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mhamilton 05-26-2006 04:22 PM

THM 200 downshift
I was wondering if there are any adjustments to make, or if I just need to overhaul the trans to get it downshifting at appropriate times.

My complaint is not the forced downshift, that still works fine (as the car's manual says, at 1/2 throttle under 40 mph and full throttle under 70 mph). The trans doesn't seem to downshift when I am at very low speeds. Mostly when I brake to turn a corner, all the way down to 5 mph, I'll still be in 3rd gear with the 2.41 rear trying to accelerate up a hill. Most of the time I just pull the column shifter into 2nd, but I can't believe this is working properly. It also doesn't seem economical if I have to floor it every time I turn a corner.

The TV cable is adjusted properly, and the trans still shifts fine. It'll hold out in 1st and 2nd appropriately if I start from a dead stop. Occasionally I notice a slight slip between 2-3 during slow accelerations, but the trans does have almost 150k original miles on it. Any suggestions?


jvsapp 05-27-2006 10:26 AM

how's the fluid? changed regularly? shouldn't be brown. also the level?

mhamilton 05-27-2006 11:00 AM

Yeah, the it's good now. When I got the car it had original fluid, 120k miles. Had the seals done back then, and fluid was changed. Just a couple months ago I changed the fluid and filter, about 150k miles. It did have a small pile of black dust under the pickup, I suppose the clutches are starting ot wear out.

Checked it the other day, the level is fine and the new fluid is clean and not burnt.

This non-downshift has been happening as long as I can remember. Unless I come to a complete stop, it will not drop out of 3rd until I really floor it and force a downshift.

jvsapp 05-27-2006 09:09 PM

hmm.. kind of sounds like what happenes to me when the the vaccum line comes off my T350. but i am not sure if the 200 has a vaccum line. from a dead stop, it would only shift when i manual shift it. but wouldn't downshift unless i come to a stop or manual shift it. then i gotta crawl under my truck and hook it back up.

mhamilton 05-28-2006 08:40 AM

The 200 only uses the TV cable, no vac modulator. As long as I come to a dead stop it will start in 1st and be fine. Sometimes if I come almost to a dead stop it will downshift, but I think it should shift much earlier. 5 mph in 3rd gear doesn't really work too well!

The odd thing is, the trans usually doesn't upshift out of 2nd until I get over 10 mph (very slow city streets), so it should downshift back once I get under 10, no?

jvsapp 05-28-2006 12:48 PM

hmm... got me then.. not sure had a trans shop take a look?

mhamilton 05-28-2006 06:35 PM

No I haven't had it to a trans shop. I was hoping one of the experts on this forum could suggest what the problem might be. I could rebuild the trans, but I'm not going to pull it out on a whim.

It could be the way the TH200 worked from the factory, I know it was never a performance trans. Or if it's a bad governor, control valve, etc, I could look into fixing those.

jvsapp 05-29-2006 12:53 AM

sorry man, wouldn't know... not a trans expert either. i was just trying to help get it to the top of the list. i had a post for a 66 impala, but that died somewhere with no one responding to it. hope someone else can help.

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