View Full Version : 12 bolt issue with Autocross use.

07-26-2005, 08:30 AM
I have a Moser 12 bolt with a Eaton 33 splice HD posi. with 3:73's. It has a breather tube on the drivers side of the cars axle tube. We looped the tube up as high as we could and tied it off to a brake line. I run on Kuhmo V710's, lots of grip.

At a recent autocross that was run clockwise (mostly right turns) the tube spilled out some axle lube. I assume some of the prolonged sweepers push the oil up the tube. What can be done to prevent this, possibly an pcv valve or some sort of a catch can. I was thinking the valve would close when oil hit it but would allow expanding gases to escape..

Thank you for your input in advance.


09-29-2005, 09:29 AM
Check out (; I've read of guys using a catch can for the 12 bolts.

09-29-2005, 10:21 AM
Check out (; I've read of guys using a catch can for the 12 bolts.

Thanks, I ened up looping it towards the center of the diff, instead of towards the out side. The problem seemed to go away. since the G forces start to push the oil back down the tube. I just had to think it out.

thanks again.


10-27-2005, 05:01 PM
this happened to me on pocono road course. i think mine was due to overfilling.

10-29-2005, 10:31 PM
How do you like that HD posi? I have the regular limited slip in my strange and think it slips a little too much. :cry:

10-31-2005, 01:46 AM
Same problem here with my 9in. Ended up being over filled......hasn't happened again in 9 months.

11-01-2005, 07:53 AM
I use a Moser 12 bolt w/33 splines. Never had an issue re excess oil out the breather tube. Nice and long and straight up from the axel. Make sure you fill correctly and don't add anthing over the fill hole.

BTW, these clutch diffs suck for the AX or road race use. I'm eventually going to get the Detroit Tru Track now available thru Moser. A true torsen diff. Unfortunately, it requires new axels and gears for my use (4.11). Over a grand.


11-06-2005, 11:42 PM
Had this same problem at Nelsons Ledges Road Course in NE Ohio this past Friday with My 01' SS with the 12-Bolt in it, damn diff fluid wouldn't stop comin out!!!! How do I solve the problem????

11-07-2005, 07:39 AM
Which hole are you using to determine when the rear is full? That could be the issue.


11-07-2005, 05:52 PM
You can put a little mini-K&N filter on it like NASCAR and Stock Car racers do. Like this one:

11-07-2005, 10:03 PM
You can put a little mini-K&N filter on it like NASCAR and Stock Car racers do. Like this one:

Failing to have a long enough breather hose could, under certain circumstances, lead to a fluid problem. If one runs the rear w/too short a breather hose it could over spill onto the rear. My breather hose is about two feet long and goes straight up. I don't run a small K&N filter, but one could to avoid ingress of debris.

When filling, the overflow hole is on the passenger side of the diff. Fill from the top with Organic fluid until it runs out the side hole. Guesses will only lead to messes.


11-08-2005, 12:16 AM
I have been using a vent that I bought from Summit when I put the 12-Bolt in Last year, and it has always leaked alittle, but when road racing it poured out of the diff!!!!! Click on link!!!!!

How can I fix the problem, get rid of the vent and put a fitting with how much rubber hose sticking up??? What works for you guys!!!

11-08-2005, 07:33 AM
Are you running a hose attached to the vent? It appears to have a nipple designed to accept a hose and clamp.

There doesn't appear to be anything wrong w/the vent. Any vent is going to be designed to allow for the change in internal pressure based on generation of heat and then cooling. You may want to run a hose straight up from the tube where the vent is attached and just secure it with wire ties onto something up there.


11-08-2005, 07:43 AM
Ah, I took a look at the enlarged picture. The nipple portion I referred to was actually the threaded portion going into the axel tube. This type vent doesn't allow for the use of a hose and when pulling high G's in a turn will allow for fluid to be pushed out. Your problem was exacerbated by the fact that Moser placed the vent on the driver side tube--exactly where the fluid is being pushed when turning mostly right on a road course.

Don't dispair. Go to an auto parts store, Lowes or a hardware store. Get a barbed hose adapter also having a threaded portion on the other end. Run two feet of hose straight up and you could even use your vent at the end of the hose if you want to keep it in operation.

The OE Moser part has an NPT thread to secure it to the tube w/o leaks. Or you could just call Moser to see if they'll just ship one to you for a couple of bucks.


11-08-2005, 07:33 PM
I also have a Moser 12-bolt, and I tried a bunch of stuff to vent it:

1. Originally tried the hose fitting that came with the rear; the one already mentioned on the driver's side tube. My 3" dual exhaust goes in that space, and a large bump made the fitting hit the exhaust. Fitting broke. Plugged hole with NPT plug.

2. Tried a -6 hose fitting off the filler hole, with a big loop in the hose to trap fluid, and a Earl's -6 filter on the end to prvent dirt from going in. Sprayed fluid any time I went fast. Correct fluid level in rear.

3. Put the same setup way up near my trunk floor, in front of the fuel cell. Still sprayed fluid.

4. The rearend is currently not vented. No problems, no leaks.

If I ever go back to a vent I'll probably put a catch canister in there with a little drain, and run the hose up higher into the trunk.