Double axle failure on the AEM 818R

[305mouse]

Better to break axles than the tranny. It's a pain, but you'll save time and money in the long run.

[Bob_n_Cincy]

By the way, Axles do bend before they break.
twisted shafts.jpg
If you have any worries, you can put some lines on them so you can eye out for pending failure.
Bob

[Santiago]

I *heart* Bob_n_Cincy.

Great idea! For a heavily tracked R-car this should be standard practice. Is there any rule of thumb for how much they'll twist before giving up or are we just going to have to set baseline data for it?

Best,
-j

[Bob_n_Cincy]

I *heart* Bob_n_Cincy.
Great idea! For a heavily tracked R-car this should be standard practice. Is there any rule of thumb for how much they'll twist before giving up or are we just going to have to set baseline data for it?
Best,
-j

I have no clue, Good question for DSS.
Bob

[bbjones121]

They might not put a rating on it simply because shock loads are likely to break them and are in excess of sustained rated engine torque. Joe blow does a clutch dump, breaks an axle and complains because his car dyno'd at 400ft-lb but his 500ft-lb rated axles broke and now he wants his money back.

Exactly!

[Evan78]

They put HP ratings on many of the products on their site. I'm guessing that what Frank is referring to is a reluctance to give a rating on a custom job. As Bob pointed out, torque seems more relevant than HP.

Frank - are you saying that they wouldn't give you a HP or Torque rating, or did they only avoid answering the torque question?

[Wayne Presley]

Torque is the only relevant factor.

[bbjones121]

Haha. Yes, torque is all that matters. They put horsepower because that is typically what the general public knows. What the general public doesn't know is that hp is derived from torque and rpm. Without a known torque value, you couldn't calculate hp. So to Wayne's point, torque is the only technically meaningful value.

[Evan78]

Even better would be torque at the axle instead of wheels since every car has different gearing.

[DanielsDM]

Even better would be torque at the axle instead of wheels since every car has different gearing.

Yes, "torque at the axle" is what matters. Which is a function of crankshaft torque and gear ratio. The momentary torque the axle sees will by much higher during a hard launch than the calculated value of crank torque times gear ratio. How much higher depends on how much the clutch slips and and how much grip the tires have.

[Frank818]

Frank - are you saying that they wouldn't give you a HP or Torque rating, or did they only avoid answering the torque question?

To me HP means nothing. Because HP is derived from torque, torque is the true measure. I said HP on my post (I think?) cuz many people use that figure (even DSS).
They never gave me a number they would stick hard on. I don't blame them, there must be a good reason. All I know is they (my shafts) will handle over 400wtq, probably 500+, but the way they answered to me meant that even with 400 they could break, they never said "if they break we refund you". They used words like "strong", "not very strong", "stronger", "strongest I got", "a lot stronger", etc... relative words.

Actually I re-read my emails... The guy said "I guess our axles would handle 450hp". Those are the chromoly axles, hardest one they have for the Subaru diameter. That is with the stock Subaru 24 splines, which are the weakest point. I have asked them to bore me the hubs for stronger splines and he said "this would make our axles a lot stronger". But no number... To me it means over 500hp or over 500tq, probably similar.

I will ask them again by saying in writing that even if I have 200wtq and they break, I won't sue them. Maybe they will give me some kind of number. I just want a ballpark, if he says they handle 700+ or not more 400, that's a huge difference, I'm sure they have an idea. They have a lot of customers breaking their Subaru parts (axles, CVs, splines).

[Evan78]

I wouldn't expect any number to be terribly precise. Everyone should be aware that once you take them out of a lab and put them in the field, there are too many variables to trust the number with much certainty. Considering that they have ratings on a lot (or all?) of the axles on their website, they must have some way of establishing a ballpark. I doubt they've faced any lawsuits from someone that broke one of their axles. If that ever happened, you'd probably find a bunch of disclaimers on their site.

[Bob_n_Cincy]

I've heard about the 4 or 5 cases of snapped axles. I think I only remember 1 MT5 issue. Were there a lot more?
Our 818 FXT engine with MT5 has been through a couple hundred hard autocross Launches. 10 to 15 feet of dual rubber each time. Rear tires were Federal 595s 205, Toyo R888s 225 or R888s 255 (current tires).

Our clutch is a KSB04-HD-OFE rated at 350 ft lbs. I feel that by limiting the torque of the clutch you can protect the transmission and axles.

Our clutch (350) times 13.5 give us about 4725 lbs of thrust. Over 2Gs.

That's my plan, it's working so far, I will keep you informed.
Bob

Like I promised 9 days ago. "I will keep you informed"
Michael and I had a great weekend auto crossing. Between us we had 27.001 runs.
Everything was running perfect until our very last run opportunity.
So Michael was on the edge of making a 60 second lap all day. So his launch might have been a little extra.
Here are the results.

https://youtu.be/HS9kN_Pd_78

[Hindsight]

Doh! Another failure.

Talked with DSS again. The custom Axles are good for 3000 foot lbs of torque which is about 450 at the flywheel. As Frank mentioned above, the weak point is the small diameter on the outer end. DSS makes larger diameter Axles that come with custom hubs which will be good for 850 foot pounds of torque at the flywheel. Waiting to hear back from them on cost but I would imagine $1900 for those. Not needed for most of us, but it's an available option.

Pretty sure they rate them at HP because that's what people know and usually torque is within 15% of peak HP so it's close enough.

[Frank818]

$USD1,300.

I know this isn't my thread, but it's about options for broken axles, so I guess it's relevant.

Here's my breakdown:

- DSS bigger/stronger WRX outer CVs: $500 (pair);
- DSS chromoly as-strong-as-possible-for-that-diameter bars: $400 (pair);
- Porsche G50 108mm inners: $200 (pair);
- Broaching Subaru hubs to fit the bigger outers: $200 (pair).

Now I got numbers. They have seen these bars and outers CVs on much heavier cars with 700whp+ and some work no problem, some failed. All parts can fail, there is no weak point a lot weaker than the other parts. Depends of all the variables, driving style, tires, weight, road condition, etc. They think with such light car (950-1000kg) there should be no problem to handle well enough 700+. Weight is helping here.

[Mechie3]

I'd be in for the $500 shaft upgrades.

[bbjones121]

Same here

[Canadian818]

I'd be in for the $500 shaft upgrades.

But when you start breaking CV's or transmissions will you still think it's an upgrade? It seems endless, I'm going to end up 7-8k in drivetrain between ppg gears, limited slip, and upgraded axles/cv's....

[bbjones121]

But when you start breaking CV's or transmissions will you still think it's an upgrade? It seems endless, I'm going to end up 7-8k in drivetrain between ppg gears, limited slip, and upgraded axles/cv's....

Probably don't need ppg. That would save you lots.

[Hindsight]

You know the saying... speeds costs money, how fast do you want to go?

I don't think I've seen anyone break the transmission with a stock engine setup. I think all the failures have been with higher than stock outputs. I THINK the same is true on the axles but am not 100% sure of that.

The bottom line is that there are a lot of weak points in the system when you go much above the stock HP rating. Known weaknesses are:
- Pistons
- Clutch
- Axles
- Transmission
- Intake charge cooling

If you want to keep costs low, just stick with the factory output. If you want to go faster, it's going to cost a lot more. It's not like working on a muscle car or a Toyota that was engineered for nearly double the stock output (though don't get me wrong, I wish it were).

[SixStar]

Another weekend, another failure.

We're looking into it but it would appear to be an alignment issue. I neglected to mention minimum track width when I had the car aligned and my guess is they're binding and snapping off from lack of plunge. The settings are all we have changed since the car was built and there's no reason they should be failing at this rate all of a sudden due to power. Going to have a pair built regardless.

EDIT: Not track width. We're 3/4" over min per side. Also this failure was a shattering of the OEM outer, I predicted this before the car was ordered, that part of the CV was never made to handle a fraction of thee power these cars can make (even stock)

Time to call DSS I suppose.

3sF39qG.jpg

[Canadian818]

Probably don't need ppg. That would save you lots.

I'll update my build thread soon, I'll need them soon enough. ��

[Hindsight]

I would not trust the 5 speed much over 250whp. Keep in mind that is well over stock HP which is 227 or something, at the crank. 6 speed would hold up to whatever you throw at it. 5 speed would need the PPG gears. Cheaper to go 6 speed but heavier and is a lot of gears for a light car.

[C.Plavan]

Again, Limited, but lots of track time since December of last year (283HP/304TQ) to rear wheels. ~2270 weight with me. No launches, but I abuse the crap out of it otherwise with Hoosiers R7's- with crazy fast laps (for 20 min each session lol). Still on original used transmission (78k miles), and original CV's- No issues. Pick your poison I guess.

[RM1SepEx]

higher than stock HP and TQ and shock loading is def the issue and remember in stock config the power is divided front and back vs just back. I would assume that the outer CVs might be a weak link... what is dist front to back with a stock Subaru?

We see axles, CVs and trans issues at autocross but they always grenade when those cars leap off the line due to such great grip. An 818 will always be limited by tires...

[RetroRacing]

That looks like an issue with the metal, I would magnaflux the next set regardless....in know we will be!

[SixStar]

We have several 5MTs in the 12s with no issue. Fluids and the loose nut behind the wheel go a long long way. Saying that all 5 speeds will grenade at X power is a bit of an overgeneralization. I've broken 5MTs on stock WRXs, I destroyed an RA box with a massive 265wtq, I've destroyed an RS transmission with 105wtq. Previous life and current abuse factor in heavily. In the end they're all just parts and results may (and do) vary.

[Hindsight]

Are the 5MTs in the 12's running front wheel drive only?

[Sgt.Gator]

I would not trust the 5 speed much over 250whp. Keep in mind that is well over stock HP which is 227 or something, at the crank. 6 speed would hold up to whatever you throw at it. 5 speed would need the PPG gears. Cheaper to go 6 speed but heavier and is a lot of gears for a light car.

I disagree. The 5 speed has a reputation for being weak but that is not what I have experienced. And there are differences between the older 5 speeds based on model of car and year. For sure old 2002 WRX 5 speeds are not as strong as newer ones. I think they made the change to thicker/stronger gears in 2008. The 2005 + Legacy trannys are stronger than old WRX trannys. I'll do some research and put together a chart with what years and models have the different gear strengths, I know I've seen it all posted on NASIOC and Legacy GT forums.

Anyway in my case my Legacy GT 5 speed survived 2 seasons of professional endurance racing on the Factory Subaru Road Race Team in the Grand Am Cup, a season of Tarzan Yamada driving it in Time Attack, then a year of my amateur shifting in the ICSCC conference racing. And that's in a 3300 lb race car. It's still fine and I will probably use it in my future 818R. Possibly one of the reasons it lasted is the SRRT installed a tranny cooler and pump after the first test session (I have the log book). I wonder when I read about LGTs breaking 5th gear if that's because they overheat the transmission for long periods (even towing).

I swapped it out for the 6 speed not because of the tranny, but because the R160 diff is very weak. As long as I was changing to the R180 diff I went ahead and did the entire swap. Since 818s don't use the rear diff it's moot here.

[PleiadsMan]

also depending on how heavy your wheels are and how sticky your tires are will make a huge difference. I killed many stock tires at the track just by using softer tries all around.

[Sgt.Gator]

I found the info in a couple of places:

http://www.rallispec.com/gea_syn_rst1140_t.html

http://flatironsrally.typepad.com/fa...d-more.html#tp

The short answer is the Legacy 2005+ and the WRX 2008+ have stronger gears in the 5 speed line.

[SixStar]

We run RA gears in the 818R. For best results they should be OEM and NOT micropolished.

[Mechie3]

But when you start breaking CV's or transmissions will you still think it's an upgrade? It seems endless, I'm going to end up 7-8k in drivetrain between ppg gears, limited slip, and upgraded axles/cv's....

I think I'd rather break something that is contained than an axle that can whip around. My donor (my former DD/AX car) already broke one trans. Third gear acceleration (not on a shift) and it popped. I still run a stock clutch to help prevent some shock loading but when I autocrossed I was able to spin all 4 on launch with Rcomps.

[Scargo]

We run RA gears in the 818R. For best results they should be OEM and NOT micropolished.

I am curious about your statement. First, I'd never heard of micropolishing till now and secondly, I looked it up and there are varying opinions of its efficacy. What about REM isotropic finishing or, as it is also called, Isotropic Super Finishining (ISF)? Combinations of processes like Microblue and REM?
One person said (http://www.eng-tips.com/) "I've had several friends swear that they have seen ~2% gains on a chassis dyno using this."
What's the problem with doing it?

[nkw8181]

looking at doing the 6 speed swap and while I'm at it upgrading the axles ( I have an 06 wrx as a donor) so I am interested in the axles. what all are they including? would you still need your own outer CV parts?

[SixStar]

Zach (Fate066) is my trans guy and he can elaborate but basically by taking metal off you're increasing lash/slop and therefore failure. I'm sure if they loosen all the wheel bearings they'll see an increase in power too.

[STiPWRD]

looking at doing the 6 speed swap and while I'm at it upgrading the axles ( I have an 06 wrx as a donor) so I am interested in the axles. what all are they including? would you still need your own outer CV parts?

The 6 speed axles are a larger diameter than the 5 speed or FFR axles so they should be much stronger. It sounds like DSS can provide either just the axle shafts or the shafts and CV joint assemblies.

[Scargo]

DSS did my axle assemblies for my six-speed to STi rear hubs. I got their heavy-duty inner CV joints and custom length axles made to couple with the rear STi outer CVJ. $755. I think the axles are 500 HP rated.
From their invoice:
2 - CVJ5114 STI rear outer CV made from 4340 with 32 spline race


2 - Inner CV Inner CV joints for front STi Diff ('05-'07 STi 6-speed)

[Frank818]

DSS can provide anything you need. If you want just the bars without CVs (as FFR), they can do that. If you want CVs with that, yes, if you want broached hubs, yes, upgraded CVs, yes, I bet they can provide a Koenigsegg inner CV (what on earth you got as a tranny?? ) but they can't go bigger than the biggest diameter possible on the hubs, whichever hubs you may use.

[nkw8181]

Can they put a larger wheel bearing in the wrx hubs if bored out? On a side note just picked up a jdm spec C 6 speed!