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Series 3 gearbox rebuil

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Hi guys,

I'm new to the forum so hello everyone.

Im rebuilding an early series 3 gearbox and have a question to ask. The gearbox has a single bush for second/third gear but the replacement I've been sent is two separate bushes. Only one bush can be "pegged" to the mainshaft. Do you think I should get a replacement single bush or use the two separate bushes? 

Thank you in advance.

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Both should be pegged, but one has a much smaller peg which may have sheared, hiding the hole in the shaft.  The single piece bushes are prone to cracking in the middle, so two piece bushes are generally considered better.

 

Welcome to the forum.

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Hi Snagger and thank you for replying.

I'll have another look at the mainshaft when I get in the workshop. I bought a new mainshaft as the peg had sheared in the old one and worn the shaft. The bush itself was intact. I'll have to check if there's a another hole for the other bush. 

Thanks again :-)

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Hi, I've checked the new mainshaft this morning. There's one small hole for the thrust washer peg and one larger hole for the bush peg. Does that mean that if I use two bushes, that one of them would be unpegged? There's definitely no hole for the second bush to be pegged. Incidentally the parts book shows two bushes but only one peg. The replacement mainshaft is a genuine part also. 

 

Any thoughts?

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No, both should be pegged, regardless of single or twin bush type.  You don't want the bushes spinning on the shaft.

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Thank you Snagger,

I think I'll have to drill the mainshaft and buy an extra peg. Thankfully I've got a drillpress and a set of cobalt drills. A bit annoying but I'd rather take my time and get it right.

Thanks again

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Don't do that.  There should be one thin peg and one large.  The thin peg is more of a pin...

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No, one is stopped by the fat peg and the other by that tiny pin.

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The tiny pin prevents the thrust washer from turning. The larger pin stops the first bush (2nd gear) turning. There's nothing to prevent the other bush (3rd gear) from turning on the mainshaft. 

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Now you say it...  Faulty memory; I haven't been able to pick up a spanner or manual in two years, and haven't had a gear box open in about four!  In which case, don't worry about it.  The torque on the rear end nut inside the transfer box, clamps the tow bushes, the 1st/2nd synchro hub, 1st bush and thrust washers together to prevent turning.  The gear will turn on the bush far more easily than the bush on the shaft, and that's what matters.

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My fault for poor memory!  I'm just glad we got there before any harm was done or more money spent!

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Just done my mainshaft, same thing occurred to me, nothing pegs the plain bush. Doing up the main shaft nut has no influence on the bushes as the end float is set by thrust washers, I couldn't see anything in the parts book to peg this bush so I assume its free to rotate.

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On 19/03/2017 at 9:45 AM, citizen kane said:

Just done my mainshaft, same thing occurred to me, nothing pegs the plain bush. Doing up the main shaft nut has no influence on the bushes as the end float is set by thrust washers, I couldn't see anything in the parts book to peg this bush so I assume its free to rotate.

The bushes should be ever so slightly longer than the gears that sit on them, so the bushes are pinched by the preload on the rear nut, but not the gears.

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Not on a Series 3 gearbox. As you say,  the length of the 2nd and 3rd gear bushes are adjusted to give the required end float for each gear. Once these bushes are assembled they are retained by the wretched C clip and the overall end float of the assembled bushes is adjusted via a combination of the 7 available sizes of thrust washers. The main shaft nut reacts on the 1st, 2nd  syncro hub and the splined 1st gear bush locking that assembly in place, it dosnt influence the float on the 2nd and 3rd gear bushes. 

Edited by citizen kane
Wrong numbers

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Damn.  I must be confusing it with the first gear bush, then.  I do remember having to adjust the gear end floats by sanding the ends of the bushes on a very flat surface and I remember seeing spline imprints on the end of a bush from the main shaft nut being tightened.

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Thank you both. I watched a few online rebuilds but didn't notice any mention of pegging the bushes. All attention was on the end float of the gears. Cheers guys 

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Glad to be of help, though very limited it was, and sorry for the confusion I created.  Don't worry about the pegs, anyway - as we discussed, the two piece bush is the later and better part and needs no shaft modification.  lick on the photo in this link to see the not-uncommon failure of the single piece bush, seemingly caused by tiny amounts of shaft flex and specifically what the two piece bush was made to prevent. http://www.nickslandrover.co.uk/gear-box-failure/

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