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Old 05-08-2021, 06:53 PM   #1
spock345
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Default M410 cover swap

I ran into an unforeseen problem when trying to swap the shifter covers on an M410.

Here is the setup on my M40.


Here is the M410, the ball and spring setup for the shifter detents are much farther forward.


Here is the comparison of the Amazon M40 and P1800 M410 covers. The M410's cover has reliefs for the springs and more meat in that area of the cover to accommodate this.


The problem arises when putting the Amazon cover on the M410, the springs are compressed far too much and the ball detents will not allow the selector rods to move. I don't think there is enough meat on the Amazon cover to drill reliefs into it. I guess the answer to the question, "does a longer M41/40 shifter cover fit an M410/400?", is a no.

Any ideas on how to make the Amazon cover work? Shorter springs? Drill whatever sort of hole I can? Just find an M41?
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Last edited by spock345; 05-08-2021 at 07:57 PM..
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Old 05-08-2021, 09:01 PM   #2
hiperfauto
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Damn, I thought it was a direct swap since they use the same gasket. I know the long shifters will interchange.

I checked to see if there was a shorter spring and there isn't. They both use the same spring.

I think the best solution would be to find a shorter spring. It doesn't look like there's enough material to drill the cover and get it to seal with a gasket.

McMaster has a good selection of springs. Just gotta find the right size.

https://www.mcmaster.com/springs/compression-springs-7/
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Old 05-08-2021, 09:35 PM   #3
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Or convert the 122 to a racing style top cover with a 240 tunnel section & rivnuts.
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Old 05-08-2021, 09:50 PM   #4
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Quote:
Originally Posted by Redwood Chair View Post
Or convert the 122 to a racing style top cover with a 240 tunnel section & rivnuts.
Kind of defeats the purpose of going with a Volvo gearbox that could fit the short shifter, which was to avoid cutting the tunnel and having to redo the carpet. Although at this point it may just be a sunk cost fallacy directing my decisions. I know 122Power has a tunnel section.

The stock springs are about 3/4" long, 0.3" in diameter, with 0.050" wire.

They protrude out the top of the box with the cover off about 5/16" and the recesses in the top are about 5/32".

I need to do some math to see if McMaster has the right springs.

Last edited by spock345; 05-08-2021 at 10:06 PM..
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Old 05-08-2021, 11:48 PM   #5
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From what I can tell McMaster likely doesn't have the right springs. At least not ones that meet the dimensional requirements. I approximated the spring rate and it seems rather high at about 60 pounds per inch. I might be off a bit there. I could always order some springs and cut them down (keeping the old ones to reverse my hacks later).
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Old 05-10-2021, 06:18 PM   #6
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Since people get aluminium cylinder heads rewelded after a failure, I assume its possible to add some material on the cover as well, and then drill the holes? Ok it won't be very cheap but...
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Old 05-10-2021, 06:53 PM   #7
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Since people get aluminium cylinder heads rewelded after a failure, I assume its possible to add some material on the cover as well, and then drill the holes? Ok it won't be very cheap but...
That is probably the best route instead of monkeying with spring rates to find the right pressure on the ball detents with shorter springs. I assume that is set in a certain way by the ZF and Volvo engineers who designed these boxes.

I hope this documentation helps people figure this out before they have the gearbox sitting in front of them.
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Old 05-16-2021, 03:41 PM   #8
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I ended up trading for an M41 with a J type. It came with the right cover I needed. When I removed the cover to replace the gasket I realized something that made me feel real stupid.

Apparently some of the covers for the 122 and early 140 M40/41s had the spring detent reliefs drilled in the M410 spots. I am guessing they went to a different casting later on after the M400/410 was introduced?

So if anyone is in my boat and wants to put an M410 or M400 in a 122, you just have to find the right shifter cover.
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