Under hard braking, car gets ?floaty?.

It doesn�t pull to the left or right, it just feels super vague and floaty under HARD braking. Think slowing down as quickly as possible from 100 down to 30. If you�ve ever ridden a motorcycle, the biggest analogous explanation is like if the head angle is too steep, it all of a sudden feels twitchy when you brake really hard. The car exhibits no other odd symptoms, it feels nice and tight when accelerating and in corners, but HARD braking just feels sketchy. Under normal braking there�s no issues. I�m guessing it�s an alignment issue or maybe a blown shock? I got a look under the car and in the fender wells and the shocks don�t appear to be leaking or weeping.

Nate, it could be a lot of things: suspension may need to be refreshed, a caliper may need a rebuild, alignment and balance may be off. Tell us about your car, what state you are in, tires you are running, suspension, etc.

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+1 what he said...there's a lot of things that can be causing this, to include your tires.

Chassis setup / condition tire wear condition / pressures chassis rake (911 like *** up a bit) diff. Open diff on a 911 causes tail wag under threshold braking. Lsd addresses.

I would probably start with an alignment. I believe OP has a 40Jahre so he's already got an LSD.

More than likely it's your suspension. How old are the control arms/shocks?

Sorry, brain farted and should have probably stated current setup. 40 Jahre @72k miles stock suspension (still on original shocks/springs) stock brakes (pads have been replaced) I got brand new tires less than 200 miles ago (Z5s at the oem size). At first I thought it was the old tires as the ones that were on the car when purchased direly needed to be replaced and while it largely went away, probably like 90%, it�s still there. Waiting on getting an alignment as the local indy is booked until the 7th. I�ll be letting him know when I drop it off, but would like to have a general idea. Car got a 60k mile service at the dealer and had the clutch and brake pads also replaced and the service receipt showed no concerns/notes on the brakes or otherwise. Then again, that�s the same dealer that replaced the clutch and didn�t feel it was necessary to change out the IMS 😂

Nate, If I didn't mention it, congrats on your new 996! Awesome car and welcome to the 996 club. Where are you located. I assume you are in a warm weather state since you have summer tires on? Since we know your tires are new, it will most likely come down to one of the following. 1. Caliper sticking 2. Alignment & Balancing 3. Suspension ​​​​​​The car is 18 years old and as such, calipers will eventually need a rebuild, suspension components will wear out and need to be replaced, aligned and corner balanced. Your shop can check all three, but keep in the back of your mind that you will pay twice for alignment if you do it first and then decide to replace your suspension. Same can be said for corner balancing which is very expensive and may or may not need to be done depending on if you plan on tracking your car. As a side note, a car that is running more negative camber will have a tendency to track every nook and cranny on the road under braking. It does freek people out if they are unaware.

The z5 need a good amount of heat to work properly also without a complete adjustable suspension replacement and performance pads your suspension doesn’t sound bad just old also a aggressive wheel alignment might help

Never take your car to a dealer if there�s a way to avoid it. Contact your local PCA chapter and find a good/great independent shop�

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Thanks! I�m located in Greenville, SC. While it�s cold right now, generally speaking we have summer tire weather year round. I don�t have any plans on tracking the car, but will soon be getting new suspension soon regardless if it�s the issue or not�just trying to decide what I want to put on the car. I didn�t think the suspension is worn, it still feels very tight, I�m just not as well versed in auto suspension to really know symptoms of anything�I come from a motorcycle background. I�ve already found my local Indy, it was the previous owner that took it to the dealer.

OP's first sentence is 'it doesn't pull left or right'. In my experience this excludes a sticking caliper as that would lead to pulling. Just sayin'... to all the contributors mentioning this as a possible cause.

Nothing a set of $4000 coil overs, $300 corner balancing and a good alighnment $250 won't fix. Also check your rear brakes to make sure they are working properly.

You're most probably experiencing small and varying toe-change due to worn rubber bushes in the suspension control arms when they are under the load of the high longitudinal braking forces As such the rubber bushing in the front coffin arms to which the diagonal arms attach are suspect and at the rear primarily the toe control arms (the most rearward arm that runs horizontally at midlevel between lower and upper arms) as well as the rear coffin arms. It will be worthwhile to check the condition of the (front) bump stops too. After that I'd look at signs of leaking shock absorbers.

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I wouldn't rule anything out on a car we know nothing about and have very little information on. Just sayin...

Agree but putting it at # 1. of 3 possibilities is considerably different from 'not ruling anything out'.

Read what I wrote again. Just a list of possibilities to review bud. Unless we review the components in question and drive the car, tough to know.

Last year I noticed that the ABS tended to come on at really low speeds, in the front. Michelins only had 1000 km on them. With more experience, I realized it was happening on rough pavement. Another issue was the rear end "wallowing" in some situations - most often accelerating through a gradual uphill curve (like an entry ramp). I didn't do anything about either, planning on first addressing the significant bore scoring... When I had the engine done, I got new engine mounts. Some of that wallowing was addressed. Then I did the shocks all around and both issues were gone. I'm replacing other suspensions bits gradually, but the new shocks made the biggest difference. I like the motorcycle analogy - whenever I felt twitchiness under hard braking, I would first blame the mechanic before questioning my technique. No matter what, it always seemed to be my own fault...

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Good info. Especially on the motor mounts. I am replacing mine in 2 weeks. Curious as to how the overall dynamics change since I am running the original mounts (57k) Then I will do the same with the transmission mount at a later date. Curious on any changes to car dynamics that each component has on the street and track. Hence staggering the replacements.

OP - Welcome! First suspect is always tires. Only contact patch with the ground. What’s their story? Brand, type, pressure you’re running, age, etc. If it brakes straight and is controllable, I’d start there. Might want to take it to Protech if you get stumped. They rebuilt my engine years ago.

There�s probably nothing wrong with your suspension or shocks or anything. Your car is acting normally. HARD braking should be done in a straight line. And your suspension and shocks have nothing to do with that after initial bite, and before brake release. Unless the road is uneven. If you try to turn the wheel at all during super hard braking, the rear end is going to feel like it�s on ice, so that�s why people trail brake in slow corners at slower speeds in this car, and not hard braking at high speed. Yes, alignment, tire pressure have more to do with this than the suspension. The 911 floaty feeling is what gives you pinpoint control over where you want the car to go next in a turn. Btw, the front end of your car could also feel floaty under WOT in anything other than a straight line. Some people come and post about this, and yes, alignment and tire pressures are mostly the issue, but the road is next, especially elevation changes combined with turning at high speed.

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They're the one doing the alignment on the 7th...kinda just bracing myself for the worst case scenario. Yeah, I've driven a few before, but this is just the first that's mine. The hard braking is definitely done in a straight line, being done before approaching the corner and it just feels really vague and the rear end feels wallowy....kinda hard to explain. Conversely, I hop in the Macan turbo and jam on the brakes and it feels PLANTED. I'm hoping this is is just an alignmen thing..... I'm probably going to replace those here before the alignment just because...simple enough job...then when my IMS solution gets installed on the 14th, have them replace the transmission mount.

You didn't tell us whether you waited for the snow to clear before these tests...or did you do them on the slippery concrete in the underground parking garage?

😂 there�s no snow on the ground.

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I always think of this video. Bushings are still on my list because of it. You Tube

Sounds like something is broken then, as you seem to know this stuff better than most. You�re onto the right clues: alignment, shocks, tires, etc.

OP - What shoes are on your car? What model, dates, depths and pressures at all 4 corners? What you describe could mostly be tires and/or pressures. This question just to help rule them out as a primary. For example, if your rears are set at drifting pressures, then guess what. Things like that.

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All 4 tires are brand new Sumitomo Z5s, 50psi all around per Sumitomo�s tire chart. Tire dates show all 4 tires are all less than 9 months old.

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Porsche PSI recommendations are more important than Sumitomos. I don't believe it's causing your issue, but man 50psi square is not ideal.

Don't know the tires, but thats a lot of tire pressure.

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What??? That is like the maximum tire pressure for each tire. That is not what you do. Try 32-36 for fronts and 38-42 for rears if they are 18 inch tires.

Op that�s a dangerous tire pressure as you drive the tire heat increase�s tire temperature this cause tire pressure inside to go up as well exceeding tire max you are one pothole away from disaster

50 PSI is whacked out. I would run about 34 F and 36-38R.

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Yep, I'm right about there on my tire pressure as well.

That could be it (tire pressure). I have tried all sorts of different pressures, but I�ve found the stock Porsche pressures work perfectly for my 99 Cab: 36/44 front/rear

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I thought it was a bit high as well. When I told the shop to use those pressures ranges, they strongly advised against it. They referred to the Sumitomo website and I just assumed they knew better given their clientele. Yesterday I lowered it to 35psi front, 40psi rear and the problem has been HUGELY minimized. It's still there though a little, but I suspect that tire pressure was a large bit of the issue and I think the remaining "floaty braking" it's having can probably be solved with the alignment scheduled on the 7th. Thanks for all the help!

This shop does not know what they are doing if their pressure recommendation default is to use the tire MFG MAX approved pressure.

OP - Toe adjustment, if it’s out of parameters now, will help with any residual skittishness. 35/40 is a good mid ground. Find a spot where you can threshold brake safely a few times and assess the handling as the car decelerates. Do this before/after visit to Protech. Now that your pressures are right, you can give the guys a better description of how the car is currently handling. See how and when ABS kicks in and how front and rear behave a few stops. Please post pre- and post-alignment numbers. This is a good post for others in the future to refer.

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Completely agree! WTF!

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Yes. Unacceptable.

Agree 100%. Of all the things a shop should know about, this is so basic and critical that I wonder if a neighbor who is �good with tools� would be better and safer than this mechanic.

Sounds like you don't have enough "toe-in". ....Toe-in is whats keeps the car stable and tracking straight. The 996 should have a lot of rear toe-in, this keeps the tail from wagging during hard braking. With the stock rubber bushings you loose some rear toe-in during hard braking, so if you don't have enough to begin with you can end up being at 0 toe-in or worse, toe-out......MUST have the proper specs. Same for the front, except a 0 toe-in or even a slight toe-out will make a faster "turn-in" into a corner at the expense of less straight line stability.

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+1 What a bunch of incompetent and ignorant people at that shop. The chart on the sumitomo site mentions no specific vehicle type pressures only the max. pressure which is always 50 psi for any passenger tyre (and it's 'written' on the side wall). It does make you wonder though why that pressure is listed if it is wrong for 99% of all vehicles and misleads most consumers... Doesn't mean it is the correct tyre pressure and the guys in the shop must know that. Every tyre manufacturer will always refer/direct to the pressures given by the vehicle manufacturer. I'd give the shop manager a right lecture that he should have his mechanics trained on the matter. OP, check out the tyre pressure sticker inside the frunk, it's all there (and in the car's operating manual too) so you know for yourself what the recommended pressures are.

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That was the local Porsche dealer, fwiw...outside of pointing me to whatever literature they showed me the max being 51psi, they mentioned something along the lines of how low profile the tire was, anything below that was a hazard to the rim, etc... You would expect a service advisor who sees these cars regularly to know such things, especially since the PO took it there regularly, so I blindly took their word for it...needless to say, that wasn't the first bad experience I had there, but this one will definitely be the last....

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Inexperience and incompetence know no bounds, even at a Porsche dealer. Kind of scary actually. I would stay away from them.

36/44 is the Porsche recommendation. NOTE : this is for full load ie. 4 persons and luggage with full fuel. This is the "safe" default used by Dealers, ( who don't know how the car is to be loaded) . It all stems from the Ford /Firestone debacle where the tires were blowing out at speeds due to low tire pressures and causing rollovers/deaths. ( and resulted in TPMS on all vehicles since 2007 ) Tires will blow out due to low pressures (heat) and not over pressure, if MAX pressures are used. "MAX cold pressures" have a safety factor that includes pressure increase due to heat. In other words running the tire manufactures MAX cold pressure is SAFE, but rides/handles like s**t, lower pressures will ride better/ grip better on turns ( more heat) , but do so at your own risk ( Disclaimer as a Professional ... )

Got the car aligned today and it's exactly as Porschetech3 said...spoke with the Indy (Protech) about it and he said "max pressures are covering their ***...but we all know we should run it a little lower else the car will handle like garbage." Turns out that's all it was. After the alignment, tire pressures are 35/40 and it's rock solid. Alignment wasn't much off either apparently. I didn't ask for a print out, but he told me it wasn't far off the mark. Had no idea these were that sensitive to alignments...good to know. Thanks for everybody's input.

Thanks for posting what it was that caused the effects you noticed. It pays to check the simple things first obviously

I knew the alignment would probably help just not to the magnitude it did. That�s not a bad thing, it�s actually preferable to me, just an observation.

The really wide tires and short wheel base do make it super sensitive to alignment.

It sounds to me it was more the tire pressures than the alignment.

Nate, glad you got it figured out. You will get to know the car and all its quirks, getting to the point that you will know when something is off and most likely what it is. All part of the fun of 911 ownership. And it is fun!

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It was the tire pressure. A tire shop put 42 up front and 46 in the back and I felt like I was set for the skating rink. Never went back to that shop again. At such high pressure the contact patches are minuscule and sidewalls don’t flex with lateral acceleration. The car will feel like it balances on the head of a pin because weight shift under braking won’t increase contact patch of fronts. Alignment will most affect turn (camber) and neutral steering track (toe), or tramlining, to a lesser extent. 48 psi is what Porsche jacks rears pressure up to for drifting exercises. The 996 is very responsive to tire pressure changes…part of why the darn things are so sweet to drive. After you get more seat time in your car you’ll probably be able to feel if a corner is a couple psi down. Try that experiment and see.

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Had this same problem. It's worn ball joints on your control forks. Replace on all 4 corners. It's the same control fork front and back. Also replace end links at the same time. Like $500 for all 4 control forks and $200 for end links front & back, and everything is EASY to replace Don't replace the struts. My struts are 20 years old with 74k and they are still serviceable. Are the bump stops rotten, yes. Would the handling improve if they were rebuilt, yes. Is it worth prematurely replacing for the small handling improvement for a car that doesn't see the track, no. For $700 and a little elbow grease, this DIY will exponentially improve the handling and "floatiness" of the car.