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Thread: Looking for a Series 3 gearbox, LT76, preferably a later one

  1. #11
    Join Date
    Apr 2021
    Location
    SF Bay Area
    Posts
    204

    Default

    Week #3 [ Update ]
    So I got my first round of parts for the outer gearbox in. Looks like they all fit. In classic Land Rover fashion, everything just takes 2 weeks to get to me by mail. But, the good news is most of these parts are still available new, with the exception of the gearbox casing. FYI.

    This week, I went diving into the parts manual to look at what parts I need, and if I can benefit from any "upgrades" over the years. My thinking is : if I have to buy 100% new parts (I'm building a gearbox from scratch) then I don't have to worry about re-use. I can get whatever is needed to upgrade to the better part. I found some interesting stuff below...

    Suffix part interchange - Layshaft
    I've attached the pages from the Series 3 Official Parts Catalog on the Layshaft, for reference.
    Click image for larger version. 

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    I'd seen in James Taylor's book above a mention that between the Suffix "A" and "B" Land Rover had beefed up the Reverse gear mechanism. Looking through the parts catalog, it shows 2 diagrams...but keen eyed readers will see that most of the part numbers are the same. So, that tells me that the only change in the Layshaft assemblies is the Reverse shaft. Looking at the next page, there is a "Reverse Modification Kit" that seems to fix the Suffix "A" issues, and upgrade the weakness. The difference in parts comes down to they replaced a brass bush with a bearing. This made for a new reverse shaft and the reverse gear(where the bearing/bush fits into). Looks like the "Kit" just gives you the "B" shaft and reverse gear. The layshafts also are matched...so if you want the upgrade you need the "B" layshaft. All the bits in front of the layshaft are interchangeable between A + B. And the back bearing is the same. So, that tells me that the Layshafts are interchangeable in the case (A & B). So I'm going to order the "B" Layshaft and Reverse shaft, and basically have a "Reverse Modified Kit Suffix A"...or essentially a Suffix B innards. Seems that C kits are the same in this respect (the Layshaft), so this info applies to them, too. Only when you get to "D" suffixes do you get different part numbers, and I suspect that's more to do with the electroplating on the gear surfaces than dimensional differences.

    I made up a parts order, and added it to the spreadsheet, here:
    https://docs.google.com/spreadsheets...it?usp=sharing

    I'll let you al know how it goes, and appreciate any insights I missed.
    Attached Images Attached Images  
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    1973 Series 3, 109

  2. #12
    Join Date
    Apr 2021
    Location
    SF Bay Area
    Posts
    204

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    Week 4(?)
    I'm loosing track of time as I'm mostly just waiting for parts and paychecks to buy said parts. I DID get to do a bit more research and order most of the internals this week. I've updated the spreadsheet link above to include all Mainshaft components and gearing.

    Mainshaft interchange
    The manual shows interchange for A+B+C Suffixes for these components. So it was easy to order the right parts. Honestly, I don't know what the difference between a "B" and "C" Suffix LT76. On paper, they look to have the same parts. I'm building a "B" internals in an "A" case.

    1 Ton
    There are a few parts at the back of the Mainshaft that differ in the "109 1 ton", which threw me for a loop. I thought maybe I wanted a 1 ton gearbox internals thinking they might be "heavy duty"(Good!). Which is misleading. After some research, it turns out the gearing is lower on 1st gear in the 1 Ton(military vehicle). Some folks saying that if you fit the 1 Ton gears, you can't benefit from an overdrive, later. Well, that's an upgrade I hope to make, so I went with the standard LT76 parts. So, that's what's listed in the spreadsheet.

    I ordered everything Monday, so now I wait. The only thing not available was one distance piece in an odd size. I guess there is exact endplay that is achieved by putting in the correct size distance piece and measuring with a dial Guage when fully assembled. If it's not in range, you take it apart and put the corresponding distance piece in(larger or smaller). Well, I can't find the middle one available anymore. But I've seen people just use a larger one and rub it on a flat surface with sandpaper to remove a few 0.001". So that's what I'll do. We'll see.

    I'll post some pics when all the parts come in and I do some final assembly. All-in-all, I've spent about $2200 so far on all new parts. The original quote was for $3600 for a "rebuild"(who knows what parts re-used?). So, not cheap, but still cheaper than buying from someone already done, by about 30%.
    ...┌───────┬──,,
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    ...d ..__ ......... |... | ..__....p
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    ..../..@........................@

    1973 Series 3, 109

  3. #13
    Join Date
    Jul 2020
    Location
    UK
    Posts
    180

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    I am glad you didn't go with the 1 Ton parts as the mainshaft is different, to fit onto a modified transfer set of gears and they are not interchangeable . The 1 ton and Forward Control transfer box has dog clutches on both High & Low gears making it easier to engage low range on the move & it is sometimes refereed to as the "Easy Change" transfer . The standard box has dog clutch on high range but low is engaged by actually moving the gears into mesh. often referred as a crash change . The gear on the mainshaft sticks out further into the transfer box and thus an Overdrive will not fit as you have already ascertained.
    I fell into this trap when I purchased a centre power take off for my 88" S2A and it didn't fit as it was off a 1 Ton.

  4. #14
    Join Date
    Apr 2021
    Location
    SF Bay Area
    Posts
    204

    Default

    It's been a couple weeks since an update, so I thought I'd post:

    Week 6(?) Update:
    My parts supplier emailed me two weeks ago to say some parts were on back-order. It was the synchos I ordered. I ordered Genuine Land Rover synchros. A bit more expensive, but I wanted Genuine for Two reasons:

    1) I saw a Britanica Restorations video on YouTube where the guy showed he got some aftermarket synchro and the teeth were machined wrong. I'm not inclined to deal with that nonsense, so I paid the extra for "Genuine" Land Rover synchros.

    2) My 3rd/4rth gears grind getting in. It's the whole reason I'm rebuilding this gearbox(at great expense in time and money). So...the hell am I going to get a cheap synchro again?

    Anyways. A word of caution, the synchros seem to be kinda rare. Or, at least they don't keep them 'in stock' and usually drop ship them from Land Rover. So, beware of unexpected delays.

    So, I'm shuffling around the garage waiting for parts for another week...
    ...┌───────┬──,,
    ...|______OD__|__\\_____
    ...d ..__ ......... |... | ..__....p
    └/ | \────┴──┴/ | \─┘≡
    ..../..@........................@

    1973 Series 3, 109

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