c5 A4 differential swap from 2.73 to 3.15

bobs77vet

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how tough is it to swap a stock 2.73 ratio differential for a 3.15 differential on a C5?


the 2.73 is stock and 3.15 is the OEM "high performance" rear end. i am thinking the least expensive way to pick up some acceleration is to change the stock 2.73 rear diff ratio for a 3.15 unit.

i can get 3.15 diff for around $300 any thoughts?

thanks bob
 
i used my best negotiating skills and scored one for $160 shipped to my house from a CF member.

I kind of like staying with the OEM specs and i think the 3.15 is the sweet spot. i had a 700r4 ( i think they are same ratios) in my C3 and if i recall right i think i had 3.33 rearend in it and i recall at the time thinking a 3.09 or 3.11 would have been the sweet spot. so when I saw the OEM high performance ratio was 3.15, i said "self you need to get you one of those"....

its a 15% increase over the 2.73 and would be turning 2100 rpm at 70. so it wouldnt be too annoying and i dont see much over 85mph even on I95

now the question is what do i do.....RTKperfomance will go over the diff and replace seals for $500 and then if it needs springs or clutch pack whatever they cost, and the install of it is $850.

looks like you need some special tools for the diff rebuild.

so basically it would be $1500-1600 installed

or do i just take my $160 expenditure and throw my self into the deep end and spend 4-8 hours and install it as is and hope for the best.
 
Sounds like just installing might be a good option. Do you trust the seller?
 
Sounds like just installing might be a good option. Do you trust the seller?

you know i dont have any reason to think any thing has been misrepresented.

and its not like its any magic.....i did more magic with my resto modding of my black c3. this is just a factory to factory swap. it looks like its alot of effort but not any real high technical skills and if it turns out not to work or leak or chatter i can always replace it with my known good unit or then take it to them and have them fix it.

i need to get the car up on stands and really eye ball the bottom of the car.
 
I think I would pop the cover for a look and if there are no obvious issues, just change the fluid and swap it in. Like you said, if there are any issues, you can always swap the other back in and send this one out.
 
well my main mechanics and me had some really highly technical conversations this weekend over this subject...that is my boys and I were at a wedding reception and drinking brewskis and getting smarter and braver by the moment...... i think we are just going to swap it see what happens...

the crew....one guy at the wedding we were talking to asked us if were were mechanically inclined and had tools...we smiled and said yes kind of

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I have read several times the sections of the following manuals Mitchell on demand E manual, the GM 04 service manual, and the rear end gear swap step by step by Andy Bolig on how to R&R a rear differential.

in my case it is swapping a 3.15 rear and replacing my 2.73.

here is the questions i have....the service gm manuals have you remove
the transverse spring, lower shock bolts and the lower ball joint, upper ball joint and rotors basically taking the entire rear cradle apart piece by piece....the Andy Boilg step by step takes the cradle out as an assembly with rotors, transverse spring and lower control still connected to the suspension knuckle. basically disconnecting everything thats bolted up top.

http://www.superchevy.com/how-to/18978/


Am I missing something or do I have this correct? and is there any reason not to do it the way Andy Bolig says to do it? His method seems very reasonable.

how many hours of a job is this to do with two able bodied decently capable corvette guys with all the tools.

I can see this is great opportunity to replace rear shocks what else comes to mind as being ripe for replacement when doing this swap?

thanks bob
 
Bolig's version is certainly the way I would prefer to do it. The use of a lift would make it much easier. If you were to do this on the ground, you would need to have it up pretty high on jack stands so you could lower the components enough to get them out from under the car. Since I'm no longer a professional wrench turner, I have no lift access, so creativity has to come in. I'm looking forward to see how you do it. You always seem to come up with creative solutions. :)
 
Lots of steps but it looks like a bolt-in without tweaks and adjustments.

Considering my current pace, it would probably take me 2 years to do this :lol:
 
so heres the link to a post over in the CF that gives the visuals to what we need to do.....I have some huge ass 6 ton jack stands that will get a car up over 24" which is almost too high unless you have really long arms. I think the guy on this thread had the rocker sills 18" off the ground. which is a piece of cake. only tools I need to get is the transmission jack. funny when I left NJ 10 yrs ago I sold the one I had along with and engine hoist and motor stand....its cheaper to sell them and buy them again then pay the movers to move them.

https://www.corvetteforum.com/forums/c5-tech/4129278-pics-quick-jack-clutch-replacement.html

I have read these articles so many times now I think I know the process inside and out....now I just have to decide if I really want to do it myself.

I think I do want to do it because I have always wanted to wrap my hands around the newer IRS systems. now I am waiting for the diff to arrive and then once I can get my hands on it I will come up with a plan.
 
now its decision time....me or a shop

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one broken cooling rib, and the cover took a it too looks like from shipping

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does that machining look right, i can see in other internet images they also have this
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now its decision time....me or a shop

]


I'm putting the hydro trans on my 4x4 Kubota back together right now. It was rebuilt before and they reused parts they shouldn't have and missed/forgot a spacer on the pto intermeadiate gear . It must have screamed when they started it up. You can see where the gear removed material on the case.....

Do you have a trustworthy shop?
 
yes RTK Performance in Frederick MD. everybody gives them very high marks they specialize in the LS platform
 
well I had the swap done last March at RTK and the car is an absolute blast to drive. definitely worth it.

they swapped the internal springs and clutches to a newer version during the install and had to reprogram the A4
 
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