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E30 325 Differential

Discussion in 'E30 (1984-1993)' started by 2bmw8288, Jan 25, 2009.

    2bmw8288 guest

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    I just bought a 1988 325. I was told that the differetial needed repaired. Underneath the rear end, it does have loud knocking sound when accelerating from a stop. With limited skills, is this something that I could do myself? I have thought about these options.
    1. Look for a rebuilt differental and swap it out myself and soemone else that has a little experience.
    2. Take to a mechanic and have it repaired. (ring/gears/etc..)

    Also, would it be easier to just replace teh whole rearend? Would a rearend froma 318 work? Would appreciate any advise on cost and what would be easier.

    Thanks, Bill
    1988 325
    1982 320i
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    mooseheadm5

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    If you need a diff, you can't use one from a 318i of any year. You will want one from a 325. You need to know what the current diff gearing is, which is on a tag at the rear of the diff. If this is a 325e (low redline) it is probably a 2.93 or a 3.25 gear. Those can be found on a 325e (sometimes no e) or 528e of almost any year (though beware of the 82 528e or the 2.79 gear - ugh) and a 535i respectively. Would be nice to upgrade to a 3.25 limited slip from a 535i or 535is. If you have a 325i (7000rpm tach) then you need a 3.73 diff, which you can find only on a 325i.
    However, there are a few things to check before looking for a diff. You need to check that the driveshaft, flex disc, and center support bearing are in good shape. In addition, the rear subframe mounts can get trashed and cause a thunk when accelerating. There are 3, technically. There are two at the outer ends of the subframe right in front of the wheel and there is one at the rear of the diff (though this is also called the rear diff mount.) if any of these three are trashed, it can cause your problem. The problem with that is that if you need the outer ones, you need to buy the special tool or find a shop that has it to replace them. Otherwise, the dealer will want to charge you 8 hours to replace them because the whole subframe will have to come off without the tool.
    First and foremost, figure out what is actually wrong with the car.

    2bmw8288 guest

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    Hey thanks for the info. It's a 325 (no e). I probably wouldn't have thought to check the mounts. I have looked at the fact that the center bearing or flex disc might need replaced. Is there a way to find out what diameter size is? Will the tag on the differential tell me that?
    Thanks Agan
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    mooseheadm5

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    You wondering anout the flex disc diameter? You can measure it directly. Or, post the last 7 digits of your VIN and I'll show you how to use realoem.com
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    granthr

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    If you do determine that it truely is the diff that is faulty, check the back of Roundel for BMW breakers, like Euro Depot, BMW Wholesalers, Vines, 2002AD, etc. You can probably get the diff you need for about 50 to 200 depend on ratio and if you want LSD or not. Try and get one from the west coast if you can, it won't be rusty! :D

    Swapping it out is not too difficult if you have a jack and jack stands. The difficult part is getting the to the four bolts that hold the diff to the rear sub frame. Also when re-attaching the half shafts to the diff make sure you have them tight enough. Go buy an 8 MM ( I think that is the correct size) hex "socket" for your wrench set. A traditional "Allen Key" will not give you enough leverage to get it tight enough.

    However, follow Pauls' advise first, before you buy another diff. It really could be something else, like the flex disk.

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