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Thread: 1971 Series 2a Ex Army Gearbox Question

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    1971 Series 2a Ex Army Gearbox Question

    Hi all,


    I have been a watcher on here for a while and figured it was time to get involved. I have picked up a ex army s2a that's been hidden on a shed/farm for a long time. It is on the register being deposed in 1990 and pretty well sat since then. Incredibly one 20 cent piece of rust on the firewall and the rest solid. I will do a picture post when I get a moment on the start and build.

    Quick question regarding the gearbox. Car runs and drives well in general as pre pull down we tested it all out (after changing fluids). When we tested it out we has a continual 'thump thump thump' which matched rotation on first and reverse only. After looking around online it's clear that first and reverse share a gear on the lay shaft so it makes sense. The main answers seem to be that there would be a missing/broken tooth on the shared cog on the lay for first.

    I have attached a picture of the lay first gear. As you can see it does look worn and there is some very fine metal shavings on it. The rest of the cogs are like new, super sharp and no missing teeth.

    The question is would this lay first gear being worn down be enough to cause the rotational thump thump thump when under load? I'm happy to replace it anyway while its open but I would love to answer if this will fix the noise or not.

    To confirm this is only in first or reverse. 2/3/4th all smooth and 1/R shift fine apart from this noise when going.


    Any input would be greatly appreciated!


    Thanks
    Attached Images Attached Images

  2. #2
    JDNSW's Avatar
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    First and reverse are neither synchromesh nor constant mesh, so the actual gears slide into each other as the gear is engaged. This, plus hamfisted drivers explains the wear on this gear.

    And it does not take much of a mark on a gear tooth to give the symptom you mention. On the other hand if the layshaft gear is being replaced, you would be well advised to replace the other two gears as well, since they will be undoubtedly worn too. But it is very unlikely that the sort of damage you are talking about will result in failure, so it is up to you whether you replace them.
    John

    JDNSW
    1986 110 County 3.9 diesel
    1970 2a 109 2.25 petrol

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    Ive also seen this caused by a bearing failure on the back of the layshaft. one roller with a flatspot in it will make a thump as it runs past the position directly opposite the radial thrust of the gears.
    Dave

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    Thank you for the replies...great help!

    I have ordered the parts to replace both as suggested as its obviously the time to do it all with bearings etc.

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    Jeez, I'm trying to rack my (old) brain and think back to very early 1970's when I did my 1969 Ser 2a box.

    It had sheared the lay gear beside the straight cut teeth which was apparently quite common. The updated (Genuine LR) lay gear had been shot peened during manufacture around the end near 1st gear teeth presumably in order to remove 'stress' in the material.

    But something in my brain reminds me I had to quote Suffix number on gearbox in order to get correct matching 1st and reverse gears otherwise the straight cut teeth were mismatched and your noise would happen.
    Maybe your box has been apart before and wrong reverse gear fitted?

    Or am I imagining that situation??
    Definitely was the case with Morris/Austin Mini's gearbox's of early/middle 60's period (I did scores of 'em!) so maybe am getting confused!!

    PS: Just called my mate who had LR's with me at same period. Yes, he agrees, common problem with mismatched gears, we think the problem was with reverse gear and definitely necessary to quote Suffix number. The photo of your lay gear looks like it is an early type that was not shot peened so you should replace that for sure.
    Before: Ser 2a LWB, Ser 3 S/W, 1979 RR 2 door, 1981 LR Stage 1 V8 (new), 1985 LR 110 V8 County (new), 2009 RRS TDV8
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    You are not imagining it - the gear ratios changed several times, so you need to quote the box suffix letter. (transfer high range remained unchanged and fourth is direct in all boxes, but low range was changed when first and reverse were, so as to maintain roughly constant overall ratio in 1st/low. Which allows for some creativity in overall low range ratio by mix and match!)
    John

    JDNSW
    1986 110 County 3.9 diesel
    1970 2a 109 2.25 petrol

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    Thanks for the extra information...but now i am a bit confused.

    Can i just confirm that shot peening is the rounding on the teeth? if i understand correctly you are saying i should not have the rounded teeth.

    I did check and my lay 1st has 15th teeth rather than 14 in the later model. I also have checked my suffix and for the life of me i cant find a letter. i have attached pictures of the numbers on the box in all locations.

    i have also attached a reverse gear picture incase that helps (ignore my bearing surround removal tool i knocked up!)

    Can anyone confirm any further details off the pictures? If I'm understanding the previous comments is there a chance that i should have the the 14 teeth first lay? The 14 teeth first gear lay actually looks to matched my reverse...

    Sorry if i have completely mixed this up...

    ***Edit - see below post***

    lrIMG_2125.jpglrIMG_2109.jpglrIMG_2127.jpglrIMG_2129.jpg

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    Just as an additional thought...

    Would it be wise for me to count how many teeth are on the current reverse gear? It will either be 17/20 or 16/19.

    Can anyone confirm that if i can clarify which reverse is in there then i can correctly select my lay 1st (14/15 teeth) incase it is currently mismatched?

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    The last picture is the gearbox number - the others are casting IDs. I thought they all had suffix letters, but either they didn't or it failed to get marked.

    Gears that are mismatched will not engage, so the gears already in the box fitted must match.

    Shot peening is surface treatment and will not round the teeth of the gears. The edges that move into mesh are deliberattely rounded, as otherwise you can't get it into gear if they overlap and the gears are not moving relative to each other.
    John

    JDNSW
    1986 110 County 3.9 diesel
    1970 2a 109 2.25 petrol

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    Quote Originally Posted by AndrewSeries2a View Post
    Hi all,


    I have been a watcher on here for a while and figured it was time to get involved. I have picked up a ex army s2a that's been hidden on a shed/farm for a long time. It is on the register being deposed in 1990 and pretty well sat since then. Incredibly one 20 cent piece of rust on the firewall and the rest solid. I will do a picture post when I get a moment on the start and build.

    Quick question regarding the gearbox. Car runs and drives well in general as pre pull down we tested it all out (after changing fluids). When we tested it out we has a continual 'thump thump thump' which matched rotation on first and reverse only. After looking around online it's clear that first and reverse share a gear on the lay shaft so it makes sense. The main answers seem to be that there would be a missing/broken tooth on the shared cog on the lay for first.

    I have attached a picture of the lay first gear. As you can see it does look worn and there is some very fine metal shavings on it. The rest of the cogs are like new, super sharp and no missing teeth.

    The question is would this lay first gear being worn down be enough to cause the rotational thump thump thump when under load? I'm happy to replace it anyway while its open but I would love to answer if this will fix the noise or not.

    To confirm this is only in first or reverse. 2/3/4th all smooth and 1/R shift fine apart from this noise when going.


    Any input would be greatly appreciated!


    Thanks
    You may find some information here. Reverse Gear Suffix A & B S1&S2 | Online Gearbox Parts Shop
    .W.

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