Shuddering from rear when losing traction

[nickmerronesucks]

So I know this is kind of a stupid post. But anytime I rip on my car while the tires are cold and it spins, I have a horrible shuddering like thudding noise in the rear. Anyone else with a highly modded Twin have this issue? Not sure what could be moving around back there as I thought i had everything figured out..My guess is that the noise im hearing is from wheel hop I guess?

Things replaced in rear that i have triple checked torque specs on:

Rear trailing arms
lower control arms
toe arms
eccentric lockout
diff insert
subframe collars
rear sway bar
Coilovers

It also happens if i try to do a burnout. kinda just sounds like something in the rear is shaking it self apart. I'm pretty sure this issue is why i broke an axle a few months ago. I'm only running 300hp so I don't see why i am having this issue, Other thought would be maybe the 2 piece driveshaft is moving in the center since nothing else can move? and that is the shuddering? I doubt it. I can't recall if there is a bushing there or not.

EDIT:
just thought about it. my 3 inch exhaust is really close to the subframe. Maybe its moving and slapping the subframe. I wonder if thats what is happening..

but then I also get a clunk if i let go of my clutch to quickly which the thing is like an on and off switch. just trying to relate to other people with highly modded cars to see if they have the same noises..lol

[strat61caster]

Is the traction control off?

[nickmerronesucks]

yes of course

[jawn]

That's wheel hop, bro.

[Yoshoobaroo]

Totally normal, as @jawn said, wheel hop. Your tire is on the verge of gripping and each 'hop' is when you cross that threshold, back and forth. You can try to tune it out with tire pressure spring rates, dampers, or tires. Changing rear camber could work too

-Josh

[Tor]

The stock car, stock suspension and stock Michelins has a lot of wheel hop too. At least mine did when bone stock. So probably some stock bushings are too soft.

I though at first it was the subframe moving and got the Whiteline inserts, but didn't install them.

According to this page, the only two things that may cause wheel hop are insufficient dampening or soft bushings. Their explanations sounds reasonable too. That you broke an axle is congruent with wheel hop as well.

http://www.mc2racing.com/tech/20061012a/

The reason is toe change if the wheel can flex too much forward under acceleration. If the toe change is large enough to cause a loss of grip, the wheel will jump back, the toe reduces and the wheel grips again - repeat and repeat.

So I didn't install the subframe bushing inserts, as I don't think it will solve the issue and I am worried about stripping thread as a lot reported when trying to put the bolts back in. I can't see how the subframe would cause toe change anyway (or can it?). My guess is that some other bushing is too soft.

It got lower priority in my case, as I don't get it a lot noticeably now though - after I changed suspension and tires. So my new higher grip level is probably masking the problem in my case. You on the other hand has 100 HP more that will break the traction, so you need to look at the bushings before you break another axle.

[cjd]

Originally Posted by nickmerronesucks

EDIT:
just thought about it. my 3 inch exhaust is really close to the subframe. Maybe its moving and slapping the subframe. I wonder if thats what is happening..

I had this issue. Mine sounded like someone was hammering on the back with a hammer, but it was clear it was from the exhaust due to the ringing. Stiffer motor mounts and exhaust hangers to the rescue (working quite well, I might add.)

I haven't experienced wheel-hop issues launching at AutoX events, but I have pretty stiff suspension and rear subframe+diff inserts as well. I really need to pay attention to what makes a quick launch, because I'm not consistent at all... every so often I go spinning the wheels for the first 10-20 yards... well, probably tires too, you know?

C

[nickmerronesucks]

I checked my exhaust earlier..has plenty of clearence unfortunately. I just wanted to make sure other people had this too. Most of my other cars when they spun didnt do this(s13,e36,is300 etc) unless the exhaust is slapping the bumper but i doubt that. Probably just wheel hop id guess. I made my rear coils softer and the car drives alot nicer just trying to sort this issue if it is even an issue.

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[nickmerronesucks]

I do see that my whiteline diff bushings are probably not holding up all to well. You can see they have moved (wear marks on subframe). I am running dunlop star spec z2 265s . Recently installed.

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[Tor]

What toe arm and LCA did you get?

It's probably not the diff bushings, as that can't cause toe change either. The problem must be in the suspension bushings.

[Yoshoobaroo]

A rocking differential can induce wheel hop, the BMW rear ends benefit a lot from differential lock down kits

-Josh

[Summerwolf]

Check through suspension bushings, and see if you can track down the play you mentioned. Another thing...


To combat wheel hop a lot of manufacturers make one shaft a larger diameter than the other. It is a harmonics thing, but one that can have a lot of time spent narrowing down the cause and fix.


Not sure if driveshaft shop or anyone makes an "anti wheel hop" setup yet or not.


Just for reference, I'd much rather spin than hop. Spinning isn't winning, but when you hop and stay in it you wind up breaking things.


http://www.shop.gforce1320.com/produ...categoryId=918 - For reference on what I'm talking about in picture form.

[jasonojordan]

Best way to combat wheel hop.....driver mod.

[Yoshoobaroo]

Originally Posted by jasonojordan

Best way to combat wheel hop.....driver mod.

This. It's often as simple as adjusting your launch RPM.

-Josh