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70 12 bolt rebuild


70MC402

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Hey everyone, this winter I'm going to to through the rear end of my 70. Last year I rebuilt the 402, nothing wild, a small (212/218) cam and an intake. Now that I have the engine running well id like to be able to take advantage of the big block more than the open rear diff i currently have in the car allows me to. A friend and coworker has a modfied Cobalt SS and its pretty sad when his turbocharged 2.0 liter can put the gap on my Monte.

 

So to improve the acceleration on the car I'm replacing the open carrier 3.31 rear gear with a TrueTrac carrier with a US Gear 3.73 ring and pinion. With either more engine upgrades or a turbocharged LS in the cars eventual future I will be replacing the factory axles with Moser 33 spline axles and eliminating the C-Clips with the Eliminator kit offered by Moser.

I work as a mechanic as a profession, so I'm somewhat familiar with the rear end setup (more proficient at the easier full floating rear ends) but havent done much with my Montes rear end other than the suspension and adjusting the brakes as the previous owner had.....lets just say poorly redone the shoes.

 

Anyone have any words of wisdom or things to look out for when going through our cars rear ends? I was likely going to just order the parts through Moser unless someone has another recommendation. Either way thanks for reading, hope everyone has Happy Holidays coming up and once I get going on it I'll add pictures.

Thanks-Rick

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Hi. From what you described, at the moment, I don't see the need for 33 spline axles or a c clip eliminator kit. 

Your 402 won't break it. 

I do recommend the detroit trutrack. Every one of my running Monte Carlos and my son's Monte plus his GTO have one. Also running strange 30 spline street axles with the c clip. 

My red 70 has a 496, th400, 3.31 rear  and has been ran at least 30+ times down the 1/4. 

No issues what so ever. 

The GTO has a ram air 3 400, M22, 3.73 and a 24yr old behind the wheel. Nuf said. Lololol His Monte just recently went to the track and was running 13.20@103 with a super mild small block and 4.10 gear. Building a big block now for it. The rear will stay the same except gears. Going 3.31.s

What is your cars combination? 

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Right now its just a nearly stock 402, with a small comp cam and edelbrock aluminum mid rise intake, nothing wild at all yet. Th400 and the 3.31 gears. Good to hear the truetrac is the way to go!! My thought process with the 33 spline axles and eliminators isnt for the current setup but over the next few years further upgrade the big block with a more aggressive cam and head setup or put a Turbocharged LS engine I built in. I know the current 402 isnt going to cause any issues with the rear end. 

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C clip eliminators are prone to leaking. With the ford housing ends you will get a larger bearing that bolts to the housing end. If you are doing the work yourself and do not want to weld the ends on than the C clip eliminator may be the way to go. 

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I'm not opposed to welding new ends on I just dont know how i would ensure that everything is kept square and positioned correctly. I would think just for ease of installation the eliminator kits might be a little more straightforward? If I have any issues with the Eliminator clips I'll look into the 9 inch ends. Thanks for the tip!

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9 hours ago, Andy's Auto said:

You can literally get a QuickPerformance 9 inch delivered to your door for around $2300. And thats a aluminum center, daytona pinion support, 35 spline axles, and Wilwood rear discs. 

I called there requesting information on their carrier, ring and pinion, and installation kits and they told me they don't use name brand components in many of their kits which helps keep the costs down. $2300 is still a $1000 more than all of the components from Moser, and the moser parts are made in America. I can see the appeal to some people i suppose. 

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  • 3 months later...

Well it took a few months but i finally found the time. Got the rear end out, and taken apart. Next step is to cut the ends off for the C Clip eliminator installation. Then its off to be powdercoated, when it gets back I'll install the new gearset and True Trac, the 33 spline axles. Im trying to decide now on a rear brake conversion too. The Wilwood kit for the C Clip eliminator s looks pretty nice. 

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  • 1 month later...

I got my rear end back from powder coating and after a thorough cleaning started the reassembly. Got the ring gear installed on the carrier, the new bearing races in the housing and I made up a slip fit inner pinion bearing for easier pinion depth adjustment. After a few times on and off ive got the carrier just about where i want it. Im at 0.0075 inches of backlash (US Gear recommends .008-0.012 for the street gears) measured at 2 different points of the gear and a decent pattern. Drive side is pretty close, im just trying to find a 0.003 carrier shim to add to the passenger side ofnthe carrier to get a bit more backlash between the ring and pinion, as well as a bit more carrier bearing preload. I called motive with the Super Shim kit but they couldnt verify the shim thicknesses. Anyone know of any shim kits that they know include 0.003? Or any shim kits that have like a 0.013 or 0.023 shim. 

 

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  • 1 month later...

Got the rear end all buttoned up and installed along with new brake lines and a Wilwood adjustable porportioning valve. The Truetrac and 3:73s definitely woke up the Monte. No noise from the rear end and definitely a different car from the open differential 3:31s. 

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