3.46 differential install...

[Gene V]

Having a Performance Gearing (Jim Blanton) 3.46 diff installed in the M next month. How much more labor would be involved to swap out the sub-frame bushings at that time. What else should I have checked while the diff is out?

[Team Neverlift]

Having a Performance Gearing (Jim Blanton) 3.46 diff installed in the M next month. How much more labor would be involved to swap out the sub-frame bushings at that time. What else should I have checked while the diff is out?

About 4-5 hours labor on top to drop subframe and replace bushings.... while the diff would take an hour max, and that's replacing all 3 bushings (2x cover, carrier).

Nothing needs to be checked while the diff is out imo, just follow the fluid change procedures from your builder.

[TostitoBandito]

It's not too much more time consuming to take the whole subframe out with the diff in it, but it's a bit of work since the simplest way to do it is to drop the entire rear suspension (subframe, diff, upper/lower control arms, trailing arms) as one unit. It's the 4 subframe bolts, 4 drive shaft nuts, 6 bolts for the trailing arms, and disconnect the parking brake cables, then the whole thing drops. Once you do that it's easy to get at all the subframe bushings, as well as three diff mount bushings (and RTAB's if you need to do those). Also a good time to do the outer ball joints if desired. All this stuff piles up of course, in terms of time. If you only want to do the diff mount bushings and not the actual subframe bushings, you can do those without dropping the subframe. Removing just the diff will get you the access you need for those.

Since you're swapping the diff I just suggest at least loosening all the bolts on the diff CV joints before you take anything off the car since it's much easier to break them loose when you can apply the parking brake to lock it.

[adamnur]

You'll have to update with your thoughts after install. Keeping the stock 5 speed?

[Gene V]

You'll have to update with your thoughts after install. Keeping the stock 5 speed?

Yes, keeping the 5-speed. Car is used mostly for autocross these days, which is held in a smallish parking lot. Most of courses, which I run in second gear, consist of turns that are slow and tight...so I'm thinking the 3.46 will pull better out of these turns and eliminate the need to down shift to first.

[MauiM3Mania]

Hows that tranny holding up, Gene?

[Gene V]

Hows that tranny holding up, Gene?

It's doing great...thanks again for the deal, saved me from a mess of frustration/aggravation...

[Rugbyfan]

I have a 3.46 in my e30 with the zf320. IMO it’s perfect gearing. I have 215/40/17 tires and I think it runs out of gear at 150? I’d have to look at the tables on diffs online. I turn 4K rpm at 80mph and it doesn’t annoy me.

[Gene V]

I have a 3.46 in my e30 with the zf320. IMO it’s perfect gearing. I have 240/40/17 tires and I think it runs out of gear at 150? I’d have to look at the tables on diffs online. I turn 4K rpm at 80mph and it doesn’t annoy me.

[Gene V]

3.46 diff and subframe + diff cover bushings were installed last week, car is tight, more responsive and has some punch...should have done this 10 years ago. I now see why they call the 3.46 a poor man's supercharger.

[TostitoBandito]

3.46 diff and subframe + diff cover bushings were installed last week, car is tight, more responsive and has some punch...should have done this 10 years ago. I now see why they call the 3.46 a poor man's supercharger.

I agree and love my 3.46 diff. I got mine from diffsonline several years ago. Definitely a lot more punchy in the low gears, but still just tolerable at freeway speeds on the street. I definitely wouldn't go any lower on a street car unless it's got a 6 speed.

[blckstrm]

I agree and love my 3.46 diff. I got mine from diffsonline several years ago. Definitely a lot more punchy in the low gears, but still just tolerable at freeway speeds on the street. I definitely wouldn't go any lower on a street car unless it's got a 6 speed.

I got a 3.38 when my 3.23 died. Not quite what you guys have, but it was a great upgrade. Like most mods, by itself I didn't notice any change in mileage. But the extra punch was immediately noticeable.

[TostitoBandito]

I certainly lost a couple MPG going from stock to 3.46. To be expected when you're like 250 RPM higher across the board.

The other thing I noticed is that the shorter gears demand a more aggressive driving style, especially in the lower gears. RPM's shoot up faster so you have to be a bit more aggressive matching revs. It took some practice to get used to the difference and be able to shift smoothly again. Probably mostly because I'd driven the car in its stock form for so long and was used to shifting by ear and feel, and all that changed slightly with the new diff.

[ArcticM]

How would a 3.38 do with a 6 speed? I know with a 5 speed it’d be good but what about 6 to much shifting for daily driving?

[blckstrm]

How would a 3.38 do with a 6 speed? I know with a 5 speed it’d be good but what about 6 to much shifting for daily driving?

All gears are the same, including fifth as the 1:1 gear. Sixth is just an overdrive. So you just get lower highway cruising revs.

[TostitoBandito]

Yep, the 6 speed just gets you better highway MPG and less revs/noise. It does allow you the option of going really short on the diff if you want since you have a new top gear, but that will shorten all the lower gears by quite a bit. That's mostly for track/racing purposes though.

In any case, on the street with a 6 speed you can certainly go at least as low on the diff gearing as people do with 5 speeds. So, 3.46 up to 3.64 even should be fine. For comparison, a stock 96+ M3 goes 68mph in 5th gear at 3000 RPM, while the same car with a 3.64 diff and a 6 speed goes 74mph in 6th gear at 3000 RPM. So a 6 speed and a 3.64 is still lower revs on the freeway than stock. A 3.91 and a 6 speed will about match the revs in 6th gear of a stock M3 in 5th gear, if you're curious.

Here's a handy link for seeing what different ratios do to your revs and speeds in each gear:
https://www.google.com/url?sa=t&rct=...cWDIKznSARGbF4