Series III LT76 Gearbox Rebuild?? - Defender Source
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  #1  
Old June 13th, 2015, 01:26 PM
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Steve LaHue
1973 LR S3 88
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Question Series III LT76 Gearbox Rebuild??

I am getting ready to take apart and rebuild the gearbox in my 73 Siii 88. I read the following about the reverse gear train. "cross drill the gear along the sliding grove to allow more oil to get in the needle bearing". Not having ever taken apart a gearbox, I am not sure what this means nor do I know if it is a good idea.
Any explanation and thoughts would be appreciated.
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  #2  
Old June 14th, 2015, 11:55 PM
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Don
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Reverse gear issues.

Reverse gears were a problem on early SIII boxes (esp suffix A) due to wear. For suffix A, the reverse gear simply rides on a bushing/shaft (561954 & 591527). The suffix B and later boxes used the "improved" caged needle bearing assembly sold in kit form (FRC1810). You will notice that reverse is a very small gear which multiplies torque and prevents the vehicle from moving too fast in reverse. Reverse gear is simply an "idler gear" which changes the rotation of the transmission power flow. Presumably, they want you to make the hole bigger to improve lubrication for the bearing.

While you have the box apart, it is wise to replace all seals, gaskets and bearings. Take a look at your 1st/2nd gear synchronizer assemblies. They get a lot of wear. Beware the 3 crazy springs with ball - they fly everywhere if you are not careful! Pay careful attention to the 3rd/4th synchronizer assemblies as well. Examine the brass contact area for wear. There should be visible raised ribs. If they are not present, the synchro's are worn. The ribs displace oil on the cones during shifting and ensure the shafts are spinning as the same speed for easy shifting. Check all gears for pitting, chips or galling. They should have a nice consistent wear pattern. Transmissions are precision machines, so make sure everything is scrupulously clean prior to reassembly. Also make sure to check all tolerances to ensure that they are within factory specification. Take your time and don't get frustrated!

------ Follow up post added June 14th, 2015 10:00 PM ------

Unless your reverse gear is very noisy and/or missing teeth, don't mess with it! If the assembly is wobbly and showing excessive wear, that is another story. But I wouldn't drill any holes in your existing gear if it's working OK.
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Old June 15th, 2015, 08:46 AM
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I just want to add that the thing is pretty simple, I was leery going into mine last year but it's very obvious how everything operates and should go together. You might have plenty of experience with this stuff, if not like me I wouldn't be concerned. Green bible covers it all.
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Old June 15th, 2015, 09:31 PM
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Don
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I should add that once you get into the gearbox and transfer case, you will find mysterious fasteners known as BSF or British Standard Whitworth. They are not metric or SAE. You will need different sockets and spanners to do the job properly and set the fasteners to the proper torque settings during rebuild. The Rover Company is also very fond of "castellated" or spindle nuts - you will find three different sizes in the gearbox. Some can be loosened with a drift pin or cold chisel. There is, however, a proper assortment of tools for the job. Those tools are critical for setting the torque on the mainshaft and layshaft spindle nuts.
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Old June 15th, 2015, 10:39 PM
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Steve LaHue
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Thanks Again

Ah thanks again,
When I was a kid we had English Austins, 2- A40 and 1-A50 and I had a Sunbeam. So I have the Whitworth Sockets and if memory serves SAE such as 19/32 and one other */32 were really really close and pretty common on the Austins. Thanks for the warning about the castle nuts. The odd nut at the back of the transmission too.
But I do appreciate the warning if one did not know about Whitworth, WTF and other words would soon follow the rounded off nuts.
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