i have a moser 12 bolt. making some noise. here the specs
Moser 33 spline gun-drilled axles
Moser Billet 1350 Yoke
Eaton HD Posi Unit
Yukon 4.10 gears/Timken bearings/races

now the problem.

i have a whine/almost grinding noise in acceleration in all gears and speeds. the noise is most noticable when i am in like a parking lot making a turn. if the clutch is fully engaged and i am turning at slow speeds. it soudns like something in the gears is warped or something. when i put the clutch in the noise goes away. any ideas what wrong??

 

The whine is pretty common with 12 bolts, but the grinding noise isn't. If you hear popping noises when turning that usually means the four torque arm bolts are loose.

The factory 10 bolt that came in these cars has a very small 7.5" gear. A variation of this rear was used back in the '70's in the Chevy Monza, then in the Chevy S-10. GM had to of known they would have warranty claims when they decided to use this rear in the 3rd and 4th gen f body's, apparently the cost of creating a stronger rear was higher than what they thought the warranty cost would be. This has been a real plus for the aftermarket, as a bone stock LS1 F Body with a manual transmission can break one of these 10 bolt rears! Many people have tried to beef these 10 bolt rears, spending a lot of money in the process. What they normally end up with is a rear that still breaks, as everything on these rears is too small.
The 12 bolt rears that are available for these cars is a step in the right direction. The 12 bolts are well known for being a stout rear that was a factory option back in the day in many performance cars. You can have a 12 bolt in an early Chevelle, Nova, Camaro, etc, and beat the snot out of it and not hurt anything. Put a 12 bolt into a late model f body that uses a torque arm, make a couple 4000 to 5000 rpm launches at the dragstrip, and I can just about guarantee you'll have a lot more gear noise on the way home. The torque arm seems to distort the housing on the 12 bolts, and it seems to happen to all the brands of 12 bolt rears. This does not happen to the 9 inch rears, and there is no price difference between the 12 bolt and nine inch rears. As the horsepower in our engines keep escalating, most people these days go straight to the nine inch rear. 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, better the 12 bolt does. The 9-inch also has a 0.125-inch larger ring-gear diameter and internal pinion support than the 12 bolt. Bob

 

Bob

Thanks alot. I actually had the same noise on my 10 bolt which led me to the 12 blot! not sure if its a grinding or it just feels like something is warped in the axel/gears. it almost sounds like a warped brake rotor sounds like, but certainly isn't. its most apparent when making tight turns in a parking lot with the clutch all the way let out. then when i go through the gears the wobble/warp sound gets louder and faster. It doesn't sound normal and kidna concerns me. i called moser and thunder racing but there both clsoed.

and Bob you nailed it on the head. both times the noise started just after a few, like 5, hard launcehs on the strip. i drive my car hard, but havent launced since the noise started. i aksed a frined of mine a while ago what the noise might be (spent a year in the middle east since then, just got back) and he said it was something like the ring and pinion on the inside. IDK what he said it was over a year ago. does any of this make sence??

 

Yes, it is common for the 12 bolts to pick up this noise after launching hard at the track. As far as what you hear when in parking lots, did you add the psi additive to the rear, as the Eaton posi requires the additive? Bob

 

i honestly can't remember.. i do not know much about axels so even if i pulled the thing apart, i don't know what i'm looking for. i'm thinking of replacing the axel fluid/gear oil and adding the the additave to see if that will help. will it?

 

Changing the gear oil and adding additive may help in what you're experiencing in parking lots. I doubt you're hear a difference in the whine you're experiencing out on the road. While you are under there, make sure the four torque arm bolts have not loosened up. If the bolts are loose, the torque arm will make a lot of noise when making turns. This could be part of your problem. Bob

 

I know this is an old thread. Do you know by chance what your preload spring is rated at? Also, any outcome if any?

 

Likely bad pinion bearing or posi unit. Noise on accel/turning points to gear setup or bearings. Check lube, then inspect bearings and gear pattern. Clutch disengaging rules out trans.

 

Does the Ford 8.8 in a Fbody hold up better than a 12 bolt?

 

Crown Victoria 8.8 housing/gears/bearings are roughly equivalent to the 8.5 10 bolt and car 12 bolt with 3"dia axle tubes. Mustang 8.8's have small dia/thin easy to bend axle tubes, while Explorer/F150 8.8's have really thick/heavy large dia axle tubes and brakes. Other than that, the differences are in the axle spline count and axle bearing size.

That said, clutch dump induced problems are usually due to overly aggressive clutch engagement. The fix is either choosing a proper clutch for the application, or if you already have an overkill clutch, add a clutch hit controller. With a properly hitting clutch, the impact on the rear will be softer than with an automatic trans.

Grant

 

Some people claim an 8.8 can hold 1000 hp.

 

Clutch induced impact is what kills stick shift rears, not 1000hp. Here's a graph showing how hard these clutch induced impacts hit this 8.8 rearend during a dragstrip pass, all from a little sealed 425ftlb crate engine...


Note that when the clutch is pulling the engine down fast, you see huge torque spikes.

Also note that when the engine is gaining rpm in 1st gear, engine torque applied to the transmission's input shaft is nowhere near the 425ftlbs this engine is capable of...


The basic takeaway is that the slower a clutch pulls the engine down, the more power the rear can handle.

Grant