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    Anyone put a 3.91 diff in their manual 535?

    I am considering a diff swap and I believe my 1990 535 comes with a 3.46....is the 3.91 really going to do much and how much worse will the gas mileage become...all opinions please, thank you.


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    Re: Anyone put a 3.91 diff in their manual 535?

    That would be a nice improvement. I went from 2.93 to 3.64 on my 540i and find it quite reasonable. I have a 3.91 limited slip for your car if you decide to do it. Let me know.-Mike Pope
    '94 540i Alusil,
    Sachs kit,
    dinan bars and plates,
    stock wheels
    That green color we
    all know so well.
    Soon to be painted.

  3. #3
    Big Dog
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    What is your objective? Do you want to make the

    car "faster" or "quicker"? Changing the rear diff can indeed accomplish either, just be aware that making the car accelerate faster will come at the expense of:
    1. Top end speed
    2. Fuel Mileage
    3. Longevity (you turn more revs)
    4. Drive train reliability (the torque on the rear CV joints, bearings, etc. is greater)

    That being said, it can be a wonderful thing, especially when you shock a Vette or Mustang off a traffic light.

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    Re: What is your objective? Do you want to make the

    Well...
    1) a decrease in theoretical top speed. Fact is, BMW's tend to be geared way taller than the available horsepower can take advavtage of. I had a 750iL where I changed the 3.15 to a 4.27. The top speed of the car with the 3.15 without the governor was about 160. With the 4.27 I was able to reach 145 because the gearing was so low that the engine would hit red line in Overdrive. If you do the math, I only lost about 9% of my top speed for a gear drop of over 30%. There were no other mods on that car, but it did 0-60 in about 5.5 sec.

    2) gas mileage is more a function of intake manifold pressure than anything else. Higher revs DOES NOT necessarily mean that you're using more gas. Cruise down the highway and try shifting your car in and out of OD and watch the economy needle. It doesn't always behave the way you'd think.

    3) As far as longevity, I don't think going from 3.46 to 3.91 is significant enough to make a noticeable difference in the usable life of the car. Over the course of 100k miles the percentages say the the engine will turn over 11% or so more times. So your 12 year old car goes another 89k miles (until the beginning 2010) or 100k (until the end of 2010). It's still the least destructive way to significantly improve the performance fo your car. Put a turbo or blower on it...then you'll se shortened life.

    4) True that the rear CV's and wheel see more torque. The other side of the coin is that the driveshaft and transmission, and clutch if you have a stick, and components BEFORE the differential get a pretty nice break because instead of absorbing torque, they're transfering it to the rear wheels. Rear CV's can be gotten pretty cheap anyway. Much cheaper than a driveshaft for sure.-Mike Pope
    '94 540i Alusil,
    Sachs kit,
    dinan bars and plates,
    stock wheels
    That green color we
    all know so well.
    Soon to be painted.

  5. #5
    zmuff
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    Re: Anyone put a 3.91 diff in their manual 535?

    A 3.91 and 3.73 rear end are both very popular upgrades, thinking about a 3.91 myself. At 60 mph, a 3.91 rear end will give you about 2500 RPM as opposed to stock RPM of about 2200. I can live with that, especially with the extra low-end grunt it will have. Of course at 120 mph, you're turning almost 5000 RPM but how often does that realistically happen? If you can get hold of a 3.91 (LSD right?), do it!

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    Re: Anyone put a 3.91 diff in their manual 535?

    There are 4.10's and 4.27's available that will fit in that car too if you want to really go all the way. I believe there was a 3 series made at one point with a 4.44 but I have no idea if it could be made to work in your car. I think the 4.10's are found in early 525's with the M20 engine. The 4.27's are found in 92 735's. Just a thought. They can probably be gotten for in the $300 range if you check www.car-part.com

    -Mike Pope
    '94 540i Alusil,
    Sachs kit,
    dinan bars and plates,
    stock wheels
    That green color we
    all know so well.
    Soon to be painted.

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    Re: Anyone put a 3.91 diff in their manual 535?

    There are 4.10's and 4.27's both available on car-part.com for around $400 plus shipping. Check it out.
    -Mike Pope
    '94 540i Alusil,
    Sachs kit,
    dinan bars and plates,
    stock wheels
    That green color we
    all know so well.
    Soon to be painted.

  8. #8
    gr8 535
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    What does a stock 535i come with??

    My car is an automatic and I am not really sure if I do want to change the gearing, because I like a high top end but I am just curious. My car is a 1989 535iA

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    thanks for the help

    Thanks for all the help guys. I think that I am going to invest in the 3.91 if I can find one for the right price. I'm frugal and always looking for a good deal. What donor cars had a 3.91 that are compatible with my 1990 e34 535i?

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    Re: thanks for the help

    91 735i for sure. You have to verify every one though. There are tons of different ratios used through that period in various cars. The one I have available is from a 91 735 and it's limited slip.-Mike Pope
    '94 540i Alusil,
    Sachs kit,
    dinan bars and plates,
    stock wheels
    That green color we
    all know so well.
    Soon to be painted.

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    Price tag?


  12. #12
    Z YA LATR 36/8s member #50
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    My '90 535iA had a 3.91LSD in it. I now have>

    a 3.15 open in it. I kinda miss the LSD in this last snow storm but I can live with it(new Blizzaks). I now have better gas milage and lower rpms. I used to average about 15-16 mpg(per OBC) and now average 18-20. As per launching off the line the car does lack some umpf but as soon as it hits about 3000 rpm it pulls like a freighttrain.
    BTW this is just my everyday car. If I want to go fast somewhere I pull out the Z3 3.0 Coupe .If it was my only car I would have repaired the 3.91 Dif.

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    here\'s some info on what diff\'s came in what cars+

    click the link + scroll down to item #11, you will see which diff came in which car.

    I have a couple of E34 diffs FS, a 4.10 open for $300, 3.07 open for $275 and a 3.46 LSD for $500. All will work in most E34's except 540i and M5.

    Thanks, Bret
    Raleigh, NC

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    Here\'s some more diff ratio info . . .

    See Vine's link below.

    Unless you plan on spending time at the track, I don't think you'd want to go more than a 3.91. I had a stock 4.27 lsd in my 735i automatic which was well suited for it, but I just did a 5-spd conversion on it, knowing in advance the 4.27 would be way wrong but drove it that way for a couple weeks anyway just for grins before putting a 3.91 in it. The 3.91 is fun & lot's of pull off-line even tho the e32 weighs ~300 lb more than an e34. After driving it with the 3.91 for 3 weeks now, I'm thinking a 3.64 or 3.73 would be better suited for it. I'm going to try the 3.73 out of curiosity since I found one for a good price but may end up going back to the 3.91 if I don't like it. Stock, the e32 manual would have come with a 3.64 but I doubt I could tell the difference between a 3.64 vs. 3.73, only a 2.5% difference & maybe a few 10's of rpm difference between the 2. Seeing as these cars were designed for driving all day on the Autobahn at 100+ mph, just about any model BMW can benefit from tweaking the diff +10% to better match them to US driving conditions.

    gale
    92 735i 5-spd, 162k

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    Re: Anyone put a 3.91 diff in their manual 535?

    I just installed a 3.91 LSD in my 92 535i and I love the power. But my question is that when I got the rear diff the right side shaft was stock in the diff, I tried pulling it out and it came out only 1/2 inches and I couldn’t push it back in to be flushed so I just bolted my drive shaft to the one that was stock in the diff. Now when I accelerate my car pushes to the right is the LSD supposed to that or its because my shaft is not in all the way or is it because its just too much power to rear and I am not used to.

  16. #16
    JOM
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    Re: Anyone put a 3.91 diff in their manual 535?

    Does anyone can give me the theorical figures of 0-100 km/h and the topspeed after the swap from 3.46 to 4.27 ?
    e34-1990-5.35i-manual
    thanks

  17. #17
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    My e34 535i was converted to a 5spd and has the 3.91 Lsd in it and I can tell u I was able to hit 132mph indicated also has a lighter flywheel I believe it to have the manual trans outta 535i
    Reply With Quote Reply With Quote 162.158.74.182

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