Downshifting too much problem

wackerb

New member
I saw some post where it was not downshifting. My 2006 3500 has the opposite problem. I initiated some downshifts for long downhills and then using + it will go back to D momentarily and the spontaneously drop into 4, or 3, or, even, 2 depending on speed. Sometimes when I start it up and take off after shifting to D it will top out ta 2 or 3 and I have to manually push it to D. Sometimes I just have to hold it on + to keep it in D.

Any ideas?

BTW, I'm in southern Mexico headed for Guatemala.
 

NelsonSprinter

Former Nelson BC Sprinter
I don't know, but I would try disconnecting the negative and positive from the battery for an hour and reconnect to see if it re-sets to normal.
 

MillionMileSprinter

Formerly Type2Teach
Have you checked for leaks at the electrical connector? Have you changed the fluid and filter recently? Have you cleaned out the inside of the tranny? There are good write-ups on the forum for cleaning out your tranny. That seems to solve many shifting problems. The leaky electrical connector (the white sleeve on the front passenger side of the tranny) is also a common problem that is well documented here on the forum. If you don't have access to tranny fluid, but need to change the leaky connector, you can park on an uphill and apparently you won't loose much, if any, fluid when changing the connector.
Good luck!
 

autostaretx

Erratic Member
My foggy memory sez that somewhere i read that you need/want to tap it in the + direction 3 times (tap tap tap) to fully bring it back to "automatic".
Tapping merely once only tells it to upshift once.

--dick (if i can find the reference, i'll edit it into this response... and i suspect it was the owner's manual)

added: it's not "tap tap tap", it's "push and hold".
From the 2005 owner's manual: (page 148)
----------------
Briefly press gear selector lever in the + direction:
The transmission will shift from the current gear range
to the next higher gear range. If the transmission is
already in gear range "D", an additional upshift of one
gear is not possible.
Press and hold gear selector lever in the + direction:
The transmission will shift from the current gear range
directly to gear range "D".
----------------------------
Then it goes on to say:
--------------------------
NOTE: With transmission in gear range "D", "4" or "3",
upshifting from 1st to 2nd to 3rd gear is delayed
depending on vehicle speed and engine temperature.
This allows the catalytic converter to heat up more
quickly to operating temperatures.
During the brief warm-up period this delayed upshift
and increased engine noise might be perceived as a
malfunction. However, neither the engine nor
transmission are negatively affected by this mode of
operation
------------------------------

There's also the possibility of "switch bounce"? As you release the handle from the + tap, might it be springing back enough to touch the - switch contacts?
 
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wackerb

New member
Thanks all for the replies. I've been out of internet, so delayed. After much more experience with the spontaneous downshift I think it is triggered by rough roads. Especially if hit a bump on descent with the brakes on it "falls" down. I've been in a lot of rain, so will check the connector when I get a chance, but, for now, I can control it by maintaining pressure. Roads here have lots of speed bumps and pot holes in addition to bridge approach bumps, so it is like a driving on a washboarded dirt road in Colorado.

For now, it appears to be a linkage problem. Does anyone know if there happen to be tension adjustments on the "- +"? Or is this a common problem on bumpy roads?

Thanks,

Bruce
 

sailquik

Well-known member
Bruce,
There is no linkage!
Your transmission is completely controlled by wiring and switches.
I take you do not have a Scan Gauge II or similar performance monitoring gauge package.
It would be interesting to know the RPM and Percent LOD you are running when it shifts in ways you do not want it to.
Perhaps the engine/transmission management systems are deciding that you should be in a different gear, but the driver is trying to override them.
Also, it could be as suggested, the connector to the transmission could be full of water or oil.
Or the selector switches in the shift control could have come loose and the jostling of rough roads is causing them to make contact when they should not and initiate a shift up or down.
Roger
 
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wackerb

New member
Thanks Roger, I suspected no linkage, but figured I'd play the fool to find out. I sure miss being able to get underneath and check things out, but travel and wet weather are not conducive.

I'll hook up a scanner, but am pretty sure it is a pure bounce problem. The lever does lean a little to the left when in D so there is some off center weight to deal with. When I do downshift intentionally for declines it works as expected, until I hit a bump. While the highways here are worse than those in the US, I'm surprised others haven't reported the problem on bumpy dirt roads. When I get time I guess I'll take apart the shift switch and see if anything is amiss in there.

Thanks,

Bruce
 

wackerb

New member
Can anyone point me to online instructons for removing and replacing the shift control box? This is definitely a bump induced problem, and back roads in Costa Rica are even bumpier than highways in Mexico:)
 

autostaretx

Erratic Member

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