Wheel hop

[heinzboehmer]

Jack up one rear wheel and turn the wheel on the axle nut with a torque wrench. Should turn smoothly especially if the diff is not new.

Transmission in gear I'm assuming, right? Also any specific torque I should be looking for or just kinda make sure it's not binding?

[bigjae46]

What would be the best way to test that? Bonus points if it doesn't involve removing the diff from the car lol

Jack up one rear wheel and turn the wheel on the axle nut with a torque wrench. Should turn smoothly especially if the diff is not new.

[Casa de Mesa]

Curious what tires / pressure you are running.. Have you looked at sway links at all? I didn't catch if you mentioned before, but are you still on stock rear sway as well?

Michelin PS4S. I run lower pressures than most people here do. Currently 30 psi rear cold, but it's the right pressure for the tire based on load index, not based on the door placard (it means nothing now that I've changed tire sizes).

Interestingly enough and if I change the equation with respect to tires, the wheel hop is worse in the rain then it is in the dry.

Sway links are stock but have only ~3k miles on them. Sway is stock. But... sway bars can cause wheel hop?

Just had a thought to help rule the sway bar out further - I do have 1 adjustable rear sway link that I have not installed. After setting the ride height, I thought I would need to compensate for L/R differences in preload but the they are exactly the same height, so I never installed the adjustable and heavier end link.

Typically yes, common issue is a groaning noise when turning tightly at low speeds. The visco-lock unit in the LSD always lags, could be an internal issue or excessive wear that might be causing the unit to lock up when it shouldn't and vice versa. I wouldn't necessarily blame the diff but its free and easy to see if the diff still has some preload.

Got it. So it's definitely possible it's the diff. My gut says it's not (no groaning, no chatter, no strange noises, fresh fluid), but your point is valid and taken. If I throttle oversteer the car in a left hand turn (e.g., think traffic circle) and in particular in the rain, the wheel hop is bad.

My next question is the same as Heinz's :

What would be the best way to test that? Bonus points if it doesn't involve removing the diff from the car lol

Swap dampers left to right, see if that does anything. That's probably the easiest and free-ist way to start diagnosing. BC are not awful nor are they great. If they are only one way adjustable, make them very soft and slowly increase the stiffness until you think it's too stiff, then back off two clicks.

I think this is the path of least resistance (time, effort and $$$) and planning on this post-Christmas.


I genuinely appreciate the suggestions and help on this, all.

[heinzboehmer]

I wouldn't necessarily blame the diff but its free and easy to see if the diff still has some preload.

What would be the best way to test that? Bonus points if it doesn't involve removing the diff from the car lol

[Nate047]

Swap dampers left to right, see if that does anything. That's probably the easiest and free-ist way to start diagnosing. BC are not awful nor are they great. If they are only one way adjustable, make them very soft and slowly increase the stiffness until you think it's too stiff, then back off two clicks.

[bigjae46]

Hey bigjae, thanks for pointing me in this direction. I've been doing some research on diffs. While I'm still leaning towards a rear shock issue, I want to consider all variables - it is the line of thinking that made me go with solid diff bushings as I [incorrectly] thought they were the issue, or at least part of it.

Do you or anyone else know if wheel hop can still happen when you do not have LSD chatter in tight corners?

From the reading I've done, it seems that if an LSD (clutch pack style like our stock units) doesn't have the proper ratio of friction modifier (or none), the slip/catch, slip/catch of the clutch packs slipping and catching rapidly can cause wheel hop. However, from most comments in various forums - 2015+ IRS Mustang, Porsche, BMW, you name it - it seems to be coupled with chatter in tight corners, and not just while attempting smoky burnouts in a straight line. I do not have any chatter in both tight left or right turns (i.e., parking lot speeds), hence my question.

Typically yes, common issue is a groaning noise when turning tightly at low speeds. The visco-lock unit in the LSD always lags, could be an internal issue or excessive wear that might be causing the unit to lock up when it shouldn't and vice versa. I wouldn't necessarily blame the diff but its free and easy to see if the diff still has some preload.

[Thrifty S50]

Curious what tires / pressure you are running.. Have you looked at sway links at all? I didn't catch if you mentioned before, but are you still on stock rear sway as well?

[Casa de Mesa]

Absolutely.

Hey bigjae, thanks for pointing me in this direction. I've been doing some research on diffs. While I'm still leaning towards a rear shock issue, I want to consider all variables - it is the line of thinking that made me go with solid diff bushings as I [incorrectly] thought they were the issue, or at least part of it.

Do you or anyone else know if wheel hop can still happen when you do not have LSD chatter in tight corners?

From the reading I've done, it seems that if an LSD (clutch pack style like our stock units) doesn't have the proper ratio of friction modifier (or none), the slip/catch, slip/catch of the clutch packs slipping and catching rapidly can cause wheel hop. However, from most comments in various forums - 2015+ IRS Mustang, Porsche, BMW, you name it - it seems to be coupled with chatter in tight corners, and not just while attempting smoky burnouts in a straight line. I do not have any chatter in both tight left or right turns (i.e., parking lot speeds), hence my question.

[bigjae46]

That said, a diff can cause axle hope?

Absolutely.

[Casa de Mesa]

Thank you for the replies, all. It's appreciated!

Check the static preload on the diff. What kind of fluid? If the diff is locked up then it will act like a welded diff and cause wheel hop. So that's the free stuff.

I would imagine that a worn shock can cause wheel hop. Guessing here, if one side has a new shock it should have more grip so long as the adjustments aren't so out of whack. If the new shock has the compression and rebound all the up to high/heavy/slow then it could absolutely cause wheel hop. A worn out shock would cause the rear end out be bouncy.

Could also be a combination of a bad diff AND a misadjusted shock.

Diff should be fine, the fluid has been changed multiple times with Castrol SAF-XJ 75w140 and only has about 50k miles on it. That said, a diff can cause axle hope? Seems like there would have to be something really wrong with the diff for that to happen. I've driven cars with welded diffs/Detroit lockers and they leave two giant gooey black marks for days on the pavement, but no axle hope.

Have you tried adjusting the rear shocks? The knob only adjusts rebound.

Yeah, I have. The BC's have 30 clicks and it's one dial that controls both rebound and compression. The axle hop seems to happen regardless of setting. More on this below...

It's normally a damping problem. Rear shocks are same L and R, so swap and see if your problem follows.

GREAT idea. I'll try this.

Wheel hop occurs due to the system achieving some resonance. There are probably a lot of things that contribute to it. The more slack in the driveline the worse it will be because there is less of a direct connection. Every rubber piece will store energy and release it like a rubber band in an uncontrolled manner.

My approach was to increase the grip so that it's less likely to alternate between grip and slip. Reducing rebound and increasing compression can help push the tire into the ground and reduce some of the tire load variation.

With the Dinan rear shocks at 1.25 turns out, the car suffered wheel hop pretty badly. I think it was packing under load.

In 2020 when COVID hit, I thought I was going to tackle this problem by refreshing the entire rear suspension. Because I'm a chucklehead, I replaced all rubber stuff with non-rubber stuff: RCABs and RTABs are Turner monoballs, new ball joints elsewhere (LEMFÖRDER), Turner aluminum diff bushings (diff whine anyone?), subframe bushings are delrin, etc.

The Lower control arm/camber arms are Turner adjustable street, with the inward bushing being rubber. I doubt these bushings are bad... but maybe? They have about 45k miles on them.

Re: the BC Racing shocks, I've run them hard (27 clicks) and soft (2 clicks), and tend to run suspension soft. They are at 7 clicks off full soft currently (23 more until the hardest setting), for example.

Perhaps counterintuitively, I actually thought that running them harder would help. My logic is that if a shock is dead/dying, it would not control the wheel hop once introduced, similar to hitting a pothole on a completely dead shock. If it was a healthy, well-matched shock, it would control it.

The reason this is so perplexing is that the car otherwise handles pretty good. I don't get any uncontrolled bouncing in the suspension any other time, other than launching the car or when inducing throttle oversteer. I don't have irregular wear patterns on the tires.

I'm wondering if these shocks are just crap, and while they can control most suspension movements, they can't control the big ones. Or perhaps BC Racing's valving between rebound and compression is screwed up. Or perhaps they are mismatched with the new shock and X-years between production runs. I'm always adjusting the rears at the same # of clicks.

I doubt it's the inner bushing on the Turner lower control/camber arms... but possibly. This condition existed before and after the full suspension refresh that replaced every bushing EXCEPT those. Wouldn't that be ironic, ha.

[cobra]

Wheel hop occurs due to the system achieving some resonance. There are probably a lot of things that contribute to it. The more slack in the driveline the worse it will be because there is less of a direct connection. Every rubber piece will store energy and release it like a rubber band in an uncontrolled manner.

My approach was to increase the grip so that it's less likely to alternate between grip and slip. Reducing rebound and increasing compression can help push the tire into the ground and reduce some of the tire load variation.

With the Dinan rear shocks at 1.25 turns out, the car suffered wheel hop pretty badly. I think it was packing under load.

[mrgizmo04]

It's normally a damping problem. Rear shocks are same L and R, so swap and see if your problem follows.

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[jayjaya29]

Have you tried adjusting the rear shocks? The knob only adjusts rebound.

[bigjae46]

Check the static preload on the diff. What kind of fluid? If the diff is locked up then it will act like a welded diff and cause wheel hop. So that's the free stuff.

I would imagine that a worn shock can cause wheel hop. Guessing here, if one side has a new shock it should have more grip so long as the adjustments aren't so out of whack. If the new shock has the compression and rebound all the up to high/heavy/slow then it could absolutely cause wheel hop. A worn out shock would cause the rear end out be bouncy.

Could also be a combination of a bad diff AND a misadjusted shock.

[Casa de Mesa]

Axle CV? I've pulled apart almost a dozen axles. Everyone had liquified grease in it. IMO, almost every E46 is due at least a cleaning, inspection, and repack of the CVs. Probably should replace the boots too.

I'd try to see if the CV is binding and then carefully inspect the ball bearings in the CV and look for flat spots or pitting.

Thanks bigjae. Both axles have been addressed. Passenger side was notchy so I replaced it. The driver side was perfect, but I tore down the axles, repacked the bearings, replaced the boots, etc. Axles shouldn't be the culprit here.