92 SC400, often when the engine and the tranny are hot, and overdrive is ON, it will stick in overdrive at any speed.

From a dead stop the car would start from 1st and shift straight to overdrive and has no power at all (over drive, no syncing torque converter) (the rpm stays around 1900rpm - 2000rpm.

From highway speed, the car doesn't downshift when OD is turned off.

What can I do here to solve this problem? I've changed the fluid in the tranny, made sure it's at proper volume.

 

Any help...?

 

i am not to sure about exactly how the 400 auto trannys work but most of us 300 guys when we have had o/d problems as much as we have checked out our trans it usually ends up being the ecu. So if you can get your hands on an ecu that you know for sure is in perfect working order test it out.

 

can u shift to all the gears manualy, L 2nd 3rd and then o/d????

 

id do a stall test all u need is to find a tanny pressure tester and hook it up the the hole on the driver side of tranny and do this after you can confirm manually shifting. This would tell you if your torque converter is bad stator, or tranny internals.. just a thought but do u have to lil or to much fluid in the tranny... always start simple. to much can also affect shifting i dont know if it owuld do exactly what yoru talking about but id look at it. also see if yoru o/d flashes or not.

 

My o/d light doesn't light up at all.

Manually it shifts fine. But when it's in limb OD (sticking OD), sticking the shifter to 2nd only get it to 3rd and intermittently it will get out of OD limb and kick back to 2nd.

 

if your o/d flashes its the transmission solenoids

 

It doesn't necessarily have to flash for it to be shift solenoids. Mine never flashed and I had two of four that were bad.

Maybe one of the accumulators in the valve body is going bad... I don't know. I haven't heard of this problem before.

 

One of the fact is it only sticks OD when the engine and tranny are hot. Does that help isolate it's mechanical issue instead of ECU?

 

If it's only when hot, that tells me that it's definitely the valve body. As the fluid heats up, it sounds like it's leaking past some isolations in the valve body causing pressure to build up and engage the OD. it would not behave the same way in an auto SC300 as it doesn't use line pressure to actuate gear changes. Might want to talk to Aliga and figure out if you can get a new valve body.

 

Thank you Durrr so much for the diagnostic man. I'll look into that.

 

NP, any more questions and I'll be monitoring the thread.

 

Bump, any fix for your problem. I am also having the same problem any not sure what to do.

 

im having a problem with mine but mine when it warms up the overdrive does not come in at all. stays in 3rd. at 3000 rpms at 55-60mph... i havent dont a fluid change but i will change the tranny filter and gasket this week. hopefully that will cure the problem.

 

OK, so what's the solution to this problem? I have the same problem with my 92 SC400. When the engine/tranny is warm, the OD sticks (in use in 2nd gear and up). When this happens, it doesn't downshift when I disengage the OD. If I manually shift, 1st gear is fine, but then goes into bog down mode upon shifting into 2nd. I think this is like the old school OD, which isn't a totally separate gear, but rather an add-on gear, and even though it should never be engaged for 2nd gear, it is when it is stuck.

Also, I have managed to get it to disengage by putting it in neutral or park and revving for a bit. I do this when I'm at a red light. It doesn't always work, but it does sometimes

More also, I have seen once or twice when the OD light blinks, indicating a problem with OD... but usually the light comes on when I disengage it (well, when I press the OD button), and off when I engage it.

I'm pretty good at troubleshooting things, but I've only had the car for maybe 6 weeks and don't know much about the technicals yet. That said, I believe something like valves or solenoids being the culprits make the most sense. Is this something I can fix myself? If it is an ECU problem, would flashing it fix it, or are we talking about physical wear (deteriorating solder connections or failing capacitors, etc.)?

HELP soon, please, its driving me nuts! I still love the car, even compared to my most recent car (09 Audi A4 2.0T Quattro PremPlus). LOVE the V8 sound!