OS Giken FAILURE

[Steve M]

For those keeping track of my Dana Super 44 rebuild (here: https://driveviper.com/forums/threads/30343-Viper-Dana-Super-44-Rebuild), you may have noticed that I haven't finished the story.

And now you'll understand why.

Background: long story short, I decided to rebuild my spare differential with parts better suited to the drag strip. I originally only wanted to try 3.73s, but Jon B also recommended "upgrading" to an OS Giken. I've read nothing but good things about them, so I decided going way over my original budget was worth the stretch.

As it turns out, I was wrong. So very wrong.

As you'll eventually find out, I successfully got the differential assembled, installed, and broken in - I busted my ass to put 500 miles on it over about a week and a half, changed the oil, and was ready for my first outing at the drag strip about a month ago.

I made one full pass down the quarter mile - an 11.07 @ 129.xx. Not bad for a shakedown pass.

Came around for a hot lap since it was still early and hardly anyone was there. Did my burnout, rolled up to the line, and was greeted with this:

Differential side:

https://i.ibb.co/n3YrNBL/Broken-Stub-Differential-Side.jpg

Axle side:

https://i.ibb.co/MyHrtPY/Broken-Stub-Axle-Side.jpg

I didn't realize OS Giken included quick disconnect stub shafts. Neat.

[Steve M]

For those that don't know, the OS Giken limited slip differential carrier uses unique stub shafts/axles - the stock stubs cannot be used.

OS Giken on the left, OEM GKN Visco Lok right-hand (longer) stub on the right:

https://i.ibb.co/020Kqj5/Stub-Axle-Comparo-2.jpg

The OEM stubs are unequal length - the left side stub is substantially shorter than the right side stub (not pictured). The OS Giken stubs are equal length.

Or at least the OS Giken stubs start out as equal length, until they suddenly aren't:

https://i.ibb.co/bKDcr7d/Stub-Axle-Comparo-1.jpg

The OS Giken stubs are retained differently (circlips are further inboard), and also use substantially different internal splines that interface with the OS Giken carrier. Here's a good shot showing the difference:

https://i.ibb.co/BCytv4D/Stub-Axle-Comparo-3.jpg

That is why you can't use the stock stubs.

[Steve M]

After I cooled off for a few days, I gave Jon B a head's up about what happened.

His response:

"YIKES !! We have never, ever had an OSG fail. Neither has Unitrax."

I just love being unique.

Jon was kind enough to reach out to Unitrax, and Unitrax told him to have me give them a call. So I did.

The good: Unitrax was very helpful. Melissa was great to talk to, and she reached out directly to OS Giken to see what they could do to fix my issue.

The bad: OS Giken said no warranty (because race car), and they'd sell me a pair of new stubs for $475.

I respectfully declined. I then said many disrespectful words that I won't repeat here.

The differential won't work without the stubs, so I'm stuck with a very oily, very expensive 25 pound paper weight.

[Old School]

Well I guess on the plus side, you were barely moving when it happened, so the loose axle didn't spin around and tears thing up....

[Steve M]

Am I being petty? Maybe, but I'll let you decide for yourself.

In my amateur opinion, the OS Giken stubs are a failure waiting to happen. They are substantially less beefy than the OEM stubs. Here are the measurements side-by-side for reference:

https://i.ibb.co/ydh8qkd/Stub-Measurements.jpg

The shaft failed exactly where you'd expect it to. The only thing I don't know is what material the stubs were made out of, but it clearly wasn't strong enough to counter the lack of material at that point. It also clearly wasn't strong enough to take what I threw at it.

And to be clear, I made 54 passes on the OEM stubs. 50 of those were on drag radials, and on many of those I was over 3,600 pounds race weight.

The night the OS Giken stub broke, I made one pass. One. Fucking. Pass. And my estimated race weight was around 3,520 pounds. And my drag radials were 3 years old. And I launched the car around 3,500 RPMs on the pass where it broke, and have the video to back it up. I've launched my car as high as 5,500 RPMs in the past on the stock stuff with no issues to speak of, minus a little gear whine afterwards.

Personally, I think their design sucks. There was no reason for them to neck the shaft diameter down so abruptly, nor as much as they did. A chain is only as strong as its weakest link, and the stubs are the weakest link in an OS Giken. And you can't run an OS Giken without their stubs.

So yeah, I'm not paying $475 for an equally shitty part, especially since I only need one (they would only sell a pair). And that's on top of the $4,000+ I spent on parts and tools, and the countless hours rebuilding the differential all to only survive one full pass.

I normally say my opinion isn't worth much, but in this case, it's worth about $4,000. I'm eating that cost because at this point, OS Giken could give me new stubs for free, and I still wouldn't take them. And to be clear, they aren't offering me anything, nor do I ever expect them to. Both Unitrax and Jon B went to bat for me, and they both struck out. For what it's worth, Unitrax said they'd likely never sell OS Giken products ever again - they were not impressed with their support, or lack thereof.

As of yesterday, that differential is completely torn down, and the OS Giken is back in its box. I'll hold on to it for now, but it'll likely end up in the trash when I get tired of the box taking up space.

Buyer beware.

[Steve M]

Well I guess on the plus side, you were barely moving when it happened, so the loose axle didn't spin around and tears thing up....

Oh yeah...things could have been way worse.

But things could also have been way better. The fact that they won't stand behind their product speaks volumes.

[J TNT]

Wow , sorry to hear that Steve ! Not what I expected but the OEM looks more robust even the chamfer looks like a better design .
Did they not warranty it because of slicks or just being at the track ?

[Steve M]

Wow , sorry to hear that Steve ! Not what I expected but the OEM looks more robust even the chamfer looks like a better design .
Did they not warranty it because of slicks or just being at the track ?

Unitrax didn't specify, and I didn't ask. I never actually spoke to OS Giken myself, but given how they dismissed Unitrax, it doesn't seem worth my while to even try. I bought everything through Jon B, so going direct to OS Giken isn't going to get me anywhere with them anyway.

I got the impression it was because it was being used at the track though.

Which is kinda the point of buying an OS Giken.

[99RT10]

Steve, Can you cut down an OEM piece to fit into the Giken?

[Steve M]

Steve, Can you cut down an OEM piece to fit into the Giken?

There might be enough meat to do it...not sure. With enough time and money, anything is possible I suppose.

I'd think you'd be trading one weak spot for another though.

Note: OEM Gen 4 stubs are in short supply. I tried ordering new ones through Chrysler, and my order was immediately cancelled. Discontinued part.

[SA Heat]

I saw this on your Instagram page....totally sucks.

In the comparison photo with the measurements, the stock shaft has a groove right above the "1.3785" inner spline measurement that the OSG shaft doesn't have. What does that groove do? Just curious, do you know what it measures? Visually it looks like it's really thin, but it may be an optical illusion with the photo.

Also, is this a different rear end than the one you've done the tutorial on in the other thread?

[AZTVR]

Thank-you for publishing this! I would have said that this was probably a manufacturing defect since the go-to Viper experts on this product have never heard of a failure before, and I assume that your application is not unique. (horsepower and drag racing). However, OS Giken is making it clear that their present product is no longer capable of being used in a Viper or other car of similar power and usage. Hopefully the message gets to other non-Viper owners also. What hp/torque are you at?

[Steve M]

I saw this on your Instagram page....totally sucks.

In the comparison photo with the measurements, the stock shaft has a groove right above the "1.3785" inner spline measurement that the OSG shaft doesn't have. What does that groove do? Just curious, do you know what it measures? Visually it looks like it's really thin, but it may be an optical illusion with the photo.

Also, is this a different rear end than the one you've done the tutorial on in the other thread?

The groove isn't all that thin - it is more of an optical illusion due to the lighting.

The purpose of that groove is to accept a circlip that's inside the differential carrier, which keeps the stub shaft locked in place once installed. The circlip groove's size and location is specific to the OEM Gen 4 GKN Visco Lok limited slip carrier. The circlip (not pictured) is the part people have a hard time getting to let go when removing the stubs from the stock carrier to do a gear swap.

That same groove exists on the OS Giken stub, but is at the bottom of the shaft in the picture as shown. The internal circlips that hold the stubs in place in the OS Giken are much farther inboard because it doesn't use a cross-pin of any sort in the carrier. The GKN Visco Lok does.

To answer your last question, this is the same differential that's pictured throughout my tutorial thread. I finished it up back in early September, got it in the car by late September, and had it broken in and at the track by 13 October. It had around 530 miles on it total. It's a damn shame I had to tear it apart - the gears were set up perfectly, and it was nice and quiet during break-in.


Thank-you for publishing this! I would have said that this was probably a manufacturing defect since the go-to Viper experts on this product have never heard of a failure before, and I assume that your application is not unique. (horsepower and drag racing). However, OS Giken is making it clear that their present product is no longer capable of being used in a Viper or other car of similar power and usage. Hopefully the message gets to other non-Viper owners also. What hp/torque are you at?

I've never dyno'd the car, but given its weight and trap speeds down the 1/4 mile, I'd estimate about 640 at the crank (probably around 520-530 at the wheels). It traps about what a well-driven stock Gen 5 in decent weather would in the quarter mile.

It's always been a street car that just so happens to do okay at the drag strip. Nothing special at all, and certainly at the lower end of the power spectrum for a mild bolt-on Gen 4/5 car.

[GTS Dean]

It looks to me like there's a machined-in stress-raiser on the OS-G stub. A sudden, sharp cut to a smaller diameter is not a good idea for high-stress shaft torsion subject to on/off throttle stress reversals. MAYBE a generous fillet would help. I've not really heard of many folks running a Giken on a drag car. Road racing usage in most cases doesn't shock the driveline as severely, unless you're racing on a very rough street course. If not for this sharp diameter step, the shaft would likely exhibit a diagonal failure along the shaft CL, but there's a lot of different machining going on right there.

[Steve M]

It looks to me like there's a machined-in stress-raiser on the OS-G stub.

Agreed. Unless they redesign them, it's always going to be a weak point, at least for this application.

It sounds like the Viper is one of the few applications where they include custom stubs, at least from what I gathered. There was some major confusion at first as to where the stubs came from (and whether or not I had sourced them myself), but I managed to get everyone sorted out after a few phone calls.

No, I didn't machine them myself in my garage.

No, I didn't buy them used.

No, I didn't install them incorrectly.

[Heysie]

That really sucks Steve.
Making a very nice how-to about the diff and with this result.
Hope somebody will come with a nice solution (in money or parts) for all this shit.

[Steve M]

That really sucks Steve.
Making a very nice how-to about the diff and with this result.
Hope somebody will come with a nice solution (in money or parts) for all this shit.

I think it's safe to assume that no one is coming to the rescue with a remedy or compensation of any sort at this point. I'd probably question their motives if they did.

But fear not - diff rebuild 2.0 is underway. All of my lessons learned to date should help me speed that process along. Unfortunately, winter is here :(

Oh, and I won't be using an OS Giken for this next go.

[J TNT]

Looking forward to your post on the resolution for the issue Steve . Are you thinking Wavetrack ?

[Old School]

But fear not - diff rebuild 2.0 is underway.

At least you won't have to set pinion depth/preload....

[Steve M]

Looking forward to your post on the resolution for the issue Steve . Are you thinking Wavetrack ?

I am not, for three reasons:

1. They aren't available
2. Yet another added expense
3. They also use unique stub shafts

I'd want to see and inspect the stubs before I'd even think about trying it. Wavetrac certainly has a good reputation, but so did OS Giken. The strongest carrier means nothing if the stubs aren't up to the task.

I originally wanted a Wavetrac for my build, but there were none to be had when I was looking back in July. Unitrax said that was still the case when I talked to them late last month. I'm not playing the waiting game anymore. I have two perfectly good GKN Visco Lok differentials sitting on my work bench; neither of them failed me over the last 11 years I've owned my car.

I lost around $3k in parts alone, and at least $1k in my own labor depending on how much value I place on my time. Spending another $1,600-$1,700 to take a chance on another aftermarket limited slip unit just isn't in the cards right now. My pockets only go so deep, and I already way overextended myself on this little project with absolutely nothing to show for it other than some new found knowledge.

[Steve M]

At least you won't have to set pinion depth/preload....

I wouldn't if I was a smart man.

But I am not a smart man.

I am rebuilding my other differential this time (the Gen 5 diff I bought back in 2017). I wanted another data point, so I'm going to see what made that one tick. When I bought it, the gears were set up dead silent, unlike my original Gen 4 differential.

It's mostly apart right now, so we'll see what shims they used for that one, and how close it'll get me to where it needs to be. The ring and pinion going back in will be new though, so none of the original stuff may matter.

[Dan Cragin]

For a drag race setup, you want a clutch type LSD, not a gear driven setup like a Wavetrac or Quaife.

The stock Gen 4-5 LSD is quite stout.

We used the OS unit in the Formula Drift Viper when I was crew chief for Mopar, it had lots of abuse and never failed. We have also used
it in the Comp Coupe's and ACRX's without issue. The biggest advantage is we could "tune" how the unit would lock and unlock. Biggest issue we had was with the half shafts. The cages first failed, then once upgraded sometimes the shaft would fail.

Having said that, drag racing is the ultimate test. Back in the day we ended up putting automatics in all our drag cars. Launching with a clutch
just hammered the driveline and stuff would fail quite often.

[TrackAire]

I feel your frustration. I'd buy the new stub axles and sell the whole system to recoup some of your costs. But first I would definitely contact OS Giken again and show them this thread and let them know that this was in all probability a defective stub from bad machining. Maybe they can sell the stub axles at a major discount.

On the other hand, if you're feeling brave these guys charge $7.69 plus two packs of Camel cigarettes to get you back on the road.....;)

https://www.youtube.com/watch?v=rghogYN-DPo

[Steve M]

The stock Gen 4-5 LSD is quite stout.

Given what I've put mine through, and what happened to the Giken, I have a new appreciation for this.

To be fair, the main portion of the OS-G appears to be quite stout. The main body + internals of the Giken weighs 25 pounds compared to 23 pounds for the GKN Visco Lok. That's a good amount of extra steel packed in there for sure.

There's still a lack of civility with the Giken on the street to contend with though - even after the full 500 mile break-in including many sessions of figure 8s in an empty parking lot, I was still getting some random popping around corners that was a bit unsettling at times. It was getting better, but I'm not sure how many more miles it would have taken to be mostly rid of it.

And before anyone goes there, the only oil that ever touched that Giken was OS-250R: https://osgikenusa.com/products/os011-ka1

That shit ain't cheap, and right now every last liter I had is sitting in a 5 gallon jug waiting to be recycled. ~20 miles on an oil change is a new record for me.

[Dan Cragin]

The OS Giken oil is hard to find and expensive, being that it is made from whale blubber.

If you use anything else the clutches wont release well.

I did not use the Giken's on the street as they are quite noisy, like a old fashion "Locker". For the Road Course
they really put the power down out of the corners.

[TheMadMachinist]

That is a tough break, Steve. No pun intended. Reading this post it sounds as if poor design and maybe the wrong parts for your application is the general consensus. Just looking at the end of the shaft it looks like someone just used a part off tool in a lathe on a piece of bar stock. I am no material engineer but it's hard to believe that shaft was even forged or heat treated correctly from the get go. It would be interesting to have the end of that shaft hardness tested along with the stock unit for comparison. Most any machine shop could do it for next to nothing in a few minutes But at this point it most likely just only add to your frustration.

[RyanLS.GEN2]

i have a spare os stub shaft, it came in axle shaft i bought. i couldnt figure out what it was for with the fine splines until i saw this post, trade for a short gen4 stub?

[Steve M]

i have a spare os stub shaft, it came in axle shaft i bought. i couldnt figure out what it was for with the fine splines until i saw this post, trade for a short gen4 stub?

Unfortunately, the short stub I have was damaged when one of my DSS axle flanges refused to release from the stub: https://driveviper.com/forums/threads/30343-Viper-Dana-Super-44-Rebuild?p=466545&viewfull=1#post466545

Ultimately, nothing ever came of any of this, minus one nice gesture: Jon B offered me a $200 credit toward a future purchase as compensation for my misfortune with the OS Giken. He's the only one that stepped up to the plate for me...never heard back from either Unitrax or OS Giken, not that I really expected to. I'll be needing new tires in the spring, so I'll certainly put his credit to good use.

That said, if anyone wants to give an OS Giken a whirl, $1,000 takes mine with about 530 miles on it + one pass down the quarter mile. It'll come with one good stub - you can either make a deal with RyanLS.Gen2 for the one he has, or you can go through OS Giken and pay $475 for a pair of new stubs. Either way, that's far less than you'd pay for a new unit.

[RyanLS.GEN2]

There is another in the parts Facebook page with a pretty twisted stub that looks the same..... maybe they had a bad batch

[Steve M]

There is another in the parts Facebook page with a pretty twisted stub that looks the same..... maybe they had a bad batch

Interesting...I'm not on Facebook, but I'd very much like to see that other twisted part to compare.

[RyanLS.GEN2]

Interesting...I'm not on Facebook, but I'd very much like to see that other twisted part to compare.

My phone won't let me post a picture. But I screen shot it and post it tonight. It shredded at the inner splines. Almost looks as if it didn't seat all the way.

[J TNT]

Shame they break and are design issue. Would Strange Axles be an option or is it not feasible at this point ?

[Steve M]

Shame they break and are design issue. Would Strange Axles be an option or is it not feasible at this point ?

I'm not familiar with that option. Got a link?

[J TNT]

I'm not familiar with that option. Got a link?

Here you Go Steve , my Drag Racing Buddies have used them and they've been at it for years .
If pricing is decent and it helps bring the cost down on multiple sets then I'll go in on a set with you ....

https://www.strangeengineering.net/

[Steve M]

Here you Go Steve , my Drag Racing Buddies have used them and they've been at it for years .
If pricing is decent and it helps bring the cost down on multiple sets then I'll go in on a set with you ....

https://www.strangeengineering.net/

So something custom made? I'm sure someone could make something that would be stronger, but I'm not sure the market would support even a small production run. You'd be talking a small niche of an already niche market.

[J TNT]

So something custom made? I'm sure someone could make something that would be stronger, but I'm not sure the market would support even a small production run. You'd be talking a small niche of an already niche market.

True but it being a small unit might be feasible , no harm in asking ?
And 9 Liter Guys may be Interested ???

[GTS Dean]

Interesting...I'm not on Facebook, but I'd very much like to see that other twisted part to compare.

Here you go! Looks to me like too much tire/too much engine-trans torque for the material spec they are using.

[Steve M]

Here you go! Looks to me like too much tire/too much engine-trans torque for the material spec they are using

Holy shit...pretty good chance it messed up the splines inside the OS Giken too.

[GTS Dean]

Possibly a deeper quench/temper program for the bar stock might help, but more diameter is the best answer IMO. That would require reengineering the diff unit itself and those parts might start getting too thin to handle these loads.

I know a guy with a low-mile unit possibly looking to sell...

[Steve M]

Possibly a deeper quench/temper program for the bar stock might help, but more diameter is the best answer IMO. That would require reengineering the diff unit itself and those parts might start getting too thin to handle these loads.

I know a guy with a low-mile unit possibly looking to sell...

Looking at that particular failure a bit more compared to the pristine one pictured earlier in this thread, it looks like it failed right where they necked down from the inner splines.

I think more diameter is also the right answer...I'll have to look at my OS Giken again and see what might even be possible.

[pokeyl]

Wow, looks like it was not heat treated or whatever hardness process... It would be worth it to test hardness of the failed stub and a good one. If there is a difference you night be able to get the manufacture to step-up. I am Not an engineer!

[GTS Dean]

After reflecting on the dimensional comparison from post #5, I frankly don't understand why the Giken shafts were turned down any smaller than the inner spline OD at any point. Even the stocker has a nice wide fillet cut at the end of the inner spline for gentle stress flow. All I can imagine is a relatively miniscule weight reduction because the carrier is 2# heavier than the stock diff. From these two Viper failures alone, I would think the owners should team up and present these instances to OS-G and try to seek some equitable remedy. I wonder if the stubs were sourced from the same manufacturing Lot? I'm also curious if Bobby Archer has ever seen this - Dan C. said he has not.

[RyanLS.GEN2]

After reflecting on the dimensional comparison from post #5, I frankly don't understand why the Giken shafts were turned down any smaller than the inner spline OD at any point. Even the stocker has a nice wide fillet cut at the end of the inner spline for gentle stress flow. All I can imagine is a relatively miniscule weight reduction because the carrier is 2# heavier than the stock diff. From these two Viper failures alone, I would think the owners should team up and present these instances to OS-G and try to seek some equitable remedy. I wonder if the stubs were sourced from the same manufacturing Lot? I'm also curious if Bobby Archer has ever seen this - Dan C. said he has not.

I talk to Archer quite a bit, he is buying my stock gen3 stubs and my os-g stub. I'll call him tonight

[Steve M]

After reflecting on the dimensional comparison from post #5, I frankly don't understand why the Giken shafts were turned down any smaller than the inner spline OD at any point. Even the stocker has a nice wide fillet cut at the end of the inner spline for gentle stress flow. All I can imagine is a relatively miniscule weight reduction because the carrier is 2# heavier than the stock diff. From these two Viper failures alone, I would think the owners should team up and present these instances to OS-G and try to seek some equitable remedy. I wonder if the stubs were sourced from the same manufacturing Lot? I'm also curious if Bobby Archer has ever seen this - Dan C. said he has not.

I'd love to see some sort of remedy that doesn't involve me shelling out more $$$, but I have a feeling I'm about 10-15 years too late here.

They've already made their profit, and the likelihood that they are going to sell even a few more Viper units is probably pretty low. It is in their best interest to just keep their heads down and ignore it until everything blows over (and it will).

Do any Gen 5 owners run an OS-G? What did they do, switch over to Gen 4 axles? The inner part of the Gen 5 stubs is identical to the Gen 4s, so they wouldn't be able to use Gen 5 stubs with the OS-G without some sort of modification either to the stubs or the OS-G itself.

[GTS Dean]

This may, or may not be helpful...

[Steve M]

I wonder how many Viper OS Gikens have been sold. I know Mark Jorgensen was a big fan, and I'm sure he had many customers that used them as well.

Seems like Nth Moto favors the Wavetrac for their builds.

[Steve M]

For posterity, here's a better look at the internal splines of the OS Giken vs. the GKN Visco-Lok:

https://i.ibb.co/jhMTxh4/Giken-vs-Visco-Lok.jpg

That's why the OS Giken uses equal length stubs vs. the GKN Visco-Lok that uses unequal length stubs.

There's also no reason why OS Giken couldn't have gone bigger on the stub shaft diameter that goes inside the differential - it doesn't neck down until the splines, which are pretty far inboard.

[Steve M]

One small and probably final update: my OS Giken and the one good remaining stub are now with a new owner.

To bring everything full circle, I'm currently in the process of rebuilding my other differential - going back to 3.55s and one of the two GKN Visco-Loks I have in my possession. I'll hopefully have it back in the car and ready to go around the spring time frame.

What happens after that? Who knows...