Shuddering from rear when losing traction
 

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

Is the traction control off?

yes of course

That's wheel hop, bro.

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

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.

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

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.

Sent from my SM-G920P using Tapatalk

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.

Sent from my SM-G920P using Tapatalk

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.

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

-Josh

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.

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

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

-Josh

Parts shop max LCA
And SPL toe arm w lock outs.


Also as for the driver mod thing. this isn't anything to do with when I launch as its not really bad if I launch the car. Its mainly if I floor it in first, and start spinning. or If I do a burnout. Which these are things I can live with out doing.

Spinning doesn't bother me as it satisfies me and makes me feel like my car has 10000 hp. Its just the hopping that I would be able to live with out.

Yes I had the active autowerke brace on my Supercharged M3. helped alot also from what I understand took off a lot of stress on the center diff bolt.

was looking into doing these. Saw a friend on facebook posting these and some werid looking brace that I cant find anywhere and say goodbye wheel hop. lol

http://www.whiteline.com.au/product_..._number=W63414

Differential brace. Several manufacturers make them for the twins.

No it went from the lower control arm area to the trailing arm, I think its the cusco one I just found. I don't believe the differential brace works when you are running diff bushing inserts.

People do it, but it mostly negates the bushing usefulness.

This thread ever get sorted?

I know mine is the rear diff bushings. Added some whiteline bits, but the bushings that bolt to the rear of the diff housings are my problem with wheel hop. Added the Whiteline bushing inserts here, and it helped, but it's still there.

People think the tire is doing it, it's not, it's those bushings getting wound up and kicking back. Mine gets in a harmonic sometimes without ever breaking loose if I have to use the clutch too much at parking lot speeds.

Never an issue before I boosted the car. I'm trying to understand if I should try some 70 Durometer bushings from RallySportDirect or try a Cucso brace. Input on either would be helpful.

For reference, I changed engine mounts as well and tried TorqueSolution. They're great, but too much NVH for my commuter. Just swapped out to group N STI mounts from RallySportDirect, NVH gone. More movement you can really feel in the throttle press/ift comparatively. But still much better than stock mounts and no NVH. Now I'm going after the rear end since the inserts aren't a 100% fix. But I really don't want to overshoot like I did with the engine mounts.

I think I saw group N rear diff bushings or STI rear bushings, not sure. Probably a Japan order. I've seen 70 Durometer bushings on Rally site. But that feels too close to the TorqueSolution engine mounts, which were 75 durometer. And I don't want to overshoot again.

Why has nobody mentioned Trailing Arm bushings. The thrust of the wheel goes straight through the trailing arm. Allowing it to move forward and backward.

I agree, but the deflection of the rear diff mounted bushings is very noticeable. I have an MCA traction mod to go on still. I'll do this before I put more bushings in. It'll lower that trailing arm a bit and may help. Gets good feedback and claims to help with traction too.