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Old 11-11-2021, 08:04 PM   #1
dandeluca
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Default Swapping an older M46 into a 91' 240

I am looking to do a manual swap and I was wondering if there would be any difficulties swapping an older M46 (pre-83) into my 91 245 auto.

I understand I would have to find the proper flywheel for my ignition system. Is there anything else I need to worry about?

Thanks,
Dan
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Old 11-11-2021, 08:15 PM   #2
Kjets On a Plane
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-1978 is 10 spline input shaft for the clutch disc, 1979+ is 22 spline.
10 spline 228mm OE sachs thickness disc for OEM 1989+ dished flywheel may be hard to find or cross reference.

I suppose you could use the OEM 218mm -'78 10 spline disc to get it to move under it's own power (same new thickness between the discs for the diaphragm style pressure place/cover springs) with the dished flywheel/228mm cover and just have less grip with the softer springs and it *might* work at all if the engine has very little power or torque driven gently...
...the spring pressure is lighter on most of the 228mm clutch covers for the N/A cars so expect all else equal, torque capacity to be lower, but the car would likely move/be drivable...at all?

Otherwise...uh it all basically bolts in & works, especially 1979+ trans.

Easier if you have a ~1983-1984+ bellhousing for the crank angle sensor with the thin spot/knockout, though you can carefully trace & cut the aluminum alloy with fairly conventional woodworking tools capable of cutting alum alloy if you wanna/no one has had the bellhousing crack or trans fall out from under the car or cut their foot off...uh..yet.
Or if they have, they haven't posted about it or fessed up to it on TB...yet...

I'm not a mech-E as such with a test lab in my back pocket/no official stamp of approval, but I've traced the pattern & cut the bellhousing carefully or read the book and swapped the bellhousing without incident BTDT many times.

Swapping/correctly shimming the bellhousing is its own little thing.

Path of least resistance is obtain the correct flywheel & trans with 'thin spot' bellhousing ~1983-1984+ or whole parts car of ~ that year or newer without having to swap the bellhousing or do any custom/improvised cutting I guess?
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Old 11-11-2021, 08:35 PM   #3
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So basically I want to make sure its 79+ with a 22 spline shaft to avoid clutch disk issues, and be willing to hack away at the bell housing. (I am)

Thanks!
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Old 11-11-2021, 08:45 PM   #4
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^Pretty much?
Good luck.

Also, be sure to get the correct release bearing for whichever style clutch release arm/fork you wind up with or pedal set.

Some are constant contact, some release bearings are not constant contact design (up to ~1980 on the L.H.D adjustable cable clutch cars/no contact spring on those pedal boxes on the -1980 gas 4 banger cars (you can add the spring to the pedal tho...pedal box and pedal is same otherwise)) & have the silly return spring on the clutch release arm to the trans mount bracket hole.

The non-constant contact earlier release bearings don't last as long & likely volvo just wanted 1 part/design as RHD cars are self adjusting hydraulic, 700T are self adjusting constant contact hydraulic as were 260; save some money, inventory fewer parts going forward, less labor time for dealer techs to inspect/adjust things all the time for the return spring design/earlier stuff.

If your pedal box is 81+ with the spring to wind the clutch pedal toward the floor, just install the correct type constant contact bearing, if your clutch release arm is ~85+ it uses the 'clip in' style base.

Stack heights to the clutch release arm from the end of the crankshaft are the same for new clutches whether 'flat' fywheel & OEM sachs 218mm clutch kit or 'dished' style flywheel & its respective clutch kit.

I find the dished flywheel more awkward to drive in most situations and extremely heavy with the stump puller first gear, but I do like the more forgiving engagement with lighter spring pressure or pedal pressure & don't really hurry anywhere anymore.

For a DD, the dished flywheel can be nice to use lower RPMs like a tractor and crawl out of off angle driveways in hilly slippery (but not snowy) areas with a lot of weight on the car loaded heavy with the OE wagon size tires & 3.54 gears & the torquier mild cammed SOHC redblocks as the factory intended for ease of use or a lutheran swedish family with the car loaded down...

OD wiring and switches and knobs vary somewhat over the years.
The 1981+ momentary switch & relay sure is convenient/intuitive...when it works...
The OD lamp should be present in all 1973+ clusters IIRC, even 92-93 though pin numberings vary slightly as does fuse # as the years rolled on.

You probably will have to trace to the cluster but the harness is stand-alone.
The 1981+ momentary harnesses are all rot prone...not such a big deal in the cabin side and like most all 240 harnesses it's an overlay harness/its own thing.
Fishing the sub harness in the lever to repair it when abused is tricky.
Knobs wear out or crack in the case of the -'80 slider switch type (which is awkward to use and I hate and british).
Volvo sold an aluminum plug with an o-ring groove for the speedo gear output if your trans comes from a cable speedometer donor prior to ''85. Or leave it exposed to possibly get damaged or have seals to leak? IIRC the speedo cable holds the hat seal in place...so you seal it with sealant or cut/hack the perfectly good speedometer cable itself to screw it onto the cable output?
Or swap the tail housing to one without speedo gear output on the M46 from a 700 or '86 240 w/od (swap with care, that's some delicate british crap with hard to find parts that can be easily damaged/thin tempermental british aluminum castings prone to leak).

Tunnel wiring is almost all rotten by now and lazily thrown over the sharp edge of the shifter hole with the cheap 240 clip-on boot with the carpet then thrown over that as they were lazily halfass manufacturing these cars, instead of a proper trans tunnel grommet or longer higher quality wires running down the firewall like the 140s had. Refresh, find NOS updated or come up with something better or replicate, up to you if using an M46.

M47 only reverse lamp wiring and the neutral safety switch bypass loop for the auto-tragic.

Last edited by Kjets On a Plane; 11-11-2021 at 09:00 PM..
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Old 11-11-2021, 08:51 PM   #5
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You need the wiring harness for an M46 which has the wiring for the overdrive. Most of the original harnesses are rotten now so you'll want to use a known good harness.
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Old 11-11-2021, 08:59 PM   #6
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This is the first time I will be working on a clutch/transmission so I definitely still have a lot of learning to do. The good news is this is my project car and its parked in a heated garage, so I have all winter to figure it out.

It is my understanding that I would need a dished flywheel from a 2.4 car, or is there a way for me to use the flat flywheel?
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Old 11-11-2021, 09:02 PM   #7
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Yes, you need the flywheel from an LH2.4 manual car. There is a aftermarket flat flywheel drilled for LH2.4 sold by STS machining.
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Old 11-11-2021, 09:02 PM   #8
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If you can get an 8-bolt flat flywheel core, STS machining/77volvo245 or Ben kaplan (Kaplhenke racing) can drill it in the OE LH2.4/EZK pattern, or if you have an indexing head lathe or similar and want to live dangerously/try your hand at it/balance at your own risk/figure it out?
Or degree wheel and a drill press/drill fixture...uh..of some kind?

A couple suppliers have done steel flywheel runs in low volume as well, bring your own starter ring gear...
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Old 11-12-2021, 05:55 PM   #9
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Another option would be a 740 M46 with the shift linkage parts, wiring, mount bracket, and output shaft flange from a 240 M46. 1990-91 740 Turbos use the M46 with LH 2.4, so the bellhousing is already modified. You'll have the heavier duty P-type overdrive which also has no speedo drive hole.
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Old 11-13-2021, 02:56 PM   #10
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The problem with 740 M46 with the shift linkage parts is those are different on a 240, the shifter is in a little bit different closer location so NO NO NO they will not work unless you cut your junker 240 floor up with a bigger further back shift hole, then yes it will work great. Also since the 740 shift cage is different length then the 240 one so is the shift linkage, other then that yeah it would work great. Hey did you know 90 and 91 740 turbos with m46 came with Garrett T25 turbo with .64 A/R exhaust housing?? Way easier to find 240 m46 they made way more of those.....

Other thing is those 90's 740 M46's have a bigger stronger mainshaft and the hole that it goes into in the P type overdrive is bigger then the regular J type that all the 240 m46's have so they do not interchange just one more factoid to commit to memory as your looking around. Other fun fact is 16v 7 series with m46 has P/J type overdrive. I have seen one of those once, but did not buy it at pick and pull so no clue what P/J's are. I no sleep.
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Old 11-13-2021, 03:33 PM   #11
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You *do* realize that those parts can be removed and swapped out, right? Four bolts and a roll pin. I've successfully converted a 1983 242 Turbo's M46 over to 700 spec for use in an '84 764 Turbo that had a bad overdrive. Both swedishiron.com and I did that many years ago. Another friend has an '86 744Ti's M46 in his '84.5 242Ti right now. In his case, he did swap the overdrive over from his old box, since he needed the speedo drive.

Volvo didn't build multiple different M46 boxes for each engine or body type. Would've been prohibitively expensive for them to design a specific box for say an '84 245D6 versus a '79 242DL versus a '94 964Ti. All three cars have the same size M45 case. The D6 uses a different bellhousing for the VW LT35 engine, but the other two use basically the same bellhousing. One's going onto a B21FT, the other's going onto a B204FT or GT block. The only differences are the length and design of the ****er cage, the link rod, overdrive wiring (and whether or not a speedo drive is needed), the release bearing, and the output flange size and shape.

Back when your 745Ti was M46, you could've taken a '79 240 M46 and swapped it in no problem. Would've needed a freeze plug to install where the speedo drive assembly goes, but everything else from your original box would've swapped over.
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Old 11-13-2021, 06:33 PM   #12
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Old 11-15-2021, 01:26 PM   #13
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Ha, yeah for sure if you gots the parts like us, OP has auto trans.. Anyway yeah one year I put in 5 different m46 in my 550 thousand mile 90 factory m46 745 that Jim Fishers best buddie, my buddies father in law bought. Kept stripping 3rd gear. That final last third gear strip out (4 years ago?) heading to Rouge pub in NOrth plains for a gig back road downshift to pass a slow boater and zinG!.. Took out all the gears but 4th worked, so I drove it home in 4th back over Cornelius pass. AFter that I was like done with these junker m46's. What I did was weld a volvo shift ball socket on the BMW cage so I could use a volvo shifter with my Getrag. OHh I know how to make sheet work... OP might need help.

Here is your m46 740 install craaaap all in a neat plastic container...

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