3.45 Differential install

Drivetrain discussion including Transmission, Differential, Driveshaft, and related items.
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kevink
Posts: 457
Joined: Sun Aug 09, 2015 5:55 pm

Re: 3.45 Differential install

Post by kevink » Wed Aug 04, 2021 3:54 pm

bstoner wrote:
Mon Aug 02, 2021 4:23 am
Here is where I had to grind the cover to get clearance to fit inside the mount.
I have the same cover. I also had to grind the left adjuster bolt down to the nut as it was hitting the cradle. Are you sure that's all you need to grind off of the case? I had to go a little deeper to make sure it wasn't touching the cradle. I didn't want any clunking or rattling.
2011 9C3: 11.48 @118.

bstoner
Posts: 49
Joined: Wed May 05, 2021 7:12 pm

Re: 3.45 Differential install

Post by bstoner » Thu Aug 05, 2021 12:54 pm

My left adjuster shaft is close but doesn't touch. Interesting how much difference there is between cars. The only thing I don't like is the TrueTrac makes a slight clunk on/off throttle. You can hear it if you have the radio and A/C off. Apparently that is normal. I was worried I did a bad install. I pulled the carrier and took it over to a 4wd shop for them to double-check my work. They said it looked good; and clunk was normal. Relief... I am mechanical but not a rear end guy. Didn't want to spend over a grand on a rear end to just destroy it due to installation error.
https://www.eaton.com/us/en-us/products ... -faqs.html

Q: When I step on and off the gas pedal, I hear the unit make a “clunking” noise. Why?

A: This happens because Eaton Detroit Lockers have “backlash” or “slack” between the drive and driven teeth and you will hear this in everyday use going through corners and when transitioning from drive to coast. Also, with the vehicle on the ground and the transmission in neutral, several degrees of lash in the driveshaft is normal. Here is a formula to calculate the degrees of rotation of the driveshaft: (differential internal lash X ring and pinion ratio) + ring and pinion backlash + driveline slop such as U-joints wear.
2014 PPV, work in progress, 3.45, eventually LSA....

JUNKYARD_JACK
Posts: 57
Joined: Mon May 17, 2021 3:13 pm

Re: 3.45 Differential install

Post by JUNKYARD_JACK » Thu Sep 23, 2021 6:03 pm

To all the guys that have installed these, what's the opinion between 3.27 vs 3.45? I see a few 3.27 LSDs in my area for $400-$500 but no 3.45s I was wondering if it worth waiting for a 3.45?

Pursuit
Administration Staff
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Joined: Tue Apr 23, 2013 8:39 pm
Location: Omaha, NE area

Re: 3.45 Differential install

Post by Pursuit » Thu Sep 23, 2021 6:18 pm

This will be subjective for each person. I haven't had the chance to try a car with a 3.27. I am NA and wasn't worried about the miles per gallon. I don't have any wheel spin with the 3.45's. I am running a 275 wide tire, 1LE lower control arms and toe links. I tried to firm up the IRS with those components. Seemed to have worked for me.

Maurice
Maurice Sheil

mhsheil@gmail.com

2011 Caprice Phantom Black 9C3
2012 Impala 9C1
1995 9C1 Caprice
1996 GMC Sierra C1500
1974 SJ Grand Prix 455 well optioned with factory moon roof

GammaFlat
Posts: 134
Joined: Mon Sep 21, 2020 2:26 pm
Location: NW Indiana

Re: 3.45 Differential install

Post by GammaFlat » Fri Sep 24, 2021 12:57 am

I have a 3.27 with no other significant mods and factory wheels. I have not adjusted anything to compensate. Speedo is off by 11.9%. It does not seem to me that there are any obvious problems without reprogramming for the new ratio.
The car definitely feels like it has more grunt. I too was concerned about gas mileage and opted for the 3.27 for that reason. I think I paid around 500 at a local bone yard. So far I haven't done any significant trips (all city-ish). The indication from the DIC says I'm doing okay with gas mileage but I'm sure its calculations are off b/c I haven't re-programmed.
Many on here swear by the 3.45. I'm glad I've got the 3.27 and not sure how I'd feel with the 3.45.
You might consider changing the ring and pinion on a Caprice Diff to 3.45 and save yourself a ton of cash. Full disclosure: I have a 50-some thousand mile 2.92 for sale for a hundred bucks :).
My understanding is that there are three diff's that will fit our cars. A "good" camaro one that came with the V8's, a crappy Camaro one that came with some V6's and ours which is a tweener in terms of diameter of the ring and general durability.
Good luck.
Current: 2013 9C3, deeper trans pan, 12VoltSolutions Remote, Class III hitch, Android Auto capable radio

bstoner
Posts: 49
Joined: Wed May 05, 2021 7:12 pm

Re: 3.45 Differential install

Post by bstoner » Fri Sep 24, 2021 1:55 pm

I have not driven a Caprice with 3.27 vs 3.45 so I cannot give a 1 to 1 comparison. I have 3.45 gears now. In my opinion 3.45 is definitely not too much gear for these cars. It's a lot of weight to get up moving. In fact my wife didn't even notice the difference. LOL. She is not a car person. 3.27 is stock for the auto Chevy SS. I think either one you will be happy with and make a noticeable difference. The 3.27 is about half the price of the 3.45 and are much more common. For a budget install the 3.27 is easy to find, affordable, and the way to go. If you want more 0-60 performance then I would recommend the 3.45 and pay the difference. You will probably be waiting a long time or have to pay to ship one to you. For me I am going for an ultimate build. So I went 3.45 with a Truetrac, milled JRE caps, diff cover, poly bushings, new seals, and bearings. I wanted to make it bullet proof to handle high HP. I would also budget for programming the gear ratio in the ECM as well. I have HP Tuners and adjusted it to get the speedo and shift points back on track.
2014 PPV, work in progress, 3.45, eventually LSA....

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