Some of the inner workings of the 5GTT's JB3 Gearbox.
Input shaft and output shaft.
The input shaft:
• Is the one that goes into the clutch centre plate splines and is driven by the engine.
• The cogs are a fixed part of the shaft so can't be removed.
The output shaft:
• The gear cogs are free wheeling and not joined to the output shaft though are all permanently engaged with the cogs of the input shaft. In other words, the cogs are spinning all the time and, due to the different cog sizes, at different speeds.
• The selector collars are internally splined to the output shaft and turn with it all the time at it's speed. As they are moved side to side their inner grooves engage with a ring of studs known as Dog Teeth on one side of each gear cog. This transfers the drive from one shaft to the other. These interlocking teeth are an area that wears and might cause the slipping out of gear that many 5GTT owners are familiar with. When engaged, they couple the engine to the wheels and all your impressive torque is going through just them so how do they remain attached to the gear cog? No-one knows!
• In between each is a toothed bronze ring that assists the selector collar synchronise speed with the gear cog and then mesh with the dog teeth. This is known as the baulk ring.
• The 5th gear mechanism, not shown here, fits over the two splined areas on the left (green glove) side of the shafts.
• Also not shown is the third cog required for reverse gear.
• The small chunky cog on the right is part of the final drive and is permanently engaged with a larger cog that turns the differential. It's fixed to the output shaft and not removable.
How the syncromesh works: see the next post.
The input and output shafts:
https://www.rtoc.org/articleimages/5G...ut%20shaft.jpg
The output shaft:
https://www.rtoc.org/articleimages/5G...ut%20shaft.jpg
The selector collar for 1st and 2nd gear:
https://www.rtoc.org/articleimages/5G...0and%202nd.jpg
The selector collar for 3rd and 4th gear. This has around it one of the three cogs that comprise reverse gear:
https://www.rtoc.org/articleimages/5G...0and%204th.jpg
1st gear selected:
https://www.rtoc.org/articleimages/5G...20selected.jpg
2nd gear selected:
https://www.rtoc.org/articleimages/5G...20selected.jpg
3rd gear selected:
https://www.rtoc.org/articleimages/5G...20selected.jpg
4th gear selected:
https://www.rtoc.org/articleimages/5G...20selected.jpg
Looks like worn reverse gear teeth leading edges maybe from all that crunching into reverse:
https://www.rtoc.org/articleimages/5G...ar%20teeth.jpg
Mostly pentagon shaped interlocking pentagons aka 'Dog teeth' from 2nd gear. The bronze baulk rings can be replaced as part of a refurbishment:
https://www.rtoc.org/articleimages/5G...2ng%20gear.jpg
Mostly non pentagon shaped worn flat sided Dog teeth from 3rd gear. This could be why the gear jumps out when backing off of the power a bit. To withstand 250ft lbs transferring through them yes they're quite small aren't they!:
https://www.rtoc.org/articleimages/5G...0pentagons.jpg
Wear on 3rd gear baulk ring:
https://www.rtoc.org/articleimages/5G...ed%20piece.jpg
Interlocking pentagon shapes inside the 3rd 4th gear selector collar;
note the extra wear on the 3rd gear side facing us
and the cleared area for the detent rollers to sit in:
https://www.rtoc.org/articleimages/5G...acing%20us.jpg
Smooth inner surface on gear cogs, ie, no splines. This one is 4th gear:
https://www.rtoc.org/articleimages/5G...ear%20cogs.jpg
4th gear and baulk ring removed from output shaft:
https://www.rtoc.org/articleimages/5G...%20removed.jpg
3rd 4th gear selector collar removed, showing one of three sprung rollers that are its detent mechanism:
https://www.rtoc.org/articleimages/5G...%20rollers.jpg
IanS27thFeb2011