As axles are the 6.7″ rear ends weak point we got some heavy-duty replacement Panic Made axles from Battle Garage. Back in the day at TRD on the Pro Rally cars, the axles would twist and would need periodic replacement. Our GT3 cars would twist the axles toward the ends and we would have to inspect them at the end of every race and replace them about every third race. When drag racing, the axles would snap at the splines. The Panic Made axles are much stronger. We ordered the Kouki version of the axles as we got a Kouki diff as the Kouki diff has slightly larger splines for more strength. It is not a huge difference but hey if you are changing everything you might as well do it right!
We ordered our axles fully loaded with bearings and retainers. As you can see the axles are bigger in diameter than stock and neck down to the stock size before the splines. This is a good design as it prevents the stress from concentrating on the splines which are the weakest parts of the axle.
The Panic Made axles are made of a proprietary stronger steel alloy. It is really hard, possibly something like 300M. Back in the day, I used to have the axles shotpeened and this would make them last about 2x as long before failure. So just to be cautious I had the Panic Made axles shotpeened. Man even with hardened shot at the machine’s maximum velocity, you could not see one bit of dimpling! These axles are harder than gears! Since shotpeening didn’t seem to do anything, I had the splines WPC treated and it did improve the axle’s surface, providing a hard compressed layer. I am pretty sure our little NA 4AG isn’t going to hurt these!
We are going to be using ARP extended-length studs for our rear end. This will allow us to use spacers to adjust the track width if we want to and are much stronger than stock. It will also fully engage our extended-length open-end lug nuts.
Stay tuned, in our next segments we will be fixing our poor cars extensive rust and crash damage that was hidden by bondo!
Sources
Battle Garage
SQ Engineering
Panic Made
OS-Giken
Mountune
WPC Treatment
CTP Cryogenics
ARP
15 comments
Open lug nuts in Southern California on an AE86…Mike you’re braver than I am!
Are all J160 gears compatible with each other? I have an NC with the J160 which also has an absolutely horrible bog on the 3-4 shift… can I mix and match ratios out of all the cars they came in? Previously I’ve only been looking at NC’s and RX-8’s… but will gears from the 86 twins and S15 work too? And aftermarket gears designed for those transmissions? I know this might be a “duh” question, but I’m having a pinch me moment about it… might finally be able to get gearing I like!
Also, are these transmissions really good for 300 ft/lbs of torque? seams a little ambitious, no? Reason I’m asking is I’ve been toying with the idea of putting a Honda J series V6 into an RX-8 but the transmissions grenading itself with “crazy V6 power” has been one of the discouraging factors… How much torque would you realistically trust to this transmission for a street car with a decent amount of track use?
From messing around with S chassis cars and the FR-S it seems like the 300 ft/lb thing is about true, Once you exceed that kaboom. at least on track driven cars. On cars like our supercharged FR-S, the transmission seemed happy and reliable at 250 ft/lbs.
We exchanged 6th gear with an S15 one so the other gears can probably change. This one Australian company has a reliability mod for the box. We never had this chipping problem, more like 3-4 loosing the teeth,
https://neatgearboxes.wordpress.com/2014/04/16/nissan-silvia-s15-6-speed-gearbox-circlip-mod/
We’re talking crank torque, not torque at the wheels, correct?
more gear ratios to play with potentially makes things more interesting… time to spend hours looking up all the ratios and mix and matching them to find the perfect spread, haha..
Thanks for the link! Did you chip the teeth with the 250tq FR-S?
Hope you meant NB – the NC and later RX-8s are an inhouse Mazda top loading transmission.
There’s some variations, I think the NB has smaller diameter shafts, certainly a different size output shaft. At some point I’m going to get ahold of a Subaru version and see how much can interchange between them.
From many sources:
Vehicles that use the J160
Toyota Altezza AS200 and RS200
Mazda MX-5 (Miata)
Nissan Silvia
Mazda RX-8
Lexus IS
Toyota 86/Scion FR-S/Subaru BRZ
Correct; but only the 1999-2005 (NB) Miatas and the 2004-2008 RX-8 used the Aisin AZ6/J160 gearbox. The 2006-2015 MX-5 (NC) and 2009-2011 RX-8 used a completely different transmission for whatever reason; if you look up photos the differences aren’t subtle. More subtly though, while the Miata and RX-8 Aisin gearbox casings bolt to one another, the Miata version has some dimension differences on the output shaft and yoke. I don’t know if the Miata version is an oddball or if they’re all subtly different on internals.
Good to know!
well thats a shame… but thanks for the detailed info Dani!
Any chance you know if the 09+ RX8 transmissions can handle more power over the earlier Asin units?
Supposedly the NC transmission holds more power than the Aisin transmission; they used it again for the Fiat 124 Spider and they have a better reputation for hard use than the Aisin transmission does. They all have the annoying 4th gear ratio though; I think the Fiat 124 just has a different input to countershaft gear pair than the NC and RX-8 as the 3/4 gear ratio split is identical.
For the record, I’m coming from all of this from wanting to put an RX-8 front case on a Subaru version of the trans to get rid of that 4th gear (and a closer ratio 6th for track use) behind an NA 13B.
There’s a version of the RX8 in the UK (think 09+) that has a taller 3rd gear (1.536) which helps quite a bit with the 3-4 spacing. There’s a guy over on the Miata forum that did it and says the difference is huge. You do end up with a little bit longish 3rd, my IMHO thats easier to overcome being a lower hear and lower speed. With the long 4th and all of the wild 150whp my NC had it was starting to hit the aero wall right around the time you bogged into 4th gear.
I plotted out all the ratios, and I think my ideal would be the long 3rd paired with the 86 4th gear. If that was a thing… which its not…
What are the ratios for these transmissions?
US NC MX-5 and S2 RX-8 (the Mazda inhouse gearbox) are 3.815, 2.260, 1.640, 1.117, 1, 0.843. The US NB Miata with the Aisin box is 3.76, 2.269, 1.645, 1.257, 1, 0.843 and the S1 RX-8 with the Aisin is the same except that 4th gear is 1.187:1. I have no idea why.
I’m seeing the UK NC MX-5 having 3.709, 2.190, 1.536, 1.177, 1 and 0.832 which, yeah, seems a little better. It looks like the JDM NC had the same ratios as the US ones.
That is a pretty big jump!
I also committed to an Aisin AZ6 (J160 is the Toyota nomenclature for that transmission) in my AE86, in RX8 guise for my 13B swap, as well as an FB RX-7 rear axle from my GSL-SE for the sake of a little extra power handling, and in my travels I’ve found out that there is supposedly a machining operation one can do to… the countershaft, IIRC(?), which allows you to install a heavier duty version of a circlip that’s somehow involved in these transmissions grenading at around that 250-300 lb-ft mark with any sort of shock loading. There’s only a couple of transmission builders that advertise doing this modification, but if you search for “AZ6 circlip mod”, it’s not a humongously difficult thing to find more information on. Said modification is advertised as allowing the transmission to handle approximately an additional 50% of the torque, but I am skeptical of that figure, as that seems like something Aisin would have figured out and made a revision for in that design in the roughly 25 years or so that it was produced in various forms.
As far as I can tell, the machining operation is effectively taking a ball end mill and continuing a slot that’s all ready in the shaft until it reaches the root of some splines, as opposed to said slot just kind of ending in the middle of them, but my memory on those details are sort of rusty; it’s been a couple years since I last really looked into it.