At wit's end with lack of inside rear traction...

[EricSMG]

Yes, frequently, and only when applying > 1/3 throttle through slower corners, and particularly from a stop and then through 90 deg corners.

Interesting - this suggests that it's the IRS at the root and not the Torsen.

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[BmacIL]

Interesting - this suggests that it's the IRS at the root and not the Torsen.

It's possible that the torsen makes it worse because of how it biases torque (I believe the stock bias ratio is 3:1).

 

[EricSMG]

It's wet out this morning - I'm going to pay close attention to what the inside rear wheel is doing in slow turns as it's virtually impossible to avoid when wet.

I'll try vertical links first since easy to R&R. I may be forced into LCA bearings to get things acceptable but this irks me as even they don't sound like a true solution (although they may provide immense benefits in other areas).

Surprised this doesn't drive the rest of you mad like it does me.

 

[Randy954]

My PP car has done that since day one. I thought it was normal but now reading all the im not so sure. Smae scenario, i go uphill on a 90 degree turn and i feel like a have a welded diff and im not even giving it 25% throttle! Should i take it to the dealer?

 

[Teezlr]

Seriously, this thing is ridiculous - I almost don't even want to drive it, desperate for a solution to this borderline terminal flaw.

Car: 2017 GTPP
Mods: BMR Lockout Kit

Problem: I simply cannot get any inside rear wheel traction when accelerating from a stop while turning. I'm talking less than 1/4 throttle, dry conditions, the inside rear wheels just skips and shakes. I can feel the control arm bind/slip/bind/slip.... etc. And if it's raining? Virtually zero traction even if I just touch the throttle.

Now - what I "think" is happening is that the LCA bushing is allowing the LCA to move for/aft too much thus causing the bind/slip reaction AND the torsen diff exacerbating the issue since it's open when traction is very low.

So, first - I'm wondering if this if common to all S550s OR just the PPs? Surely many of you are experiencing this same dreadful behavior. I want to determine if it's the suspension and/or the Torsen.

Second - I want a solution, not bandaids.

The goal: to be able to briskly step away from a dead stop while turning without any sipping/binding/wheelspin without making the car an NVH nightmare.

Any input here? Please, I want to love this car but this is really killing it for me.

What cars have you previously owned?

 

[EricSMG]

My PP car has done that since day one. I thought it was normal but now reading all the im not so sure. Smae scenario, i go uphill on a 90 degree turn and i feel like a have a welded diff and im not even giving it 25% throttle! Should i take it to the dealer?

Today in the rain was quite telling. If I provoke it even slightly (like 25% throttle) I get severe wheelhop even with the BMR lockout kit. The inside rear wheel spins/bangs away with little forward push.

I am 99.9% sure it's just the "way it is" and there isn't anything wrong other than parts that don't work well together.

What cars have you previously owned?

A '78 Pinto, why?

This IRS sucks balls and we all know it.

Now, back to a solution.

We know it's not only the PP cars which tells us that the IRS is the root cause - big surprise. The Torsen seems to exacerbate it with its high bias/open nature, yes. And the short 3.73 gear also probably makes it worse to a degree.

It seems to me that the solution would involve solid cradle/diff bushings and LCA bearings, but this would be a miserable car to drive. So, perhaps we shoot for the 80/20 rule here - sounds like LCA bearings and links might eliminate the lion's share of this which would be acceptable.

 

[Bluemustang]

I can't speak from a lot of experience with cars in general. But if I can say this - after the FRPP toe knuckle bearing was put in, I can feel a difference in how handle slower tight turns with throttle. Before it felt like the wheel was moving (shaking) really bad and it was difficult to know where the car would end up so I had to back off the throttle. This sensation is much decreased now and cornering consistency on throttle feels much better. I have more confidence on hitting the throttle and knowing where it's going to go. Maybe a LCA bearing would help solve it.

I'm not sure if I have experienced the same thing you are talking about. Mine is an auto and doesn't have the Torsen. But still I think these problems are related to yours. I would bet it's the IRS. Perhaps if you replaced the UCA and LCA bushings to bearings and put in the FRPP toe knuckle bearing, you might solve your problem. I don't have those but I do have the CB005 as you do and also vertical links, that's it for IRS mods. I can't say that I'm experiencing what you are, at least not as bad where it bothers me.

And while I do not experience any appreciable noise from these mods right now, I have experienced a decrease in refinement or added harshness if you will. So it's likely with more IRS mods you may get a little more harshness over certain roads and things.

 

[Ryan1112]

I have the same problem with my GT PP with just under 2000 miles. It was bad stock. After my first track day I changed the diff fluid to BG 75-140 and I didn't notice a difference. I put on BMR springs and the lockout kit for different reasons and its just a bit better. Still annoying though.

 

[JayC]

I just when for a drive around town and not once did I experience any problem on sharp turns for a stop. Perhaps my superior driving skilz make up for a lot of the cars problems. Or could my Torsen be working a little "looser" than some of the tire scooters? Could me IRS be set up tighter or just aligned better....hell I don't know?

 

[EricSMG]

I just when for a drive around town and not once did I experience any problem on sharp turns for a stop. Perhaps my superior driving skilz make up for a lot of the cars problems. Or could my Torsen be working a little "looser" than some of the tire scooters? Could me IRS be set up tighter or just aligned better....hell I don't know?

Seems to be hit or miss. What IRS mods do you have? How many miles on your car?

Let me ask - when you roll into the throttle from a stop while turning (right is the worst), what happens for you, exactly? No jitter, no skipping, no hop - just clean smooth acceleration?

 

[jabrax]

I have experienced this from day 1. Not as bad as it used to be when I first got the car. I think I noticed a big difference after I changed tires - wierd.

I had it slightly today in a spot were it usually happens. - Backing st8 out of driveway, full turn left of the steering wheel turning uphill. This movement is the only time i get the funky little hops

 

[JayC]

Seems to be hit or miss. What IRS mods do you have? How many miles on your car?

Let me ask - when you roll into the throttle from a stop while turning (right is the worst), what happens for you, exactly? No jitter, no skipping, no hop - just clean smooth acceleration?

Car just rolled over 3k and the Steeda shifter bushing and a cat-back are the only mods. Yes just clean smooth accel. Only once I felt some slippage crossing a damp intersection ( a bit too much throttle) but I was not turning at the time. Seems very hit or miss to me.

 

[Ryan1112]

I need to add that my car doesn't do it if I'm starting at a "normal" pace. I have to give it moderate to spirited throttle to make it hop. I'm thinking there's no one thing that's causing this. The cradle lockout helped and I'm betting that it will take a combination of other mods to cure it like vertical links, LCA bearing, shocks might help, and tires. I've committed to not getting tires until I wear the stock ones out but I'm betting Michelins would have better grip.

 

[IvanCRF]

It seems to me that the solution would involve solid cradle/diff bushings and LCA bearings, but this would be a miserable car to drive.

I have a manual car with 3.55s, solid aluminum differential bushings, LCA bearings, toe bearings and more. When taking a turn slowly from a stop, I notice the inside tire still wants to spin especially on gravel roads, but the car is planted otherwise.

It's not too miserable inside, but cruising around 60mph produces a sound similar to a vacuum cleaner that is very noticable. Vibration only slightly increased slightly at the shifter. Road imperfections are felt quite easily and large imperfections or transitions jolt the entire car.

 

[Doctor Fishtail]

According to Kelly's/BMR's observations, this is the main area that upgraded vertical links notably improve.

This ^^^ I installed the BMR vertical links and it does the job. Get them, install them and your problem will be over with. BMR seriously is on top of the mountain. The rest are struggling to get where BMR is. Just look at all the competition that copy their products.

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