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Discussion Starter #1
I have a 70 Chevelle with a 582c.i. BBC that made 780 hp & 760 ft. lbs. tq. It is a pump gas motor that will mainly be driven on the street. I am just gathering specs on a new 12-bolt to replace the stock SS one. I talked to Mosier awhile back, they said go with their new 12 bolt housing with a Detroit trutrac diff, 33 spline axles, and their street gears ( 3.90) . My question is , will a Detroit trutrac live in a 12 bolt with the power that I make? I do have a trans brake in my Coan TH400, and will have a Wilson Manifolds 250hp plate. I am thinking to just go with a spool to be safe and live with drive-ability issues( tire wear, turning manners). Is the Mosier complete rear end setup the way to go in your opinions or assemble with Strange & Mark Williams components with another company. I am just looking to do this the most efficient/reliable way possible... Thanks for any info! Jay.
 

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Discussion Starter #3
Thanks for the reply! I would really like to stay with a 12 bolt because it is a super clean SS that I am rebuilding. It will be ran maybe once or twice a year on the plate and trans brake, and mostly driven on the street. I have had 12 bolts with spools on the street years ago in Chevelles... never had a issue, but not at this HP level. If I updated to 35 spline axles and pro gears, how many street miles will they take? I have heard that they will wear very quick due to the gear softness. Do you think I can get a 12 bolt to live for me? If there is really a big issue with reliability in a 12 bolt.. what would be your preference for a rear... a 9" ford bolt in A-body or a Dana 60? I have experience with 9" rears and really like how easy service is on the center section and setup. Again thank you for your reply! Sorry for all the questions, just to get things right the first time and pick other peoples brains that went though this process before... Really don't want to scatter this one! Thanks! Jay.
 

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You can only run a pro gear for 2-3 miles safley, they can not hold up to the heat like a stret gear. I like the Ford 9 inch also since they can be built with light weight aluminum and are easy to service. But it seems you want to keep your car all Chevrolet and thats fine. Once built up with a street gear and 35 spline spool and axles you would be good for high 9's, anything faster than that and you will break the gear.
 

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Discussion Starter #5
Thanks for the info Scott! I will be calling you tomorrow for a quote on a complete rear end setup. Jay.
 

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Jay...

1. why are you intending to replace the original/stock housing?

2. if you do stay with a 12 bolt and go with the Mark Williams housing/rear over the Moser.

3. at your power level I recommend a spool and 33 spline axles.

That said, my original 39 year old 12 bolt housing broke a factory weld for the lower control arm mounting point last season after ~ 4000 passes of which 1500+ have been wheels up behind my nearly 2 ton Chevelle running low 10's!

I replaced it with another original housing and welded BOTH sides of all the factory mounting points.

You don't NEED an aftermarket 12 bolt housing, you don't want a 9" and while I wouldn't recommend Pro gears for a daily driver, I have and you can certainly go far longer than 2-3 miles !!:roll:
 

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Oh and my original GM 12 bolt housing has Moser 33 spline axles, Moser spool, Richmond Pro gears, LPW cover, 2 quarts of Mobil 1 synthetic gear oil and I've sinced logged north of 300 passes since installing it early last season.
 

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SILVER, FOOTBRAKER IS ON THE LOOSE AGAIN...WHERE YOU AT???????????
 

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Discussion Starter #9
Jay...

1. why are you intending to replace the original/stock housing?

2. if you do stay with a 12 bolt and go with the Mark Williams housing/rear over the Moser.

3. at your power level I recommend a spool and 33 spline axles.

That said, my original 39 year old 12 bolt housing broke a factory weld for the lower control arm mounting point last season after ~ 4000 passes of which 1500+ have been wheels up behind my nearly 2 ton Chevelle running low 10's!

I replaced it with another original housing and welded BOTH sides of all the factory mounting points.

You don't NEED an aftermarket 12 bolt housing, you don't want a 9" and while I wouldn't recommend Pro gears for a daily driver, I have and you can certainly go far longer than 2-3 miles !!:roll:
I am definitely going with a aftermarket housing , keeping my original on in the shop. Mosier is really close to me and have done some work for me and alot of freinds of mine in the past, great people to deal with and quality work. I am also looking at Mark Williams and Strange housings and components as well. I feel that going to 35 spline axles and spool and a 3.90 street gear will give me a good safety zone ... can always use a little extra insurance in strength reliability, can't hurt! Thanks! Jay.
 

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from evrything I hear the moser 12 bolt housings arent worth a damn... the ears for the upper arm mounts are too high. Many people it seems spend alot of time chasing problems with not hooking after the swap and then have the ears cut off and moved.

put 9" ends on the stock housing?
 

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Discussion Starter #11
from everything I hear the moser 12 bolt housings aren't worth a damn... the ears for the upper arm mounts are too high. Many people it seems spend allot of time chasing problems with not hooking after the swap and then have the ears cut off and moved.

put 9" ends on the stock housing?
Thanks for the info! I am still gathering information on parts for the rear end. Definitely will be looking closely at different housings after hearing this. My car is going in for paint soon...don't really need a rear end in the car till spring. This is what I really like about the Bullet... all the info that is given out to those in need.:smt023 This is the last rebuild of my 70 for me... Just want to get everything right this time around. Jay.
 

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Actually most 9" or 60 are larger and will cause issues installing to the factory GM 4 link set-up. You will need at least adjustable uppers or to relocate the mounting ears. It rea tough to get the 60 in due it's large size.

We have been 9's @145+ with a N/A 540cid bbc on the stock 1970 12 with Moser internals in a 1985 Monte Carlo It got driven on the street also.
 

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FWIW I'm on the same "Street" gear in my 12-bolt since I built my car in 2000.
High 1.2x 60ft's w/ a Trans-brake similar power as you described.
Spool and 33 spline axles as well.
 

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Heads up on abuse that a 12 can and will not handle

I haved raced 12 bolts for many years in chevelles and nova,s
behine 454,s and small blocks with 4 speeds. 4 speeds are the most violent launches in a hooking chassis.
9000 rpm 454 launches with a 3600# clutch is brutal on everything. without rear end girdle but with axles and a spool you will never hurt the housing welded at tubes. Your chassis with oem rubber parts in arms will do alot of harm by not keeping rear end Geo correct. Without a rear end girdle over time with 14 slicks in a 3000 car track conditions only ring and pinion willnot survive the launches as ring gear will get pushed rearward as much as 3/8 of a inch and strip the teeth off. Over a course of 25 runs. harden axles will twist one full turn. A 4 series oem posi case well prep,ed and put together will also handle the hp. and will even snap the clutches around the corner on the street . I ran 989 at 138 mph in the 70,s when all the new parts just wernt there yet but you have no ideas on what oem good parts can handle. On the street with all the dirt and oil to get any kind of traction like the track your up in smoke so i dont believe you can break a well put together system with oem parts done right. That oem 12 bolt can take alot more then you know.
For all out racing Dana 60 with axle improvment and stock carrier blueprinted and your all set for well over 1200 hp with a 4 speed and a real clutch with some balls and a Sinder iron disc. a cover girdle will always be a nice improvment and look good.
Get the adjustable after market control arms for that chevelle and what ever you do reinforce the upper frame horseshoe were the upper copntrol arms attach otherwise youll have a junk car later.
Douglas
 

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Discussion Starter #15
I have Hotchkis adjustable upper control arms with the braces to the lowers that are also Hotchis. The rear end cover is a TA performance cap support one, with a 4.10 gm posi diff with Moser axles in the car now.I hear some 12 bolts when you start to hit them with moderate HP, the axle tubes were the weak link along with trying to push the ring gear back out the cover. If i could get away with welding the axle tubes and going with Strange or Mark Williams 35 spline spool and axles in the stock rear, it would put me way ahead of the game. Thanks Robert, Gary & star393 for the info! Jay.
 

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Oh by the way

U joints and improper Min. 4 degree earthward pinion angle is the most everyday reason why driveshafts break and without welding the tubes for any type of drag racing even on the street will break parts. All real race cars with any HP have tubes welded. I have never broke a older muscle car drive shaft because of HP. Again improper set up and alignment are the causes. HD u joints are a must. without the grease hole. I am still using my 35 year old oem driveshaft. I dont care who,s upper or lower control arms you buy without Trianglating the upper horseshoes to the front of the main frame Youll rip it apart. The horseshoe is what we used to call the frame member that the top of the rear shocks and the upper control arms attach to and is welded to each side of the main frame were the main frame arc,s up at the rear tires. The chevelle is a natural 4 link system. Ref, to the A body. If i were to have had better carrier caps and a supportive girdle back then the 12 bolt proably would have lived.
 

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at 900 hp the gears are the killer weld the tubes a rear girdle/ support cover the spool and 33 spline axels are fine, t brake and slicks to 9.50s the street gears die at 35 passes and a pro gear will die @50 the 3.90 and 3.73 have the same life a 4.10 lives a little longer and a 4.56 will go a little further yet..on the street they will go a long way i have a cup of dead teeth (from the car) sold the 12 bolt bought a strange dana s60 over 150 pass @8.80-9.90 not even a leak thanks strange!!mark williams is the only one that makes 35 spline stuff and the housing and caps have to be modified to ues them for what it's worth...
 

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I am running stock 12 bolt housing with 33 spline Strange axles and a spool with 4.33 pro gears. It has been working well with lots of street time.



 

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1967 chevelle 12 bolt

I have a 12 bolt out of a 67 chevelle with a moser spool,moser 33 spline axles, 4:88 gear, and c-clip eliminators that I will sell for the right price. My motor is going to make to much power and I don't want to hurt the rearend.It also has drum breaks it is ready to bolt in.
 
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