3.42 Differential Help
 

Hey guys, I have searched and found some answers but I know I can count on you fellas for some better and more specific guidance and advice, so here it goes...

I just bought my first c5, 2004 a4 with the 2.73 gearing and before I start with any other major mods other than an intake/exhaust and tune I want to wake it up with some gearing. I want to go to the 3.42 as opposed to 3.73 for my application down the road.

With that being said I found a great deal on a used 3.42 diff from a 97 for $400 and some change , but from what little I have been able to find, it seems like the earlier year diffs aren't quite as strong as the latter years. (I don't know how true or accurate this is, which is why I would like some input based on your personal experiences). I will eventually do stall/torque converter when I go with a heads and cam package but for right now I'm just looking to do a diff swap with the 3.42 gearing to wake her up a bit.

Has anyone had any issues with your earlier year 3.42's? Are all of the 3.42 diffs in all of the C5's interchangeable? Any input or advice would be greatly appreciated!

All the diffs are interchangeable, you will need a tune for the new gear ratio

what you want is the three rib diff. (stronger) I don't know what your level of mechanical skills, but just about all of the C 5 diffs have posi plate issues, the bellville washer is the weak link, they break and could end up ruining the diff !!!! just did our C 5Z and was lucky no bearings were damaged, the fluid looked like silver paint !!!!!

Mike, all the C5 differentials are interchangeable.
Going from a 2.73 to a 3.42 gearing will give you a noticeable difference in performance. Adding a higher stall converter will also add a SOTP feel, but only if you are really punching it. Around town driving will be no different or perhaps even a little more sluggish at very slow speeds - but hitting the gas to pass a car is...............:yesnod:
Most early differentials were single rib and I believe GM went to 3 rib diffs for all C5s in 2002. My understanding is the 2001 Z06s all had 3 rib diffs, but I have known of 2001 Z06 owners that only had a single rib unit. Perhaps the earlier diff had died and a prior owner swapped in the single rib unit. (?)
If you are not producing tons of horsepower, or wanting to use a 4000rpm TC with slicks for a drag launch you would probably still get good use out of a single rib differential. Of course, many of us are prone to mod, mod some more, and then even mod some more. So, getting a 3 rib diff case will prepare you for any potential adds later on. You can also look to forum vendors for some strong differentials and transmissions. RKT56 (http://rktperformance.com) and RPM Transmissions (http://www.rpmtransmissions.com) are two that come quickly to mind.
For a good discussion on beefing up the C5 differential look at https://www.corvetteforum.com/forums...ld-how-to.html.
Good luck with your build.
Larry

:iagree: Good advice...

That is extremely helpful thank you Larry. The 1997 diff I'm looking at is listed as two rib belt from a reputable ebay seller. This is the quote with the sale pictures "You are bidding on a used differential from a 1997 Corvette with only 91k miles. Has 3.42 ratio. Will only fit C5 Corvette which uses rear mounted transmission. Everything in excellent condition.. Auction is for differential only. If you have been pricing these units, you know how expensive they are!! Don't miss out!!

EARLY TWO RIB CASE"

I didn't see anything about a single rib case so that's where I'm getting confused..can you please enlighten the unelightened haha

Thanks Larry

if it has any big miles on it, (and it has never been touched) don't think the clutch plates would be good ???? lot of work to take a chance ?? IMO

Mike, I looked at what I think is the same listing. If so, the part number he references 12551769 is for a 1-rib differential. I'm not sure about "two ribs".
I've never heard of a two rib, but hopefully one of our members will have more insight.
Cheers, Larry

one for sale in the parts for sale here (C5 parts)

https://cimg7.ibsrv.net/gimg/www.cor...459b0cd306.jpg

Mike:
Here's a photo that shows a simple comparison between the 1-rib diff (on the right), and a 3-rib diff (on the left). In addition to how much cleaner the 3-rib diff is, :D you can clearly see the added bracing (ribs) along the center spline of the case. (Sorry – not the best artist).

The purpose of the extra ribs is to add strength or rigidity to the differential case. This added strength is intended to reduce flexing of the case which will then help keep the internal diff parts in alignment.

you can get a good low mileage z06 diff for that price, personally I'd skip the one you are looking at... the z06 also has shot peened gears, I don't know how much that really helps but hey why not haha

Are you referencing the one from Vengeance out of the z06 on ebay or another listing? Thanks pal

Wow thanks for the extra effort, I can definitely see the difference in the two, much appreciated man!

Without a doubt, early older C5 differentials with higher mileage will have broken or excessively worn Belleview springs problems. When the spring wears, it flattens outs and then cracks. IF, you are lucky, it only cracks in one place. IF, it fractures into pieces, the can and most of the time do fall into the spider gears and destroy them. If you have a C5, you will experience belleview spring failure in one for or another.

The belleview springs add compression force to the limited slip clutches so that the clutches provide the correct slip and grip friction when the car is turning. The limits slip additive that is required to be added to the differential lube allows the clutch plates to have the proper slip when the rotational speed of the rear tires are unequal (in a turn).

Another issue with ALL C5 differentials is the output shafts are weak and if you put a lot of power to them OR induce wheel hop/drive train shake, it will break an output shaft. You can easily up-grade the output shafts, clutch packs and Bellville springs to the more durable C6 ZO6 parts, (direct fit).

The differential can easily be inspected by removing the side covers and removing the inside center section. At a minimum, inspect the lube and see if its full of metal. Inspect the metal catch magnets in the bottom of the diff. See if there are any chunks or excessive wear. You can clamp one output shaft in a vice (padded jaws) and use a strap wrench on the other shaft apply a rotational force on the shaft and see how much force it takes to slip the clutches. A brand new differential with new clutches will easily require over 100 ft/lbs to rotate the free shaft. Flip it over and do the same for the other side.

If, you feel that you don't need to or don't want to inspect the internals, at a MINIMUM, you should replace the side cover output shaft seals. Its a very easy procedure while the diff is out of the car!! You will not know that they are bad and will leak until the car is ALL back together again and you take your first drive!

so whats stronger on the 3-rib diff. and by how much? just the added rigidity of the case?

Earlier this year, I swapped out my 2.73 for a Z06 3.42. Before it went in, I changed out output shafts belleville washers, plates and put everything back with new seals. All parts were C6 Z06 which interchange easily and stronger. If you track the car go for harder aftermarket output shafts.The case is a 3 rib. Boy it woke it up rudely. That with only long tubes, Corla exhaust, and a Vararam cai made 366 at the wheels with no engine work except a tune. Happy camper with that gear and all C6 Z06 suspension. Sill traction will come tough with street rubber.

Tune for different gear......
 

I am not sure why you would need a tune due to changing rear end gears, at least in an A4. If it is because of a presumed speedo error, it is unnecessary on an automatic equipped C5. Why? I am not certain, but I changed from the G92 (3.15) to a 3.42 gear from a C5 Z06, and I assumed I would need the tune you mentioned to get correct speedo reading. I was told by the shop that did the changeover that no tune was required, because the Auto equipped C5s automatically compensate for the gear changes, and the manual 6 speeds do not. Again, why I dont know. But the shop was correct, I didnt need any tune. Just my .02......

Shift points are regulated by your tune. Most likely a change in ratio will result in the desire to establish different shift points. My tune allowed me to customize this adjustment to my liking. Perhaps yours were fine.

TCC slip table and the WOT shift MPH value need adjustment, you will damage your transmission if the proper adjustments haven't been made.
the speedometer sensor runs off the axle output gear ratio changes dont affect the speedometer, changing the diameter of the rear tires affects speedometer. 3.15 to 3.42 isn't much of a change, 2.73 to 3.42s you would have issues with shifting and a transmission slipping codes. My vette is a 6spd I went from 3.42s to 4.10s no speedometer or tune adjustments needed, don't understand where your shop got that info