Son of a *****!

[Cyrix2k]

So I got my car back yesterday with the new 3.15 diff installed. I drove it about 50 miles and every so often I'd hear/feel a clunk when starting off. I went to move it into our garage to check it out and while switching between 1st/reverse, it clunked noticeably every time. ****! back to the shop... The guy there looked it over and he thinks it's coming from the diff itself. He's giving Dan @ diffsonline a call right now. I want my car back :(

For those wondering about the performance, I didn't get to drive it too hard. 1st gear felt *really* short but I seemed to be able to shift into 2nd real smoothly compared to usual. I can't really give speeds because I'm pretty sure the speedometer was off, but it felt like the car was running pretty strong. I'd have to drive another car with a 2.81 to make a good judgment.

[Orxan4ik]

3.15 is good for back road or track driving and will most likely pull on a 2.81 past 120ish mph. Other than that, 2.81 owns :)

Hope all is well with your diff :)

[curt2128]

sorry to hear that man... ask for a discount do to the inconivence

[mattmartindrift]

sounds like the lash may have been incorrectly set.

[Cyrix2k]

sounds like the lash may have been incorrectly set.
that's what I'm thinking. This was presented as a rear pulled from a car that hadn't been fooled with though.

[MPD47]

3.15 is good for back road or track driving and will most likely pull on a 2.81 past 120ish mph. Other than that, 2.81 owns :)
2.81?
Wow.

What is it geared to 220mph?

I've been debating a Dinan diff as I think the stock 3.15 is geared to high!

And I would agree with Matt, it does sound like the lash may have been incorrectly set. However, is your mech SURE the diff and axles are properly torqued?

[mattmartindrift]

2.81?
Wow.

What is it geared to 220mph?

I've been debating a Dinan diff as I think the stock 3.15 is geared to high!

And I would agree with Matt, it does sound like the lash may have been incorrectly set. However, is your mech SURE the diff and axles are properly torqued?

220?

it's not a double-overdrive transmission. 5th gear is 1:1. So, to compensate for the somewhat close-ratio transmission the rear is geared tall. At 75mph I cruise around 2.5k rpms IIRC. I know LSx cars cruise around 1500rpms on the highway.

[andyffer]

i lke my 3.46

[djt5150]

Symptoms sound just like a bad u-joint. I'm sure you already checked that though.

[MPD47]

220?

it's not a double-overdrive transmission. 5th gear is 1:1. So, to compensate for the somewhat close-ratio transmission the rear is geared tall. At 75mph I cruise around 2.5k rpms IIRC. I know LSx cars cruise around 1500rpms on the highway.
Well it is a 540i/6 which is why I made the comment (completely without having looked at gear charts). What is the 6th ratio in the 540's?

[Michael Star]

.83 I think, or maybe .88, or .86. I know it is .8x

[Captain Morgan]

Well it is a 540i/6 which is why I made the comment (completely without having looked at gear charts). What is the 6th ratio in the 540's?

Some info from my site...

BMW 540i/6

Getrag S6S 420G
1st Gear Ratio 4.23
2nd Gear Ratio 2.51
3rd Gear Ratio 1.67
4th Gear Ratio 1.23
5th Gear Ratio 1.00
6th Gear Ratio 0.83
Reverse Gear Ratio 3.75

Rear Differential 2.81:1 Open

**Final Ratio in 6th - 2.33:1**


Pontiac GTO

Tremec T-56 6-Speed
1st Gear Ratio 2.97
2nd Gear Ratio 2.07
3rd Gear Ratio 1.43
4th Gear Ratio 1.00
5th Gear Ratio 0.84
6th Gear Ratio 0.57
Reverse Gear Ratio 2.90

Rear Differential Dana 3.46:1 Limited Slip

**Final Ratio in 6th - 1.97:1**


Despite GM having a lower rear diff ratio, 6th gear provides a higher ratio than BMW

[MPD47]

Yeah, and .83 is also 6th in the M5 (3.15LSD), which is geared out to about 190mph @ 6500rpm in 6th. Which is why I was curious. 2.81's are LONGGGG.

[PixMan]

That's a very interesting chart of ratios! It explains why my '04 GTO felt kind of slow off the line after I'd driven a 540i/6. No contest on the torque of course, but the two cars felt similarly fast in two different ways.

[mattmartindrift]

I was just thinking about this.

You paid to have this done, right?

Shouldn't your mechanic have caught this during their test drive?

[Captain Morgan]

That's a very interesting chart of ratios! It explains why my '04 GTO felt kind of slow off the line after I'd driven a 540i/6. No contest on the torque of course, but the two cars felt similarly fast in two different ways.

yeah BMWs 1st gear is like granny low, but it needs it to get things rolling with that steep rearend, once its rolling things settle back to normal.

[Cyrix2k]

I was just thinking about this.

You paid to have this done, right?

Shouldn't your mechanic have caught this during their test drive?
In short, yes. The main mechanic/shop owner was out for the holiday so he never drove it. He's the only one I really trust to work on the car. I was talking to him on the phone and he said the U joint seemed to be fine, the CV joints had a little play but they weren't bad (they haven't changed since I bought the car), and he didn't think it was the gear lash. Everything is torqued properly. The saga continues.... :(

[racerx0911]

3.15 is good for back road or track driving and will most likely pull on a 2.81 past 120ish mph. Other than that, 2.81 owns :)

Hope all is well with your diff :)
who told you that?? im pretty sure i would put car lengths on a 2.81 diff... from a dead stop.

[Orxan4ik]

who told you that?? im pretty sure i would put car lengths on a 2.81 diff... from a dead stop.

Not with the same mods, you won't

[Cyrix2k]

who told you that?? im pretty sure i would put car lengths on a 2.81 diff... from a dead stop.Coming from a person who's had both so far, I'm not so sure. With race tires, yes, but on the street I don't have traction through first gear in either gear ratio. After the shift to second, the gearing difference is negligible until higher speeds. The biggest difference is that the car will pull at x speed in 4th gear with the 3.15 the way the car used to pull at x speed in 3rd gear. Same rpms, same power to the wheels, just a different gear.

[racerx0911]

the fact is i can launch my car at a much higher rpm with out losing traction. Where as the open diff lost traction at 3K rpm.

im just able to put more power down to the ground, but i guess im talking more limited slip than gear ratios.