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Diff and Trans


dbgeek
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So... What do we think about the stock diff and trans?

 

Both of mine are starting to whine - I blame the Royal Purple gear lube that drained out with the consistency of water. Are they worth a rebuild, or simply junkyard replacement? I slapped in some decent fluid, and we'll see how they do in October.

 

On a related note, on bimmerforums, the consensus was to junkyard replace the engine when it goes, since you can get 3-4 used engines for the cost of a rebuild. Transfer your baffled oil pan (uh... something I need to do).

 

Anyone look at the stock replacement diffs that would increase performance? 3.91 anyone?

http://www.bokchoys.com/differential/GearRatios.htm

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Gear ratio and lock-up/ramp angle characteristics are of course spec'ed per OEM BMW. Could we enjoy more performance from a multi-clutch pack 35-40% diff, sure, but imho it's not necessary.

 

I do agree that fluid is a huge component of longevity; I recommend Motul products as they have served me tirelessly in multiple cars. The rules allow for a vent tube out of the top of the trans which should ensure you are able to maintain proper fluid levels under racing conditions (ie, fluid will not spill out of the venting hole). They also allow for a finned diff cover.

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I'll have to look at the rule again, but the aftermarket finned cover I know about is twice the fluid capacity...

 

I've also read about swapping a Z3? diff cover, as it is also finned.

 

The next time I have the trans out, I will be adding a tube. Since this tranny's days are numbered, I'll wait.

 

Gotta love 200K driveline components

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Anyone have a link to the vent tube mod and/or parts? Mine is out...like to get that upgraded now.

 

Basically they say to just run a tube up into the engine bay:

 

http://forums.bimmerforums.com/forum/showthread.php?t=1690214&highlight=trans+vent

 

The PDF in the last post is very descriptive - perhaps I can slap that in there with it in-car...

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I think the best way to do it is with the trans out and I would recommend some sort of a breather filter at the top of the hose (pick one up from the likes of Summit Racing or similar for cheap).

 

One other item, the Spec E30 guys have spent time upgrading clutch material, I would recommend against it for this trans as it will only increase the wear on the trans synchros as opposed to slipping the clutch a little. Just one person's opinion. I'd rather replace a clutch every 4 seasons instead of a trans.

 

J

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I use redline fluid...I forgot (or didn't know) that we can have a finned diff cover. With the increased fluid amount I'll def be interested in doing that...probably on my next diff. I just change my fluid yearly. I have never done the torque test to see when my diff breaks away. We should all do it on our cars to see who has the most open diff! Our getrag transmissions suck...and are known to be a weakest point in the drivetrain. Changing fluid in them every season is as essential as changing oil IMO.

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I use redline fluid...I forgot (or didn't know) that we can have a finned diff cover. With the increased fluid amount I'll def be interested in doing that...probably on my next diff. I just change my fluid yearly. I have never done the torque test to see when my diff breaks away. We should all do it on our cars to see who has the most open diff! Our getrag transmissions suck...and are known to be a weakest point in the drivetrain. Changing fluid in them every season is as essential as changing oil IMO.

 

Those covers ain't cheap I keep a fully rebuilt one for max lock up, and semi worn for a little lock up, and a completely worn for fully open, depending on the situation, track, how my rear tires feel, how the stars line up, what kind of ketup I had on my hotdog the day before etc.

 

But in all seriousness, I use Redlie as well and I'm surprised how well my diff is doing. The transmission too. Engine valves is my thing

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I keep a fully rebuilt one for max lock up, and semi worn for a little lock up, and a completely worn for fully open, depending on the situation, track, how my rear tires feel, how the stars line up, what kind of ketup I had on my hotdog the day before etc.
and wow
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I keep a fully rebuilt one for max lock up, and semi worn for a little lock up, and a completely worn for fully open, depending on the situation, track, how my rear tires feel, how the stars line up, what kind of ketup I had on my hotdog the day before etc.
and wow

Yes, well... some of us don't have wives that are as tolerant as Lindsey.

 

If I had 1 parts car hidden somewhere, I might be able to swing it - but only if she didn't see it on a daily basis (I'm ready to have a 5-bay garage, btw).

 

Although, we all know where to get our spare parts from now on AND it's convenient to SP.

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I think junkyard is the way to go, but maybe that is just because I have too many stair parts laying around. There is no way in hell I'd drop the money for a fanned diff cover, I've yet to have issues with any BMW diff. I should do the vent tubeon the trans and re seal it at the same time I've always had trouble keeping a good fluid level in that thing

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I really only have one very well used LSD even my one spare car has heated seats/winter package, but doesn't seem to have an LSD. Though I have to make sure. The tag didn't have an "S" on it which I think the LSDs has.

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  • 4 months later...
Our getrag transmissions suck...and are known to be a weakest point in the drivetrain. .

 

Talk from our Toy Run Collective on our way to a meal resulted in the discussion of transmissions...

 

If the gear ratios are the same for the ZF tranny, why can't we use it? It is supposed to be more robust as it was used in the M3 and 328.

 

Discussion?

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