C5 : 3.06 x 3.42 = 10.46 'Effective' 1st Gear ratio

10.46 div/by 2.48 (1st Gear in a THM 400) = 4.21

My '82 had the same A4 transmission ratios, but far-less power, even after swapping the Cross-Fire for a carb & intake, so 3.73:1 gears were just right for that car

I've been contemplating a cam / exhaust / converter / gear swap in this '03 Z51 (3.15), but am starting to question the need for more rear gear with additional power

 

I finished the teardown and rebuild of the diff last night and glad I did it. It wasn't hard at all. My machinist friend made the press tool for the RH shaft disassembly but a piece of pipe the appropriate dimensions with slots cut in it for the cross bar holding the spider gears in place would have worked just fine. The most difficult part was putting the bar that holds the spider gears back in and making sure that the bolt holes for top of the LH shaft assembly line up correctly. Just taking my time and a little drift punch and hammer persuasion after back in the vice for reassembly brought everything back into alignment.

I found that the Bellville washer on the LH shaft was cracked but the one on the RH was not. I replaced both and noticed that the replacement was wider and looked stronger to resisting the cracking in the future. The magnet didn't have any bad surprises. Some metal dust but no flakes. Clutch discs and spacers looked great so I did not replace.

The one thing I did find is that one of the bolts that holds the upper section of the LH shaft to the lower section was finger loose. Odd, I thought. I removed it and upon inspection it looked like it had one thread that was buggered about halfway on the threaded portion. I thought that I would just chase it again with a die but when I put the die on the bolt just came apart and the buggered thread. It wasn't buggered, it was just about broken through. Just for knowledge during reassembly I put the broken bolt back in and it was not ling enough to engage a single thread. If that bolt had broken while the car was moving it would have would have been like a grenade in the diff. Luckily we had a suitable replacement bolt and finished the job less one of the half shaft seals that I damaged while installing. Damn it, another $17 on the bill. We weren't able to determine what caused the failure other than possible overtightening of it during another or factory assembly.

Note: 89060114 $9.02 as an alternate that looks more like a traditional gasket is not needed and will not work. I don't know what diff it fits but not this one.

It took me 4 hours to tear the diff down and reassemble but I didn't have the greatest working space to do it in and was sharing tools with my mechanic. I washed in in a parts washer and that probably took 45 minutes. If I was set up to do it on a good table, clean areas, tools readily at hand and not investigating the broken bolt for causes didn't have to wash it I could have done it in 2 hours without ever having done it before.

If I get the replacement half axle seal in time we plan on swapping the diff tomorrow.

I also corrected the parts list as I found an error in qty of a part (seal plate should be 1, not 2).

 

Easier to stay with one formula. 2.48×4.11 (350 OR 400 Turbo 1st gear ratio, with 4.11 rear gear)=10.193
3.06×3.42=10.47
2.48x4.22=10.47
As I said, you would need a 4.22 rear end in a 350 or 400 Turbo trans to equal a 4L60E 1st gear with a 3.42 gear. If you went with a 3.90 gear...
3.06x3.90=11.93(!!) Overall 1st gear, or equal to
4.81 rear gear in 350/400 Turbo. Tire wear and traction issues would be constant. I suppose you could setup the car to hook somehow, but that would probably be a great way to deposit the transaxle all over the road!!!!🤣🤣😂

 

This should work as long as your ABS is not located in the back (early years) like mine. I used a trans jack to grab the trans/diff as one unit. Leave the torque tube and cover plate in place.

 

Yes, very true. If you have a 97 or 98 this will likely be more difficult, and everything will need to come down and out, due to the ABS being in the rear. The 99's forward have the ABS in the front.

 

Yesterday was the big day and got the diff swapped, blew out all the crap in the radiator and mounted a new set of tires in a total of 6 hours. Time to do the diff swap was 5 hours in a full shop with a 2 post lift and high lift transmission jack and two of us working on it. Had the diff on the ground in 2 hours. Took 2½ to get it buttoned back up. Spent the rest of the time cleaning the radiator and dismounting old tires and mounting new ones and installing them. Half hour fooling around with "stuff" that happened that had to be dealt with. If everything had went perfectly it could be done in 4 hours.

Troubles that we ran into were:

Drop in Customers coming in for 3 tire repairs that took about 45 minutes of my friends time but I was able to keep working.

The front drivers O2 harness connection broke when plugging it back in and probably spent 15 minutes fooling around with it to make sure that it wouldn't come unplugged in the future. Good thing is it can be checked during oil changes without any disassembly.

Also spent about 15 minutes fooling around with the harness connections on the side of the transmission (where the shift cable connection is) thinking they would need to be unplugged but they do not need to be disconnected if only dropping the system far enough to get the diff out. Same goes for the round connection on the passenger side of the transmission. Be careful putting your axle back exhaust back in as I hit the wires on the drivers side of the transmission with the pipe and had to spend a few minutes checking to see if any wires were damaged. Ended up putting some liquid wire covering on a small cut I found and then wrapping it in electrical tape and then wrapping all together in electrical tape.

Putting the passenger axle back exhaust back in and it just wouldn't go, It came out no problem but going back in it just wouldn't go. The flange was welded to the pipe to prevent rotation at the exhaust tips and we just couldn't get it past the connector and heat shield on the passenger side of the transmission. Had to cut the weld and then it went back in easy.

Last issue of the swap wasn't related to the diff but to the new tires. Front passenger tire pressure sensor would not connect when we started the car and was giving flat tire warning. Some diagnostic time with his tire sensor equipment really didn't help as none of the sensors were detected by either sensor checker that he had. That took 20 minutes. Decided to take it down the road and see if that would wake the sensor up and it did so the job was done.

From all of the instructions I found most were correct except where instructing to disconnecting the wire harness and shift cable from the transmission and no mention that the axle shafts have to go over the brake lines so to drop the cradle you have to get the axles under them. I check the bushing in the shift cable connection though and it was still a pliable bushing so I didn't change it out for the one I had on-hand in case it needed changed. You cannot get to the other end at the shifter without completely removing the torque tube so checking / replacing that one will have to be from inside the car. Also found that no instructions addressed that you have to remove the clips that hold the brake lines and harness to the cradle. It was pretty obvious that they had to be freed before you could drop the cradle. When we lowered the diff to remove it we just took it where the top of the diff was even with the lowest part of the center floor compartment. As we pulled the diff back it will actually start to drop a little further as the shaft starts to come out so probably didn't need to go that low but we didn't have to rotate it at all to get it out or in. As the car was up in the air we couldn't see how close the back of the engine got to the firewall but looking after everything was done I didn't see any witness marks of contact.

We had sprayed down all of the bolts the week prior with PB Blaster but probably didn't need to as none were rusted. On the front exhaust hanger one of the spot welded nuts broke off the bracket when removing the bolt so we could drop the exhaust. I was able to put another nut on top of the bracket and hold it with my fingers and it bit and I was able to get the bolt tight during reinstall. Bolts were tight but all broke free willing enough.

I would not want to do this swap in my own garage unless I had some serious equipment in it. Doing it on a creeper and knees with a 2 foot transmission jack would be killer. I would not want to do it alone either especially putting the half axles back in. Having the lift and especially having the high lift transmission jack really made the job so much easier. The half axles came out with a pry bar easily and went back in easy with two of us being able to tag team it. One to guide the axle into the diff and one to lift up on the hub assembly and push on the hub. It also helps with the 2nd person as the axles have to get around the brake lines. Then to hold it in place while the other got the A arm bolts in. Having the jack also helped getting the top of the shocks back in position to get the bolts in. The only specialty hand tool needed that some home toolboxes don't have was the prybar to get the axle half shafts out of the diff. It doesn't have to be U shaped but it does have to be thinner edged than a typical pry bar. A long socket extension is appreciated when doing the shock bolt removal and install. Both regular and deepwell sockets are needed. 8, 10, 13, 15, 18, 21mm sockets and a 10mm hex covered all fasteners if I remember correctly.

So the big question is how does it feel as compared to the 2.73? Hard to give total feedback yet as I have to get the tune to correct the shift points but I could tell an immediate difference. The powerband is available almost immediately and is a consistent pull instead of the slam you get when the 2.73 finally gets into the powerband about 3,000RPM. Before at 70mph I was running 1,750RPM. Now 70 looks like it will be about 2,300RPM so the tone of the care, (how it sounds), will take some getting used to. It sounds like it needs to shift into overdrive compared to the 2.73 which was so smooth and quiet even with my Stainless Works chambered round axle back exhaust when just cruising. Shift from 1st to 2nd is hard right now but the tune will take care of that. Other shifts weren't bad at all. Hope to get the tune done in the next couple of weeks before winter makes driving less frequent.

New Michelin Sport Pilot A/S tires took care of the slight pull I had to the right. Glad I won't have to add an alignment to all of the cost. When examining the old passenger front tire it felt like there was a bulge to it but we couldn't find anything visually. They hook up really nicely compared to the old design Pilots that were pretty low on tread.

I did confirm that there is no o-ring or gasket between the transmission differential so I corrected the parts list further up in this thread. I had the diff rear place o-ring identified as the seal between the diff and transmission so I corrected that description as well.

 

I yanked my diff today! Did it with the car on jack stands. Will start to disassemble the diff tomorrow in prep for new clutch packs / springs / long shaft. Swapping out a wheel bearing as well.

Only issue was some idiot (me) installed a heat blanket on the tunnel plate and covered all the bolts! Installed the heat shield without removing the exhaust and knew it would be a hassle when the plate needed to be removed.

Now to find where to buy all the parts from.

 

Ive done it twice on jack stands and a trans jack, by myself. FUN FUN

 

Got the differential opened up ... two broken springs.

 

there is a sticky note on the procedure on this at the top of the forum

 

Got my car "tuned" Saturday by Brian Turner of Dyno Tune Motorsports in Columbus, OH as I had to make a trip there to pick up a glass targa top that bought. got in touch with Brian on Wednesday and asked if he could to the shift point adjustment and could squeeze me in Saturday morning. He was able to do both and I arrived at his shop opening at 10am and was out on the street at 10:15 to see if the adjustments were good. Shifting was perfect and back to his shop to pay him $100 for the work. If you need tuning work in the Columbus area I hear that Brian is very good. He has an 800+RWHP C5 of his own. He was tuning a stock 2018 Camaro as a I left and had another car lined up for later in the day. He is in an easy and safe area to get to just on the west side past New Rome.

Final cost of the swap:
$235 for the diff
$200 for diff tear down parts
$300 time on the lift at my mechanics shop
$100 for the tune
$ 835 total