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BW M40 Auto Trans - any issues paired with a 390?

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Stink View Drop Down
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    Posted: Apr/18/2021 at 7:03pm
I found out a previous owner replaced the original auto trans in my 1969 AMX (which has a 390) with a BW M40, which went with the 290 engines. Is there any trouble I can expect with this combination? It currently shifts great and there are no issues that I can feel when I drive it. I pulled the pan and fluid looked good, nothing in the filter either. 
Thanks for any insights...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Apr/18/2021 at 7:24pm
All I can recommend it go easy on the gas! The M40 was made for a 210 hp engine, not for a 315 hp one.  If you drive it gently, it may last. If you like to squeal the tires, it will be toast.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stink Quote  Post ReplyReply Direct Link To This Post Posted: Apr/19/2021 at 11:27am
Thanks Ramblin, I'll do that, although if it goes, then I have my excuse to drop a modern 4 speed automatic in it! 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: Apr/19/2021 at 2:24pm
I would start planning for a replacement.  Why have a powerful car if you have to drive it like there's an egg under your foot?  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Apr/26/2021 at 7:05am
I have to agree with Steve. At least with an operating trans you don't have to be in a hurry to find a replacement, but better start looking. You don't have to exactly drive like there is an egg under the pedal, but I wouldn't be hard on it either. Normal driving will be fine. Even the 290/4V got the heavier BW M-11, as AMC knew people would be trouncing it with the 4V.
Frank Swygert
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