I went to MIR (Maryland International Raceway) with my 95 Z this weekend. I put on a set of ET Streets for the first time. My first pass was with the tires at 16psi, and I ran an 11.90 with a 1.7 60ft. That's the good news. Yeah! The bad news is that I let the car cool down for a while, then went to make a second pass, and the rear exploded on the line. This is a Moser 12-bolt, 3.73 rear gear, 33-spline axles. What has been the experiences with people breaking the 12 bolt, and what did it turn out to be? Also, what was done to reconcile the problem? I've heard the carrier possibly? This is barely an 11 sec car and it broke?! I thought these things were good to 10 seconds and beyond. Help!

-Ernest Nichols
95 Z
11.90@117.5

 

Who set it up? Did you actually take the cover off to take a peek at what happened?

 

Prob. moser!

But they dont always supply the carrier! Yeah, take a peek at what happened and post some pics of that thing!

~*~ RAYNA ~*~

 

My initial unit had bad spider gears in the posi. They were not hardened properly and broke the second day out at the track. Moser supplied a replacement and it's been good since. PITA though.

You need to tear it down and see what broke.

Rich Krause

 

Agreed. I will be tearing it down shortly, I'm hoping to get feedback concerning any particular items that might consistently break on a Moser so I can zoom in on those issues. To my untrained eye, I may not notice that there are hairline fractures in the carrier, or a clutch disk is crooked . To answer the previous post concerning setup, Moser did it all, and sent it to me complete. I just bolted it in, and ran with it.

Thanks for the responses so far, if anyone else knows of a Moser that broke and what the result turned out to be, I would love to hear about it.

-Ernest

 

FWIW, I have a spare Eaton posi (new, in box). I imagine Moser will make it good whatever the problem, but if it's the posi and you need one, I might want to sell it. It is for the 33-spline axles and has the 800lb springs.

Good luck.

Rich Krause

 

Thanks, Rich, I will keep it in mind.

-Ernest
95 Z

 

Ernest,

I'm assuming your running an M6. Are you running a Street Twin also. This is a violent combination and it can and will break 12 bolt rears. I'm living proof!. I've trashed about 6 Ring & Pinions in 2 different 12 bolt housings. 12 bolts are not bullet proof by any stretch of the imagination. My whole winter project is working on a Revloc adjustable clutch for my 94 to try to soften things up a bit at the line and make my rear happy.

Good Luck

Steve

 

I know alot of people do not like doing this or do not believe in it but did you do a 500 mile break in?

We are finding more and more it is helping the rear end stay together. The heat cycling is helping both the gears and Spiders stay together. Alomst every time I see one broke it is on a unit that was installed and driven to the track with in a day or two. Even on the race cars We have them heat them up and let them cool off about 10 times or so and then make a few easy test and tune passes IF they can.

To many this seems like over kill. Then again how many time you want to take your rear end in and out

Hopefully you bought straight from Moser or a local vender. IF NOT all warranty claims MUST be handled throgh the Co you boght the rear end from. We recently had a guy who an Online co. It had some problems. We had to send the parts back to the online co and then they had to go throgh Moser to get it taken cars of. EVEN thogh Dan is a Moser dealer because he did not sell it he could not deal with moser on this warranty.

Good luck man!

 

i am thinking the driveshaft angle. those are susposed to be a tuff rear. though i would not know (home built 9")

 

To answer the questions posted:

It is a 95 Z-28 with an M6 trans. Yes, it does have a Street Twin installed. Yes, the rear is broken in, I have several thousand miles on it.

I understand that a 12-bolt is not indestructable, but, really, there are people running far, far faster that have not broken it, and I find it hard to believe that a high 11 sec pass should be considered too much for a $2000+ replacement, heavy duty rear advertised for racing. That's all, if this was running 8's in the quarter, I would have a much different outlook.

As for further info, I took off the rear cover to inspect the damage. It looks like the damage is in the carrier. All the teeth on the drivers side of the carrier are gone, and the passenger side is missing 1 or 2 teeth also. I need a place to post some photos, as I snapped pics of all the damage.

-Ernest
11.90@117.5

 

Ernest,

Sorry to hear about you rear. Destruction of a rear in an M6 car depends more on the weight of the car, rotating mass of the clutch & flywheel assembly, the rigidity of the torque arm, and the hit on the tire. The actual HP level and Torque output don't even come close to the shock loads produced by inertia. I was busting 12 bolt rears in my bolt on Formula when I was only running 12.80's at 105 at the time. I'm still way slower than your car and I'm still having problems. I can get a R&P to survive almost a whole season of bracket racing but ther's no way it will go any further. In my car, I can put in a new R&P with a nice quiet setup, break it in for 500 miles, head to the track and turn it into a whining dog in 2 or 3 passes. The bigest problem IMO is that the clutch (although wonderful on the street) is just too much hit for the track.

I'd like to hear some of the 9" guys chime in and share their experiences with M6 & Street Twin combos

Good Luck

Steve

 

There has to some other factor(s). Luck? Mine's been in three years with both street and strip use. The first two years were with an M6/ST combo. My car+driver weighs over 4,000lbs and has over 700rwhp (now way over) and I run it with a 10" slick at the track. There was the initial posi failure, which was clearly defective, and since then no problems.

Rich Krause

 

I'm sure luck comes into play, I'm also guessing that setup is also critical with a rear. I'm always hearing about tight vs loose ring and pinion setups for various items, I'm wondering if there isn't the same kind of thing that has to be done with the rest of the rear. I'll be sending the pics to Moser to see what they think.

-Ernest

 

Moser is the bes rearend money can buy it had to have been a bad pert or something and if you will call them they will make it right I promise they know they are the best and will stand behind all their stuff! I feel like it was the spider gear but you will just have to take a look!