Can the notorious 3/4 synchro hub be replaced easily?

[IdahoDoug]

My gearbox is quiet, smooth and shifts well, gear oil has been tended to all its life. Last gear oil change had almost zero filings on the magnetic plug - way better than other Syncro drain plugs I've seen posted on healthy boxes. Yesterday the well known 3/4 hub cracked. I'm pretty good with tools, and was looking at the Bentley and had a question. Can I simply separate the low gear housing and gear carrier from the trans housing, pull 4th gear and the offending cracked synchro hub off the exposed main shaft, replace, regasket and drive off? Or do I have to completely strip the box just to get to it? It looks like the 3/4 synchro is fortuitously placed on the end of the main shaft where this would be possible. So, anyone who's had one apart have a comment?

Thank you in advance.

DougM

[Roving Rich]

Aidan !

He will be along in a minute I'm sure, and he will know exactly how to approach it.
Good luck
Rich

[IdahoDoug]

Thanks. Happened yesterday on the way home from our maiden voyage. Will be draining the tranny oil this evening as I changed it Friday literally hours before we left. So if it's clear and free of debris and color shift then I'm one of the lucky ones where it cracked but remained in position, vs shattered and destroyed the rest of the gearbox. No bang, no bad sounds and did not so much as ATTEMPT either 3 or 4 gear from that instant. So I think I'm good other than having to pull the box.

Looking forward to input, and thanks in advance.

DougM

[Aidan]

it is possible to do what you describe but that's not the way to do it, risk of damage to shafts and other components - I'm pretty sure the two syncro gearboxes that had sheared their pinion shafts had had that done to them - full strip down, it's the way to go - at least measure the syncro ring clearances on the the other 2 gearsets on the pinion shaft otherwise you can leave alone, once you get past reverse you'll know if pinion bearing has play and what the wear on the pinion bearing is like; enjoy
DentedDevon is doing his box on his V8 thread on alt engines, making the tools he needs, worth a look, tools available aftermarket in the states or used come up on ebay

[IdahoDoug]

Aiden,

Risk of damage due to a worn gearbox not being attended to? Or risk of damaging something in the disassembly?

I drained the gear oil and no fuzz on the magnetic plug and poured it through a fine screen to check for nonferrous bits. Nothing, so happy camper here. Thanks for the tip on the other thread - remarkable! Great photos, too though he has the 4 speed and I have to deal with the low gear aspect and not sure if that's a game changer versus what Devon is working with.

Aiden, if you have a minute, I'd love a quick sequence to follow just directionally. To wit:

Remove output shaft housing
Remove low gear housing
Pull reverse gears
Pull gear carrier case off trans case, but leaving both shafts hanging from the transmission housing? Is this even possible? Or do the shafts come out with the gear carrier like Devon's and then I press the shafts out?

Anyhow, a short sequence to follow would be stellar. Just literally a rough outline of the steps and I'll fill in the blanks.

Thanks, Doug

[Aidan]

Doug the whole gearbox strip and build procedure is in the bentley manual, only real thing different with syncro compared to 4 speed is removing the intermediate housing complete with g gear; on a 4 or 5 speed you just lift off the end case but g gear won't pass reverse idler gear so has to come with the case and the internal reduction gears, if no damage it's fine
remove one way valve and 1st 2nd slider bearing cover before splitting the box and it's possible to remove pinion shaft without pressing it with the mainshaft which is good when working one person, ie only 2 hands when pressing mainshaft out of mainshaft bearing in gear carrier
enjoy

[IdahoDoug]

Aiden,

Thanks for the input. I read the Bentley to see what's what, then reread a couple more times. It, and the sequence are designed for a full teardown, and as a layman it was difficult to discern where I could diverge and do it my way, or if I could at all. So, it is difficult for me to "see" by reading it if I were to try it my way, I might discover there is an inaccessible circlip holding a shaft in place such that I could not separate the case. A circlip that following the Bentley's conventional teardown sequence I would have already removed. So, your input is priceless as you've seen the inside of a few of these girls!!

I'm going to pull it this weekend, I hope. Will follow up here. Regards,

Doug

[IdahoDoug]

Aiden,

Embarking on this soon, and may have it figured thanks to your input. Question on your post above - what's the "one way valve" you refer to? Also, so the pinion shaft comes out of the gear carrier without pressing? So I'd be able to press the main shaft out, and the pinion shaft would most likely come with less persuasion? Or am I missing something on your "without pressing" comment regarding the pinion shaft?

To elaborate on my scheme, there's a gear puller here in the US available that has arms I can attach to the gear carrier thread holes where the low gear housing attaches. My plan is to carefully even the pressure out, then apply pulling presssure and tap with a plastic hammer to ease the gear carrier off the main shaft if your comment about the pinion shaft was taken correctly (meaning it will come out as well, without too much pressing). Then I'll put it back together pressing with the diff ends of the shafts braced. Thanks, Doug

[Aidan]

ball valve 35.107

with that removed from case it's possible to do the reverse of 35.109 illus 34-1318 rather than 35.109 34-1770 which you then do with just the mainshaft in on it's own, less to worry about when pressing