Diffs. Real Talk

Drivetrain articles (gearbox, torque tube, diff)
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Jonno
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Diffs. Real Talk

Post by Jonno »

Aight guys.

So my Gemi has successfully done just shy of 2000ks now with the new motor and bits.

The diff is the weak point again. I binned the locker.

Now before omg do an altra 9 bro this is just to humour me for the moment.

I grow tired of doing axles, diffs and torques so I've been toying with other options.

What's peoples opinion of shortened commodore/hilux/R31 diffs? I don't want "yeah bra heaps sick ya know"

What are they like to drive with with them in? I'm thinking of doing a 4 link setup, coil over rear and the diff actually shortened to fit wider wheels.
Not setup for burnouts or anything maybe a few solid runs down the quarter.

Thoughts friends?
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Re: Diffs. Real Talk

Post by archangel62 »

Alright, well I'm sure you've seen my Hilux conversion in the drift car. I've only driven it for say, 6 hard laps between all the issues on the day, and I haven't adjusted or tweaked anything on it. It's kind of hard to give an honest comparison in some regards because I only subjected the old setup to 56rwkw, this one was getting around 200 at the time. Here are my uncomposed, scattered observations:

- There's nothing fundamentally wrong with it, no slap, slop, thuds or strange movement
- It seems to handle the power without batting an eyelid
- Mine has some axle tramp when powersliding hard - this is on decent tyres, late corner full tilt. It doesn't do it unless drifting and pushing hard, nothing in a straight line etc
- The tramp could be due to the less than ideal upper arm geometry in my setup. In brief, layman's terms, the top arm should be higher at the front than it is at the back. Flat is probably okay. Sloping up towards the diff is not good. The floorpan makes this hard. I'll be tweaking mine soon.
- The car feels different, handling-wise. Throwing it in it's far less linear, far less predictable, there's lots of grip and then there's none
- The above is probably due to the squat geometry. Similar to the previous point with the arms. My upper and lower arms converge angle wise pretty much where they mount to the body. This gives it a bit of squat geometry, which is good and bad, but I think mine has too much.
- I had to maim a few things to make this happen. I wouldn't run out to do it on a street car. The exhaust hanger before the diff is gone. No cabled handbrake due to the brake swap either. No room for an over diff exhaust, within reason.
- I spent almost as much on my Hilux diff as I would have spent on an Altra9, Commodore rear brakes in 4x100 and a strengthened torque tube, and I did all of it myself and scored a few things very cheaply.
- My diff is from an RN25 Hilux and didn't need shortening. It also means it has the earlier axles which are less strong apparently, but still bulletproof compared to a Gemini.
- I don't feel like the Hilux diff is greatly heavier than the Gemini diff, all things considered. Maybe a little due to the axles, not much.
- I kept springs and shocks for now because I didn't see any real benefit in coilovers for me, and most coilovers have uselessly bad shocks.
- Standard diffs don't need engineering, have linear geometry, things fit, you don't need to maim the floorpan.
- Hilux diffs foul on the forward facing swaybars I tried. I had to go a rear facing swaybar to the tiedown points or none at all.
- Hilux diffs have a wide range of LSD centres and ratios but be prepared to spend a lot and still wonder if it will fit. Some people say IRS items (read: everything you will find) need modification to fit the live axle centres if at all - others say this is codswallop and they fit straight in. I'll let you know how I go... haha. I have a full spool in mine currently.

I was going to Hilux diff my street TX, now that's definitely going Altra9 assuming the centre works well.
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Re: Diffs. Real Talk

Post by Jonno »

I'll re-read your thread on them again but this is pretty much what I wanted to hear.

Ill come back and reply when I sus.
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Re: Diffs. Real Talk

Post by F3ARED »

I'm going to whack you over the head when I see you next week. For once just listen to me and KEEP IT SIMPLE. Go Altra9/strengthened torque tube and just leave it alone.

What Eli outlined above is the main issue you'll face with trying to get a 4 link setup under the rear of a Gemini - getting the top arm lengths and/or angles correct. Which you'll remember is what I told you a week ago on your work email ya clown. I think from memory when I looked at it, to get the setup "right" [ie geometry, correct lengths] would require cutting into the floor under the seat pan area, obviously costing you the back seat and making it very hard to engineer later. Get it wrong and it will be a death trap and impossibly hard to control, which is not what you want regardless of what you plan on using it for.


I grow tired of doing axles, diffs and torques so I've been toying with other options
2 out of 3 of those problems get solved with the Altra9. The 3rd [the torque tube] is easy enough to make stronger. You wont be running slicks, so none of these will be a problem

What's peoples opinion of shortened commodore/hilux/R31 diffs? I don't want "yeah bra heaps sick ya know"
Commodore diffs are s*#t, you should know this. Centers are rubbish so you'll pretty much need a bare housing and replace all the bits inside. They arent strong either. Anything VS and earlier will be M78. The one in the SS is an M80 [bigger/stronger] and I broke it pretty easily, that tells you all you need to know.

Coil over rear and the diff actually shortened to fit wider wheels.
You know shortening the diff isnt going to get you to fit wider wheels right? Wheel tub is still the same size, all you'll be doing is changing the offset of the wheels. Cant widen the wheel tubs without huge amounts of work [moving fuel tanks, chassis rails run right through there etc]. All this will mean the coil over will essentially be going where your standard shock is now, which aint strong enough for those sort of loads.

Seriously. Just Altra9 it.

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Re: Diffs. Real Talk

Post by Jonno »

Ok so I had a skim through Elis thread couldn't see any pics of it :(

Is it 4 linked or using a mcdonalds brothers setup?
F3ARED wrote:What Eli outlined above is the main issue you'll face with trying to get a 4 link setup under the rear of a Gemini - getting the top arm lengths and/or angles correct. Which you'll remember is what I told you a week ago on your work email ya clown.
Yeah I hadn't forgotten.
F3ARED wrote:I think from memory when I looked at it, to get the setup "right" [ie geometry, correct lengths] would require cutting into the floor under the seat pan area, obviously costing you the back seat and making it very hard to engineer later. Get it wrong and it will be a death trap and impossibly hard to control, which is not what you want regardless of what you plan on using it for.
F3ARED wrote:I grow tired of doing axles, diffs and torques so I've been toying with other options
2 out of 3 of those problems get solved with the Altra9. The 3rd [the torque tube] is easy enough to make stronger. You wont be running slicks, so none of these will be a problem
The torque tube is the killer though man. It's pretty much the weakest point of the whole diff.
Yeah cool for anything less than 150hp but even when I had 140 I broke two.
I've got the gear at home to 'strengthen' it so I'll try that and see how we go.

My overall perspective is to completely f*#k the torque tube off and run a one piece tail shaft.
F3ARED wrote:What's peoples opinion of shortened commodore/hilux/R31 diffs? I don't want "yeah bra heaps sick ya know"
Commodore diffs are s*#t, you should know this. Centers are rubbish so you'll pretty much need a bare housing and replace all the bits inside. They arent strong either.
Anything VS and earlier will be M78. The one in the SS is an M80 [bigger/stronger] and I broke it pretty easily, that tells you all you need to know.
Yep exactly. So I'm thinking IF I even consider diff conversion I want to do exactly that. More leaning towards a TruTrac and billet axles. Then for the next bit

Coil over rear and the diff actually shortened to fit wider wheels.

So the ultimate plan IF I go with the above is to run larger wheels. Offset has nothing to do with it. The car is far from omgjdmazfuck. So I'd like to set my wheels up with a large amount of back space.
Ideally I'd like to match all the wankers with 9.5 rears.

Csh why do this? Cause it looks f*#cking mad and I want that.
Seriously. Just Altra9 it.
N-
See how this torque tube bs goes. I could chat to them directly and see how I go about shorter billet axles?
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Re: Diffs. Real Talk

Post by firebug »

This might be a good opportunity to show off some how-tos when it comes to torque tube strengthening and diff upgrades etc. The search and the tech section show little. And not just, "ahh ya just do this and ya sweet" comments, I mean pics and progressions.
If you know of any threads containing this then the links in here would be great. Otherwise if someone wants to chime in with their own detailed options then also great...

McDonald bros link --> http://www.mcdonaldbrosracing.com.au/geminicontrol.html
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Re: Diffs. Real Talk

Post by F3ARED »

Ill be doing mine sometime soon [altra9, torque tube strengthening etc]. Ill be getting the center installed by someone else but i suppose i could grab a few pics of the tube strengthening. From memory, all I did last time was get some 3mm walled tube slightly larger than the torque tube shaft, slide it over, weld it top and bottom.
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Re: Diffs. Real Talk

Post by Jonno »

Matt Egan just had his done and has had nothing but dramas to the point he actually went back to the original.

I'll PM him and get him to chime in here.

I'll dig the 'kit' I got out of my parts division and make as 'best' of a guide as I can assuming Nick doesn't beat me to it.

I had a look into the Mcdonalds brothers kit a bit before I posted the thread Bill.

No mention of price which is a tad annoying. I did see a kit on bookface floating around for $480 delivered.
Looking at some pictures reminded me of a mate that's done this in Geminis before so I might drop him a line and see what he says.

His er fab works pretty fancy to say the least.
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Re: Diffs. Real Talk

Post by firebug »

While this thread helps you make a decision Jonno it could also serve as a guide for others, hence the link. Maybe you could drop it into the diff or upgrade section instead of chat so it doesn't get buried?
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Re: Diffs. Real Talk

Post by Jonno »

firebug wrote:While this thread helps you make a decision Jonno it could also serve as a guide for others, hence the link. Maybe you could drop it into the diff or upgrade section instead of chat so it doesn't get buried?
Ahh that makes sense :P

Yeah sure :)
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Re: Diffs. Real Talk

Post by Javi »

Currently running a standard diff with a MIG LSD with my 4ZE1-T drift car. Was running 205 rears and didn't break it yet.

Dafuq are you doing to yours? :P
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Re: Diffs. Real Talk

Post by archangel62 »

Pics of my Hilux diff conversion are all on Failbook because I'm time poor and hate picture hosting websites that f*#k out after a week:
https://www.facebook.com/media/set/?set ... 117&type=3

Javi - based on local Ben Candy's drift Gem, you won't break the diff but you will kill a million axles. His kept twisting at the spline end.

Jonno - running 9.5" rears still isn't a reason to shorten the diff - if you want to tub it, you can tub it without shortening the diff and just run higher offset. You'll still have the same dish anyway. Or if you don't want to tub it, make up flares and go that way instead - either way you don't have to shorten the diff unless you want to run like, 12" wide wheels and they won't make them in the offset you want. If you shorten the diff or add more to the inner barrel of the wheel, after a certain point you will foul on things like the springs, shocks and lower trailing arms. If you want to turn corners, leave these things where they are.

Torque tube rubber - you can run solid rubbers which you definitely shouldn't kill. And/or you can make up your own torque tube rubber with high density rubber strips cut down and sikaflex the lot in. Since the TT is essentially your "upper control arm" you can't get rid of it without adding upper arms or triangulating the lowers so they can't rotate.

Geometry further discussion - I can definitely get mine better than it is without cutting through the floor, so I'll try that with new bushes and report back. Either way it's a lot of stuffing around.
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Re: Diffs. Real Talk

Post by Jonno »

archangel62 wrote:Pics of my Hilux diff conversion are all on Failbook because I'm time poor and hate picture hosting websites that f*#k out after a week:
https://www.facebook.com/media/set/?set ... 117&type=3
Thanks i'll sus tonight
archangel62 wrote:Javi - based on local Ben Candy's drift Gem, you won't break the diff but you will kill a million axles. His kept twisting at the spline end.
This times 328734255 I think I mention tired of changing axles. It's stuffs the inputs on the centre to. Ask me how I know.
archangel62 wrote:Jonno - running 9.5" rears still isn't a reason to shorten the diff - if you want to tub it, you can tub it without shortening the diff and just run higher offset. You'll still have the same dish anyway.
I'll have to investigate offsets and stuff then yeah.

No flares thanks.
archangel62 wrote:If you shorten the diff or add more to the inner barrel of the wheel, after a certain point you will foul on things like the springs, shocks and lower trailing arms. If you want to turn corners, leave these things where they are.
I was looking at another setup the other week. I'd more than likely need to relocate and run coil overs some how. Same deal with the lower trailing arms and If I deleted the torque tube integrate this with a third link or thrash the whole lot and roll with a 4 link.

archangel62 wrote:Torque tube rubber - you can run solid rubbers which you definitely shouldn't kill. And/or you can make up your own torque tube rubber with high density rubber strips cut down and sikaflex the lot in. Since the TT is essentially your "upper control arm" you can't get rid of it without adding upper arms or triangulating the lowers so they can't rotate.
I'll mess with this a bit. See how we go.
archangel62 wrote:Geometry further discussion - I can definitely get mine better than it is without cutting through the floor, so I'll try that with new bushes and report back. Either way it's a lot of stuffing around.
Ok Cool. Appreciate the feed back.
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