechanics are too eager to “overhaul” a transmission!! I have never had one repaired. However, I have only been driving 63 years!

Two new/rebuilt transmissions doing the same thing as the first?? If the original was burned up, like op said in his header then I don’t doubt that it needed replacement but if the first rebuilt had the same symptoms as the original then they should have done some diagnosis before throwing another rebuilt unit in it. It’s much easier on an electronic transmission to throw a scanner on it to see if the computer is commanding the shift or not. You never want to lock out overdrive because the transmission is hunting. Fix the problem.


EVERY SINGLE ONE of thos early E4ODs (89 and 90) needed overhaul regardless of maintenance performed… I overhauled 100s of them then, holding them together internally with coat hangers welded to all moving snap rings and other paarts just to make them work at all past 20K miles…they were terrible examples of US engineering of the time. It is far better now than then but I can provide examples of many other units that no matter what you dooo…you will have a mojor failure iin <100K miles guaranteed.

times have changed , I hope

Yep, and I STILL work on those earlier units from time to time. I know where you are coming from.:slight_smile:
Problem here is that 2 different rebuilt units have been installed both with the same symptoms as the original.
Somebodies not doing their diagnostics.


It would be nice if Marworth, the OP, checked in…he has the answers everyone is seeking…