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

  1. #21
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    Apr 2021
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    SF Bay Area
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    Week 13

    Bush troubles resolved.
    Didn’t get any advice this week, so I decided to go to some local machine shops. First one couldn’t do it, so I asked them where they go when they need that type of thing done. They referred me to a racing shop across town. I walked into the racing shop - a cool place with hopped up Italian sedans and tubular frames. The owner is “out racing and won’t be back for a week.” Must be nice. I had a talk with a guy welding on some aluminum heads in the back, and he referred me to a place 2 cities over that I’d been to a number of years back. Went there with my gears and brass bushes and explained my problem. The guy in the back lapped them slightly and they worked much better! Asked how much? He said it’s free. Car people can be amazing, sometimes. So many characters and good folks helping each other out. I gave the guy $20 tip.

    Back home, I assembled the main shaft again. Before I put the spring clip in, everything rotated fine. After the spring clip went on, it was tight as hell. I was really bummed. So, I took matters into my own hands. I went to the auto parts store and bought a long v-belt (alternator belt). Put it on the gear, and flushed out the gear oil with brake cleaner. I wanted no lube, just friction. I spun the gear back and forth with the v-belt. Took it all apart and looked at the “witness marks” where it was rubbing. I also noted that the spacer piece under the spring clip rotated a slight bit(it’s keyed into the main shaft, so it doesn’t go anywhere). This told me there’s clearance/end float. But the bronze bush is so tight on the main shaft as to be a press fit. I saw witness marks on the inside of the bush, the outside, and the top.

    Grinding
    Seems Series ownership requires a $10k lathe, but I don’t have one. So, I make due with 400, 600 , 1000 grit sand paper and a glass plate. Same as sharpening my woodworking chisels and planes. I took the end through the grits, and removed the witness marks. I used 600 grit to polish the parts rubbing. Just enough to remove the marks. Put it all together, and worked it again…look at the marks…polish again. I did this about 5 times. I also didn’t like that the mainshaft seemed to scratch the bush every time it went on. This is a brand new, freshly machined part..so it was bur sharp. I took some 400 grit paper cut into strips and did a “shoe shine” polish on the mainshaft, too. Mainly to just get rid of the burrs. After this, the bush fell onto the mainshaft by gravity…no rubbing. Dit the same process to the outside of the bush until all parts spun nice and left minimal witness marks. I think this is me manually “breaking in” the parts, without the risk of the gearbox heating up. Cleaned everything up, re lobbed and re assembled. Everything spins great now! Checked end float and I’m at 0.004”, right in range.

    The moral of this story is: when getting 100% néw parts that have never worked together, expect some machining artifacts. At least with Land Rovers, that is.

    One piece bush or two piece?
    A mystery to me is the one piece vs two piece bush on the mainshaft. 100% of the rebuild videos and forum posts show this part failed, and sheared into 3 pieces: the front part under 2nd gear, the collar separating 1st/2nd, and the back part under 1st gear. So, LR now superseded this with a 2 piece. Like “it’s going to break anyway, so just make it 2 pieces”. The part that confuses me is the oil flow. Oil channels and holes are only on the outside of the bush(between the bush and gears). In the 1 piece, the entire bush is held onto the mainshaft by a pin. It doesn’t spin. The spin happens on the gear. In the two piece, it’s the same, but nothing stops the piece without the collar from spinning. So, it spins on the mainshaft with no lube. This sounds like an obvious point of failure. What am I missing? I feel like I’ll be doing this gearbox again every 2-3 years, replacing this part. Is that your plan, Land Rover?

    Next problem…something else is seized.
    Finally got all my parts in, and proceeded to put the bell housing on. Earlier in the post I dry fit the layshaft and bell housing to check end float. I know it fits perfectly smooth. I put the mainshaft in now…got all the bits together the right way and put a gasket in. Tightened the bolts and layshaft screw. Everything is seized! I took it apart after 24 hours and checked everything. Reverse gear and 1st gear were engaged at the same time. It’s possible without the shifter mechanism stopping this. I scrapped all the gasket goop, confident that I resolved it this time. I put it all together again, fresh new gasket covered in goop. I tightened down all bolts. Move reverse out of the way with a long screw driver. Made sure 3rd/4rth synchro is centered, and slid 1st/2nd synchro to first(it kinda falls there by gravity on the bench, upright). Still seized!! I back off the bell housing bolts, tap the housing forward off the gasket…everything spins. Not fully, but it clicks back and forth maybe 5-10 degrees of arc. Tighten the bell housing bolts, and it’s seized again.

    I don’t know what to do. Everything dry fit fine. At least it LOOKs like a complete gearbox:
    Click image for larger version. 

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    I’m hoping it’s just my understanding of the gear shifting that’s wrong. Going to leave it another week while I learn some. Any help, much appreciated.
    ...┌───────┬──,,
    ...|______OD__|__\\_____
    ...d ..__ .........° |°... | ..__....p
    »»└/ | \────┴──┴/ | \─┘≡
    ..../..@........................@

    1973 Series 3, 109

  2. #22
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    A couple of things come to mind , have you got the end float on the Layshaft correct and am I correct that it is seized even with the gears in neutral . It may be worth fitting the main output gear onto the rear of the box and tightening its retaining nut to make sure the main shaft is pulled hard against its rear bearing. I vaguely remember when I built up a box 20 years ago that if the end float and the position of the gears on the layshaft were not 100% it jammed the constant mesh gears.
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  3. #23
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    Apr 2021
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    Thanks @RoverP480, I got excited and did what you said...tightened up the castleated nut on the back to try and seat the mainshaft better. I was avoiding this part until I had the transfer case out. Seems there are two part numbers for these tin-y "Oil thrower" things, depending on which transfer case you have...and I didn't want to smash them before I knew which one I needed. But I threw one of them on there and tightened the castleated nut(a true pain, even with the gears seized). Dang it, it's still seized. I took it all apart and I'll have a good look again this weekend.

    Good thing is I got a 10 pack of those bellhousing-to-casing paper gaskets. Ruined 2 already.

    Side question: Do you folks use gasket sealer on that gasket? Or smeared in grease and just put on? I've always used gasket sealer on American cars. But a lot of these LR paper gaskets go on dry or with just grease to hold them on while you tighten bolts elsewhere on the truck(swivel balls, hubs, etc). Gasket sealer sure complicates meshing up the pinion gear to the layshaft gear. Seems to get all over my hands while I'm reaching around in tight spaces! Also, it's a 1 shot thing, and I have to scrape it off between tries. I'm inclined to not use it...but I'd hate to leak gear oil there. When's the next time I'll have it all apart again after its installed in the truck, right?

    I have the smallest of three distance pieces on the layshaft (0.125", I think).

    I can't work out how reverse is supposed to work. It seemed jammed. Looks like it will fit either fully forward, or fully back...but won't clear 1st/2nd Synchro. I mean, the Synchro/layshaft won't turn...so maybe it would clear if the gear teeth meshed and it could slide by?? It's hard to see in there with the bellhousing on. I even got a small ear wax pen camera in there to see.

    The worrying thought I have is maybe the brand new bellhousing is machined wrong...maybe slightly askew, and pushing the shafts over a bit? It wouldn't be the first time a brand new aftermarket LR part was machined wrong. Meshing up the pinion gear and layshaft is the usual pain...but even when I do get it lined up...the last 1/4" doesn't want to go. I chalked it up to having to press in the layshaft to the bearing. But I wonder if something is just going in crooked? I have to use the bellhousing-to-case bolts to drive it down the last 1/4".

    Also, a couple times I offered up the mainshaft, I tilted it down a bit and everything just slid off the back. So maybe I don't have everything seated? Those 1st/2nd Synchro brass pieces just fall off like bracelets. It's like I have to keep all the back half together while driving it into the bearing. Gravity is not my friend. The best position to keep it all together is with the front side of the casing pointed down. That puts the mainshaft loose bits on top, held in place by gravity. But driving it in like that is near impossible. Maybe I'll use the castelated nut and an impact wrench to "draw it up", like RoverP480 said.

    Oh well. I guess I'll try again next weekend.

  4. #24
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    You say its only when you finally tighten the 4 bell housing bolts that it seizes solid. How about just fitting the bell housing without the layshaft and see if it seizes , if it does its something to do with the primary shaft and mainshaft & not the layshaft. You shouldn't have to " Pull" the two pieces together with the bolts. Something is stopping it if you do need to , and it should go together, perhaps with a tap with a mallet, but nothing else . Just an obvious point, is the reverse gear fitted the correct way round? I think you need the reverse to be forward , to get the first speed gear on the layshaft around it, to align up the roller bearing. It should, if in any one gear or neutral all spin easily. I have had in the past one of the rollers on the rear layshaft bearing tip when trying to assemble, and stop the shaft going fully into the bearing. Just a thought, will it turn freely with just the mainshaft , reverse gear and layshaft assembled into the main box, ie without the bell housing with the First motion shaft ? I am just trying to eliminate and obvious clashes .

  5. #25
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    Apr 2021
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    Week 14 Update:

    Troubleshooting...
    I had a good "stare and fiddle" at it this week. Sometimes, you gotta just look at something for a few days to sort it out. There's so many bits that could go wrong, it's hard to relay over a forum post. I also tripple-checked my part numbers. I definitely have the right parts. But I think I identified 3 points of "binding". Some are obvious. Some are subtle. Let me know what you folks think.

    Binding #1: Reverse
    This one is by design. If reverse slides to the rear of the casing, it is enguaged...and will "fight" any forward gears. Obvious, I guess. The trick is sliding reverse by the 1st & 2nd gears on the back of the mainshaft. The gears have to mesh for an instant so that reverse can slide through. My mistake was trying to grab the mainshaft and spin it to let reverse mesh with, and slide by 1st. Mainshaft was siezed(by reverse) so it wouldn't spin. But - and this is the key- the mainshaft assembly spins at 4 points(gears) along the shaft. So, you don't spun the mainshaft...you slightly spin 1st gear to create an opening for reverse to slide by. It's like a "crash" shift, with no synchronizer...just gears touching and pushing by. Once you do this, reverse slides by no problems.

    Binding #2: Oil thrower(s)
    I noticed when I tightened the Castel nut on the back of the mainshaft, it seized the mainshaft. The parts catalog shows 2 different part numbers fir a tin "oil thrower" on the back. This oil thrower goes right up against the oil seal.I have both on hand. I compared them:
    #232415
    #FRC5116
    They are matched with different transfer case numbers. I can't really tell, but FRC5116 is smaller in both diameter and thickness(see pics). I tried both. Both pinch the output gear against it and bind up the mainshaft as you tighten the Castel nut. Seems wrong, because that nut needs 50/60ft lbs? It seizes at about 20 ft lbs. Any advice here? I left it hand tight while I work.

    Binding #3: Synchro suction lock
    Now that I saw the gears spin at different rates on the mainshaft(I know, I know, obvious)...I saw that the 3rd gear synchro coupling spins much faster than the mainshaft it sits on. Here is a close up video:
    https://drive.google.com/file/d/1hBq...w?usp=drivesdk

    Well, the Synchro unit -which is brand new machined part - is so tightly machined that it creates a suction lock against that conical coupling. It's like when two pieces of really flat glass come together and if they are wet, they stick together with a suction effect. The Synchro locks itself to that coupling, almost like it's solid. I think this is how the synchronizing works...just the fluid dynamics and capillary action. Anyway, after 3 or 4 turns, it seizes solid! See video demonstrating:
    https://drive.google.com/file/d/1h8G...w?usp=drivesdk

    So, I can get it to Bind any of 3 ways without even having the bellhousing on.

    #1 is my mistake, so not to worry about.

    #2 is concerning. I don't know what to do about that. Does engine force overcome this? Should I put the mainshaft in a press and see if I can get it in a few 0.001" further, to give more room? This feels like a new endfloat measuremnt?(exterior rear?)

    #3 seems like #1...like an "as designed" thing. Should I ignore this, and assume shifting gears will resolve this?

    Mainshaft might be going in crooked. Also fresh machined, might need bedding.
    Another thing I noticed taking it apart 2 or 3 times. The mainshaft can go in crooked. I don't have a press, so I'm tapping it into the bearing with a mallot. I noticed one time I was able to put it in slightly crooked and it wobbled when spun. That's no good. I pulled it out and put it in again straight. I smashed it down with more mallet whacks...then "pulled" it in with the Castel nut. It spins true now, but it got me thinking I might still not have it seated right. I am going to go buy a Harbor Freight hydraulic press this weekend and try to press it in instead.

    Also, as with other parts on this fresh new mainshaft...I suspect the front bearing seat might be slightly over-size. Maybe just 0.001". Just enough to make sliding into the bellhousing bearing a little uncomfortable. I will take some 600 grit sandpaper strips and burnish this surface slightly to make it fit easier. As you said @RoverP480, this should just be a single tap with a mallot...not a press fit. I noticed this with other new parts from BritPart. Just a little too tight.
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    ...┌───────┬──,,
    ...|______OD__|__\\_____
    ...d ..__ .........° |°... | ..__....p
    »»└/ | \────┴──┴/ | \─┘≡
    ..../..@........................@

    1973 Series 3, 109

  6. #26
    Join Date
    Jul 2020
    Location
    UK
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    Regarding item 3 . The oil thrower should be a light press fit on the spacer bush that fits between the bearing and the drive gear and be clearance to the oil seal . I can only assume that somewhere in this assembly there is a wrong/faulty part .

  7. #27
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    Apr 2021
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    SF Bay Area
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    Hol up!

    You mean there's a spacer on the outside of the casing at the rear? Between the bearing and the oil thrower??!!

    Here's the parts manual exploded view I'm working with:

    Click image for larger version. 

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    Do you mean part 576735? The drawing shows it on the inside?!
    ...┌───────┬──,,
    ...|______OD__|__\\_____
    ...d ..__ .........° |°... | ..__....p
    »»└/ | \────┴──┴/ | \─┘≡
    ..../..@........................@

    1973 Series 3, 109

  8. #28
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    Apr 2021
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    Dag-Nabbit!

    @RoverP480, You're a genius!!

    Part number 502482!

    I missed it in the diagram. I ordered it, bit didn't pit it on the back of the output of the mainshaft. Check it out, it's easy to miss. Compare this drawing to the one in the Parts manual:
    Click image for larger version. 

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    That image doesn't even show that Effer!

    Okay, so now with that metal collar in there:
    Click image for larger version. 

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    The output gear sits nice and far away from the oil thrower! Tightening down on the castel/flange nut seats the gear against the collar, which presses the inside(rolley) part of the bearing! No longer pressing against the oil thrower! Ha-zah! You got it, @RoverP480! That was it for #2.

    Now the insides spin nice, no binding. Got that flange nut tightened to 85 ft lbs. Still spins nice. One more problem off the list.

    Something is still up with the front.

    I got the machinist calipers on layshaft end and the inside of bearing. There is about a 0.03" discrepancy in the bearing inside and the layshaft end. Weird thing is I've had the layshaft thru that bearing before. But now, it won't go through full to the end. Gonna investigate there.

    Another possibility is the mainshaft end. Going to get a dial indicator on there and see if somehow it's forward too far. Seems likely.

    Again, the gearbox spins nice now. Only tightening the last 1/4 to 1/8" siezes the box. It's like the Pinion might be pressing down on the 3rd/4rth sunchro...driving it down on it's race on the mainshaft.

    Will figure this out sooner or later. I've got the bastard on the ropes!!!
    ...┌───────┬──,,
    ...|______OD__|__\\_____
    ...d ..__ .........° |°... | ..__....p
    »»└/ | \────┴──┴/ | \─┘≡
    ..../..@........................@

    1973 Series 3, 109

  9. #29
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    UK
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    The oil thrower should be up against the gear end of the collar not the oil seal , see attached early S2 cross section , but in essence its the same as yours. I am sure you will resolve it all.
    Click image for larger version. 

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  10. #30
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    Also my extract from my S3 Book.Click image for larger version. 

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    Last edited by roverp480; 09-04-2022 at 03:15 AM.

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