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Old 09-20-2011, 08:14 AM
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75 Monte Rear End

A guy mentioned to me that I should consider switching out rearends on my Monte. I've heard this before, but I'll be honest, I know nothing about the gear ratios here, so looking for some help and recommendations.

Firstly, does anyone know what the gearing is on this car? It's a stock 10-bolt with a TH350 auto.

Due to my larger cam, I had to go with a 10" conveter (3500-3800rpm). I know this comes into play with the gearing, but why?

Lastly, what would you recommend? Car needs to be streetable, but will see some track time next year. Looking to keep power, and good drivibility.
Thanks
/D

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Old 09-20-2011, 08:36 AM
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75 Monte came with the 8.5" 10-bolt, a very strong Rear.
If your Cam requires that much stall a 373-410 gear would be better.

The larger Cam moves the engine's power band to a much higher rpm, so you need a numerically higher gear ratio to optimize acceleration.

An O/D Trans would give you the best of both worlds, use 3rd in the 1/4mi and O/D for cruising.
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Old 09-20-2011, 08:55 AM
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Quote:
Originally Posted by SSedan64
75 Monte came with the 8.5" 10-bolt, a very strong Rear.
If your Cam requires that much stall a 373-410 gear would be better.

The larger Cam moves the engine's power band to a much higher rpm, so you need a numerically higher gear ratio to optimize acceleration.

An O/D Trans would give you the best of both worlds, use 3rd in the 1/4mi and O/D for cruising.
Thanks for the info.
Do the gears literally just swap right out? Or does the whole back have to drop and replaced? And what other mods would need to be done in order to make new gearing work properly?
Again, totally new to the rearends right now... so sorry for the nOObie questions. I do appreciate the help!
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Old 09-20-2011, 10:43 AM
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It can be done by a 1st timer but, can be quite a tedious job if you've never done it. Also requires a few special tools and close tolerance precision work.
Look thru these links & see if you want to try & tackle it, if not let a Shop do the work

Some very good Gear Swap Info:
http://www.hotrod.com/techarticles/d...install_guide/
http://www.thirdgen.org/techboard/tr...axle-gear.html
http://www.yukongear.com/Downloads/M...structions.pdf
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Old 09-21-2011, 06:42 AM
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Hmmm, looks a little difficult. I'll probably just have a shop do it

Any recommended brands on gears or anything else I need to know?
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Old 09-21-2011, 12:23 PM
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Yukon has good quality parts. Their Master Install kits come with Timken Carrier & Pinion bearings & Super Shims. Shop around for best prices.
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Old 09-11-2012, 10:54 AM
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I wanted to bring this thread back from the dead since it's my thread and I'm expanding on it.

It looks like I want to get the gear swap done. It feels like the car takes too much throttle in order for it to move. Feels like the power is there at the motor but it's not transferring to the wheels like it should be.

So my question is, what would be the best gearing for me? Was recommended 373-410, but what would be good for getting the power down AND still be good on gas mileage? The car will see some track time but it's a street car, so want good driveability. Again, I have a 3500-3800rpm converter.

Next, does having a POSI make a real difference for street cars? Is it worth the extra money?

I'm pretty sure going to have a shop do the install. What I would like to do it drop the rear end before winter gets here, and then get the whole thing powdercoated and cleaned up. Then take it to a shop to get the gears swapped. Do places do that or does the rear have to be on the car in order for a shop to do it?

Thanks in advance!
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Old 09-11-2012, 11:21 AM
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Your car probably has something in the 2.73 to 2.41 range. This isn't good for what you want to do. A 3.73 with a 700R4 or 200 4R transmission would be good. There is no way that you are going to get better performance and keep the gas mileage without using an overdrive transmission.

Swapping the gears is going to require a 3 series differential. If you ahve a 2.56 or 2.41 gear then you have a 2 series and it will need to be swapped. I recommend using a Yukon Dura Grip and a set of Yukon gears and installation kit. This will get both wheels pulling so that you are not just spinning one wheel. The Dura Grip is not that expensive and it works well. There is a member on this sight that is a Yukon dealer. Prostreet6t9 can help you with the parts.

You must know how to set the pinion depth, bearing preload and backlash to set up a set of gears. You must be able to read the contact pattern so that you wil know what adjustments need to be made to the pinion depth and backlash. Changing gears is not a bolt in job. It requires shims and patients.
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Old 09-11-2012, 12:43 PM
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You might consider buying a complete 12 bolt to swap in.There are companies that sell complete units with w/e gear set you want.If not cheaper its certainly faster.The monte carlo my friend Mike had came with 2.73 gears. We used that rear end until we put a bigger cam in the engine then bought a complete diff. A posi is essential or you will spit spider gears and burn 1 tire out regularly.The car cannot use a 3k stall converter with out a posi,,,
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