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Discussion Starter · #1 ·
hi all, as part of the complete overhaul of the transaxle from my GTV6, the next stage is the Gearbox.

Full disclosure - I only know the basics around gearboxes, and never opened one up before. Watched a few youtube videos and been reading the shop manual to get some insigfhts.

Having baulked at the 2k cost quoted to me for rebuilding the gearbox from a reputable Alfa shop I wanted to inspect myself and determine the outcome with my own hands.

The car was a non-runner when I purchased it and I never started it so I can't tell you if the gearbox had second gear crunch or any other issues.

Today,I pulled apart the speed gear - clutch casing by undoing the 13mm nuts, then carefully pried apart the casing leaving the intermediate flange, which I then pried apart and removed the shafts and gear assembly onto my workbench.

I inspected the gears and turned the shafts. And here's the rub. what am I looking for when determining if parts need replacing? I can't spot any obvious wear points in any of the teeth and as far as I can tell the gearbox is immaculate. However given my zero knowledge on this, I am relying on any gear whisperers to help me ascertain whether the gearbox needs work or should be left as is, cleaned and re-installed.

Below are couple of short videos of me inspecting the gears, if that helps. Any insight or advice on next steps will be most welcome. Meantime I will get to work cleaning the casing before I move on to inspecting the differential.


 

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Some of the primary things you're going to be looking for to figure out what shape the gearbox is in are:
  • Dog Gears...these are what grind when things go bad. Once they get chewed up a bit from grinding, they will always have the propensity to grind...new synchros will only "hide" the problem for awhile. See: Dog Gears, how to remove and what to look for.
  • Synchros...obviously. Look for smooth spots/edges on them. The way they work is that moly coating (the rough coating) grabs the next gear cluster to get it spinning up to speed to facilitate smooth gear meshing/change. When the moly gets smooth, it can't grip the gear cluster it is trying to speed up...so rough gear changes ensue (and starts to wear your dog gears per above).
  • Shift levers...the things that move the gear around. They can bend, burn, get worn down. They you get jumping out of gear, etc.
These items you can (mostly) inspect without further teardown. I'll look at your vids and comment more tonight if someone else doesn't get to it first.
 
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Hi baz
I use a vice to hold the intermediate flange and use aluminium to protect the flange surfaces from damage from the jaws. Start with the mainshaft nut and lay out each component in sequence onto your work area as you dismantle the gearset. It is very important to take note of the pinion height shim #30 between 4th gear #31 and the mainshaft bearing race this as the name suggests determines the depth that the pinion sits into the crown wheel. The mainshaft has a series of steps and splines as you remove each gear so the gears and hubs can only go back to their original position. You should look for wear in the synchro baulking rings #19 and look for damage to the teeth on the synchro hub #16 and the dog teeth that are pressed onto each gear. I would not disemble the flange bearing unless you suspect damage, you will be able to inspect the bearing balls once you remove the mainshaft. You should'nt need to remove the input shaft just feel it's rotation and only remove it if you suspect bearing damage. Also check for wear of the selector forks. This is an overview, ask as you go about how to determine wear of the components, there are many knowledgable people on this forum only too willing to give advise and help you through the process eg. dismantling the synchro assembly.

Cheers Glen
 

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Discussion Starter · #6 ·
thanks Glen, I wasn't comfortable putting the intermediate flange into the vice as it wasn't holding securely so I was planning to fabricate a bracket to secure the flange to the vice cleanly. I am going to do a more detailed inspection of the gears for any signs of damage or wear before doing any teardown. the hidden components will be more difficult. at this stage, I'm still nervous about doing more harm than good with my intervention. all advice noted though.... now I know about what dog gears are and how they wear I can check those first thing tomorrow.
 

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Hi Baz-

Couldn't see enough detail in your video to comment on condition of any of the items, but the dog gear stuff will be easy to see after you look at the thread I sent. There are probably some threads on how to tell if your synchros are "too worn". If either of those or shift forks look worn, it'll be time to start disassembly to replace those items.

If they all look good (which would be surprising, but maybe it's a fresh-ish box or a good Alfa driver before you), then chances are the rest of your box is good too as long as the bearings feel smooth when turning the shafts (seemed good in the video) and you see no signs of heat on the bearings (e.g. bluish coloring of hot metal that's cooled). Bearings tend to last as long as the box always had correct adn sufficient oil.

--S
 

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Discussion Starter · #8 ·
thanks Scott. did a bit more close-up investigating. From what i could see the dog gears were not dog eared so not needing any replacement.

However.... the fifth/reverse gear (?) at the front had a section chewed off so that will need replacing. Any tips for removing without having to take each gear and component off the shaft and where I can buy the replacement? will continue cleaning and inspecting....

https://flic.kr/p/2kQFDjT
https://flic.kr/p/2kQFDke
 

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Looks like you have a 4.10 R&P, 3.5 ratio first gear GTV6 type trans. If you can, get your hands on a full 75 gear set and input shaft. It will make 1st and 2nd gear much more usable on the street. The ratios are much improved if you're using a 4.10 final drive.

The videos don't show enough to comment fully of course but I it appears that the 2nd and 3rd synchro are showing steel substrate and the dog teeth on 2nd appear to be pretty worn. You will need to disassemble the shafts completely to perform service work.

2K for a full rebuild is not a bad price...it's a lot of labor to properly rebuild one of these. And synchro rings are over $120 a piece.

Your damaged 5th/Reverse cluster gear on the input shaft is a fairly common sight. Check your reverse idler gear carefully too. I have a like-new V6 5th/Reverse cluster to replace your damaged one if you cant find one.
 

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Discussion Starter · #10 ·
thanks Rob, I might take you up on the 5th/reverse cluster. I have a spare transaxle I bought off EBay so I will first pull that apart for a comparison before diving into this one. Either way one will remain complete unlessI have to take parts off it.

pardon my ignorance but what's a 4.10 R&P, 3.5 ratio first gear GTV6 trans ? is that modified or factory ?

I will take a longer video tomorrow.

If I do start disassembling the shafts, where would you suggest I begin? the main shaft and pinion shaft seem connected by the gears so not independent. If I start by removing the nut connecting the damaged 5th/reverse gear then that whole shaft will still not come out on its own. Or do I follow the manual disassembly steps and start by removing the rods and forks ?
 

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Some of the primary things you're going to be looking for to figure out what shape the gearbox is in are:
  • Dog Gears...these are what grind when things go bad. Once they get chewed up a bit from grinding, they will always have the propensity to grind...new synchros will only "hide" the problem for awhile. See: Dog Gears, how to remove and what to look for.
  • Synchros...obviously. Look for smooth spots/edges on them. The way they work is that moly coating (the rough coating) grabs the next gear cluster to get it spinning up to speed to facilitate smooth gear meshing/change. When the moly gets smooth, it can't grip the gear cluster it is trying to speed up...so rough gear changes ensue (and starts to wear your dog gears per above).
  • Shift levers...the things that move the gear around. They can bend, burn, get worn down. They you get jumping out of gear, etc.
These items you can (mostly) inspect without further teardown. I'll look at your vids and comment more tonight if someone else doesn't get to it first.
Nice summary
 

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Discussion Starter · #12 ·
quick update: been doing some reading on the gearing of these cars. looks like the 4.1 was the standard for my year and model of car so happy to keep it, all things taken into consideration.

Today I removed the gears from second spare gearbox for comparison. Overall it has some good and bad points, as this one didn't come out of my car it will be the guinea pig and I will disassemble this one. learnt another new term, molycoating, now need to understand how to spot worn surfaces vs. usable ones.

https://flic.kr/p/2kQRyog
 

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You could use a combination of synchro parts from the two gearsets for the final rebuild, one tip to save on costs is to use the 5th / reverse synchro hub on the 1st /2nd gear. reverse has no synchro so the hub should have no wear on that side, you could then put that old reverse side of the hub against 2nd gear with the dog teeth off 5th gear as these parts usually wear much less than the rest of the gear set. Only change the synchro parts if you swap the gears the pinion height will change and you will need to reshim the mainshaft not an easy job. As I mentioned earlier take note of the pinion height shim between 4th gear and the mainshaft intermediate flange bearing. If you use the original gears and the same shim you can pull down and rebuild the gear set many times over. In the 25 yrs I have owned my GTV6 I have done three synchro rebuilds.
I will collect together and photograph some worn synchro parts and post them so you will know what to look for.
 

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Here are a few photos showing different degree of wear of synchro rings, hubs and dog teeth
1681293
1681294
1681295
 
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The first photo shows synchro baulking ring wear, The surface of a good baulking should be matt or rough any smooth or shiney surface is wear. Check the shape of the teeth on dog rings and hubs, dog ring teeth or hub teeth should be picket fence like, without sideways lean or missing teeth. The final check is thickness.The thicker the better
 
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Discussion Starter · #16 ·
thanks for the pointers Glen, will be starting the disassembly hopefully next weekend once I've fabricated a suitable stand to secure the gear unit into my vice. I'll take pics of the components as difficult to tell whether the parts are worn or usable with my limited knowledge.
 

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Rob did a nice video for AROC a couple of months ago. I have rebuilt a couple of boxes before, but learned a couple of new things from this that I will apply next time.
One thing I will say is that the ALFA shop manual is excellent. Read it carefully and it will give you all the in / out specification tolerances. I have used it on the boxes I have built and they have been reliable (including ring and pinion setting)

Given that you have two gearboxes, it is likely that you can make up a good one with minimal investment. Maybe not "factory fresh" but certainly very good.

This really is a fun job to do. :)
 

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Discussion Starter · #18 ·
thanks for sharing Mark, just watched it and it's an excellent video, well presented and sharing loads of wisdom by someone who has done it many times. have been making some notes whilst listening and will ensure I follow the advice.
 
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