Mlyons Posted January 8 Posted January 8 Hey guys, I want to rebuild my rear end on my 1971 Monte Carlo. This spring I will be installing a 454 bb and a th400 trans. I don’t know where to start with rebuild the rear end. What brand names what gear. Any advice would be appreciated. thanks 😊 Quote
cbolt Posted January 8 Posted January 8 obviously a 12 bolt housing. Eaton and Auburn are the two most popular differentials, with the nod usually going to Eaton as those units are rebuildable where the Auburn (from what I understand) is not. Sometimes the Eaton units are on backorder, which is why I opted for the Auburn unit. The gears would be a matter of preference and how you plan to use the car. If you want to get mileage and cruise the interstates you gears would be different than if you want to do the stoplight to stoplight tire burning type of fun. Richmond is the most popular ring and pinion manufacturer. 5 Quote
Dtret Posted January 8 Posted January 8 Yukon is also a nice affordable option. I agree, it all depends on what you’re planning on doing with the car. 5 Quote
cny first gen 71 Posted January 8 Posted January 8 I'm no expert on this but it's another one if you ask 10 different people and probably get 7 different answers. It mainly depends on your driving as stated above and how badly your going to abuse your car. Eaton, Auburn, Detroit locker are names I've heard many times, also the ford 9 inch is an option too, and gear ratio varies depending on driving too. Good luck on your choice and on your build too. 2 Quote
Blackhawk Posted January 8 Posted January 8 Quick Performance has some decent prices on rebuild kits. 2 Quote
FrankOC Posted January 8 Posted January 8 Also not an expert but to upgrade to positraction and based on recommendations to me from club members I went with Eaton Trutrac and Richmond gears in my 12 bolt. Another thought. If you want to get an idea of costs for these parts, lookup Quick Performance Racing on eBay. https://www.ebay.com/itm/372206140398 4 Quote
72 Monte Carlo Posted January 8 Posted January 8 The gear ratio will solely depend on the height of the rear tires, which transmission is in the car, and your cruising rpm in the manner you wish to drive the car mostly - highway or city rpm driving. If you'll be running a taller rear tire, then you will want a lower gear ratio (numerically higher) ring and pinion set, than the common 2.73 gears that come in the rear. I have 28" rear tires on my 72 and I'm installing a brand-new Yukon posi and factory GM 3.31 gears in my 12 bolt. I have the factory 2.73 gears with the factory posi in it currently. 4 Quote
420ponies Posted January 8 Posted January 8 Is yours a 12 bolt rear axle? If it is , you could just upgrade to a good set of axles (Moser comes to mind), a good posi (mentioned above) I have a Yukon, Richmond gear set. I know that you have some stock car racing in Illinois, and there might be a good builder of rear axles in your area too. I know that my gears is above normal(3:73 ratio) but that's what I chose behind the 427BBC I installed &(turbo 400). It's going to be a totally different car after those upgrades. 4 Quote
Mlyons Posted January 8 Author Posted January 8 My car will be used for city/highway driving. I would like to smoke the tires a lil bit on take off lol. I have 20inch rims in the rear and 18inch in the front. Its 12 bolt rear end I pulled off a 1971 Chevelle. 3 Quote
jft69z Posted January 8 Posted January 8 These may help you figure out MPH/Engine RPM to give you an idea what fits your needs. https://tremec.com/aftermarket/resources/gear-ratio-calculator/ https://spicerparts.com/calculators/transmission-ratio-rpm-calculator 4 Quote
DragCat Posted January 8 Posted January 8 Since your smoking tires, might want to upgrade axels while your in there, I went with Strange 3 Quote
72 Monte Carlo Posted January 8 Posted January 8 Also, I forgot to mention, that a big role in picking your gear ratio and rear tire size, will be which camshaft you install in the engine. You'll want to match up your cruising rpm range of your camshaft with the correct gear ratio and rear tire size, otherwise you'll be losing power and fuel mileage. 4 Quote
Grant MacPherson Posted January 9 Posted January 9 Why the axel change? Has anyone ever broken an axel in a 12 bolt with street tires? Quote
Michael Boyte Posted January 9 Posted January 9 1 hour ago, Grant MacPherson said: Why the axel change? Has anyone ever broken an axel in a 12 bolt with street tires? Yes !!! 2 Quote
Grant MacPherson Posted January 9 Posted January 9 Good to know, the results are never good! More details please, how much horse power? 1-2 shift? Sticky track? Quote
Michael Boyte Posted January 9 Posted January 9 The first axles that I sheered off was with a 538 hp Gene Fulton engine along with a 250hp NOS setup, off the line 4000 stall with 4:56 gears and a Super Brute posi unit along with a set of Lakewood ladder bars. I also would suggest a set of C- clamp eliminators with your 12 bolt . We installed the Strange axles and never had another issue. 3 Quote
420ponies Posted January 9 Posted January 9 I installed the Moser street/strip axle for the extra strength , but did not install C clip eliminator's. Something else to consider?? I can't remember any of my street cars snapping an axle...... guess not powerful enough? Even our '72 Vega with the Don Hardy kit didn't use them, and that car had a 400hp small block with 4:10 gears! 4 Quote
Michael Boyte Posted January 9 Posted January 9 The C-clamp eliminators came after we had an axle/wheel slide out halfway down the track, luckily there was very little body damage but definitely a scary situation ! 2 Quote
714024SPEED Posted January 9 Posted January 9 Have had good luck with the Eaton Detroit Trutrac . Now would be the time to upgrade your axle so you can match your posi to it. Stock 12 bolt axles are 30 spline you may want to upgrade to a stronger 30-33 spline axle 3 Quote
420ponies Posted January 9 Posted January 9 I'm hoping to get the same results out of my Yukon unit. They use these in almost all of the tall tire trucks I see running around here. Seems to be the way to go. Not many issues with them. 3 Quote
Scott S. Posted January 9 Posted January 9 7 hours ago, Michael Boyte said: The first axles that I sheered off was with a 538 hp Gene Fulton engine along with a 250hp NOS setup, off the line 4000 stall with 4:56 gears and a Super Brute posi unit along with a set of Lakewood ladder bars. I also would suggest a set of C- clamp eliminators with your 12 bolt . We installed the Strange axles and never had another issue. And you were expecting a 50 year old factory axle to take that kind of torque ???? Michael, Michael, Michael......... 1 3 Quote
Michael Boyte Posted January 9 Posted January 9 😂 I was 18 years old at that time, A friend of mines dad owned Piedmont dragway, We would meet there every Wednesday and would test our cars, then return on Thursday for Test and Tune and grudge racing , Return on Sunday for bracket racing. I quickly realized that drag racing was more addictive than most any drug, You will spend whatever it takes to win. 6 Quote
DragCat Posted January 9 Posted January 9 23 hours ago, DragCat said: Since your smoking tires, might want to upgrade axels while your in there, I went with Strange I also upgraded to 1/2" wheel studs. 3 Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.