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Thread: popping out of 3rd gear

  1. #1
    Join Date
    Jun 2008
    Location
    Southern California
    Posts
    78

    Default popping out of 3rd gear

    My S2a gearbox (C suffix) was recently rebuilt and is now popping out of 3rd gear...

    The gearbox suffered a broken mainshaft. I removed it (not a joyful task) and found a highly-recommended (though not Land-Rover specific since there's not one of those around here) manual gearbox shop. They tore it down and built it back up. I gave them the green bible and the Haynes manual for guidance and found them the parts they said it needed: the mainshaft and the needle bearing. I also replaced a missing synchro detent spring clip and the 3rd gear set since there was one very small chip in one tooth, but now was of course the time to do that and anything else that was amiss. They saw nothing else out of place.

    I put it all back in (also not a joyful task) and drove for about 35 miles. All seemed fine. Then, for the first time ever and to my surprise, it popped out of 3rd gear when driving twice over the course of several miles. To remedy this I replaced the 3/4 shift fork detent ball spring with a new reverse detent spring (since they are thicker/stronger), which I shimmed a bit too since it's also shorter. This put more pressure on the 3/4 shift fork, which I thought would do the job. At the same time I removed the overdrive to look at the mainshaft nut, which seemed to me to be tight. I don't have special tool for this castleated nut so I did not loosen or tighten it but, again, it seemed good. The only thing I noticed there was that the bearing that sits within the forward side of the overdrive had some forward to back play, but this merely sits under the overdrive and would not seem to affect anything upstream...the overdrive is fine.

    I drove it a short bit after this and it seemed to have solved the problem...yay...but apparently that's not the case as it's again popping out of 3rd gear when driving now...damn.

    I've heard that popping out of 3rd might be due to the shift fork spring being too loose, a loose mainshaft nut, or worn 3/4 synchros but all of these seem to check out ok -- the spring is new (and thicker and tighter now), the nut seemed ok, and the shop mentioned nothing about the synchros being worn (nor did they look worn when I saw them through the inspection hole before the rebuild). Also, it never popped out of gear before the rebuild or even after many miles thereafter, as mentioned.

    Ideas? Next steps? Thanks in advance to all of you who are gearbox-knowledgeable for any ideas...

  2. #2
    Join Date
    Oct 2011
    Location
    Mountains of Western Pennsy.
    Posts
    546

    Default

    The only thing that comes to mind is a synchro problem. Maybe an assembly oops? Worn gear lever?

    '99 Disco II
    '95 R.R.C. Lwb (Gone...)
    '76 Series III Hybrid 109
    '70 Rover 3500S (Gone...)

  3. #3
    Join Date
    Sep 2014
    Location
    ...dodging tumbleweeds...
    Posts
    4

    Default

    I rebuilt a SIII box nearly 20 years ago and had the same result. I knew what the problem was but just lived with it until last year when I pulled it out for an Ashcroft T-case mod. I'm not positive this is your problem but here is what I found.

    The 3/4 sync assembly (brass spool looking thing) is NOT symmetrical. After the fact I read and re-read my manual to see if I missed something but my book said not a word about putting this part in the right way. If you look at the inside splines, where is slides onto the shaft you will notice that one side has a machined recess to accommodate a spring clip that is on the shaft. If this part is put in backwards the box will work fine but 3rd gear will not fully engage. When coasting or nearly neutral power and in 3rd, it will pop out of gear.

    You can check by taking the top cover off and using a piece of wire in the 3/4 sync assy. spline to see which side the cutout is on.

    Good luck.

  4. #4
    Join Date
    Jun 2008
    Location
    Southern California
    Posts
    78

    Default

    To close the loop on this one, after some more driving (100 miles or so) 3rd has stopped popping out of gear, so it would appear that the new gears needed some time to seat and be happy. Happy conclusion.

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