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M46 gearbox stiff in neutral

OK, I think I know the answer to this...I've just put new gaskets, seals, etc in the M46 gearbox going into my yellow 245. When I pulled the bellhousing off the input shaft came partly out. When I re-assembled everything I noticed that when I have the gearbox in neutral and turn the input shaft clockwise by hand, it rotates fairly freely for about 1/2 turn then seems to get stiff and the output shaft turns. If I hold the output shaft it seems like quite a bit of friction (ie hard to turn) the input shaft. So, I was hoping this was just because I hadn't filled it with oil yet, but same thing after I filled the oil. I'm assuming the only thing it can be is the bearing in the end of the input shaft where it goes into the output shaft, or something dicky with the first set of synchros. I know the synchro set has those spring clips and 3 small bits that sort of spring load the synchro slider. Wonder if the spring clip came off and is jamming between the input shaft, synchro ring and output shaft? I couldn't see anything amiss...thoughts? I'm certain now I have to at a minimum pull the bellhousing back off and pull the input shaft part way out to see if I can see anything going on there. I don't think I can pull the input shaft all the way out IIRC as I think it fouls the lower shaft. Or, I could just put the whole thing in the car and run it? Hmm.



  • 1971_144GL1971_144GL @1971_144GL Launceston, Tasmania

    Hello Greg, there is a set of shims that load the bearing and go between the gearbox and the bell housing. Did you put exactly the same ones in, and was th new gasket exactly the same thickness. If you changed the bearing, then the shims may not be correct anyway.

    I would slightly back off the bolts between the bell housing and the box just a touch and see if it frees up. Hopefully it's as simple as that? Then find or make some correct shimms.

    I've had the slider springs come out inadvertently during assembly. The gearbox goes bang once a slider gets free and ends up breaking gear teeth. I always tripple check after that learning experience.

    Good luck with it.

  • carnut222Greg S @carnut222 Daylesford VIC

    Thanks for the feedback. I used the same shims, however it is a new gasket. I guess the gasket could be thinner resulting in the bearing being too tight? It seems odd that it seems to turn freely counterclockwise but not clockwise? I realise it only ever turns clockwise (due to that's the way the engine rotates)...but you'd think if a bearing were too tight it would be tight in both directions? Hmm...but yes, I'll try backing off the bellhousing bolts a fraction and see if that makes any difference. Very frustrating to say the least! :)

  • carnut222Greg S @carnut222 Daylesford VIC

    OK, update. I'll be F**Ked. I loosened the bellhousing to relieve pre-load on the bearing - no change. Removed top cover, removed bellhousing and pulled input shaft out about 10 mm (as far as it will go). Everything looks OK with the 3x synchro dogs and synchro ring notches were aligned with the dogs. I do have a feeling it's something funky with that first synchro set on the output shaft (4th gear?) So, I put it back together and will just see if it explodes when I drive the car. On a side note, every one of the 4 trans top cover OD interrupt switches I have doesn't seem to have continuity in either state (plunger pushed or released)...WTF? I'm sure the OD worked on the 740T M46 I have...anyway, ordered 3 new ones. Getting really sick of it now! :(

  • carnut222Greg S @carnut222 Daylesford VIC

    OK, I've had a look at a couple other of my M46 transmissions. Only thing I can think of is the needle bearing on the input shaft (where it interfaces with the output shaft) must somehow be damaged, dry or ??? Not sure what would/could cause it as this box worked OK prior to me pulling it all apart. Thoughts? I'm still trying to decide whether to run with it an see, or totally dismantle and inspect. Not happy Jan!

  • jamesincJames @jamesinc Oz Volvo Ice Fortress

    When I rebuilt my M46 everything moved freely after being reassembled. I'd take the input shaft out and have a close look at the synchro and bearings and reinstall carefully.

    The reverse switches sometimes they need a good spray with brake cleaner to work properly.

  • carnut222Greg S @carnut222 Daylesford VIC

    Hi James. Thanks for feedback. I'm struggling with it because it means total disassembly of the transmission, or at least nearly so, just to get the input shaft out...OD off & rear extension housing off in order to drop the secondary shaft as that's required to remove the input shaft. I don't think it can be done by just removing the bellhousing as the secondary shaft won't drop down enough by just removing the front bearing race on the secondary shaft??? Just going by instructions in the Greenbook anyway.

    Re: the switch, it's not the reverse switch it's the OD "inhibitor" (4th gear) switch. I tried some electrical cleaner but still no continuity between switch body and the single terminal whether the plunger is depressed or not. Hmm. I still find it odd that I have a 4 out of 4 failure rate on the switches I have, unless I forgot how to do a continuity test on a multimeter! ;)

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