swapping a 1.8 5 speed transmission into a 2.8 - keep the 2.8 front diff?

[scottinalaska]

As I understand, the transmission ratios are slightly different between the two engines. Are the differential ratios different, or just the transmission gear ratios?
Thus, do I need to split the transmission from the front differential to ensure I don't have binding in my AWD system when I install it with my original front diff in place?
Or, easiest, throw it all in as a unit? audi 5 speed transmission.jpg
Thanks,
Scott

[grayjay]

Ratio for the rear differential and the front differential (in gearbox) must be matched. If you tried to run with mis-matched differentials, the center split differential would be constantly trying to compensate while you are driving and center diff would quickly wear out. As alternate to opening gearbox and swapping the front differential, you could also swap the rear differential from the 1.8t donor car into your car getting the matching gearbox but then final drive ratio would of course be altered.

[scottinalaska]

Therefore, the different ratios between the 1.8 and 2.8 engine configuration vehicles are found IN the differentials, NOT the transmissions themselves. Yes?
Thanks,
Scott

[QuattroBucc]

I'm pretty sure you can just swap the transmission.. People blow their 1.8 transmissions all the time and swap in a 2.8 and I have never read that they had to swap in the rear diff from the 2.8 also. Pretty sure the gears in the transmission are different, the rear diff just changes the final drive ratio

[walky_talky20]

QuattroBucc is correct.

The differential ratio ("final drive ratio") is 3.89:1 for *ALL* 5-speed quattro (01A) gearboxes which were original to a B5 chassis.

The other factory final drive ratio available for 01A gearboxes is 4.11:1. This is only found on earlier cars (B3, B4 chassis). You will also find 4.11:1 final drive on the B5 Tiptronic cars, and all B5 S4 (6-speed 01E and Tiptronic).

The difference between B5 1.8T gears and 2.8 gears is indeed the gears themselves. The final drive is the same. You need not worry about swapping the front or rear differential. They already match.

[scottinalaska]

YES! That is the answer I was hoping for. The ONLY difference is the transmission ratios (not the final, of course) between the two engines. The diffs on both the 1.8 and 2.8 cars are THE SAME, no matter the transmission or engine. Smart of Audi to not screw those up! This helps so much. Thank you, QuaattroBucc and Walky-Talky20!