Question for those who have upgraded their rear diff with 4.10s

[spdracer35]

I have a Z4M, and I have been considering upgrading my rear diff with a 4.10 ring and pinion. I was under the impression that I could purchase the 4.10 ring and pinion and have it installed in my current diff, basically just a swap. After speaking with a bunch of local shops, it seems most will only rebuild my current diff completely, or swap in a new diff (like from dinan). Both of these options seem a lot more expensive than just swapping a ring and pinion, which I thought was in the $1600-$1800 range.

So, for those of you who have upgraded:

Did you install a new diff, or did you just change the ring and pinion?

If the ring and pinion was changed, outside of things like fluid, did you replace anything else?

Am I completely misunderstanding what is involved with doing this mod? Please enlighten me.

[epbrown]

Originally Posted by spdracer35

So, for those of you who have upgraded:

Did you install a new diff, or did you just change the ring and pinion?

If the ring and pinion was changed, outside of things like fluid, did you replace anything else?

Am I completely misunderstanding what is involved with doing this mod? Please enlighten me.

You'll find more experience with this on an M3 forum like, well, www.m3forum.net; it's a pretty common upgrade on the E46 M3, and comparatively rare on the Z4M. Offhand, I can think of 3 posters here that have done it and as far I know both of the otherss have sold their cars.

I did the Dinan swap (3.91:1 gears), where I got a complete diff already rebuilt with the new gears inside. It's more expensive, but faster - took about 4 hours (both times, because the first was bad).

From what I know about the ring and pinion swap, most shops do what Dinan does - they rebuild the diff with the new gears, just as you've been told. The gears should run you $600 or so, a shop will charge $1200-$1500 depending on your market's labor rates. The Dinan swap was $3300 all in, so yeah, the rebuild route is cheaper.

The chief reason for going with the Dinan swap is convenience and, supposedly, Dinan's expertise. I'd say find a competent shop and have it done. Fully half of the Dinan swaps I've heard of require a second install because the first diff wasn't rebuilt properly; mine was replaced after 600 miles. They stood by their work, but doing it twice was a hassle, and one I paid a premium to them to avoid.

[DarkstarZero]

Originally Posted by epbrown

I did the Dinan swap (3.91:1 gears),.

Why didn't you get the 4.10?

[Blind32]

Originally Posted by DarkstarZero

Why didn't you get the 4.10?

Haha, I saw in a thread that he said it is better to get the 4.10 because they save you time so that you don't have to explain why you got the 3.91 instead. I believe he got a good deal or they were available local for him.

[epbrown]

Originally Posted by Blind32

Haha, I saw in a thread that he said it is better to get the 4.10 because they save you time so that you don't have to explain why you got the 3.91 instead.

It's always the first question.

Actually, I went with the 3.91 for the same reason I added Aerodynamic Sideskirts and CSL wheels - I wanted to build the Z4M as I felt it should have been. While you can get the 4.10, every BMW tuner recommended the 3.91 for the Z4 (Hamann, Hartge, AC Schnitzer).

To me, them and - I suspect - even BMW, it enhances car's performance without ever being obnoxious, and doesn't require an extra shift for the 0-60 sprint (about 4.5-4.6secs) like the 4.10 does. BMW uses a 3.85 in the E90 M3, Porsche uses a 3.88 in the Cayman S (iirc).

It was pretty much the limit in a street-drivable sports car, before emissions and mileage concerns lengthened everyone's gears and added cogs.

[fatmatt0116]

Originally Posted by epbrown

It's always the first question.

Actually, I went with the 3.91 for the same reason I added Aerodynamic Sideskirts and CSL wheels - I wanted to build the Z4M as I felt it should have been. While you can get the 4.10, every BMW tuner recommended the 3.91 for the Z4 (Hamann, Hartge, AC Schnitzer).

To me, them and - I suspect - even BMW, it enhances car's performance without ever being obnoxious, and doesn't require an extra shift for the 0-60 sprint (about 4.5-4.6secs) like the 4.10 does. BMW uses a 3.85 in the E90 M3, Porsche uses a 3.88 in the Cayman S (iirc).

It was pretty much the limit in a street-drivable sports car, before emissions and mileage concerns lengthened everyone's gears and added cogs.

this

[Starscream]

4.10's here

Just bought the gears, Didn't buy a complete diff, (at the time a complete diff wasn't available in 4.10)

No need to get all crazy, inside the diff is the same parts as any other rear end,
just go to a shop that is a specialist in setting up differentials,
The shims, bearings, crush collars are going to be the only thing that would need replacing,
Thankfully mine didn't need any shims, no noise, and love the feel of it,

Was a total bastard to do, Hopefully I never have to do it again, and I did it on my back with the car on jackstands,
That diff weighs a ton when you have zero clearance on your back lol,
and it doesn't lift straight up either, you have to aim the pinion side up first then rotate the arse end as you clear the rear subframe,
Very little clearance under there, Everything so tight,

I figured if your going to make the switch go big or don't bother,
3.62 to 3.91? not worth the hassle for me,

and I don't shift any higher then 2nd to hit an "indicated" 60, From what I've read you might only be at 58 or so but with 4.10's you can even pull away in 2nd,
and 1st gear IS usable, contrary to what people tell you,
I did do an install thread a few years back when I put them in, Not much technical info as I was alone doing it so I didn't have time to stop and snap pics, I just wanted it in and out asap,

[fatmatt0116]

how much for the shims, bearings, and crush collars from bmw? Any other parts I should get ahead of time?

I figure, is it that much of a difference between 3.91 and 4.10 that I should hold out? I've been offered a REM polished setup from CFoote that's never been installed at a fair price... the car is my DD.

[johanness]

Haven't done it yet, but am planning on getting the R&P (3.91) done at a qualified shop in the spring. My car only has about 4K miles, so why swap out the entire diff with Dinan and roll the dice on having them put a 'refurbished' one in that more than likely has been around the block a few times? Epbrown's story is here somewhere for your perusal.

[epbrown]

Originally Posted by fatmatt0116

I figure, is it that much of a difference between 3.91 and 4.10 that I should hold out?

The difference between 3.91 and 3.62 is 8%, so your rpms increase everywhere by that amount and your car feels like it has 284lb-ft of torque (meaning your car should feel like it would if it had the stock gearing but more torque).

The difference with 4.10 is 13% and the car feels as if it as 296ft-lbs, so the difference going from stock is much more dramatic and noticeable coming from stock, not a huge difference from 3.91.

Here's my final take: I would only get the 4.10 gears if my car almost never saw daily driver duty, and was simply my weekend/nice weather toy. I'd also get headers, aftermarket exhaust, aftermarket chip to raise the rev limiter a smidge - the Z4MC would likely be at 4.3sec 0-60 or better and pull like a pitbull playing Frisbee in 3rd gear with the Sport button on. You'd have more of an animal, yet it would still be reliable and cheaper to maintain than most any European car in its performance bracket, but not require supplemental upgrades like suspension and brake work to be manageable.

[fatmatt0116]

I've already got the ESS DME remap....I think this would be the final piece of the puzzle for me. Took headers off when I moved to Cali.

[Z4-VILLA]

cali emissions sucks

[fatmatt0116]

Originally Posted by Z4-Villalona

cali emissions sucks

true, but Cali does not.