I just put a used 12 bolt in my car and have a couple of questions. First, I have no idea what the rear went through but all looked good after going through it prior to install. This is my first experience with a Moser and don't know if what I am hearing/feeling is normal. The rear has 373 gears and replaced my stock 10 bolt with 342s. First question, the rear whines quite a bit both during accel and decel. Is this whine normal for a Moser? Next, there is a huge clunk you can feel in the car when the car transitions from on the throttle to off if going down hill. For example, I was coming off the top of one of our mountain passes here in town and when just at idle in gear following traffic down hill, almost like engine braking, and then getting back on the throttle, there is a loud clunk and you can feel it in the seat. It almost seems like there is some kind of drive line slop. If I just pump the gas peddle the clunk just keeps repeating itself. Any ideas on either of these and are they normal or do I have issues with the rear? Thanks for any ideas you might have.

 

the clunk sound might be u-joints

 

Also could be too much backlash in the gears.

Lack the car up and pull the E brake, with the trans in neautral try and rotate the driveshaft back and fourth. It will move a little, bit if you are getting a large amount of movement something is wrong. Pay attention to how far the pinion flange is moving back and fourth and also if the u joint at the pinion flange has any play. Then put it in gear (or park if its an auto) and with the E brake still on try and move the driveshaft. It should not move at all. If it does, you have a bad front U joint.

Take a look at your torque arm mount bushing while you are under there.

 

I have similar symptoms from my Moser. Mine SCREAMS cruising anywhere from 45-65 MPH, but is pretty quiet in every other situation. Mine clunks the exact same way yours does though. My sound comes from the floorboard right around my seat.

 

If the backlash is within range, there should not be any excessive clunking.
Put a 12 bolt into a early Chevelle, Nova, Camaro, etc and you can beat the crap out of it, and not hurt anything. Put one into one of our cars with a torque arm, make a couple 4000 to 5000 dragstrip launches, and I can just about guarantee you'll pick up gear noise. If it is a drag only car, you'll never know or care about the gear noise. Drive your car home from the track, and the noise will drive you nuts. I feel the torque arm stresses the 12 bolt housing, causing distortion. We have never seen this happen with the 9 inch housing.



Exotic Performance Plus strongly recommends the Moser nine inch. This rear is even tougher than the Moser 12 bolt, and the horsepower of the late model F Body cars keeps escalating every year, which requires a very strong rear. With the recent introduction of the 6.2L GM aluminum block and the excellent flowing 6.2 litre heads, the horsepower of these cars is going to just keep climbing at a very fast pace.The nine inch will handle the power, plus we prefer the way the torque arm is bolted to the nine inch in the same way the oem rear-end is attached. (This is the only good thing about the stock 10 bolt...) The Moser 12 bolt uses four short bolts to attach the torque arm, and they have a habit of loosening up, even when loc-tite is used. Why the nine inch is stronger than the 12 bolt. The 9-inch has an internal rear-pinion support that also supports the gear end of the pinion to limit gear deflection under high torque loads. This seems to be the major reason why the 9 inch doesn't start whining after high rpm clutch dumps, when the 12 bolt will pick up noise.The 9-inch locates its pinion gear lower on the ring gear to improve tooth contact, than the 12 bolt does.The 9-inch has a 0.125-inch larger ring-gear diameter and internal pinion support than the 12 bolt does. This is not much of a difference, but it is worth noting. Bob

 

Bob, why do you always post that same thing in every thread about a Moser 12 bolt? We've all read it 500 times by now. We aren't going to just throw away our 12 bolts and buy a 9".

 

My 12 bolt has been loud, noisey, whiney since day 1. And after launching at the track at 4-5k it got louder. But it still holds. What tq arm are you running with it? Reason I ask is because I destroyed 2 stock tq arms with mine. I went with a spohn, and I still get clunking, but thats from the tq arm, which I really dont like. But the whinning in a 12 bolt is normal. I called Moser and asked them if my 12 bolt will hold with my new set up (414 iron block) They assured me I would have no problems! I even asked them why it whines, they said we dont know either, it just does

 

Why, because people ask questions. The OP here asked about gear whine, which is pretty normal with a 12 bolt. I'm certainly not saying to throw the 12 bolt out, but gear whine is pretty common with them. Bob

 

I've got the Spohn also. I feel a lot better now about what's going on but still kind of ruins the drivability of the car. It is so streetable with the power it makes and was great on the stock 10 bolt, just could go from a dig. Now with the 12 bolt it's like driving a noisy rough race car. Not as much fun.

Thanks for the info Bob...at least I can sleep at night now.