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Posted: Mon Sep 08, 2014 2:53 am
by archangel62

So my Piazza decided it didn't like its gearbox oil. On a ~150km round trip in the country on a Sunday night. My only warning was a little bit of oil around the inspection plate the other day, which I was convinced was spilled engine oil else a rocker cover leak.

In the middle of nowhere, like the flick of a switch, 5th gear started whining pretty loudly. I completed the trip in 4th, having no option but to do so. Every gear except 4th makes a fairly strong whining noise, and there's a whine present with the clutch out regardless of gears/neutral. So it sounds like whichever shaft has the other gears on it has eaten its bearing. I drained a whopping 800ml of oil out when I got home (if that) and it was silver-grey. Filled it up with new oil - whine still present.

So who wants to step me through an idiots guide to rebuilding a gearbox? I have exactly $0 and my daily is similarly f*cked. I think I must have run over a gypsy a year ago or something.

Posted: Mon Sep 08, 2014 3:59 am
by Skrilla
Sorry to these that hope all works out!

Posted: Mon Sep 08, 2014 9:31 am
by IZU069
Was it low on oil?
My usual solution is to get another box - eg, $90 from Pick A Part.
I try to get 0.785 ratio 5ths from early Geminis (and then swap bells for my left side startermotors) and then match clutch centres and output splines to suit.
But they are not the stronger steel sandwich plate Piazza types.
I have intended MUA gearboxes (off 4ZE1s) but they are not a straight fit. That's with G200Ws in mind, as well as my OEM G161 OHV engines. (FYI - I read an amusing thread on OzFem last night where Poida pointed out the various G-serines engines & hence how maybe a 2L (or whatever) could be stroked to a 2.6L. It was amusing because someone "attacked" Poida saying just because they are "G" engines doesn't mean they are of the same family. Poor idiot. Probably doesn't realise that the G-Z series is the exception to the "G-series. IE - the DOHC heads will bolt on to the OHV and (Jap) SOHC blocks. And that the G160 had a different stroke to all other G's.) Sorry, I digressed. Must have been triggered by the issue of interchangeable parts etc that many Memmers & Belletters etc don't seem to realise.

Otherwise I'd say it's just a matter of pulling down and replacing bearings. The only difficulty I ever had was removing the big circlip in the mainshaft which I've never replaced.

If the box is noisy with engine running in any gear except in 4th or when the clutch is disengaged, then that's a noisy central mainshaft needle bearing (the one between the mainshaft front & read halves). But check for shaft condition - the hardening is prone to wear & cracking.

But "blown" gears... Gears should always be replaced as a matched pair. Usually not much can go wrong other than breakage or discolouration which means gear replacement. Most use bush gears and I guess they can be replaced.
Other bearings are available ball or needle bearings. (The Piazza front layshaft should be ball bearing rather than earlier weaker needle bearings.)

Maybe swap synchro rings ie, 1st to 4th, 2nd to 3rd, or get 3rd & 4tj rings from other boxes if 2nd or 1st is worn.

On reassembly, make sure al gears are fully "home" when tightening the big nut.

Posted: Tue Sep 09, 2014 1:23 am
by Bugle
The silvery oil is probably aluminium, the original box on mine was like that. One of the shift forks had broken off on one side and got munched up.

Posted: Tue Sep 09, 2014 4:40 am
by IZU069
Eli - what oil were you using in the gearbox?

Posted: Sat Sep 20, 2014 8:07 pm
by archangel62
Sorry for the belated reply - been pretty buggered lately.

Yeah it's a bearing for sure. Being run too low on oil killed it! The gears themselves are "fine" pending inspection..

I've never rebuilt a gearbox, and I must say that compared to an engine rebuild, gearboxes sound hard, but it's definitely something I need to learn. The Isuzu manual calls for several custom tools, here's hoping I can make do without!

I hadn't changed the oil since buying the car. As is always the case, it was on my to-do list (and getting pretty high up there too) but let go before I got to it. After a few years of owning the car, I was about 1-2 months away from doing it, pending rego running out. No real news since then - the BA Falcon was fixed the day after the Piazza broke... Turns out I'd fixed the BA, but the CV in the tailshaft had shifted too far inside itself, but its rubber boot was hiding the problem. As soon as it was up on a hoist, my mate levered on it and it popped in and was fine.. lol. Also somewhat annoying, since we probably would have taken the Falcon on the long trip if it wasn't for that. Such is life.

No real news yet. The Piazza's rego is about to run out and I haven't touched it yet. I've been working on the Geminis, because I need to make some headway there. I'll come back to the Piazza in a little while, get this gearbox out and go from there. I'd toyed with the idea of running a Gemini gearbox temporarily, but it sounds like the tailshaft is too hard basket...

Posted: Sat Sep 20, 2014 11:02 pm
by IZU069
LOL... One thing I always do with a "new" car - change all oils, and lube the speedo cable. Usually flush the brakes too.
Mind you my last car was the Wasp some 15 years ago and that was an engine rebuild etc. And I usually rebuild the brakes with any new vehicle.

I remember not worrying about a slight Florian diff leak (front seal - a 10 minute replacement job). When I heard the diff noise I "simply" replaced the diff. I learned how much work hub-hub diff replacements were, as well as how heavy!
And later I got worried - wtf fits the Florian if the new diff packs up? (Of course now I know they are limitless...)

The short of it is that sometimes I'll do the quick maintenance even if I do plan to replace the lot.

And re new engines or rebuilds, you've probably read how I replace ALL rubber hoses; new thermostat (with jiggler); & and have the radiator professionally flushed. And welsh plugs, and clutch thrust bearing; flywheel bearing...

Re tools, I don't recall the need for any special tools other than the odd bearing puller (if that) and maybe whatever is required to remove or replace the mainshaft circlip.
But end bearings shouldn't be a drama and I'd suspect they're the ones that have probably gone else the central mainshaft needle bearing (only quiet in 4th, or clutch in or no gear rotation).
If gear bushes or needle needle & shaft surfaces are damaged, then it's a special repair job.

I'm glad the problem was low oil. I was expecting a failure caused by synthetic oils or using some fools' recommendation (like using gearbox oil in Isuzu passenger etc boxes with a synchro 1st gear...).

Posted: Mon Feb 01, 2016 12:49 am
by archangel62
Texty update, I have finally sourced a replacement gearbox, so the old one is out with the expected tedium of working on a Piazza, and I'm currently waiting on replacement seals for the new box to make sure it hangs onto its oil a little better than the last one did before fitting it up. I'm considering tightening up my shifter linkage while I'm there, it's not really too bad but you can see a little bit of play so I might see about fitting a thin washer to pick up the slack a little. Seems it'd be difficult to impossible to get to without taking the gearbox out so I may as well do it now.

While I wait for the seals I'm also swapping out the rocker shafts - the two actual shafts that the valve rockers pivot on. Mine have significant wear and scoring, either from a hard past life or from that damn bug that packed dirt in the turbo's oil feed back at day dot, and it made the valvegear noisier than it had to be. The new pair I bought from the wreckers were filthy so I spent a few hours today cleaning them inside and out.

Micro mod, while I have the centre console out, I'm fitting a boost gauge somewhere discreet where the holes won't be noticed if removed later.

And a bit of back story, after sitting parked for nearly a year, the Piazza wouldn't start. We spent three weeks straight troubleshooting the thing, basically reinvented the piston engine, you name it - compression tests, three sets of spark plugs, resistance checked leads, cleaned dizzy cap, moved dizzy a tooth and back again about three times, locked the timing in the ECU, changed the static timing about 20 times, checked the fuel pressure, ran another EFI pump from a jerrycan of fresh 98RON, freaking everything... Until we found out the Microtech had decided it was for a 6cyl engine. After dodgying it up to start, we realised it had wiped the tune - or so we'd thought. Nope, it had just selected the other of the two tunes it allows you to store in the unit. And, since we hadn't touched that one, it thought it was for a 6cyl. So, in a few seconds and after pushing a few buttons, we fixed the issue that had plagued us for three weeks... I don't even know if I should be happy about that. I suppose so?

Sidenote, I now have a kickass welder. The exhaust is a major power killer at the moment, as a 3" dump pipe flatly joins a 2" midpipe at the firewall, no taper, nothin'... so I'll be continuing the 3" into a highflow cat at the very least, before either tapering down to what appears to be a 2.5" rear half, or making up a full 3" system. At this stage I think post-cat 2.5" would probably be sufficient, but I really need to get rid of the bad join, 2" piping and shitty standard cat near the front.

I've also settled on getting the Piazza-listed Koni shocks customised to my specs, since starting with another part number ended up confusing them more than helping... Finances pending here, hopefully in the next month or two. I have some lowered springs for the front, then the car will be fairly sorted, besides the standard LSD's sheer inability to limit slip...

Posted: Mon Feb 01, 2016 6:26 pm
by eyecon
Hang in there mate. Thanks for the update too.

Posted: Mon Feb 01, 2016 7:52 pm
by IZU069
Similar to above, I always replace the front seal before changing boxes, and often the speedo seals - inner & outer - though like the rear seal, they can be done later - especially if a bit of oil loss isn't a big deal.

Shifters are hard to tighten being a stick-fork relationship, but the Piazza has its intermediate pivot linkages and rubberised carrier which can add slop (or am I confusing ZZR etc with Piazza?).

Rocker shafts can make a heck of a difference wrt to oil pressure. I wonder if they accounted for my Wasp's G161U holding oil pressure for up to 40 seconds - or maybe 20 seconds if really HOT. (Let's not mention oil pressure controlled fuel pumps spewing out petrol for 20-40 seconds after an accident... TX/TC Geminis solved that issue!)

And kinda fun (sorry!) hearing another argument against multi-map ECUs. You probably recall my arguments against Haltech etc multimaps (especially when they have 32!!), but if they can mis-switch or even call 6 cyl maps... [ But utech is like most isn't it - fuel & ignition maps only; they don't switch "ECU programs" as done for switched Delcos etc? I wouldn't have thought 4-6-8 would have made much difference unless perhaps throttlebody (then again, maybe not...). ]
But glad you got it fixed. My view is once fixed, who cares? Only if I've wasted tests because I've accepted or trusted what others have said do I get shirty.

3" should fit. My red auto Piazza has a 3" system. Not that I know of it was a good tune - bigger isn't always better (except when bigger-enough), and these are turbos...

So, do you want my Detroit locker? (:yawinkle:!!)

Posted: Mon Feb 01, 2016 8:43 pm
by eyecon
Full 3" system def does fit nice and snug over the rear axle if done properly. Didn't drone either. But tell me more about your Detroit Locker.

Posted: Tue Feb 02, 2016 4:20 pm
by IZU069
The Detroit (Eaton?) was one I picked up from Pick A Part from a Rodeo else Jackaroo not unlike the ones on - eg:

with guts like....


I only reassembled it a few weeks ago after pulling it a part a few years ago...
Mine has an inner "floating" sleeve/spacer not shown in the above fig (nor any others I have seen) which I intend to omit since IMO it does nothing practical other than possibly float around.

Originally planned for my UBS17 (4ZE1) Jackaroo front diff, it may eventually join my G200W Florian stable unless it is a constant clunker.
I really want a Torsen but haven't found one that's Isuzu compatible...

Like Eli I wanted a Limited slip - not a limited lock - though I admit I never got to trying brakes-on to lock my Wasp's (Isuzu clutch) LSD when free-airing, nor changing the slip to racing specs.

Posted: Wed Apr 20, 2016 7:53 am
by archangel62
First and foremost, Peter, if you're looking to part with that Detroit Locker, inbox me a price, I'm definitely interested!

Yeah, the Piazza shifters have the rubber linkages on the pivots. I tried to look at tightening mine up but it seems they really can't go any tighter, short of adapting a rose joint of some kind, so in favour of finishing my cars before I'm too old to drive them or the world runs out of fossil fuels, I just threw the shifter back in as it was.

The new gearbox is back in, nice and clean with all new seals bar speedo linkage, but as mentioned at least I can come back to this. Turns out after removing the old gearbox, I realised what "that random hose I blocked off was supposed to be for" - and it also turns out the Piazza MSG-5 gearbox that's supposedly so identical to a Gemini box has a hose to vent excess air pressure to ambient, where the Gemini just has a capped plastic fitting. So I'm thinking, working backwards, that by blocking that off, once the gearbox got hot on a long trip it pressurised and forced oil past the seals, causing an oil leak that didn't exist when parked. Surprisingly the same car lasted a 3000km round trip interstate and a hillclimb, but alas. At least there's a reason behind the phantom oil loss and subsequent failure, even if it is me. At least I have a spare Piazza gearbox to rebuild one day, else re-task into one of my other cars.

The big issue with it going to the 6cyl map is ignition timing. A 4cyl fires spark at 0deg and 180deg +/- timing advance, but a 6cyl would fire at 0deg, 120deg, 240deg +/- timing advance. So it'd go to start and then fire back on itself. The second map option would be handy if it was easily accessed and more difficult to accidentally trip. It'd be good to have a "power" and "economy" tune, for example. Basically, the uTech is primitive and cumbersome, low resolution and fiddly. Sure, it's fairly simple, once you make sense of its strange abbreviations and clunky interface, but if I'd known it'd be this... rough... I'd just have bought another Megasquirt. I wouldn't recommend a Megasquirt, since you basically need to spend a solid consecutive year reading and googling without sleep or social life to understand them properly, but now that I do (more or less) I may as well use the knowledge and MS a few more cars. Maybe.

Anyway, with the gearbox back in I just need to finish swapping the rocker shafts, put the rocker cover and inlet piping back on and fill up the gearbox oil (mustn't forget this) and she'll technically be ready to go... but I'll be fitting the front springs and making up a new midpipe with highflow 3" cat first. I still need to buy those rear shocks, and I'll try an LSD I bought from Elky while I'm at it, just in case it limits slip...

Posted: Wed Apr 20, 2016 12:24 pm
by IZU069
Good gearbox analysis. Hose and hole plugging can be disastrous - from us older G-OHV people that used to block the mechanical fuel pump hole that leaked petrol (because the diaphragm & plunger seal leaked thereby causing fuel to drain out the intended drain hole, or into the sump if it was blocked), to causing pressure-ruptured oilseals or oilseal bypass (which can also be caused by overfilled oil).
I ensure vents & hoses are free and will usually extend them to higher air (since I still occasionally creek or flood cross).

Yeah, 6 cyl EMS in 4 cyl engines ain't too successful. I still think Delco/Delphi is the popular choice though I have a mate hooked on MoTeC - but he does hold a world speed record thanks to them.
Alas I don't know of any 4ZC1-t Delco tunes (they exist for G200Ws & GZ engines) but it shouldn't be too hard... (??)

One advantage we have is the possibility of using the optical dizzies as used on G200W Piazzas and 4ZE1 engines. Their 360 outer slots can be filled for almost any required number of slots (ain't "perfect" numbers great?) the usual limit being the 4 equal slotted inner slots- ie, if the timing disk requires 6 slots. The inner(s) can be elongated for sequential injection & ignition (ie, in the advanced direction - timing is usually taken of the trailing edge of slots) - I know of one Gemini & a G200W Piazza that used a Nissan type disc with elongated slot (SR20DET?, 240SX?). (I'm using an elongated-slot G200W Piazza D4P80_01-250 dizzy in an attempt to replace a factory EFI-prototype 117's Bosch points bank-switching dizzy.)

I'll keep you in mind for the locker, but I figure its future is sealed in the front of my Jackaroo. When that goes it will be for a Florian though that may depend on its lack of noise.

Posted: Thu Apr 21, 2016 4:47 am
by archangel62
No worries! I'd be interested to know how it goes, if nothing else :D

Re E1 dizzy, I'm currently using one in my 4ZE1 turbo drift car. I'm about to change out the trigger wheel though.
My write-up: ... 29&t=27104
Other trigger wheels: ... 51&start=0
I don't like the idea of modifying an existing wheel. Any changes made need to survive heat, oil, vibrations, time, and let's say 4000rpm. In my mind that rules out paint, glue or solder. The wheel also needs to be flat and strong enough not to fall apart, they're made out of thin metal so I suspect any attempts to cut or press holes could render the wheel useless. I'm definitely not saying it can't be done, just that I wouldn't. They're generally laser cut originally. Apparently the trigger wheels from FWD Nissan SR20 engines, with 54mm OD, can be fitted to the E1 dizzy. Some that I've seen only have one locator hole (centre "D" and one set out a bit) and others have two locator holes (centre "D" and two on the same radius, offset 90 degrees). The E1 uses the two offset 90 degrees but apparently you can cut one off in the dizzy if need be. I'm also told that our dizzy spins the opposite way to the Nissan items so we need to fit the wheel upside down for it to be technically correct, else just adjust trigger wheel offset in ECU.

Re ECU choice, essentially as long as it can tolerate the CAS input and run the injector impedance and spark trigger output you need, it doesn't really matter what you run for a specific motor, it's more an operator/tuner choice to work with something you know and can implement and understand easily. A tune's a tune once you're looking at it on screen, it's kinda like Windows or Mac, some people like one, other people like the other, but both can do most of the same things (except run games, mac... pfft). Also I don't believe in running someone else's tune, since motors can be so different, or the slightest details overlooked. Someone else's tune can save a lot of time as a starting point, but if I adjust anything major on a car, I tune it or get it tuned. I'm hoping to get my hands on a wideband o2 and knock mic so I can do most of my tuning myself, then maybe rent a dyno to hone it, since tuning to peak power for a given load is infinitely better than tuning to knock and then retarding.

Speaking of Delco, I have a JT191S Irmsher-R now too, and that runs a Delco of some form. I'm hoping to open up the ECU in a few weeks and check which Delco, to see if I can NVRAM it for live tuning. That'd be real nice. It needs it, even the stock tune has gone to shit - probably old sensors - and it makes bugger all power once the laggy turbo has spooled. I'd like to change turbos, but I'm not going to invest time and money into that unless I know the ECU can be tuned. I have way too many cars to get bogged down on an ECU swap on that one just yet. If anyone's curious to see the JT191S, here it is: ... e=57B8E9D6