Diff Swap with random junkyard auto e46

[spacecase]

Hey all. Think my pinion gear is starting to go on my differential and I thought it would be a good opportunity to upgrade to a 3.38 final gear ratio.

This is another ebay seller with an ok looking diff but I was wondering to see what folks thought of the reliability of a used part like this?


https://www.ebay.com/itm/2001-2006-B...59077103224b3e

[legobumb]

I have a manual transmission 325xi e46 and I had to replace the rear diff last year due to the old one's pinion just exploding and all the gears getting mangled in the process (happened while I was on the highway; rear wheels locked up on me). I went to a salvage yard and got another whole pumpkin for about $80, painted it, installed it, and it's been running just fine since. Granted, I got an exact replacement, I think the ratio on it was 3.38 or something close to it. I think my point is that the one you found on ebay, unless it was rebuilt using new parts internally, isn't worth that much at all. The one I got from a salvage yard had a grade A rating (which just means it was in great shape). But of course ALWAYS check out the part physically before leaving the salvage yard.

[dezand]

I bought a used one from LKQonline, it had 114K miles and i verified it using carfax since they supply the VIN and pictures of the car.
shipping from Oregon to SoCal was $50 on a pallet to a friends business address. Shipping to home address would have been $150
works good

[spacecase]

Thanks, 300 is too much and I called my local junkyard. They have 3.38 auto for 150 bucks, I think I can find it cheaper lot of parts for these cars, very cool.

[Jackson42]

Why would a 3.38 be an upgrade? Isn't that the ratio for all E46s with automatics?

[spacecase]

My 330i 5 speed comes with a 2.98 final drive ratio. And since all e46s autos come with that 3.38 they are cheap from a junkyard. Taller gears...

[Jackson42]

My 330i 5 speed comes with a 2.98 final drive ratio. And since all e46s autos come with that 3.38 they are cheap from a junkyard. Taller gears...

Yeah, my 330Ci 6-speed came with a 2.98 and I replaced it with a 3.05 (also out of a 330Ci 6-speed). I'd consider a change to a 3.38 a downgrade.

[spacecase]

Yeah, my 330Ci 6-speed came with a 2.98 and I replaced it with a 3.05 (also out of a 330Ci 6-speed). I'd consider a change to a 3.38 a downgrade.

That makes sense with the 6 speed (lucky you) you convert top speed into torque and with the 6th gear you fill in the 60 mph plus range.
Thats why the e46 M3 has a diff ratio of 3.62

3.62 revolutions of the drive shaft equal one revolution of the axle, more revolutions produce more torque at the wheels. Im still trying to get my head around this..

[Jackson42]

That makes sense with the 6 speed (lucky you) you convert top speed into torque and with the 6th gear you fill in the 60 mph plus range.
Thats why the e46 M3 has a diff ratio of 3.62

3.62 revolutions of the drive shaft equal one revolution of the axle, more revolutions produce more torque at the wheels. Im still trying to get my head around this..

Let's see if we can create an analogy that will make it clearer. Torque is defined as a force times a distance. Using a wrench and a bolt as an example, I can put 2 foot-pounds on the bolt by applying a force of 2 pounds one foot from the bolt or by applying a force of one pound two feet from the bolt. In the latter example, you've applied less force to the wrench, but the price you pay for the torque multiplication of the two-foot lever arm is that you have to move the wrench twice as far to get the same "twist" on the bolt. Now let's compare the effect of a 3.62 rear end to a 3.05. In the case of the 3.62 rear end, you apply less force but you have to turn the input of the differential 3.62 times to move the output shafts the same distance as you would by applying more force but only turning the input 3.05 times. The price you pay is that with the 3.62 rear end, at a given road speed, the driveshaft is turning about 19% faster than with a 3.05 rear end. The math is as follows: difference = (3.62-3.05)/3.05 = 18.7%. Hope this helps.

[spacecase]

Let's see if we can create an analogy that will make it clearer. Torque is defined as a force times a distance. Using a wrench and a bolt as an example, I can put 2 foot-pounds on the bolt by applying a force of 2 pounds one foot from the bolt or by applying a force of one pound two feet from the bolt. In the latter example, you've applied less force to the wrench, but the price you pay for the torque multiplication of the two-foot lever arm is that you have to move the wrench twice as far to get the same "twist" on the bolt. Now let's compare the effect of a 3.62 rear end to a 3.05. In the case of the 3.62 rear end, you apply less force but you have to turn the input of the differential 3.62 times to move the output shafts the same distance as you would by applying more force but only turning the input 3.05 times. The price you pay is that with the 3.62 rear end, at a given road speed, the driveshaft is turning about 19% faster than with a 3.05 rear end. The math is as follows: difference = (3.62-3.05)/3.05 = 18.7%. Hope this helps.

Wow thats a much clearer, thanks.