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      12-16-2018, 09:47 PM   #1
Proctor750
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Wheel hop and other observations - A closer look underneath

I finally had a chance to get the car on my buddy at zakspeed's lift so we could poke around at what BMW did with M2C.

The car tends to wheel hop in the rain and his though was diff bushings.

Once we got it in the air it became apparent that BMW decided to go with a single mount! That's a bit shocking but I can see that some of the electrical component are directly in the path of where the hole in the subframe could accept a second one...

The Front of the diff has 4 bushings, two of which connect to the subframe. The subframe itself is directly mounted to the chassis.

Not really sure of a solution at the moment. It's also bizarre to push the wheels around freely as if it didn't have an LSD since it's electric.

I also noticed the front venturi looking vents on the front bumper are useless.

The tension arm has a giant rubber bushing but I think fall line makes a spherical bearing replacement so that's going to be high on the list.

Also - the gap between the 788 and the 2NH caliper is intense. You might be able to fax a sheet of paper through it. I can see where a stone managed to get stuck there and made a circular scrape on the inside of the wheel drum.
I'm nervous about tracking with these calipers and have no clue how they hold up. That combined with the wheel/tire issue having these brakes cause at the moment makes me wonder if switching to a smaller aftermarket BBK and switching to 18's wouldn't be a better idea...

The transmission tethers seem pretty wild to me.

The window seal was bent backwards on the passenger side. Had to peel it back carefully then shut the window. May need to take a heat gun to it.

I noticed some oil on the inside of the skid plate and sure enough the turbo appears to be leaking... You guys may want to check that as well.

My plastic oil cooler shroud has a crack in it and scuffs (not from me)

Some pictures below.
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      12-16-2018, 09:57 PM   #2
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Wow! These are extremely interesting findings. Taking delivery of mine in late October, I didn't do my usual thorough inspection like this. I will definitely be booking some time on a friend's lift in the next few weeks to take a look myself. I'm interested to hear what some of our more technical members think of the suspension setup. Also, great job finding that oil leak! Damn dude! Sorry to see that on anyone's new car
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      12-16-2018, 11:51 PM   #3
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The oil leak is normal, it's apparently just blow-by from the PVC valve and a common S55 issue..


Turbo leaking, but dealer says nothing is wrong https://f80.bimmerpost.com/forums/sh....php?t=1545217

As far as the other issue, not sure why you have wheel hop but if I had to make an educated guess, I would say it's just the tire loosing traction due to colder weather, on summer tires..
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      12-17-2018, 09:18 AM   #4
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It was a warm day but not ideal conditions. Regardless I thought BMW learned their lesson with single ear diff on a "performance" chassis.

Thanks for the link - figured I would check on it again when I change the oil, Just wiped it down with a rag and brake clean. My CDI does the same thing but much worse. A proper catch can may help.

Quote:
If there is a complaint of high oil consumption and oil is found in the turbocharger, it should not be
immediately concluded that the turbocharger is faulty. If oil is present in the fresh air pipe before the
turbochargers, then the entire engine must be checked for leaks. The cause of an excessive blow-
by gas flow rate may be faulty gaskets or crankshaft seals. Loose crankshaft seals may generate oil
consumption of up to 3l/1000km(3.2qt/621miles).

Quote:
PUMA case was opened and BMW NA states that the residual oil is due to blow by. They said that the blow by on the car is within the normal specs so they won't be doing anything about it.



Imagine if you bent the wheel on track at speed with that kind of caliper clearance... I can't get that out of my head.

Does anyone have any experience with the BMW calipers on track? What coating did they use on the pistons? How do the seals hold up (how long before they fry and crisp up without ducting)? What is their longevity before rebuild like compared to say a stoptech setup?

Last edited by Proctor750; 12-17-2018 at 09:34 AM..
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      12-17-2018, 09:56 AM   #5
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This is a significant post, how many have ever inspected the underside of a new car, perhaps few. This may open Pandora's Box until this gets sorted out, that single mount point that could use two is especially troubling, why would BMW have two mounts and use just one? Kind of like a double barrel shotgun and just one barrel discharges, makes little sense. Great post, you have my attention.
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      12-17-2018, 10:10 AM   #6
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Quote:
Originally Posted by ContactPatch View Post
why would BMW have two mounts and use just one?
Cost cutting, at its finest..

There was a time on the new E92 platform, BMW stop using bolts and instead welded the differential gear carrier shut, to save on the cost of freaking bolts.

At a result, it made it difficult to install an LSD on a 335i or 135i, which desperately needed one due to its squirrelly back-end traction..

BMW historically have never been shy to cut corners, in the name of saving a buck..

http://www.vacmotorsports.com/news/3...483338466.html
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      12-17-2018, 11:00 AM   #7
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There were also tiny details that were nice as well. The stock exhaust has a little heat shield tacked on directly below the rear axle boot. They haven't lost their German soul completely but something like a single ear diff on a 400+hp rwd manual car with serious mechanical traction potential...

Also - the oil sump/pan has "waffling" on the exterior which I thought was interesting. Traditionally the waffling is on the interior of the pan surface.

We also noticed several bolts they use appeared to be LIKE a Etorx bolt but actually a special bolt head pattern which appears to be bespoke for BMW... Can't wait to buy that socket.
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      12-17-2018, 11:09 AM   #8
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Thank you Proctor for a great post..... my OCD will now be in full overdrive until i can get my car on a lift and examine it thoroughly!
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      12-17-2018, 11:26 AM   #9
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The missing part is a vibration damper.. I guess they assume the hard-core M2C didn't need it or maybe they're just being cheap.. :

It does look like you can purchase another one and just add it, if you please..


https://www.newtis.info/tisv2/a/en/f...ive/1VnYngfQTr
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      12-17-2018, 02:57 PM   #10
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Quote:
Originally Posted by Poochie View Post
The missing part is a vibration damper.. I guess they assume the hard-core M2C didn't need it or maybe they're just being cheap.. :

It does look like you can purchase another one and just add it, if you please..


https://www.newtis.info/tisv2/a/en/f...ive/1VnYngfQTr
Do you think that would fix the wheel hop? It's really annoying.
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      12-17-2018, 03:17 PM   #11
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Quote:
Originally Posted by 3tekcorps View Post
Quote:
Originally Posted by Poochie View Post
The missing part is a vibration damper.. I guess they assume the hard-core M2C didn't need it or maybe they're just being cheap.. :

It does look like you can purchase another one and just add it, if you please..


https://www.newtis.info/tisv2/a/en/f...ive/1VnYngfQTr
Do you think that would fix the wheel hop? It's really annoying.
Sorry to hear that but the truth is I'm not really sure..

The part that's missing is described as a "vibration absorber" so I am assuming its main purpose is to even out possible vibration.

That being said, the fact that an engineer originally designed it for two bushings, leads me to believe that it does serve an importation purpose but was decontented because someone else down the line felt they could cut it to save funds on each car.

I will do some more research on the subject, even in the M4's technical manual and get back to you on that..
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      12-17-2018, 03:17 PM   #12
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That single rear "mount" isn't a main mount its just a vibration damper, you can see that by the tuning counter balance fitted to control the frequency that the damper works at.

The main torque reaction mounts are at the front end of the diff by the prop entry.

Last edited by doughboy; 12-17-2018 at 03:24 PM..
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      12-17-2018, 03:18 PM   #13
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I don't think it's that simple.

The rear of the differential itself only has 1 mounting ear not two. There is nothing that can be done about this short of developing a new diff cover with 2 ears OR welding/adding one OR using a different diff (non electric??)

This is a common issue with older BMW and many people would upgrade to twin ear mounting.

The good news is the subframe does have the spot as you can see in the original post where the second mount would go. But as I pointed out if you look at the part of the diff cover where a second ear would go there is electrical components in the way.

An example of someone adding a second ear to a single ear diff:




EDIT: disregard - I just saw doughboy's post and wasn't aware that the majority of the load is managed by the front 4 bushings and the rear is simply a dampener. If this is the case then adding a second ear would probably not fix the issue. I knew the end piece was for dampening but assumed that it doubled as a mount since it connects through the subframe itself.


EDIT 2: Looking at Real OEM paints a different picture. It appears the vibration damper is attached to the rear of the actual rear diff MOUNT which there is only 1. Since it indeed has a normal rubber mounting, and only one at that - having a second one would certainly help. Sorry for the poor photoshop my red line goes to the wrong bush in the pic
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Last edited by Proctor750; 12-17-2018 at 03:35 PM..
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      12-17-2018, 03:27 PM   #14
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Proctor, although seeing your picture of the twin ear modification maybe the rear flexI mount does provide some kind of stabilising too?

I must say I've not had any wheel hop, have you tried it with MDM on or DTC off to reduce traction intervention to see if that is causing torque oscillations in low grip conditions?

BTW great to see an enthusiast looking at the most mportant (and telling) side of a car - not the shiny side

I've always said if you want to see the real design intention / the way a car is built - look underneath it!

Last edited by doughboy; 12-17-2018 at 03:33 PM..
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      12-17-2018, 04:02 PM   #15
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Quote:
Originally Posted by Proctor750 View Post
Does anyone have any experience with the BMW calipers on track? What coating did they use on the pistons? How do the seals hold up (how long before they fry and crisp up without ducting)? What is their longevity before rebuild like compared to say a stoptech setup?
There are brake ducts in the front bumper either side of the lower center opening, prime position for high pressure air. Unfortunately they stop short of a custom silicon hose attached to the brake shields millimeters away from the rotors type of setup, instead making do with aiming air at the hat from the fender liner but that's significantly better than nothing which is what most cars have to deal with.

The rear brakes are the same brembo OEMs as I have on my GTR (which doesn't have ducts) and the fronts are probably also some custom brembo OEM caliper, do BMW ever make their own calipers? I think you'll find you are right about the seals and they wont hold up to heat, maybe there's some aftermarket higher temp seals that can be swapped in when they fail?
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      12-17-2018, 04:03 PM   #16
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Quote:
Originally Posted by doughboy View Post
I must say I've not had any wheel hop, have you tried it with MDM on or DTC off to reduce traction intervention to see if that is causing torque oscillations in low grip conditions?
I had both MDM at one point to see what it was like but usually just everything off.

It just seems like a weak point is all. I am more concerned about how these 2NH brake perform. I'm not sure if they are built well and will last or if they are just glitter tits that "look cool". I really want to know what they coated the pistons with.. I suppose I could take one apart when I swap fluid and examine.
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      12-17-2018, 04:07 PM   #17
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Quote:
Originally Posted by OGM2C View Post
There are brake ducts in the front bumper either side of the lower center opening, prime position for high pressure air. Unfortunately they stop short of a custom silicon hose attached to the brake shields millimeters away from the rotors type of setup, instead making do with aiming air at the hat from the fender liner but that's significantly better than nothing which is what most cars have to deal with.

The rear brakes are the same brembo OEMs as I have on my GTR (which doesn't have ducts) and the fronts are probably also some custom brembo OEM caliper, do BMW ever make their own calipers? I think you'll find you are right about the seals and they wont hold up to heat, maybe there's some aftermarket higher temp seals that can be swapped in when they fail?
Ah thanks, yes I knew they outsource to ATE, Girling in the past, Brembo etc these days. The specs are just different than a true performance aftermarket setup so maybe you are right and being brembo they should have "uprated" rebuild kits for them?
But then you weigh in the fact that they BARELY clear the 19s (scary) and the lack of rubber/wheel choices.... It makes me think an 18 with aftermarket calipers would be a more logical choice. I should shutup if I ever want to sell these..
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      12-17-2018, 05:02 PM   #18
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Quote:
Originally Posted by doughboy View Post
Proctor, although seeing your picture of the twin ear modification maybe the rear flexI mount does provide some kind of stabilising too?

I must say I've not had any wheel hop, have you tried it with MDM on or DTC off to reduce traction intervention to see if that is causing torque oscillations in low grip conditions?

BTW great to see an enthusiast looking at the most mportant (and telling) side of a car - not the shiny side

I've always said if you want to see the real design intention / the way a car is built - look underneath it!
Mine still does it with DTC off. Or at least what I'd consider wheel hop in 1st when launching on wet pavement. Instead of just spinning the back end you feel this horrible shuddering through the chassis.
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      12-17-2018, 05:32 PM   #19
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Not sure what kind of design M3/M4 has (if any different at all) but wheel hop was one of my complaints in the M4. With DSC fully off, whenever I tried to spin the wheels intentionally, I would experience wheel hop in my M4 especially in the wet (similar to what 3tekcorps described above).
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      12-17-2018, 05:58 PM   #20
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Taking it back-to-basics, according to the article below, wheel hop is mainly caused by soft suspension bushings..

The solution is stiffer bushings; something like [COLOR="DarkRed"]polyurethane[/COLOR] would help..

Did not figure an M car for having soft bushings, being that even subframe doesn't contain any rubber damping, since it's flat out bolted on from metal to aluminum.

I guess you learn something new here everyday..

http://www.mc2racing.com/tech/20061012a/
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      12-17-2018, 06:25 PM   #21
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Single ear diff? That remind anyone of BMW M's other cars?

http://archive.mcoupebuyersguide.com.../tag/subframe/
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      12-17-2018, 06:52 PM   #22
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I give up.
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