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C5 A4 What is needed to run 3.73s and where to get it all
Hey folks! I have 2.73's in my 01 c5 auto, I want to run the 3.73's and have some fun. I did some research, is the Z06 diff/rear the only way to run 3.73's in my A4? Also curious as where to get em, I haven't seen any used for sale, I only seem to see people say get the RPM transmissions build rear/diff with them instal'ed for the price. Are there any other websites/options I am unaware about?
I am assuming the car will feel drastically different jumping from a 2.73 to a 3.73 eh? I know my old mustang gt did...so I can only imagine this car.
Last edited by zinsavage123; 05-25-2020 at 11:20 AM.
A 3.73 gear won't fit into the 2.73 case, you'll need a complete rear diff. Used units can be had on ebay and are generally available locally if you you aren't in a very rural area. There are many good posts on how to swap rear ends on this site and others, but be aware that it is labor intensive and will probably take a couple of days if you're doing it at home in your garage. A 3.42 rear is a good choice for a A4 and they are more readily available than 3.73's so you might want to consider that route.
So is it just the diff/carrier I need, or do I need the entire rear axles all that good stuff. Here are some on ebay I found. Does it have to be and/or matter if its a base c5 manual diff or z06? Here are some I seen and wanna be sure fellas...much appreciated.
My 2001 A4 originally had a 3.15 rear drive. In 2016 I replaced it with a Stage 4, 3.73 rear drive with Wavetrac differential from RPM. On the track I only use 2nd and 3rd, 1st is too low and both 1st and 2nd will roast rear tires from a standing start.. On the track a 2-3 wide open throttle upshift will sometimes activate traction control because of wheel spin. With a stock engine.
The only difference that I'm aware of between a z diff and base is the z diff has shot peened gears to make them a little stronger. Tag on diff has sp after gear ratio iirc. If you're going through the trouble, look for a 3 rib case instead of a single rib. Probably won't make much a difference with the auto but cost difference is negligible.
It makes no difference whether it's from an auto or manual trans car. Any differential out of any C5 Vette will work in any other C5. You just need the complete differential - your existing axles and other components all work fine. Manual transmission cars generally come with a lower rear end than an automatic because the auto can multiply torque from a from a standing start giving them an advantage or a manual.
Like he said they all fit, the auto diffs came with a 2.73 or 3.15 ratio 6spd cars 3.42. The only difference the diff case will be a 2 rib or 3 rib case, the 3 rib is supposed to be the strongest. They both fit.
From that what I understand, you need to buy a series 3 differential to install 3.73 gears. So differentials with 3.15 to 3.42 gears will work. Series 2 differential will not support 3.73 gears, the vss (speed sensor) will not line up with the ring gear reluctor teeth because the housing are different.
It makes no difference whether it's from an auto or manual trans car. Any differential out of any C5 Vette will work in any other C5. You just need the complete differential - your existing axles and other components all work fine. Manual transmission cars generally come with a lower rear end than an automatic because the auto can multiply torque from a from a standing start giving them an advantage or a manual.
I am a bit confused now...if it doesnt matter if its an auto or manual diff that I need to run 3.73s...than why am I getting one in the first place? Why cant I put them in my auto diff that I already have than? Gotta admit lost there fellas. Or is the 2.73 diff not able to period and still different from a 3.15 aito diff as well?
Last edited by zinsavage123; 05-27-2020 at 11:52 AM.
Reason: added quote
St. Jude Donor '08-'09-'10-'11-'12, '14-'15-'16-'17-'18
Originally Posted by zinsavage123
Hey folks! I have 2.73's in my 01 c5 auto, I want to run the 3.73's and have some fun. I did some research, is the Z06 diff/rear the only way to run 3.73's in my A4? Also curious as where to get em, I haven't seen any used for sale, I only seem to see people say get the RPM transmissions build rear/diff with them instal'ed for the price. Are there any other websites/options I am unaware about?
I am assuming the car will feel drastically different jumping from a 2.73 to a 3.73 eh? I know my old mustang gt did...so I can only imagine this car.
Any 3.15 or 3.42 (97-04) will work in your application. The 2.73 case is different and carrier has a different offset where the ring gear is mounted so that will not work.
From our experience, stay away from high mileage units since the clutch spring normally break and ruin the inside of the carrier.
If you use your vehicle for cruise and not races, single rib diff will be fine.
I am a bit confused now...if it doesnt matter if its an auto or manual diff that I need to run 3.73s...than why am I getting one in the first place? Why cant I put them in my auto diff that I already have than? Gotta admit lost there fellas. Or is the 2.73 diff not able to period and still different from a 3.15 aito diff as well?
Removed to not confuse op, the above poster is the person to ask as far as any differential questions.
I went the RPM route when I swapped out my blown 3:42 for a nice 3:73 unit from them, Great quality & installed by Next Level Performance in Maitland. I ended up doing n auto tranny change at the time, also from RPM plus I had my Torque tube completely rebuilt by Next Level performance.. Tranny fluid looked bad & the torque tube bushing was shredded to the point of giving out on the next run or so. Happy I did it & noticed a boost in the rear when giving the pedal a little push. You will need good tires though. I recommend the Continental W/D. Best tire for street IMHO. BTW 2000 C5 coupe
05-25-2020, 11:19 AM
C5 A4 What is needed to run 3.73s and where to get it all
