Diff'rent Strokes

[mcflux]

(Stephen Hawking sp33k): Oh Boy. I am so over the. Moon. Oh baby yeah. (/sp33k)

Have just had an expensive education in the wonderful world of diffs. As some of you may know, I have been intending on changing my diff ratio from 3.27 to 3.7-3.9 for a while now. When enquiring about having a diff specialist to do this for me using new components, my best quote was $950. When I looked into supplying 2nd-hand parts and having a specialist or mechanic experienced with diffs do the changeover for me, it came to being about half that in $$$. So I thought that the only gamble I was taking was whether the diff I bought was r00ted or not. How wrong I was!

Mistake 1: I bought a 3.9 ratio diff (borg warner, 28 spline axles) from an R31 Skyline that was being sold off in parts. Since the car wasn't running, I never got to hear/"feel" the diff in action, so it was purchased for $150, condition unknown.

Mistake 2: Thinking that there would be nothing wrong with my current 3.27 diff!

OK, my car has just ticked over 310,000km. I was under the impression that the diff was original and hadn't been touched. It was showing signs of age by having a small leak, but it didn't whine at all or clunk. The LSD felt tight, and if I wanted to be silly, both tyres would light up at the same time.

Anyhoo, my diff must've had a problem sometime in the past and was subsequently worked on. EVERY bolt was treated to a healthy dose of Loctite, making it a to remove the housing (especially with the plan of attack being doing it while the EB was up on a hoise with the axles, etc, still in place, rather than pulling the whole lot out and doing it on a workbench).

Also, BW diffs (and probably all others) have calibration numbers etched/stamped onto the crownwheel and pinion, which indicate what kind of shims are needed to have the diff assembly all balanced correctly. Having "0" etched/stamped onto the gears means that no shims are needed for balancing. Having "1" means 0.001in shims are needed. "2" = 0.002in, etc.

For some reason, these etchings had been GROUND OFF by whoever worked on the diff last (before I bought the car). Hooray. That meant that it would be guesswork for seeing what correctional shims would be needed due to the skyline gears having different tolerances (I've forgotten what their calibration numbers were at the moment, but say they were "2" and the EB's were "4", that would mean 0.002in would be needed to be machined off the EB's shims, or something like that... I think)

Anyhoo the diff was pulled apart and put back together a few times before the skyline gears were fitted in OK. The EB was taken for a test drive down the street and it was quickly discovered that the skyline gears were r00ted. My car had been at the mechancics for 2 days now, and would have to stay over the weekend. I work on weekends, and my parents are on holidays at the moment, so I had to "borrow" mum's car over the weekend.

My old gears were put back in this morning (as they ran out of time on Friday and had kept the shop open for an extra hour anyhoo), so now I'm $$$ out of pocket, with my original diff settings (I don't have the time/$ to keep it there until suitable diff gears are found, so I'll have to cut my losses)! At least I've learnt an important lesson out of this... Things aren't as simple or black/white as they seem. I thought my only issue would be the the skyline gears being , but the problems with my diff far outweigh that.

I should've gone to the diff specialist offering $950 for new stuff! That is, assuming that that guy would've been able to work around my dodgy diff...

Consider every possibility before diving into something you're not 100% aware on.

Cheers,

-Dave-

[Kenaz]

Damn! That sucks to hear Dave. That's some bad luck right there :(

Originally Posted by Ghia5L

I should've gone to the diff specialist offering $950 for new stuff! That is, assuming that that guy would've been able to work around my dodgy diff...

Hindsight is a wonderful thing.

Ash

[Walkinshaw]

Are you sure the 3.9 gears would have fit in the 3.27 housing? i hope they did

[niko]

327/345 geared diffs are 28spline and fit straight in, u woulda been better off finding a ty old pintara with 4.11's!

[tommo74]

jesus dave !thanks heaps for the early warning signs mate1
so sorry about that happening mate but youve damn well persuaded me to just go for the new stuff AND have my oldie checked out!
so...damn man...but thanks for the lesson that probably would have been mine.

[EFFalcon]

its more so the housing is sometimes too small to take 3.9 gears.
3.23 is the one that causes issues, but seems there are sometimes ways around it.

[sphell]

sorry to hear that dave, but are you sure that the skyline gears were rooted? It just sounds as if the whole assembly wasn't lined up properly. It's pretty easy to tell if the gears are rooted by looking at the wear marks on the crownwheel and pinion. Just grab a Gregory's manual and it has a pic of what the correct wear marks should look like. It's pretty hard to fck a set of gears since they are solid metal. If they were rooted it would be something obvious like a tooth being broken or chipped etc. And why does he think they are stuffed? Cause they are noisy? That's just misalignment.

When the guy rebuilt the diff did he use some bearing blue on the gears to check their contact pattern. I think it was Rob that suggested that I do this with my diff and it's a bloody good idea. You can see exactly where the teeth are gonna touch each other.

Also, if you just kept the original shims out of your diff (dont swap them left to right either) and didn't change ANYTHING except for the crownwheel and pinion it should be fine. Sounds like the mechanic has pulled out bearing cups and swapped shims everywhere......no wonder he's having a hard time getting it all lined up.

And as for the housings they are all the same, dunno why people say 3.9's dont fit in 3.23s or 2.77 etc. it's just the axles that are different.

[Psycho Chicken]

Not knowing the thickness for the shims shouldn't matter. You should check clearances and tooth contact before it goes in. And you would be able to see diff gears worn that badly they would be noisey.

I reckon the guys who did it have no clue.

[mcflux]

Thanks for all the replies

Niko, the 3.9s were also 28 spline and *should* have fitted straight in.

Sphell, yes he used that blue dye stuff and it took him ages to get the gearing to sit right (using the dye as a guide when marking the teeth). He didn't drive the car until the teeth were lined up properly, but said it was making a "miimiimiimiimiimii" kind of whine, and that the crownwheel's teeth were slightly rounded (or something like that). He pointed out the wear to me.

Yes, it does sound like he must've pulled the whole lot apart, but due to my lack of understanding of the finer points of diff internals, I thought that that had to be done anyway (plus reusing my shims). He did say that 3.9s would fit, but also that I had purchased a buggered example. He also (surprisingly) said that the 3.9s didn't seem that much quicker once the car was up & going, and that it was only good from actual launch, however he only test-drove about 5km or so due to the "miimiimiimii" issues.

It would have been better if I had the time & money just to leave the EB at the mechanics and source a GOOD diff, but with rego coming up and my bank account dwindling, I'd rather just cut my losses for the moment and lick my wounds. And then I'll think about whether I want to venture into Diffland again...

Meh, I'll focus on the engine once I get some more funds up. It's frustrating having the Explorer manifolds gathering dust in the cellar, and the GT40P heads I put a deposit on ages ago *just* out of reach in QLD (which I'll have to save up for now...)

Looks like I'll be running mid 15s at Heathcote :

-Dave-

[Age182]

im interested in gettin an LSD too but id much rather pay for a new one wat other quotes did ya get on a new one other than $950 and r there axels ya hav to get to suit

[Dezza]

Not good, Dave. Nothings working out with your EB at the moment, is it! From wombats to shoddy diffs! Talk about an expensive mod. Hope you get it all worked out. Cheers

[mcflux]

Originally Posted by Age182

im interested in gettin an LSD too but id much rather pay for a new one wat other quotes did ya get on a new one other than $950 and r there axels ya hav to get to suit

My diff already has LSD, I was just looking at changing the ratio. I recall someone mentioning that converting to LSD as well as 3.9s would be around $1400 all up. Pricy!!!

Dezza: After driving 4 cylinder cars all weekend, the EB still feels quick :P

*Edit* Sorry Rob, I missed your post! To be honest I would have no idea myself, I'm just taking what he said in good faith. A mate of mine swears by him, and I'm just seeing this whole debacle as a case of bad luck. Same goes with the guy who I bought the crap diff off, he bought the skyline as a whole (but undrivable - motor r00ted) car for wrecking, so he didn't know the condition of the diff either.

-Dave-

[LUXO_8]

again dave, that sucks.....

[INJECTED_250]

Originally Posted by sphell

And as for the housings they are all the same, dunno why people say 3.9's dont fit in 3.23s or 2.77 etc. it's just the axles that are different.

The 2.77 is the only one thats differnt, as the pinion of a 2.77 center is large and the crown gear has to be either ultra thin or moved over, they run a differnt of set carrier. A 2.77 lsd is totally usless . Axels ARe all the same.

2.92,3.08,3.23,3.27,3.45;s use all the same size carrier and just use differnt thickness in the crown gear to allow ratio... If u look a 3.45 crown gear is ultra thick and a 3.08 is thinnner.. i

Ive Had 3.7 skyline gears fitted and they were noisy from DAY one, the diff place said they will be noisy as nearly all skyline gears are....
Those gears lasted about 2 mounths then the pinion gear snapped 3 teeth of and dammaged the crown..

I had a set of 3.7 cortina bw gears fitted, special colars are required to fit these as they use smaller bolts to hold the gear set to the carrier. These were whisper quiet, and now a few mounths on are now starting to get noisy.

The problem is that as the ratio gets higher less teeth are in mesh at a time, meaning a 2.77 diff has the strongest gear set as more teeth are in contact at a time. 4.11's are the weakest ratio.

They make Brand new gear sets, But if you are buying some get the FINE TEETH set, these have many more teeth one the gear sets and are lots quieter and heaps stronger as there are heaps more teeth in contact at a time meaning less load on each tooth..

Ive spent over 600 now on 2 diff re-builds doing it the cheap way using second hand gears but new bearings each time. getting them installed by a pro is a must.
my next set of gears will be a new set... im getting over it

[Walkinshaw]

Its the housing size i was debating before. A way arround for 3.23:1 lumberd diffs hey???

[INJECTED_250]

as far as housings .. the only one ive ever heard was differnt was the 2.77 one.. BUt it all depends on who u ask,

[sphell]

Originally Posted by INJECTED_250

The 2.77 is the only one thats differnt, as the pinion of a 2.77 center is large and the crown gear has to be either ultra thin or moved over, they run a differnt of set carrier. A 2.77 lsd is totally usless . Axels ARe all the same.

2.92,3.08,3.23,3.27,3.45;s use all the same size carrier and just use differnt thickness in the crown gear to allow ratio... If u look a 3.45 crown gear is ultra thick and a 3.08 is thinnner.. i

yeah that's right, the carrier is different but what I mean is that the actual housing, as in the whole outside case of the diff is all the same. People seem to think that 3.23, 2.77 casings etc can't fit higher ratio gears. If you had a 2.77 just **** off the carrier (which you would anyway if you changed to 28 spline) and you can put whatever you want in there.

[Sox]

I agree with 'sphell' and 'Psycho Chicken', fitting diff gears is easy, and the gears should have been identified as being stuffed before being fitted.
If they were fine, then it is a setup problem.

Go elsewhere.

Rick.

[Pilch]

Tough luck there Dave! Hopefully things will go a bit better with the upgrade of the engine.

As for the people questioning the workmanship behind the diff swap, the quality would be unquestionable as this shop's mechanics are all quite skilled, and the manager will do things himself if he doesn't beleive they are up to the task. He wouldn't even let his son do all the work on his own engine for a formula ford, insisted he did it himself. And there is plenty of experience in diffs there too, i've seen plenty of diff work go through there with plenty of success!!! And the engine in my car which was built from the ground up hasn't missed a beat for almost 50,000km's now.

[mcflux]

Hrm I wasn't aware of the whole less-teeth-meshing business. I suppose that the pinion would be smaller then for the 3.9 set for this to occur. (Hrm... makes sense, small pinion & crownwheel with more teeth in it)

Anyhoo it's only money, & the car's fine now. I'll save up again, it's "excess" money anyhoo (I save like crazy to pay off any debts, and whatever extra I make I just spend because I have no interest in saving for the sake of saving).

Cheers all,

-Dave-

[tommo74]

thats it pal!If you have no wife and kids just spend money on your machine,why the hell not?
If you die tomorrow someone elsell get it anyways.
by the time im "finished" with my ed i wouldve spent upwards of 25 grand
Rational? .. hell no.....but its only money and i only have to worry about me
so go for it pal...mod out all ya can!(i just hope you dont have a hit and miss experience like THAT one again)...usually happens to me lol.

[EB6]

In regards to the housing thing there is a different size housing in the early ea diffs. i was lookin at using a pintara 4.1 gear set for my eb but there was too much hassel to get it to work. To get the pinion depth right on the pintara grears in my eb i would have to use an early ea housing because the size of the bearing surface was the same as that of the pintara ,but it changes after the early ea's by about 5mm making the late diffhousings not being bale to be used on pintara gears otherwise the gears wouldnt get the correct depth stuffing up the teeth wear pattern causing backlash between teeth and noisy operation. That was for the 4.1 ratio im not sure if the 3.9's are the same.

[Damo]

that sucks Dave, sorry to hear buddy. I kinda agree with Doug and Sox though, if the gears were stuffed and this 'mechanic' is soo reputiable then shouldn't he have noticed that before installing the gears... ?

Tough luck, my diff is snafu too. I cbf replacing it atm as I get to drive mums fully sik VS, while she is on Holidays` in Uk, plus i need to replace all the bushes, mainly the lower control arms bushes which are kinda non existent.

[mcflux]

That's the spirit, if ya CBF factor is high, "borrow" someone elses car :P