Author Topic: lsd swap? (Read 2536 times)

cyborgben · « **on:** July 20, 2012, 07:33:45 PM »

is it worth it to swap a 180k 4.10 lsd that sounds and feels good into my good condition original 91 to replace the known good 130k open 4.10? i would have to do a double swap since the "donor" car in fair to poor (but running) condition is going up for sale... thoughts?

current plans for the keeper is stock+suspension+chip summer driver.

DesktopDave · « **Reply #1 on:** July 20, 2012, 09:21:26 PM »

I'd do it. The LSD makes the car faster...

OTOH, according to the PO's records, my car is on her third diff. Both the previous units were small case 4.10's. I have since fixed the problem with a medium case 3.73.

cyborgben · « **Reply #2 on:** July 20, 2012, 10:50:49 PM »

hmmm, that is a thought. but this one is basically free except for labor. Is the going rate for a lsd about $150-250?

You cant really get much taller on the ratio than a 3.73 on a stock m42 and still get out of your own way can you?

DesktopDave · « **Reply #3 on:** July 21, 2012, 08:29:21 AM »

When I was looking for mine, I used to see good low-mileage LSD's in desirable ratios going for $400. Seems to me that the economy has taken prices down a few notches recently.

I ended up buying my 318i basically because I had the diff, if you can believe it! The 3.73 came in a 325is that (unfortunately) had terminal frame rust. The diff could have fit in my e34 but it would have needed a case swap. The e34 isn't nearly as much fun as the e30...and since I now had this whole parts car, I ended up buying an M42 sedan with a bad diff. I figured I'd try out the swap and sell it all off if I didn't like it.

So, three years later, I don't notice much difference with the 3.73. A stock M42 isn't all that fast to start with, and the 3.73 is only 9% taller than stock. I am running stock 14" tires though...I'll bet in combination with larger diameter tires it'd be annoying.

I also used that car mainly for work - a lot of highway driving - and the stock ratio is a little too buzzy on the highway. The new diff makes 2nd gear good for 60mph, and 4th gear is perfect for passing at my usual 70-75mph typical speeds. Fuel mileage seems to have improved as well.

cyborgben · « **Reply #4 on:** July 22, 2012, 09:35:21 AM »

thanks dave. as always, good insight.

the point is moot. it rained yesterday, so i couldn't finish painting the soffit, so i went ahead and did it. 2 diffs out and 2 diffs in in one day with no lift (yet.) Needless to say, i am a little sore today.

note - imho the smoothest method to install is to attach the ujoint drive shaft first, then the upper center bolts, then the lower center bolts, then the rear hanger, then the axles. i tried doing the lower center bolts first and could never get the uppers to line up. hopefully this will save someone some time, swear words, and bloody knuckles.

i am saving a 30k 2.93 lsd to make a hyper miler out of when gas hits $6 a gallon.