Author Topic: 4.10 LSD Question (Read 4645 times)

dlmrun2002 · « **on:** July 16, 2007, 07:11:21 AM »

Does an open 4.10 (small case) cover fit a 4.10 LSD (small case)?

Cheers..
DLM

tjts1 · « **Reply #1 on:** July 16, 2007, 10:52:56 AM »

Vladi · « **Reply #2 on:** July 16, 2007, 02:59:57 PM »

oldtimer · « **Reply #3 on:** July 17, 2007, 06:34:35 AM »

Okay this forum is as good as any place to admit ignorance. Can someone explain this 4.10 ration and Limites Slip Differential? What's turning at what speed. I read sometime back that changing the Diff. is the good start for mod, 4.72 LSD. and one can find another model for them because they are stock on particular E30 models. Which one? The ignorance part is I do not know anything about diff. other than change the oil and remove and replace them.

gearheadE30 · « **Reply #4 on:** July 17, 2007, 11:19:11 AM »

The 4.10:1 ratio means that for every 4.1 turns of the driveshaft, the wheels turn once. The numerically higher ratios (like 4.27:1, which is the one you heard about) mean that the driveshaft has to turn more times per 1 rotation of the wheels. This is why the numerically higher diff ratios will make the engine run at a higher RPM for a given speed.

Limited-slip just means the the differential only allows a certain amount of speed difference between the two driven wheels. Open differentials transmit power to the wheel with the least load, which is why the inside wheel tends to spin when going around a corner under throttle.

The 4.27 diff was in the e30 318i convertible, and is very rare in LSD form.

Another option is the 4.44 which came in the e36 318ti clubsport. Im not sure, but I think this one only came with the automatic tranny.

oldtimer · « **Reply #5 on:** July 18, 2007, 06:04:19 AM »

Thank you for the lesson. Now I have a mission to find one I can install or getting one from a junk yard not the way to go? Can they be purchase new from a reputable source? I would feel better if it is new or re-built through a reputable source. By the way which ratio is best for daily driving and at time xcross?

gearheadE30 · « **Reply #6 on:** July 18, 2007, 09:31:53 AM »

The junk yard is probably your best bet, although there may be some on ebay. These diffs will last forever provided that the oil was changed somewhat regularly. As far as I know, the only place to get newish ones are from metric mechanic, and they are fairly expensive.

IMHO the stok 4.10 is the best as a tradeoff. Anything numerically higher (e.g. 4.27) will be very noisy on the highway, and first gear will become impractical. I've driven a 318 with a 3.73 diff, and it was much quieter. It really did sap the performance of the engine, though, because the transmission ratios weren't close enough together to keep the engine in its power band.

kramerica5000 · « **Reply #7 on:** July 18, 2007, 12:38:27 PM »

I agree with gearheadE30 that the 4.10 is the best ratio for most drivers. Some may disagree with me on this, but IMHO don't think switching to an LSD is necessarily the best place to start modding. I just don't think the 318is in stockish form has enough power to really require it for typical street driving. That's not to say that there aren't times during spirited driving where it could make a difference, but for as few as those times are (unless you are making regular track excursion or hooning on wet roads) I can't see getting an LSD over, say, a lightweight flywheel, which is a mod you will definitely notice. I definitely plan on swapping my open rear end with a LSD at some point, but its not on the top of my list.

Quote from: oldtimer;29789

Okay this forum is as good as any place to admit ignorance. Can someone explain this 4.10 ration and Limites Slip Differential? What's turning at what speed. I read sometime back that changing the Diff. is the good start for mod, 4.72 LSD. and one can find another model for them because they are stock on particular E30 models. Which one? The ignorance part is I do not know anything about diff. other than change the oil and remove and replace them.

tjts1 · « **Reply #8 on:** July 18, 2007, 12:45:24 PM »

All I can say is don't knock it before you try it. I'm living with a 3.64 and loving it.

b318isp · « **Reply #9 on:** July 23, 2007, 11:01:39 AM »

Quote from: tjts1;29882

All I can say is don't knock it before you try it. I'm living with a 3.64 and loving it.

Nice having 2nd, 3rd, 4th, 5th and 6th gears ! :p

Changing to an LSD is one of the most important upgrades to make on the E30. A 3.91 or 4.10 is fine and are the most commonly available.

BrandC · « **Reply #10 on:** July 24, 2007, 01:34:39 PM »

Going to a 3.91 will give you better highway mileage which keeping the torque advantage of a shorter gear ratio. Plus 3.91's come in medium-case size and can be rebuilt to higher LSD lock-up characteristics.

b318isp · « **Reply #11 on:** July 25, 2007, 08:45:01 AM »

Quote from: BrandC;30292

Going to a 3.91 will give you better highway mileage which keeping the torque advantage of a shorter gear ratio. Plus 3.91's come in medium-case size and can be rebuilt to higher LSD lock-up characteristics.

3.91 is a longer gearing, so reduces torque at the wheels slightly, but that doesn't matter. Don't think it affects fuel consumption much either as peak torque is quite high in the M42.

Wise Old Dog · « **Reply #12 on:** July 25, 2007, 10:08:08 AM »

I have a small case 3.91 on my car. Can't say that I notice any loss of speed, but the couple hundred rpm's drop on the highway is nice. I would do it again unless I tracked the car. Nice for a DD.

gearheadE30 · « **Reply #13 on:** July 27, 2007, 08:53:46 PM »

yea, with the exhaust I have, 3700 RPM at ~80 can get a bit tiresome.