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Old 05-11-2013, 04:39 PM   #1
Argermacher
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Differential Help for a Noob

I'm a "basic" car guy, with no experience in big-ticket repairs or even how a differential works. I just had mine go out on me (2003 330i), and my mechanic asked me if I was "hotrodding" (yes, but I played dumb & let him continue) and then he told me that the mount pulled on the casing & let the fluid out, and subsequently I burned up the differential. (Yeah, I was hotrodding it with the radio up and by the time I smelled smoke & turned down the tunes to hear that horrible noise it was already smoking & screaming). Pulled over, got it towed in, and voila--he tells me I'm looking at $2600 for a used replacement job, $3700 if I wanna go new.

I'm a really nice trusting guy for the most part, but I also have a cynical side--I'm starting to lose faith in this mechanic, and am wondering if he's inflating prices on me. I'm going to get his estimate in writing on Monday, and get some second quotes. He's not gonna like that, but screw him. I'm not gettin' taken for a ride on this job!

I'm seeing diff prices on car-part.com in the $3-500 range.

Questions:

1. - From what I have read, the 3.38 ratio is the correct one for my car, so can a bunch of you confirm that for me so I don't end up with the wrong one, and

Question 1B: does anyone recommend I go with a different ratio & why?

2. - What's the difference between a differential and a carrier, or are they the same thing?

3. - Are the mounts included when you order one of these apparatuses, and/or what other parts might I need to order while I'm at it to get the job done?

4. - Is this the kind of job that can be done with jackstands in a driveway and a highly recommended mobile mechanic, or do I definitely need to have it done in a shop?

Thanks everyone. I'm really in over my head (and pocketbook) on this one...

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Old 05-11-2013, 08:04 PM   #2
Argermacher
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Wow, don't everyone reply at once...
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Old 05-11-2013, 09:06 PM   #3
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1. - From what I have read, the 3.38 ratio is the correct one for my car, so can a bunch of you confirm that for me so I don't end up with the wrong one, and
3.38 came in the automatic and 2.93 in the manual transmission.

Question 1B: does anyone recommend I go with a different ratio & why?
When my 3.07 differential failed at 292k I opted for a 3.46; or a poor-mans supercharger. It increased my punch off the line, slightly-lowered my top-end speed and slightly-lower my gas mileage but made my 323i much more enjoyable to drive at the track and autocross.

2. - What's the difference between a differential and a carrier, or are they the same thing?
I'm not aware of any differences between the two, the carrier should be the casing...

3. - Are the mounts included when you order one of these apparatuses, and/or what other parts might I need to order while I'm at it to get the job done?
Not unless you order them, which you should do...

4. - Is this the kind of job that can be done with jackstands in a driveway and a highly recommended mobile mechanic, or do I definitely need to have it done in a shop?
No, you should do this job on a lift along with an engine stand to support the differential as you pull it and re-install.

Additionally, I paid $250 for my 3.46 replacement differential and I had it installed for under $120 dollars. Your mechanic is over-charging you I would seek a second opinion. Lastly you should change your differential fluid every 60k along with your transmission fluid. Just my two and a half cents worth.
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Last edited by Zchild; 05-11-2013 at 09:08 PM.
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Old 05-11-2013, 09:16 PM   #4
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Differential Help for a Noob

I'm not 100% sure on your ratio, but that sounds about right.
Reasons for a different ratio would be if you we're looking to increase your acceleration for example you could go with say a 4.10 diff if you wanted insane 0-100 mph times, or you could lower the ratio if you wanted a higher top speed assuming you had the additional horsepower and torque to compensate. A new OEM diff should have the bushings already mounted in it. The diff carrier is the brace that the diff casing mounts to, so you have the diff gears inside the diff case, mounted to the carrier, mounted to the subframe, mounted to the chassis. Your diff carrier and case should be fine, your gears inside are what is most likely trashed. This is a very long job to do, considering you need to jack stand the rear end, pull the axles, RTA's, driveshaft, etc... Also if you plan on pulling the gears from the diff and just swapping those, I would highly recommend only having a very qualified transmission shop do it, but if you plan of just changing out the entire diff it is possible to do in your driveway or garage with a skilled mechanic... Preferably a BMW fanatic that knows what they are doing and is fairly familiar with the job.


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Old 05-11-2013, 09:38 PM   #5
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Old 05-11-2013, 10:55 PM   #6
fiveightandten
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Quote:
Originally Posted by Argermacher View Post
1. - From what I have read, the 3.38 ratio is the correct one for my car, so can a bunch of you confirm that for me so I don't end up with the wrong one, Question 1B: does anyone recommend I go with a different ratio & why?
If the car is an auto, it has a 3.38. If it's a manual, it has a 2.93. You can use either, depending on what kind of gearing you want. 3.38 is more aggressive. 2.93 revs lower on the highway and will save some fuel.

Quote:
2. - What's the difference between a differential and a carrier, or are they the same thing?
The differential is a casing with gears in it. It takes rotational energy from the drive shaft and transfers that to the axles, which ultimately turn the wheels. The diff mounts to the carrier, which is responsible for holding the diff into place (among other things).

Quote:
3. - Are the mounts included when you order one of these apparatuses, and/or what other parts might I need to order while I'm at it to get the job done?
If you order a used diff, if will have mounts with it. But there's no guarantee that they're in good shape. If you order new, you will have to ask the supplier. I doubt it. Though i've never known someone to order a brand new BMW diff. They're insanely expensive. For the same kind of money, you can get a custom limited slip diff made for you.

Quote:
4. - Is this the kind of job that can be done with jackstands in a driveway and a highly recommended mobile mechanic, or do I definitely need to have it done in a shop?
You can remove the diff with simple hand tools, a jack and stands. It takes about an hour tops to pull it out. I can have the diff out of the car in about 30 minutes, as could most people that have done it before.


You can get a used diff in good shape on the forums for a few hundred bucks, including shipping. Just make sure it has the same input flange as your current diff, or it won't mate up to your drive shaft. I don't care what anyone tells you, if you swap the flange without specialized tools, there's no gurantee that the diff will last. It's very easy to mess up when torquing the collar nut down, and the pinion bearing will die 5K to 10K miles later. I found this out first hand, when a shop improperly torqued mine.

Anyways...I think you know that $2600 to install a used diff is absolute insanity. Are you sure he's not quoting you to install a whole new subframe (carrier)? $2600 isn't even on the same planet as what it should actually cost. I'd say $500 for a used diff tops, and $200 for labor. $700 would be more like it for a typical shop to do it.
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Old 05-11-2013, 11:18 PM   #7
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Just buy a replacement diff fromanother e46 of the same model, if the bushing is ****, replace it, all in all cheap replacement

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Old 05-11-2013, 11:22 PM   #8
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Just buy a replacement diff fromanother e46 of the same model, if the bushing is ****, replace it, all in all cheap replacement

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Old 05-11-2013, 11:37 PM   #9
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Differential Help for a Noob

Shouldn't cost more than 700 let's say with a used diff


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Old 05-12-2013, 10:43 AM   #10
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They sell those diffs on ebay for $200 to $300..
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Old 05-12-2013, 01:29 PM   #11
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that is a VERY high quote to fix.
Buy a used diff($150-$350) and install yourself or have a shop. They should charge like 2hr or maybe 3 hrs labor max.

Seems everyone has the diff mount wrong in their replies and shop. There is no rubber mount incorporated into the aluminum diff cover. I'm not sure what the shop is talking about. If the covers tab broke off, it could leak there. So you would need a new cover. I haven't seen a used diff not come with the cover. So you should not have to buy a new one. Now if the mount that fits into the rear carrier cage (where the diff bolts to) is bad you should replace while the diff is out. Actually I would replace now as when the diff is out is so much easier. Although that job is another DIY project in itself.

As said if you have an automatic 330 you have a 3.38:1 ratio and manuals have a 2.93:1.
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Old 05-19-2013, 08:29 PM   #12
Argermacher
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Thanks everyone. I took your advice & found a used (carrier) 3.38, and actually shipped my car to the yard where the part was & got the whole job done for $1K including the part. Yeah, still a bit high but still not $2700, either!

NEW PROBLEM:

I test drove it around the block & it felt great. BUT--on the way home I discovered a horrible vibration between 60-75 MPH, which is mist pronounced when decelerating. I also tested it in neutral and it still happens. If I'm around town, it's quiet. If I'm up above 75MPH, it's quiet. But right in the freeway cruising range it's more than a little annoying. There's obviously something wrong. IDEAS?

(I've got 90 days parts & labor warranty, but it's a long drive back to that yard, so if it's something small...I'll do it locally). IDEAS?
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Old 05-19-2013, 10:51 PM   #13
Steve///M
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Differential Help for a Noob

I would take it back and tell them something isn't balanced correctly, be it your driveshaft/half shaft, axles, center support bearing etc... Did they support anything during the install or just leave things hanging? Burn the gas to make a trip back while its still under warrantee, well worth it.


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