Broken diff housing
 

I put my car up on the lift and happened to notice this. Diff arm cracked right through the machined in break here feature. I hadn’t noticed anything weird but from the fracture surface it doesn’t look like it was broken all the way through for very long. Might have broken my last autocross run last weekend and I just happened to see it. Anybody else breaking these? I cringe every time I see people jacking up there car by the diff and It is something I’ve never done.

https://www.miataturbo.net/attachmen...2-1024x768-jpg

Many break there, thats why everyone uses the FC housings. P.S. I have some for sale!

jacking by the diff isn't going to do that.

but that's a factory break point so you don't ruin the motor/drivetrain on a rear end collision

Will those fit the Miata front section? I might be interested.

Yes. When I swapped in my RX7 clutch diff I used the 7 housing/ring and the miata nose/pinion.

https://www.miataturbo.net/attachmen...ine=1377455044
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I never Jack by the Diff. I was surprised seeing 949 racing jacking by the diff at the 25 hours of Thunderhill.

FWIW looks like the crack initiated at the top slot.

Wow not only does the RX7 one not have a notch and looks beefier its got a big flat spot that looks like it was made to be a jack point.

factory manual shows it as a jacking point.

yep. no notches, and MUCH beefier "legs"

I was thinking about selling one I received a few weeks ago. Shoot me a PM if you can't procure one locally. If not, I might just keep it as a spare now knowing its a little stronger.

Went through two at a pro solo last month.

https://www.miataturbo.net/attachmen...ine=1377472219

I broke mine exactly like that with my f20c. I didn't fuck around with it I'm ordering boosfrog 8.8 diff bracket tomorow

The Rx7 one looks heavier. If I find it to be a problem on my car I'll fully box the arms and send it out to be re-heat treated.

I'm not sure how people jack by the diff. Even with my super long reach ultra low HF racing jack I cant reach it, the jack hits the stock 94+ "cannon brace" before I get in far enough. When I jack the rear I jack from the rear most bolt of that brack. Hasn't bent anything yet.

I've seen two like that. Sporting the RX-7 one now.

Theseus has had an FC housing for a few years now.

What causes these failures, axle tramp...hoosiers......+300 WHP...Auto X only?

Having built and continuing to develop my circuit racing car. I am interested to know if this is something that should be on my radar or not?

Well I'm guessing in my case over 300 ft-lbs of torque 275 A6 Hoosiers and I recently did a bunch of autocross. western states champ win Packwood Prosolo win and Canadian National Autoslolom championship win in SSM also having a co-driver. The energy suspension diff mounts may not be as nice to this part as well.

So I Guess I found another weak point. I have already determined the inner CV’s wear out fairly rapidly. About half a season and the balls imbed themselves into the outer cup and they start developing lots of slop. I suspect Mazdaspeed axles would fix that.

Given the location of the relief notches the housing must be snapping from front to rear movement of the drive train. What kind of motor mounts are you guys who broke em running?

Would something like this help?

Joy Fast PPF performance bars - MiataRoadster - High-performance customer service...and parts for Roadsters

It would stop the twisting and front to rear movement of the drive train.

I have one of those but a Beatrush one. I bought it to try and alleviate axle tramp in the damp conditions of my first race but quickly took it off becaues in the wet the transition from grip to no grip was instant and undetectable, on the road....frightening. Can't imagine it being better on the track..

I do wonder if it is an improvement to the standard setup in the dry though....in for anyones experiences....

I haven't had a chance to do a back to back test, due to combination of building car and the wet winter has prevented much driving/testing....but intend to at some point.

sounds like someone belongs in the CR slammed thread.

AWR engine mounts energy suspension Diff mounts. I suspect the failure is more related to torque reaction. High input of engine torque puts the top flange where the notch is in tension. From the fracture surface I can see evidence of periodic crack growth from the top notch over time about half way through the part then snap from the lower notch.

1.5 lbs heavier, most definitely stronger, disappointingly less effective looking cooling fins.

https://www.miataturbo.net/attachmen...5-1024x768-jpg
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Thanks for posting the side by side. I guess I'll be getting 3 of these soon. One for each gear ratio. Due to the location of the weight, I'm not worried about the extra 1.5 lbs.

Bummer, now the diff will run 350*F instead of 340*F. ;)

Looks like there are at least two different designs... the one that Bob posted with the cast in triangulation and then this one. The top side looks pretty much the same as Bob's. Either one should work fine, yes?

https://www.miataturbo.net/attachmen...ine=1377640016

https://www.miataturbo.net/attachmen...ine=1377640016

Yea the salvage yard had two different looking ones I think the one I got was a later year range FC. The big pad on the bottom is different as well. The ring and pinion on the diff from the one I got was blown up so I got a good deal on just the aluminum part.

I can guarantee the CVs used on the MSM axles won't do that, if only because they don't have any balls in their CVs. The MSM uses tripods.

I have no idea if the tripod joint has a higher torque capacity, but the guys at Taylor probably do.

Problem is the Mazdaspeed Axles won’t fit the OS-Giken or my spare Torsen that I currently have. so besides the cost of the axles it’s an expensive swap. I'm pretty sure the tripoids will handle torque better. I haven't blown any axles up yet but the noticeable wear and sloppiness they develop has me replacing them every season.

I bet the splined pieces insides the giken can be had for reasonable money and will drop right in the one you have now.