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Old 23-01-2014, 03:49 PM   #1
Dutchy
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G Series G-box rebuild

Hey Guys,

I've been rolling my Asti round for the last 8 years now with the GT-X motor and having little to no problems. But she is getting pretty tired and so I am soon to give her some much needed attention.
1st things 1st, the tranny is getting refreshed. The box in her is the standard G5M-R and has like 280,000kms on it.
I have a spare G5M-R gearbox with far less ks that I have been planning to rebuild. About a year ago, I was sure that I had seen rebuild kits available for the box on ebay. However I no longer can see them???
So a few questions:
Does anybody know where I can get a rebuild kit for one of these gboxes?
Specifically what is in the rebuild kit? Synchros, seals, bearings etc??
Has anybody rebuilt one of these themselves? What are the gotchas?

Hopefully our combined knowledge can get me the answers that I need!

Cheers,
Jeremy
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Old 23-01-2014, 04:10 PM   #2
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I'm not sure if this will help, but I realised I was a little vague with that first post too. The box to be rebuilt is from a 92 Astina SP.
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Old 23-01-2014, 04:44 PM   #3
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I can definitely help a bit, I have a fully built G series behind my BPT.

Many people recommend getting the PAR straight cut 3rd gear as they are apparently weaker/take more torque. But you've been going solid for 8 years on your box so don't bother I guess. it's $700 you can save. I have it in mine, and it sounds awesome, which is probably the main benefit lol.

As for rebuild kits with synchros/seals I have no idea. I do know that I got 2 piece, triple cone synchros on my 1st, 2nd and 3rd gears. This kind of synchro tech is present in MPS gearboxes. Get yourself a 626 5th gear though for highway cruising. I have a Familia GTR 5th and I'm already doing over 3000rpm at 110kph.

One thing you should absolutely get though, is an LSD. I run the mFactory 26 spline gear type LSD in my box. Was only $700 USD and it's AWESOME!!! Full boost through a corner means you just keep going round it faster and faster. It never breaks into a one wheel skid no matter what direction the wheels are facing. I swear you can do a 180 degree turn at 60kph and not lose any speed. You will have to peel your face back off the windows when that happens though.
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Old 24-01-2014, 01:38 PM   #4
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I can vouch for the difference an lsd makes.
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Old 24-01-2014, 02:07 PM   #5
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+1 for MFactory.
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Old 24-01-2014, 02:45 PM   #6
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In regards to the syncro set up you can change it to the latter multi syncro setup but you need to change the hub and gear as well. Only one side as long as it's same ratio. but it won't attach to earlier models.

The other thign ot consider is you have done XXXK kms on these hubs. It will cost but changing the selector hubs and gears as well as syncro's as well. Keep its all shifting like new.
Chanigng out the syncro ring only on a box 200,000kms or more - especially if it's city box with lots of 1-2-3-4 only last so long the wear on the hub selector can cause shifting issues. Same goes for 5th gear if you do lots of 5th gear driving and with hi torque/boost motor 5th gear can cop a hammering on it's selector hub so again changing that is important if its shows Hi wear.

Everything else noted all important Diff - etc.
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Old 28-01-2014, 04:36 PM   #7
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Thanks for the great replies guys!

Yeah I have deliberated on the diff for so long... and I know its a fantastic mod for the BG but I got talking to a guy at a local suspension shop who used to rally lasers in the Vic PRC circuit in the 90's. He told me about a mod that they used to do on the control arms on them to get more traction in the dirt without going to an LSD (because they weren't allowed). This worked fantastically and also given that this is my daily driver and its been working well for so long I am inclined to still use the standard diff. The straight cut 3rd has a similar story to the diff.

The 5th gear mod though, is definitely on my list and if anyone has the gear set lying around not in use I'd love to buy it off them!

I sort of have funny requirements for my Asti, I just love how fun it is to drive and I'm cautious about making to many track focused mods that may compromise how it feels on the street. Also I do hold reliability quite high, thus never increased boost and maybe thats why the box has lasted.

Derb - What is involved in fitting the triple cone synchros? and what's their benefits? Did you do the rebuild yourself?

Rodhog - I think this box has 140,000ish kms, but thats a good point about the selector hub. Would I get them aftermarket do you think? Or a Mazda only item?

Thanks again for the input guys, if I can get all this gear together the plan is for a serious build thread too!
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Old 28-01-2014, 04:43 PM   #8
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I should also say I'm happy putting a bit of cash in this to get it to a near new condition. And I'm happy with only a marginal improvement in performance over std from the box.
I am running the GT-X flywheel and have already bought a Exedy HD clutch to match and new drive shafts left and right. So finding the parts to rebuild the box well is my only real hold up to this whole driveline refurb.

Cheers,
Jeremy
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Old 28-01-2014, 07:33 PM   #9
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My gearbox was built by Hart Transmissions up here in QLD and a lot of the parts came together from a guy who gave up on his gearbox build.

From him I got the the gearsets, G casings, PAR 3rd and some provided synchros and misc bits. I took it to Hart and told them to buy me a mFactory diff, then build the box to take 250hp daily as that was, and still is, still my end goal.

$6k later I had a finished gearbox [custom clutch included in that]. Granted mine was definitely on the pricier side, but it's been absolutely faultless. Fluid always comes out clean, no metal shavings, etc. The motor will blow before this box does.

Story time over, for you just give it a standard rebuild. Talk to them and explain that the box is taking more power than it should and are there any options in terms of strength and reliability? Fresh synchros, fresh bearings and seals and it should do you for another 8 years mate.
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Old 30-01-2014, 03:24 PM   #10
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Derb that box sounds hardcore! I bet it would take more than the 250hp you speak of if it had too! I vaguely remember people throwing around a rough number that the g-series boxes will handle stock?? Cant remember exatly? 220-230 or somewhere there rings a bell, can anyone confirm?

Yeah I am looking to go a bit cheaper than that though, the 3rd gear upgrade would be really nice (anyone got one for sale cheap?). I actually have another toy that takes the focus of my finances, so the asti doesnt get full reign anymore.

I have done alot of reading over the last couple of days too, which has given me confidence that this rebuild wont be tooo hard... I talk to some local gbox rebuilders and the answer were pretty blatant "No, Holden or Ford RWD or nothing" (Damn Regional!). A trip to the local Mazda dealer armed with some info proved much more helpful. Seems that most of the parts can be obtained on a pretty short timeframe by order. Prices actually being semi reasonable.

So now i am interested in knowing key points of wear. So far i have synchonizer rings 1-3 with 4,5 and rev being generally ok. Diff bearings and gear shaft bearings, driveshaft and input shaft seals. Though I am still unsure about the selector hubs or selector as a wear point. Is the selector hub the same as a gear clutch hub assembly? Do any of the clips or washers wear in there too?

Getting deep now!! Thanks again for your replys
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