replacement 12 bolt rear
 

Since original 12 bolt rears are getting harder to find, Is a moser replacement 12 bolt rear legal for stock class? Forgive me for asking and maybe sounding dumb, I am new to stock class racing. I need to get a new rule book, lost the one i had, but if memory serves me correctly you have to use a factory type rear. I know that there are grey areas where rules are concerned, so I was wondering if anyone is using a newer repacement 12 bolt like the Moser and passing tech. It just seems like it would be nice to use a new setup.
Any information appreciated. Thanks

Re: replacement 12 bolt rear
 

Chupiw,

Yes, you can and that's a good move..They make a very good set-up, that bolts right in to your car.............LOL................ Dave...1033/stock(350 pont)

Re: replacement 12 bolt rear
 

Thanks Dave, I figured I could go that route, I am hesitant about building up a housing that is 30 years+ old, I would rather invest the money in a complete moser setup that will bolt right in with all new parts. I am trying to build as solid and reliable setup as possible and I dont want to do things twice.

Re: replacement 12 bolt rear
 

Most all of the companies that sell rear ends use the KTRE housing for their heavy duty 12 bolt stuff. The KTRE housing is great, because it is thick, and stiff, and you can get it with a 3.250 carrier bearing bore, so you can use an aluminum spool and 35 spline axles.

Re: replacement 12 bolt rear
 

If you are going to get a Moser rear check prices then call Lynn McCarty at 317-839-8378 and he will beat any price. The rear will ship from Moser direct to you. Any other questions call me 903-277-9947.

Re: replacement 12 bolt rear
 

I think you will find that most of the replacement 12 bolts have the upper trailing arm mounts already raised up, which is another good reason to go with the new unit.

Re: replacement 12 bolt rear
 

It's interesting that you point that out. I was internet recently researching aftermarket 12-bolt options, and I wondered how many companies actually cast their own center sections.
The companies I looked at are Mark Williams, Moser, and Strange. MW says they use DTS Express/KTRE cast ductile iron center sections with cast caps, available with stock 3.062" carrier bores or larger 3.250" carrier bores for people who want to run 35 spline axles.
Strange claims they use a "Strange designed 12-bolt case with torque arm provision." It's nodular iron, and the caps are chrome-moly. They make no mention of carrier bore diameter, but they don't offer 35-spline axles in any of their crate rearend packages.
Moser uses nodular centers with high nodular content cast iron caps held in with 1/2" bolts. They don't mention carrier bores, and they don't package 35 spline axles with these rearends.
Based solely on that information, I think I would go with the MW/DTS/KTRE unit with the larger 3.250" carrier bore so I could use 35 spline axles. I also think it's cool that MW makes FED chassis kits and parts for '57-64 Olds/Pontiac rearends.

Re: replacement 12 bolt rear
 

I use the DTS 3.25 12 bolt with strange 40 spline gun drilled axles and chrome moly tubes in my firebird...luke

Re: replacement 12 bolt rear
 

Then this is the aftermarket block of rear ends? Looking at the rulebook it says "same type from the automobile manufacturer"

Re: replacement 12 bolt rear
 

Mike Pustelney from MPR set me up with the Mark Williams stuff, which the housing is made by DTS, with the 35 spline axles. Great guy to deal with and great prices. Call him at 810-798-8998.

Re: replacement 12 bolt rear
 

Yes. Some have'm; some don't. Same deal. The rich get richer and the poor still have to struggle.

Re: replacement 12 bolt rear
 

Seeing as how one of the services I provide at the shop is rear ends, I looked at the prices for building them, and I also looked around to see how hard it is to find cores. Considering that around here a USED, 35-40 year old 12 bolt housing, with no guarantee that it is suitable to build a good rearend from, is about $400 to $600, and you'll spend another $500 or so
prepping the housing with caps, studs, and other parts/labor, at a minimum, the aftermarket unit is cheaper.

Re: replacement 12 bolt rear
 

Alan - I agree with you 100%. If you are wanting to build a top quality rear end, and I think it is a good investment, the aftermarket pieces are definitely the way to go. Looking at the stocker population, the majority of the cars are serviced by aftermarket housings - 12 bolt GM, 9" Ford, Chrysler 8 3/4 & Dana 60. Maybe there should be an accepted "definition" that says any GM product can use a 12-bolt, any Ford product can use a 9" and any Chrysler (and I guess AMC) can use an 8 3/4 or Dana 60. It's almost like that now; in fact, most would argue that it is. It would just simplify matters to make it a ruling and put it in writing.

Re: replacement 12 bolt rear
 

Suppose you already have a couple stock GM 12-bolts, but you don't have piles of cash lying around. What would you do? Beef up the better of the two stockers, or sell one (or both) and get an aftermarket unit?

Re: replacement 12 bolt rear
 

Beef it up. Nothing wrong with the old stuff if done well. Just if you are starting from scratch with nothing (no housing) the new stuff is a good consideration. I know top A, B, and C stick cars running old housings and have for 20+ years.

Re: replacement 12 bolt rear
 

Tom's Differentials sells a carrier cap kit for about $70, it upgrades the driver side cap, and comes with 1/2" cap screws for the driver side, 7/16" upgrade cap screws for the passenger side.

On a side note, when the new housings were introduced, Tom refused to sell them because in his opinion, the cases were not within usable tolerances for his standards. That was the last word I had from him on the subject 3-4 years ago.

I have 2700+ passes on my old A-Body 12-bolt with the Tom's cap kit, no troubles, and have a car out there that is 3200# + driver running 8.60's with the old M/W cap kit, he kills a Pro gear about every 300+ passes, but no housing troubles.

Re: replacement 12 bolt rear
 

The MW unit is the best out there. All my cars have them, and the big Ford ends, etc. MW is one scenario where you get what you pay for.

Re: replacement 12 bolt rear
 

Ditto to what Robert said. If you do use the stock GM housing, use the billet caps. Some type of rear end brace is a good idea, also.

Re: replacement 12 bolt rear
 

Alan Is it possible to run the "Gun Drilled" 35 spline MW axles in the "factory GM 12-bolt housing?
I've already replaced the tubes w/ DOM tubes, and added MW caps?
Is it safe to run the smaller bearings?
The Moser housings for the A & G bodies do not incorporate the "bumper tab" for Weibe Suspensions?
Greg

Re: replacement 12 bolt rear
 

Yes, you can. You will have to use MW housing ends for large axle bearings. Call MW and tell them what you are doing.

Re: replacement 12 bolt rear
 

Agreed. I have Mark Williams 35 spline axles (no drilled) in a 12 bolt which has been in service since the mid 90's. All the internal parts are holding up extremely well and have not replaced anything other than gear sets for tweaking of ratios with combination changes.

The MW captured bearing housing ends are really nice as well.

11/16" drive studs, billet caps and a girdle cover should be on the parts order list as well.

Re: replacement 12 bolt rear
 

I thought you could only fit 35-spline axles in a housing with a 3.250" bore, or is that only if you want to run an aluminum spool? Or is that just completely incorrect?

How much better is a billet driver side cap than a support cover with factory caps? What about two billet caps compared to one?

Re: replacement 12 bolt rear
 

Only if you want to use an aluminum spool.

Two different approaches. The support cover will support the bearing cap to keep it from breaking and give support to the whole housing to keep it from deflecting. The steel bearing cap will not break and adds some strength to the housing because of the bigger bolts and larger footprint.

Just adds more rigidity to the housing and will not break.

Re: replacement 12 bolt rear
 

Can a "stock" GM 12-bolt be machined to accept the 3.250 bearing to use an Aluminum Spool?

Re: replacement 12 bolt rear
 

From a machining standpoint, I have to believe it's possible - it was done once when the housing was built. But from a strength standpoint, I suspect it would weaken the housing too much: your billet caps would probably take it, but there isn't much meat to spare ahead of them in the case, and it also wouldn't leave much metal between the bore and the bolts.
http://images.chevyhiperformance.com...journals_z.jpg

How do you remove the stock axle tubes, and where do you find DOM axle tubing?

Re: replacement 12 bolt rear
 

According to Mark Williams, yes, a stock housing can be machined to take the 3.250 bearing. They charge $550 or so. We have a stock housing in the car that takes the 3.250 bearing. But I think it was originally in a Kingwood Estate wagon, not a Camaro. If you want 3.250 bearings for an aluminum spool, buy the KTRE housing. It's not money well spent on a stock housing.

To remove the tubes, you cut them off flush with the housing, drill out the plug welds, and take a torch or a grinder and cut slots in the section of tube left in the housing. I did the 12 bolt in my Cutlass that way. I took the stock tubes, turned them down in a lathe, heated the housing, and drove them back in, plug weld them and then weld them all the way around. My housing is narrowed but the tubes are not cut and welded. WAY more work than most want to do. I'd say several of the steel supply companies can get you the tubing.