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      08-28-2019, 09:14 PM   #1
dre99gsx
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ECS Poly rear diff bushing MELTED

Stay away. How the hell does this happen at the rear?

Any suggestions without going solid for a heavily tracked car?
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      08-29-2019, 01:31 AM   #2
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Quote:
Originally Posted by dre99gsx View Post
Stay away. How the hell does this happen at the rear?
Maybe because you put 600hp through your diff?


Be thankful that you discovered this, and that that bush has melted, because do you know what this means? Your diff is running way way waaaaay to hot!

Going solid is the last thing you want as that doesn't solve the problem.
You need a proper diff cooling system and a temp gage on your diff to monitor the heat.
The finns on the diffcase clearly aren't enough to handle the power of your 2jz.
What kind of diff do you use atm?

Also maybe inspect your diff, mainly the seals and replace the oil.

Also why is that center bushing oval? Isn't that made of steel? If not, than that's a big ECS fail.
If that inner bushing isn't made of metal, you run the chance that it cant hold its tension enough and that can result in your rear diffbolt breaking.
That oval hole also can cause that, as any play on that bolt is a nono (it also has quite a high torque setting therefore)
All the quality brands (Powerflex, Strongflex, superflex) all run a thick steel/stainless steel bushing in there.

TBH I always thought polyurethane couldn't melt as it's a thermosetting polymer. But this is some kind of melting, or partial disintigrating at least.
I wonder what kinds of temparatures that takes. Can you test that with a soldering iron that has a wide temp range setting? Then you also know how hot your diff got at least.

If you have a clutch style diff it could also point to that you have a diff problem to begin with. Also check backlash.
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Last edited by GuidoK; 08-29-2019 at 01:51 AM..
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      08-29-2019, 09:00 AM   #3
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More like 700hp+ but who's counting

I've rebuilt the diff a few times already, fresh Motul 75W90 300 gear oil in there actually. I do have all the bottom pans on, one which enables fresh air to hit the fins directly.

I suspect my sewer pipe of an exhaust runs very close to that area, could be causing additional heat.

The center bushing is oval, and so is the stock bushing. It is supposed to be installed horizontally, but I don't know the reason. It is aluminum as well.

I have a Quaife in there, no clutch, and backlash was set at .003", within spec.

The melting is more excessive on the diff housing side than on the exhaust pipe side, thus I agree this is probably diff heat. I wonder if more fins would help...
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      08-29-2019, 10:07 AM   #4
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Quote:
Originally Posted by dre99gsx View Post
More like 700hp+ but who's counting

The center bushing is oval, and so is the stock bushing. It is supposed to be installed horizontally, but I don't know the reason.
Maybe fitting reasons, that how far the front bushings are pressed in the frame can give variations in where the diff sits. But I've never had any problems with fitment in this place and the powerflex bushings I use (that have just a round hole). And I use a bolt that has a tighter fit in the core of the bushing than the normal bolts (I use a din 931 style 10.9 bolt which has a long piece of the shaft unthreaded and thicker)


Quote:
The melting is more excessive on the diff housing side than on the exhaust pipe side, thus I agree this is probably diff heat. I wonder if more fins would help...
Maybe more room has to be opened up inbetween the fins to stimulate airflow? I've never really looked at how efficient the airflow through the fins is apart from that I know about the cutout.
But its not uncommon for cars with that kind of power to have a diff cooler. (lots of diff cooler kits in the gtr scene)
But you have a serious heat problem. I wonder how hot it got inside the diff/oil
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      08-29-2019, 03:58 PM   #5
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Isn't some flex necessary? I say just replace it every year.
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      08-30-2019, 01:58 AM   #6
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The ECS bushing has been known to fall apart on the e46 M3, I run AKG 95A poly for my diff.
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      08-30-2019, 07:55 AM   #7
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Another vote for AKG. All my rear bushes are AKG.
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      08-30-2019, 08:01 AM   #8
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Quote:
Originally Posted by dre99gsx View Post
More like 700hp+ but who's counting

I've rebuilt the diff a few times already, fresh Motul 75W90 300 gear oil in there actually. I do have all the bottom pans on, one which enables fresh air to hit the fins directly.

I suspect my sewer pipe of an exhaust runs very close to that area, could be causing additional heat.

The center bushing is oval, and so is the stock bushing. It is supposed to be installed horizontally, but I don't know the reason. It is aluminum as well.

I have a Quaife in there, no clutch, and backlash was set at .003", within spec.

The melting is more excessive on the diff housing side than on the exhaust pipe side, thus I agree this is probably diff heat. I wonder if more fins would help...

Preface...I am no expert....but riding along in a lot of BMWCCA events I've noticed that most of the the track dedicated and instructor cars (E46, E36, vettes) all focus on having a diff cooler in the mix. I think it would be worth looking into given the extensiveness of your build already.
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      08-23-2020, 11:30 AM   #9
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I've begun investigating diff cooling options. Pump/cooler/routing.

Anyone have any tips on 3.0si diff cooler mounting and installation? I may have seen one or two guides online for a E46M, but curious if anyone on this forum has done it to non-M diff.

I assume that routing should be simple enough: feed line to the lower drain bolt, and return line to the upper drain bolt.

Also,since my rear floor is completely covered with a diffuser plate going up to about where the floor plan starts, I have no where to mount a cooler. I've seen folks mount cooler inside the trunk with an aux fan. Any thoughts on this?

Prefer anyone who has experience with doing this and races their z4!
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      08-23-2020, 12:06 PM   #10
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Quote:
Originally Posted by dre99gsx View Post

I assume that routing should be simple enough: feed line to the lower drain bolt, and return line to the upper drain bolt.
Afaik the SI (facelift) diff casings don't have drain bolts, only the pre facelift ones.
Of course they are a 100% swap fit so easily solved.

Aux fan is always a possibility, but when mounting a cooler above the oil level inside the diff, you also need a pump, and as the oil gets thrown around in the casing there is not really an oil level to speak from, so it needs to be a self priming pump as well.
But no expience with this (well, with pumps yes, plenty, but not with diff coolers on this level)

Does your diffuser plate interfere with the normal designed airflow through the diff cooling fins? Could that be the root of the problem?
If so it might be easier to make custom ducting to those finns. If the ducting exists the rear of the car there is automatic airflow as the rear of the car is an underpressure area.
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      08-23-2020, 01:33 PM   #11
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https://www.redlineautoparts.com/bmw...tic-83k-z4011/

Link above is same diff I have, there is a drain and fill hole.

Interesting thing about the OEM naca duct diff cover is that it directs air to the cooling fins, but right behind the finds is the chassis crossmember. The air essentially hits a wall. I did create a downward-scoop to help move the air back down to the ground (this didn't seem to make a difference since I am starting to see melting occur again on the new poly bushing)

I may try to redesign some ducting to help get the air OUT of that area more efficiently. Z4M's ducting seems to be ideal but it breaks up the smooth floor I designed.

I attached some examples of Z4 3.0si VS Z4M rear cooling ductwork. It seems the 3.0si naca duct is substantial for the fins, but there is not exit ducting even from factory.
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      08-23-2020, 01:42 PM   #12
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That naca duct plate on REALOEM is 51487047808 which shows up as the same for Z4M and 3.0si. Odd.... I found an ebay listing for this part number 51487895023 but realOEM doesn't show it. Did they change the plate design?
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      08-23-2020, 07:15 PM   #13
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Hmm didn't know some facelift diffs had drainplugs. Mostly you hear facelift owners complain when they want to refresh the diff oil that there is no drainplug.

The partnumber you're looking for is 51487896023, you made a typo.
https://www.turnermotorsport.com/p-1...uine-bmw-part/

That's the intake piece for the z4m diff. But I have doubts it will work as good for the 188 diff. The 210 diff has a different cover with finns at the lower side; the 188 z4 diff has finns down in the middle.
But you can experiment with it. It's not a really expensive part and I believe a direct swap.

Indeed a crossmember is behind the fins with the 188 diff, but I think lots of air can escape from that, it's still quite open. At least I wouldn't cover up that centerscoop in the middle (don't know how your current diffuser is made)
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      08-26-2020, 12:32 PM   #14
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Quote:
Originally Posted by dre99gsx View Post
I attached some examples of Z4 3.0si VS Z4M rear cooling ductwork. It seems the 3.0si naca duct is substantial for the fins, but there is not exit ducting even from factory.
Wow. That is some difference. I think I'll stop griping about the battery location on my Moupe.
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      05-31-2023, 10:41 PM   #15
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Long term update: I replaced the bushings but have been running a 'large' cooler in the rear for the diff for the past 3 years and 6 HPDE events. The bushing still looks "new" and no longer melted. Trans temps have not gone above 220F ever since.

I do wonder what temps the diff case had to get for that bushing to melt multiple times, and even more curious of what temp the fluid inside was getting. Anyone know what temp Poly bushings melt at?

I've also installed a trans cooler and it too has not gone over 220F since. Hoping this keeps the trans alive longer.
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      06-01-2023, 12:44 PM   #16
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Quote:
Originally Posted by dre99gsx View Post
I do wonder what temps the diff case had to get for that bushing to melt multiple times, and even more curious of what temp the fluid inside was getting. Anyone know what temp Poly bushings melt at?
https://www.matweb.com/search/datash...d5cb4c7462dd33
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      06-01-2023, 01:38 PM   #17
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>Melting Point 71.0 - 221 C 160 - 430 F Average value: 151 C Grade Count:74

= 303F

Seems like it's possible, diff could have been hitting 300F yikes...
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