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Old 07-19-2021, 08:55 AM   #1
williebox
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Default Auto-X'd M46 not downshifting 3-2

Hey, Just wondering if anyone else has experienced difficulty downshifting from 3rd to 2nd when driving their M46 hard.

I auto-X my '76 240 with B21F+T with a stock M46, new clutch, pilot and throw-out bearings and the aliexpress short shifter. Yesterday was a 2.4km power course and was mostly 3rd gear, with some downshifts to 2nd on a couple tight turns.

When trying to downshift from 3rd to 2nd, it felt like I was being locked out. I had to stay in 3rd once I was there for the entire course. During normal driving I haven't experienced this so I'm not sure if its me trying to shift too fast, Ive always heard people complain about the slow 2-3 shifts so maybe it needs to also be a slow 3-2 shift? I beat it pretty hard, no grinding, just not sliding down to 2nd.

I had to modify the short shifter to fit my early style transmission, as Ive found many "bolt-on" parts don't fit my early VIN Canadian car without some tweaks. Normal driving the shifting feels pretty smooth, its got the brass shifter bushings and finding a gear has never been an issue.

Just wondered if anyone else had experienced it or could point me in some direction whether its just a shifter adjustment or if I should look at something internal to the transmission like a synchro or shift fork issue or something else. I do have a spare M46 and M47, the M46 supposedly being "built", but I'm not sure I trust the guy who sold me it with a B23FT that ended up having a melted piston.
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Old 07-19-2021, 12:26 PM   #2
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What flywheel do you have?
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Old 07-19-2021, 02:46 PM   #3
dl242gt
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I had this issue with my M46 in my turbo. Sometimes when turning left and trying to downshift from 3-2 it would resist putting the shifter into second. This improved when I changed to stiffer diesel motor mounts and a 164 motor mount for the trans mount.
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Old 07-21-2021, 09:57 AM   #4
williebox
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Flywheel is whatever came from factory, I believe its the 8.5 "flat flywheel". I didnt pay much attention to it when I had it out and resurfaced last year since I'm running an oem clutch set-up - my power output didnt really warrant anything fancier

The car has new oem motor and trans mounts but it does feel like the trans moves around a lot so maybe ill look into poly bushings and/or a more solid trans mount

Last edited by williebox; 07-21-2021 at 10:45 AM..
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Old 07-29-2021, 08:41 PM   #5
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I've no direct experience with this on the M46, but in various other gearboxes I'm used over the years it is generally 2nd gear synchros that go first. And inevitably you experience it first when you're going for a high rev 3-2 downshift and you're in a hurry. Which I'm sure you are when AutoX-ing.

Can you rev match (cue Fast n Furious "granny shifting, not double clutching" quote, though here it may actually be accurate) and get it to drop in nicely? If so then I'd very strongly suspect worn synchros.
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