Changing rear ratios

Drivetrain discussion including Transmission, Differential, Driveshaft, and related items.
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elc32955
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Changing rear ratios

Post by elc32955 »

Brought this topic over from the General forum.

I was musing over the SS coming out later this year with 3.27 gearing and the thought occurred to me, why not just change gears in our rear ends like many of the Caprice's before us? We could go from a 2.92 to basically whatever we wanted. LeadFart told me that the 3.45's were standard in the new Camaro, and the rear is a plug-n-play for ours. Recalibrate the car via HP Tuner and you're good to go.

So, I started looking around a bit. Turns out there's several ratios available, 3.45 is common and already loaded in the Camaro V8 rear ends. There's also after-market 3.73, 4.11, and 4.33 available it seems. 3.45's might be an easier swap if it's already loaded into a pumpkin, but darned if 3.73's wouldn't light us up some more. I went from 2.73 to 3.73 rear in my 95 Caprice and what a difference! Sure, you're going to lose a few MPH on the top end and maybe 1 or 2 MPG, but count the times we routinely drive above 120 MPH. There's some extensive discussion about swapping pros/cons over on the G8 board. For quicker times off the line and 1/4 mile times, seems like it'd be worth it.

Comments/discussion anyone?

Eric
System Manager and your tour guide for the day. 2015 Caprice w/LFX, former NC DPS staff car. Partial hybrid G8/SS/Camaro SS interior mods, SS MyLink radio upgrade, 2016 Camaro V6 rims, GMPP Malibu chrome exhaust tips, otherwise bone stock for now.
Navy Lifer
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Re: Changing rear ratios

Post by Navy Lifer »

The 1LE Camaro uses a 3.91 ratio, too--behind the TR6060 manual, with a 2.97 or 3.01 first gear. Not sure about what is available for ZL1--that may be a larger ring gear package. The thing that everyone needs to remember is that the 6L80 has a DEEP first gear (4.027:1), so you would find that gear becoming almost useless and potentially problematic with too much rear gear--running in sport mode and hitting 1st at too high a speed will put some hellacious stress on the entire driveline when it finally is allowed to downshift to 1st....bad enough with 2.92, and will be much more dramatic (possibly breaking forward traction/skidding) with higher axle ratios.

If I knew the wheel/tire sizes I may use in the future, or if any engine changes might be implemented (cam swap, for example) that would work better with a higher numerical gear, a change might be appropriate, but I'd stay conservative with the ratio choice. A 6-speed manual conversion (GXP parts, anyone?) would open up the gear choice options much more realistically.
leadfart
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Re: Changing rear ratios

Post by leadfart »

Even with my setup, 3.45 is all I would go, based on what I've seen from the G8 board, a small converter, 3000 or so, with dr's should be good for some 1.80's on a stock PPV. That should equate to some easy low thirteen's, with good air and a tune.

These cars can be DD's in the twelves for relatively little change. :mrgreen:
Bob Dannelley
2011 Alto Gray 9C3 Caprice PPV-Maggie-11.64@119.68-Sold!
1995 DCM Impala SS-409-Stroker!-11.83@115
2014 Silver Ice LTZ Silverado Crewcab 4X4
2007 Black Z51 M6-Corvette Coupe
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elc32955
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Re: Changing rear ratios

Post by elc32955 »

OK, compatability question. There's several of the 2010-11-12 Camaro diff's running on EBAY that have 3.45's with LSD already pre-loaded. They are all advertised as manual transmission (6-speed) diff's however. Does anyone know if they will work on our cars, not sure about the interchange. Everything I see checking the part number references manual transmission.....

Thanks
Eric
System Manager and your tour guide for the day. 2015 Caprice w/LFX, former NC DPS staff car. Partial hybrid G8/SS/Camaro SS interior mods, SS MyLink radio upgrade, 2016 Camaro V6 rims, GMPP Malibu chrome exhaust tips, otherwise bone stock for now.
leadfart
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Re: Changing rear ratios

Post by leadfart »

All I know is, they work in the automatic G8's. Plus, the GXP came with a stick. I can't confirm it, but I think they are the same. That might be an OZ question. :D
Bob Dannelley
2011 Alto Gray 9C3 Caprice PPV-Maggie-11.64@119.68-Sold!
1995 DCM Impala SS-409-Stroker!-11.83@115
2014 Silver Ice LTZ Silverado Crewcab 4X4
2007 Black Z51 M6-Corvette Coupe
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storm9c1
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Re: Changing rear ratios

Post by storm9c1 »

Also keep the driveshaft in mind. Bigger gear ratio means that the driveshaft spins faster. Everyone I know who put 3.42s (me), 3.73, and 4.10s in their B-Bodies had to upgrade to a MMC driveshaft due to vibrations. Not sure if the PPV will have a similar problem. Just keep it in mind.
Tom (AKA: Storm)
2011 Caprice 9C3: L77, 8K miles, first-owner, purchased July 2011.
1995 Caprice 9C1: LT1, 178K miles, summer car.
1995 Impala SS: LT1, 21K miles.
1995 Caprice Wagon: LT1, 62K miles.
1995 Caprice Wagon: LT1, 128K miles. Rust In Pieces
1994 Caprice 9C1: LT1, beater winter car.
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elc32955
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Re: Changing rear ratios

Post by elc32955 »

Well, I pulled the trigger on a Camaro diff this morning with 3.45's in it out of a 1,100 mile wreck. We're about to do the experiment and see what happens. I know 1st is going to become a very quick range gear, although from the traffic I've seen on the G8 boards it is supposed to lighten the car right up with this mod. Of course I don't plan on road racing it but this should give the off-line performance a shot in the arm. It'll kill the top end a little but it's not a big deal. Next major mod will probably be opening up the motor and dropping new lifters in, the AFM will be programmed OFF when I do my tune (at the 3.45 install time).

I figure the goal here will be to mod enough to spank a stocker SS off the showroom floor when they come out.... so I'd need the equivilent in mods to do that without breaking the bank. Slow process, one step at a time.
System Manager and your tour guide for the day. 2015 Caprice w/LFX, former NC DPS staff car. Partial hybrid G8/SS/Camaro SS interior mods, SS MyLink radio upgrade, 2016 Camaro V6 rims, GMPP Malibu chrome exhaust tips, otherwise bone stock for now.
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Re: Changing rear ratios

Post by elc32955 »

And.. just FYI for everyone, I've dropped a email to the good people over at BMR suspension on the applicability of their bushing kit (BMR003) to the Caprice. I'll be taking my car over to their plant in Seffner on the 29th as part of the Florida G8 meet, so they'll get a chance to eyeball a Caprice first-hand.

Also I invited them over to the site so they may pop in here.... Since I'm going to do the diff swap, it makes sense to do bushings at the same time, IF the need is there to do them. Don't know if GM made any changes between the G8 bushings and the ones used on the PPV.

Eric
System Manager and your tour guide for the day. 2015 Caprice w/LFX, former NC DPS staff car. Partial hybrid G8/SS/Camaro SS interior mods, SS MyLink radio upgrade, 2016 Camaro V6 rims, GMPP Malibu chrome exhaust tips, otherwise bone stock for now.
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Re: Changing rear ratios

Post by elc32955 »

OK, my rear diff swap is done and my tune is in from Chris Henry. Basically to outline the procedure for you that was used on my diff swap, this is what was involved. Total time in the air was just under three hours. Chris can fill in here any holes here that I may leave. Note using this procedure you have to only remove one wheel, not both as many others do.

1) Raise the car.
2) Disconnect exhaust from the mufflers, leave the mufflers hang.
3) Drop the remaining exhaust with a helper and set aside.
4) Right side rear wheel needs to be removed. Remove the wheel, rotor, slide the caliper off and set it up still connected (so you don't have to bleed/purge brakes when you're done), disconnect suspension as needed.
5) Drain the old diff for storage.
6) Remove the securing plate (4 bolts), then drop the drive shaft out of the diff. It's a two-piece drive shaft so the rear half will just hang down. Expect heavy prying to get the drive shaft out.
7) Remove rear right side axle.
8) Remove the vent tube from the diff.
9) Unbolt the diff, slide to the right and down unhooking it from the left shaft in the process. Use prybars as needed to get it to move. When loose, lower the old diff and set aside.
10) Lift the new diff using a helper (heaver diff. then the old one!) and put it in place. This means at the same time sliding it to the left and up onto the hanging left shaft. (NOTE - proper tooling really pays off at this point such as a transmission jack!) Bolt in when seated properly.
11) Reinstall right axle.
12) Reinstall vent tube onto the diff (note the Camaro vent tube ends up in a different place so you just plug into the new location).
13) Reinstall drive shaft back into the diff and reattach drive shaft plate.
14) Make sure to fill the new diff with either the GM approved fluid and LSD additive, or use Royal Purple 75W-90 with the additive already in the juice. I used the Royal Purple. The fill is 1.2 quarts with a completely dry diff, we filled mine with one bottle as there's always a little residual left in the diff after it's drained.
15) Put the right rear wheel back together.
16) Raise the exhaust with a helper & bolt into place.
17) Connect mufflers back up. Make sure to check positioning on your tips when bolted up as there is a little slop in the flange and it's possible to get them off-center if you're not careful.
18) Lower car, take it for a little test drive making slow figure 8's or circles, etc... to allow the new fluid to populate into the diff, it might be a little noisy for a mile or so until everything gets lubricated up.

It's interesting that we found that GM used the smaller differential in our cars (at least the 2011 9C3) then was placed in the Camaro. For a severe service application you would think we would get the larger diff.

Also, be aware there are snap rings on the axle ends that go into the diff. We had the left side hang up for a while and this somewhat added to the time. The drive shaft was a very tight fit onto the diff and it took a little while to move it out as well. On the G8 this service can be done in about 2.5 hours, the Caprice probably 2.8 if all goes OK.

I can say after a few hundred miles of driving the car with the new diff that this definitely was, in my opinion, a worthwhile swap. The car is more responsive with the new gears with less throttle needing to be applied. Obviously the downside is you lose a few MPH in top end. But for what you gain, the swap is well worth considering.

My total cost for the diff & shipping, fluid, and swap labor was just over $1,400 out the door. You can get it done for less if you settle for a older diff (mine was out of a 1,100 mile 2010 Camaro), and if you can do the labor yourself. The Royal Purple was $20.99 per bottle (1 qt.) plus tax at Advance Auto Parts.

I'll post about the tune separately.

Thanks
Eric
System Manager and your tour guide for the day. 2015 Caprice w/LFX, former NC DPS staff car. Partial hybrid G8/SS/Camaro SS interior mods, SS MyLink radio upgrade, 2016 Camaro V6 rims, GMPP Malibu chrome exhaust tips, otherwise bone stock for now.
Navy Lifer
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Re: Changing rear ratios

Post by Navy Lifer »

When you say Camaro diff is "bigger" you are referring to physical size of the housing/case....is that considered to be a good thing? Is the G8/PPV diff considered or known to be inferior or weak compared to Camaro? I know the ZL1 has a much beefier unit, but what else makes the Camaro 3.45 a good thing beyond ratio change? Durability--larger bearings, more fluid capacity?

Was the 3.45 offered only on manual transmission cars? With the very "deep" first gear, how does the trans calibration (computer tune) seem to work with that? 1st gear = 4.02, so overall starting ratio is 13.87 - who needs a loose converter with that gear(?)!

Was the tune strictly for accommodating the gear change, or did you do some other things? (AFM status, timing, etc)

Will the optional ratios (3.27 or 3.45) fit PPV diff?

Is ring gear same size for all ratios (G8/PPV/Camaro)?

What about the bushings you mentioned...replaced or not? If so, can you detect a difference?

Surely you have more pictures than just this one!

Traction control off--fry the tires at will......!
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