Car jerked violently to the left - what to check in suspension?

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langsbr

Lieutenant
Apr 5, 2017
909
I wasn't quite sure how to list the topic, and I've never experienced this before. I have MMPs on 20psi on pump gas and I've been data logging to get the tune set.

Typically, in a 3rd gear pull from 2500ish to redline, the car has traction and tracks dead straight. The other night though, and it may just have been me being a dummy when it's too cold (37 degrees), but I did the same:

3rd gear pull with DSC off, from 2500rpms on. The car felt like it was 'fighting' for traction, for lack of a better word - like spin, traction, spin, traction. I don't recall the exact speed or rpm (as I was now trying to hold my bowels) but the car jerked VIOLENTLY to the left, and the car started to slide. Thankfully it was an empty 5 lane road fairly late at night, and I recovered, but had there been any traffic, it could have been BAD.

Other than just tires with better traction (and avoiding cold roads), could this be indicative of something in the rear suspension that is worn or needs service?

I have a diff lockdown and it cured the high speed "shimmy" the rear always felt like it had, but I've never experienced wheel hop.

Is this just "what happens" with an open diff? I would have figured it would have just broken loose and done the one wheel peel rather than 'kick out' like it did.

Car is an 07 E90 6MT
Rear tires are 265/35/18 MPSS (about half their life left)
 

langsbr

Lieutenant
Apr 5, 2017
909
Other than an open diff, lame tires, and a cold road, nope. I got some Federal 595RS-RRs and they grip MUCH better, and luckily I have not experienced a similar scenario. I also don't do datalogs when it's below 40 degrees anymore just to be safe.
 

ShocknAwe

Lieutenant
Jan 24, 2018
682
SC
Other than an open diff, lame tires, and a cold road, nope. I got some Federal 595RS-RRs and they grip MUCH better, and luckily I have not experienced a similar scenario. I also don't do datalogs when it's below 40 degrees anymore just to be safe.
Fwiw, lsd will do it just as violently if not worse when it finally let's go. Glad you're not logging at 40 anymore heh.
 

Torgus

Captain
Nov 6, 2016
1,187
Boston
I'm going to say it was the cold 37 degree weather.

My car with a diff tries to kill me on my summer tires whenever it gets below 50 degrees and I go WOT. I don't even bother driving it unless I know I will have traction.

I know the desire to log and get your tune all squared away, but I would just hold off until the weather is better.


edit: What suspension are you running? When you say 'High speed shimmy' do you mean the rear end shimmy while WOT?
 
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fmorelli

Colonel
Staff member
Aug 11, 2017
2,303
Virginia
I know the desire to log and get your tune all squared away, ...
What? You can actually have your tuning all squared away?! No one ever told me this. :oops:

"Here's my dyno sheet with my mods and tuning all squared away," said no one ever on an N54 forum.

I think of my N54 as that really fun girlfriend I had that I just new was never really going to work out in the end lol. :grin:

Filippo
 

langsbr

Lieutenant
Apr 5, 2017
909
My car with a diff tries to kill me on my summer tires whenever it gets below 50 degrees and I go WOT. I don't even bother driving it unless I know I will have traction.
Cars are such a pain. Heat helps traction, cold helps the engine. Yeah 55 degrees is probably the sweet spot for heat/cool.

The thing that threw me was that it didn't just break loose and spin, but gripped on one side and jerked so bad. All of my cars in the past have had an LSD and have never experienced this.
 

Torgus

Captain
Nov 6, 2016
1,187
Boston
Cars are such a pain. Heat helps traction, cold helps the engine. Yeah 55 degrees is probably the sweet spot for heat/cool.

The thing that threw me was that it didn't just break loose and spin, but gripped on one side and jerked so bad. All of my cars in the past have had an LSD and have never experienced this.
My single turbo did the same this year at like 45 degrees. It was much cooler all day, I am sure the road was cold. I was trying to get one last pull in for tuning reasons. Didn't seem to lose grip just tried to fling me into the guard rail iirc. Im glad I started in the middle with nothing near me or I and possibly the car would have been done. The rear end went out drivers side, if that makes sense and jolted the car all over the place. Car has been parked since. No sense in driving if I can't use it.

Next up is a real suspension for me. I know it had something to do with it...but fuck cold weather and pulls on summers.
 

Twisted Tuning

Lieutenant
Platinum Vendor
Oct 25, 2016
869
New York
Cars are such a pain. Heat helps traction, cold helps the engine. Yeah 55 degrees is probably the sweet spot for heat/cool.

The thing that threw me was that it didn't just break loose and spin, but gripped on one side and jerked so bad. All of my cars in the past have had an LSD and have never experienced this.

good old E-diff. VERY unpredictable. Its decent on Flat clean ground. outside that it will toss you all over the place.
 

langsbr

Lieutenant
Apr 5, 2017
909
I suspected it was the ediff but I have an 07 with a March 07 build date and I didn't think it had the ediff. Was it coded on 07s?
 

Torgus

Captain
Nov 6, 2016
1,187
Boston
Just because I like being spoon fed what is the easiest way to code out or get rid of the Ediff? I have a real differential etc. I was wondering if that was my issue as well. I can't think of why to keep it.
 
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langsbr

Lieutenant
Apr 5, 2017
909
I didn't check mine since I didn't think 07s had it, but this link should work. This guy has a few good tutorials on what and how to code. Or I guess you could be a noob and buy Protools and maybe do it :p

 

langsbr

Lieutenant
Apr 5, 2017
909
I guess I should quit being a slacker and check to see if I have it. Easy enough to read that module.
 

Torgus

Captain
Nov 6, 2016
1,187
Boston
Would the bimmergeeks protool app allow me to do it?

Edit: Found my own answer, yes it can. Chassis->DSC->coding
 
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[email protected]

Corporal
Platinum Vendor
Jun 4, 2018
136
Would the bimmergeeks protool app allow me to do it?

Edit: Found my own answer, yes it can. Chassis->DSC->coding
Was going to say the same thing but @Torgus beat me to it. I saw the option to turn it off in ProTools as well. Along with Corner Brake Control that the 1M has.

Barry
 

langsbr

Lieutenant
Apr 5, 2017
909
My thought would be that in a highly modified car, it may be safer to disable it even without an lsd. Can the DME react get enough and to the proper degree in a situation with 500+ whp? Is it possible to modify the braking pressures it uses? If not, an old school open diff may be more predictable if not "safer".
 
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hellokitty

Specialist
May 23, 2018
53
Just experienced this at partial throttle when it was a little wet out on PS4S tires. Scary as fuck. Time to get a LSD and disable the ediff garbage lol
 
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