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

  1. #31
    Join Date
    Apr 2021
    Location
    SF Bay Area
    Posts
    221

    Default

    Thank you! I DID have to drive that sucker on there to get it to seat against the oil seal like that. I'll take it off and put a new one on. Luckily, I have a couple new ones. You know, it's much harder when you didn't take apart the old one. I've been building it up on the bench out of new pieces. I usually snap some pics with my cell phone as I take something apart, to double check when putting it back together. With this one, I'm going in cold.

    Further inveatigations
    I took it apart again. Tried to fit pieces together individually:

    * Layshaft fits nice in Bellhousing bearing. Two light taps with a rubber mallot sinks it home all the way.

    * I have a pic earlier in this thread where I checked the layshaft in the case and bellhousing for endfloat. Fit like a glove, no problems.

    I can eliminate the layshaft.

    * The mainshaft spins nice with the main casing and bellhousing about 1/8" apart. As soon as I try to seat the two, it jambs shut. The jambing happens because the Synchro comes down hard against 3rd. I can get it to bind if I drive the Synchro back. Tap it lightly to unstick it...and I'm free again.

    * Removed the Synchro and roller bearing collar. Removed the layshaft. Put bellhousing on. It fits great. Slides flush on the gasket surface.

    * Add Synchro. Re-assemble. It won't won't go flush, and tightens the Synchro against 3rd.

    * Removed the Synchro, and just put the roller bearing on (no synchro) and re-assbled. Again, it won't sit flush.

    So, either the mainshaft is too far forward...the pinion is too far back...or the Synchro and/or roller bearing are too fat???

    * What are the chances 2 separate parts are wrong(Synchro and roller bearing)??

    * Mainshaft seems to have NO endfloat adjustment in the case(that I can tell) There are lots of endfloat adjustments for the gears that ride on it. But once you get that spring clip on...that's it. That measurement is fixed. There is a distance piece in the back(#576735)...but it doesn't come in different sizes, like the others. Just one part number...one size. So it just has a fixed length, when driven into the bearing in the main case.

    * Pinion has some endfloat adjustment. It's just mostly to get the little spacer between the circlip and the bearing to just...bearly...spin. There might be some adjustment here, but it feels perfect. Just rubbing, but able to spin.

    * Incorrect part numbers are out of the question here. Pinion, mainshaft and 3rd/4rth Synchro are all the same for Suffix A+B+C. There literally is no other part number. Different drawings, but the part number is the same. I didn't order Suffix D (ECM plated) parts...so it's literally impossible I have the wrong parts. But, could be bad machining(not the first time).

    I was thinking of rubbing down the distance piece (#576735) on the back of the mainshaft. I could adjust the fit. But I'd be guessing. I wish I had detailed measuremnts..then I could tell which part is out. Can anyone measure theirs? If you have a disassembled gearbox laying around?

    1) Pinion gear end-to-gasket surface distance.
    2) Lengrh of 3rd/4rt Synchro.Brass to brass.
    3) Length of roller bearing.
    4) Depth of the mainshaft, from gasket surface.
    ...┌───────┬──,,
    ...|______OD__|__\\_____
    ...d ..__ ......... |... | ..__....p
    └/ | \────┴──┴/ | \─┘≡
    ..../..@........................@

    1973 Series 3, 109

  2. #32
    Join Date
    Jul 2020
    Location
    UK
    Posts
    214

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    Given there is a 1/8" gap you are trying to close, it seems to me that is a lot more than a tolerance stack . Some part or parts are either incorrect or not seating properly. Even though you have ordered the correct parts , there is still the possibility one or more are wrong. Looking at the picture you posted showing the oil thrower, the mainshaft nut 217477 doesn't look to be screwed on far enough, I believe there should be a couple of threads exposed when tight, is something not seating properly along the shaft? Given your statement "* Removed the Synchro, and just put the roller bearing on (no synchro) and re-assbled. Again, it won't sit flush." , is the roller bearing you refer the one into the 1st motion shaft or did you mean the main ball race at the rear of the mainshaft?
    I have just come across video clips which may be of help eg https://www.youtube.com/watch?v=S-CyOvRJQo8
    Last edited by roverp480; 09-05-2022 at 08:58 AM.

  3. #33
    Join Date
    Apr 2021
    Location
    SF Bay Area
    Posts
    221

    Default

    Geoffrey Corker videos are great. Very funny guy. I've seen these.

    The roller bearing I was talking about was the little plastic one that sits on the front of the mainshaft, and is cupped inside the Pinion gear. Part#6397.

    I'll try a hydraulic press to seat the mainshaft. That HAS to be it. Even though I drove that sucker in with a sledge hammer and wood block(to protect the shaft). Maybe get some PlastiGuage putty to see if I'm getting flush seat down in there where I can't see.
    ...┌───────┬──,,
    ...|______OD__|__\\_____
    ...d ..__ ......... |... | ..__....p
    └/ | \────┴──┴/ | \─┘≡
    ..../..@........................@

    1973 Series 3, 109

  4. #34
    Join Date
    Jul 2020
    Location
    UK
    Posts
    214

    Default

    I have just been following a post on the LR S2 Club forum regarding 3rd/4th synchromesh parts. The post is from a well respected member who has rebuilt many gearbox and used to work for Land Rover. https://www.series2club.co.uk/new_fo...topicseen.html
    " In answer to Craggle's question about how to spot a dodgy one from a genuine one, the answer is not easily! One area to look is how well the brass rings sit on their respective gears. If they don't sit comfortably against the brass ring, it means they can't engage properly in the teeth. That sometimes manifests itself as an extremely tight box which moves better when you slacken off the bell housing.
    On a genuine new synchro, the brass ring grooves feel smooth, but the ridges are clear and obvious. On a copy ones, the grooves can feel sharp and almost abrasive as if they haven't ben finished properly."

    Just thought it may have a bearing on your problem

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