Which diff to drop-in a 2005 A4 car ???
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 972
Likes: 11
From: Dawsonville, GA
Which diff to drop-in a 2005 A4 car ???
I'm 'gonna start shopping for another diff for my car... and wondered what the easiest/best swap would be ?
I have an '05 A4 car and plan alot of future abuse that the OEM diff will not likely survive.
Should I be looking for a C5 ? or C6 diff ?
Will I need any adapters ? or is there a simple drop-in swap available ?
I have an '05 A4 car and plan alot of future abuse that the OEM diff will not likely survive.
Should I be looking for a C5 ? or C6 diff ?
Will I need any adapters ? or is there a simple drop-in swap available ?
Team Owner
Joined: Feb 2001
Posts: 27,254
Likes: 136
From: Short Hills, NJ
You can use either a C5 rear (make sure you go for only the later series III cases that housed either a manual's 3.42 gear or an automatic's 3.15 (not the series II 2.73 type) gear only.
You can also use a 2006 and up C6 rear but I believe it has to be from a manual car (not Z06) only but neither option is going to be a simple 'drop in' unfortunately.
Any of the rears can be made to fit with some transmission shaft changes and fabrication of course.
Yes, you will need some adapter if you go with the later C6 manual rear.
The C5 rear is going to require some alteration/fabrication to the crossmember/mounting area.
You can also use a 2006 and up C6 rear but I believe it has to be from a manual car (not Z06) only but neither option is going to be a simple 'drop in' unfortunately.
Any of the rears can be made to fit with some transmission shaft changes and fabrication of course.
The C5 rear is going to require some alteration/fabrication to the crossmember/mounting area.
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 972
Likes: 11
From: Dawsonville, GA
You can use either a C5 rear (make sure you go for only the later series III cases that housed either a manual's 3.42 gear or an automatic's 3.15 (not the series II 2.73 type) gear only.
You can also use a 2006 and up C6 rear but I believe it has to be from a manual car (not Z06) only but neither option is going to be a simple 'drop in' unfortunately.
Any of the rears can be made to fit with some transmission shaft changes and fabrication of course.
Yes, you will need some adapter if you go with the later C6 manual rear.
The C5 rear is going to require some alteration/fabrication to the crossmember/mounting area.
You can also use a 2006 and up C6 rear but I believe it has to be from a manual car (not Z06) only but neither option is going to be a simple 'drop in' unfortunately.
Any of the rears can be made to fit with some transmission shaft changes and fabrication of course.
Yes, you will need some adapter if you go with the later C6 manual rear.
The C5 rear is going to require some alteration/fabrication to the crossmember/mounting area.
Is one better than the other ? (C5 vs C6)
Team Owner
Joined: Feb 2001
Posts: 27,254
Likes: 136
From: Short Hills, NJ
There was a time when the C5 rear conversion was the only option and also much cheaper than any of the options that became available later on but not sure if that still applies.
A 2004 Z06 rear would be a great choice if going that route.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
It's hard to say which is actually stronger, I've seen (strengthened/beefed up) C5 rears cut 1.2x sixty foots on their way low 8 second 1/4 mile passes but the later C6 rears (both manual and auto) are quite strong as well.
There was a time when the C5 rear conversion was the only option and also much cheaper than any of the options that became available later on but not sure if that still applies.
A 2004 Z06 rear would be a great choice if going that route.
There was a time when the C5 rear conversion was the only option and also much cheaper than any of the options that became available later on but not sure if that still applies.
A 2004 Z06 rear would be a great choice if going that route.
To go C5 you need to fab a diff mount and weld a plate on your cradle.
To go c6 you have to swap the rear trans extension...it's about a $500 part on a manual c6...not sure how much it is on a automatic or how hard the swap is.
If I was running an automatic I wouldn't worry about swapping. They don't seem to break like us manual guys. If you get any wheel hop get right out of it, it's wheel hop that seems to break parts. And if you're really worried about it you can go with a bias ply setup, the softer sidewalls seem to help over the radial stiffer sidewalls.
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 972
Likes: 11
From: Dawsonville, GA
If I was running an automatic I wouldn't worry about swapping. They don't seem to break like us manual guys. If you get any wheel hop get right out of it, it's wheel hop that seems to break parts. And if you're really worried about it you can go with a bias ply setup, the softer sidewalls seem to help over the radial stiffer sidewalls.
I also have no problem fabbing a mount for a C5 diff. That sounds easier to me than using an adapter plate.
Last edited by Dragracer_Art; Mar 3, 2012 at 07:01 PM.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
There are a lot of good choices in 17", shorter is better for ET but taller is better for the rear due to the sidewall.
Probably the best radials, with a real soft sidewall, would be the Hoosiers. But you can't drive them on the street (no siping at all) if there's any chance of rain at all and they wear out much quicker than the M/T's which are good on the street and last a long time.
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 972
Likes: 11
From: Dawsonville, GA
Yea they are pretty proud of those. I guess it cost a lot of R&D time and machine time to build them so can't blame them.
There are a lot of good choices in 17", shorter is better for ET but taller is better for the rear due to the sidewall.
Probably the best radials, with a real soft sidewall, would be the Hoosiers. But you can't drive them on the street (no siping at all) if there's any chance of rain at all and they wear out much quicker than the M/T's which are good on the street and last a long time.
There are a lot of good choices in 17", shorter is better for ET but taller is better for the rear due to the sidewall.
Probably the best radials, with a real soft sidewall, would be the Hoosiers. But you can't drive them on the street (no siping at all) if there's any chance of rain at all and they wear out much quicker than the M/T's which are good on the street and last a long time.
I see ECS has spindles too... but they are also pretty salty.
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Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
If you really want tall tires the 26" bias ply 17 M/T's are really tall, have a soft sidewall, and are light.
But you'll be quicker with 275/40/17 Hoosiers... I'll guarantee it.
Team Owner
Joined: Feb 2001
Posts: 27,254
Likes: 136
From: Short Hills, NJ
Marc the c6 option has gotten a lot cheaper than it was when I did my c5 option 3 years ago, now that you can buy diffs from wrecked Vettes. The cost of the core differential is about the same now; back then all you could buy was a new c6 diff.
To go C5 you need to fab a diff mount and weld a plate on your cradle.
To go c6 you have to swap the rear trans extension...it's about a $500 part on a manual c6...not sure how much it is on a automatic or how hard the swap is.
To go C5 you need to fab a diff mount and weld a plate on your cradle.
To go c6 you have to swap the rear trans extension...it's about a $500 part on a manual c6...not sure how much it is on a automatic or how hard the swap is.
There is an adapter that I believe RPM Transmissions makes that can allow for the 2006 and up manual C6 rear case to be used in an automatic 2005 C6, but it's not cheap either. 
I don't think there is any need to change the transmission tail housing or output shaft though which is a plus. Dennis's car cut sixty foots well into the low 1.4s on a 3.73 equipped 2005 rear and lived to tell about (for a while at least) and Tommy D's car has cut many high 1.5s/low 1.6s on it's bone stock '3.15 geared' 2005 rear and is still going strong. But I think Dragracer Art is going to be throwing some nitrous (hits VERY hard) at his as well and that might ultimately require more strength than a 2005 rear is willing to give. Or it might be fine.
