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3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

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Old 04-04-2006, 11:59 AM   #1 (permalink)
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3.73 ratio LSD type?

Hello everyone,

please help:

I have replaced my diff in 325e with an limited slip differential with a ratio of 3.73 two years ago. It was my first LSD and the shorter gears were awesome too.

But. Now two years ago I start to feel like my LSD has gotten very weak I don't know if it is possible or is it just my adaptation. Over these years I hadn't done any maintanance for my diff (because the seller's mechanic told me it is totally closed differential) and now I have a few questions:
What type of LSD is mine (clutch, viscous or torsen)?
Should I do some maintanance?
If it is a clutch type, maybe I should change the clutches?
Are there some other way to stiffen my LSD?

Thank you!
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Old 04-04-2006, 01:41 PM   #2 (permalink)
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Its a clutch type diff and it isn't totally sealed the guy that told you that was a dumb ass. I change my diff fluid about 2 times a year since i drive my car hard. I'd recomend a Red Line gear oil with a GL-5 rateing, DO NOT put GL-4 rated fluid in a diff. There are ways of making the diff have more lock-up but unless you know what you are doing when taking a diff apart I wouldn't recomend doing this on your own. I have taken my diff apart before to inspect the clutches and doing this isn't something that the average joe can do and with out the proper instruction or know how it is really easy to mess up the diff if you put something back in the wrong place.
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Old 04-04-2006, 01:46 PM   #3 (permalink)
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E30s come with clutch LSDs? Oh fucking rockin!
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Old 04-04-2006, 03:30 PM   #4 (permalink)
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Quote:
Originally Posted by triggrhaapi
E30s come with clutch LSDs? Oh fucking rockin!
Yep. This is why using the proper fluid makes a difference in how the LSD unit works. I have an extra set of friction plates and spacer plates for mine in my tool box. E28 uses the same diff as an E30 just a different rear cover and I think the E36 LSD's were also clutch type units like the E30 and E28. If you know what you are doing you can swap ring and pinion gears out of an E36 diff and use them in an E28/E30 diff and vise versa. You just can't use an E36 diff housing in an E28/E30 because the exterior casting and mounting points are different.
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Old 04-04-2006, 03:59 PM   #5 (permalink)
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So I guess I'll have to have my rear diff rebuilt before the frankenmotor goes into it. Any suggestions?
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Old 04-04-2006, 04:41 PM   #6 (permalink)
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Quote:
Originally Posted by triggrhaapi
So I guess I'll have to have my rear diff rebuilt before the frankenmotor goes into it. Any suggestions?
Depending on how much you want to spend www.diffsonline.com makes a really nice product and has any ratio and lock-up % you want.
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Old 04-06-2006, 07:43 AM   #7 (permalink)
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Originally Posted by AJ's320i
Its a clutch type diff and it isn't totally sealed the guy that told you that was a dumb ass.
To be honest, I start too think that too. But still it would be of great help if you could provide me with some photos of the BMW LSD's insides, of course if you have some... And where to put the oil... Then maybe I would be 100% sure that I have a differential which IS possible to dissasemble and maintain...

Quote:
Originally Posted by AJ's320i
I change my diff fluid about 2 times a year since i drive my car hard. I'd recomend a Red Line gear oil with a GL-5 rateing, DO NOT put GL-4 rated fluid in a diff.
Thank you for recommendations! But should I try to change the disk plates before that? I must have woren them?

Quote:
Originally Posted by AJ's320i
There are ways of making the diff have more lock-up but unless you know what you are doing when taking a diff apart I wouldn't recomend doing this on your own.
I'm not a pro that's for sure... But me and my friend had locked one car's differential totally With no garage, rain and cold it was hell of a project, and the car has become a gravel monster Maybe you have some manual or instructions or a link on how to go on with my LSD to stiffen it up? I think I would manage to do that :}

So as I understand it may still be possible to make my current LSD more stiff?

Thank you
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Old 04-06-2006, 01:35 PM   #8 (permalink)
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Quote:
Originally Posted by Oxy-
To be honest, I start too think that too. But still it would be of great help if you could provide me with some photos of the BMW LSD's insides, of course if you have some... And where to put the oil... Then maybe I would be 100% sure that I have a differential which IS possible to dissasemble and maintain...


Thank you for recommendations! But should I try to change the disk plates before that? I must have woren them?


I'm not a pro that's for sure... But me and my friend had locked one car's differential totally With no garage, rain and cold it was hell of a project, and the car has become a gravel monster Maybe you have some manual or instructions or a link on how to go on with my LSD to stiffen it up? I think I would manage to do that :}

So as I understand it may still be possible to make my current LSD more stiff?

Thank you
Oxy-
Get a Bently manual, it will have all the answers to your questions. As far as increasing the lock up on your own I wouldn't do it. If you use the wrong parts there is a good chance that the bolt heads that hold the LSD unit together will pop off. I don't have any pics from when I rebuilt my diff, I just did it from knowledge and I was somewhat in a hury to get it done so taking photos of the process wasn't in mind.
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Old 04-06-2006, 10:21 PM   #9 (permalink)
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"FYI" 75w-145, 75w-90, 80w-90 and 80w-140 and others are all API Service Classification GL-5 rate. I sugest valvoline 80w-90 full synthetic, found local for about $9 a quart (you'll need two). No need for fricton modifiers so don't worrie about LSD additives. Ordering redline may not be the best way. There is a surcharge to ship oil, 99% of the time will cost more that the fluid itself.
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Old 04-06-2006, 10:28 PM   #10 (permalink)
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Upping grip % will only make it bark more when powering out of a bend and when it's wet or icy you may find yourself facing where you just came from.
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Old 04-06-2006, 10:44 PM   #11 (permalink)
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Quote:
Originally Posted by Starmavin
"FYI" 75w-145, 75w-90, 80w-90 and 80w-140 and others are all API Service Classification GL-5 rate. I sugest valvoline 80w-90 full synthetic, found local for about $9 a quart (you'll need two). No need for fricton modifiers so don't worrie about LSD additives. Ordering redline may not be the best way. There is a surcharge to ship oil, 99% of the time will cost more that the fluid itself.
Every Napa and CarQuest I have been in carries Red Line fluids. Kragen, a.k.a. CSK, sometimes has Red Line products too but not as commonly as the Napa and CarQuest stores.
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Old 04-08-2006, 09:03 AM   #12 (permalink)
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Get a Bently manual, it will have all the answers to your questions.
Don't really have where to get it from without waiting few months shipping...

I've been to a recommended mechanic today. He told me that I should have a clutch plate type LSD too. Also he told me that these BMW LSDs are not ment to be disassembled. That means that the clutch plates cannot be replaced (why o why?).

Is it possible that those plates are not worned out (i.e. they have a HUGE resource), and that I should get a proper lockup again only by changing the fluid? How to check are those plates ok?

Thank you!
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Old 04-08-2006, 10:15 AM   #13 (permalink)
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Have you replaced your fluid yet? If the clutch packs are anything like in the Ford 8.8" rear (and they 'probably' are like every other clutch pack out there...) you should notice a significant difference just by replacing the fluid. You could always give it a try and go from there. If there is no difference you can always reuse that fluid for either the rebuild to wear in the packs or with the new unit if it comes dry.
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Old 04-08-2006, 12:55 PM   #14 (permalink)
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Quote:
Originally Posted by Oxy-
Don't really have where to get it from without waiting few months shipping...

I've been to a recommended mechanic today. He told me that I should have a clutch plate type LSD too. Also he told me that these BMW LSDs are not ment to be disassembled. That means that the clutch plates cannot be replaced (why o why?).

Is it possible that those plates are not worned out (i.e. they have a HUGE resource), and that I should get a proper lockup again only by changing the fluid? How to check are those plates ok?

Thank you!
Well it sounds like your shop has no firm grip on BMW repair knowledge, I would look for a different shop that knows BMW's well. The Diffs are cake to take apart and replace the friction and spacer discs if you know what you are doing. Once you have the LSD unit out you just inspect the plates to make sure the friction plates still have friction material on them and arnt worn down to the metal backing and that the spacer plates don't have heat spots on them.
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Old 04-08-2006, 03:45 PM   #15 (permalink)
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Originally Posted by AJ's320i
Once you have the LSD unit out you just inspect the plates to make sure the friction plates still have friction material on them and arnt worn down to the metal backing and that the spacer plates don't have heat spots on them.
What should I do if there would be no friction material? Original BMW dealer suggests me only a brand new diff with LSD for around $1300 - maybe you know some afterpart online store where I could order ONLY plates for a decent price Maybe you have some photos?

I think I will go like this:
1. take my diff apart, take some photos and make sure what I really have
2. if my clutch plates are dead, try to find good ones from somewhere
3. put everything back together and fill with a new good fluid
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