2005 350Z Enthusiast 6 spd.

I just changed final drive ratio to a 4.08. With the TC engaged, I started having issues with the slip light and engine RPM cut out since doing the changeover. On occasion and under hard acceleration, the light flashes and the engine speed is cut. Doesn't seem to be able to be duplicated on the same road surface. Happens on a straight road and is random. Never know when it will happen.

The changeover was done by a Nissan master tech so I know it was done right but even he can't explain why this is happening. The car has been run with a Nissan diagnostic computer hooked up and all speed sensors check out OK but with a 1, and on occasion, a 2 mile per hour front to back difference when the issue does arise.

Tires are 245/35/19 front and 275/35/19 rear, which seems to be a common tire upgrade. Never a problem before the ratio change and these tires are within the tolerances for the TC suggested in 350Z forums. Anyone have any ideas?

It seems like the computer can't properly calculate the wheel speed since you've changed the gearing. I haven't put those wheels on a comparison calculator, are they plus or minus sized? That combined with the final drive seems like you'd have to change a constant in the computer for it to calculate properly. The NMT didn't do any programming then?

Or, you could just be experiencing errors in the traction control system that need to be addressed. Dirty sensors or something like that maybe.

The sensors check out OK via a Nissan diagnostic program, so they don't seem to be the issue. They have also been checked out physically. Nothing is apparent.

No reprograming was done. Really don't think it is necessary for this change or even if anything can be adjusted. I'm certainly not an expert on this though. There are no codes in the computer to indicate a fault in any system.

The only thing else would point to the tires but again, they are within the recommended numbers as far as what has been posted on the various Z forums. These 19 inch tires have a 0.8 inch stagger compared to the original 17 inch tires which had a 0.4 inch stagger. Anything less then 1 inch stagger should be OK and these tires have been fine until this installation. Yes, the change in ratio could have hyped the issue but according to others that have made this same change, there were no similar issues with their cars.

A Z1 diff cover was installed to get some extra capacity along with a plenum spacer but we can't see how either would bring this TC issue to light. But along those lines, it could be something entirely unrelated to the gear change and coincidental. We've run out of ideas.

I have searched the forums but haven't discovered an answer that applies directly to these facts. That's why I'm asking for suggestions or ideas because maybe someone here has experienced this or can suggest something that we haven't checked. Sometimes you can't see the forest for the trees

I'm starting simple here, so apologies if this sounds patronizing.

You mentioned tire sizing & stagger, but what's the actual condition of your tires? My nanny will occasionally wag her finger and I've got a stock diff and run grabby Michelin Pilot Super Sports with just at 12k miles on them. With that 4.08, you're spinning up much faster than you normally would. That, combined with a less than ideal tread situation, could be making the nanny put the brakes on the fun train.

If they're in decent condition I say try driving for a while with more gradual throttle modulation and see if the slipping happens less often.

Last, as much as you might not like to hear it, it could be that the non-OEM sizing is the issue. Like the potential amplification of any tread issues, the non-standard sizing that was ok with the factory rear end might now be an issue with the 4.08. My suggestion would be to find someone with a set of standard setup and drive on their tires and see if the slip light & throttle cut occur again. You might even do that before worrying about the condition of your tires, because if sizing (doubtful) is the issue there's no sense buying another set of tires that's going to give you the same problems.

Keep us posted!

I don't consider your, or anyone elses, thoughts to be patronizing :--). I appreciate any thoughts that you can pass on and encourage others to suggest things in the hope that I have missed something.

So, to respond to your thoughts, the tires are in what I would consider to be good condition. I have tracked the car this past year, maybe 4-5 days since putting these 71Rs on but I would guess that I can get another season off them based upon their condition and thread depth. The car is mostly used for tracking days now, not a daily driver.

The issue with trying to borrow another's tires and wheels for a test is that my car has an Akebono BBK on it so fitment/clearance is more of a problem. I will contact Z1 again on Tuesday as they say that changing the diff gears in their cars did not produce issues for them. I will find out what size tires are on their cars so I can get more information on a direction I need to go. This, of course, doesn't eliminate that something in my system is faulty but as you said, it might just be a combination of things. Something needs to change.

Although this is a costly, I had planned to go to 18 inch tires this season and I will still do that but try and pick a tire and a size that will reduce the stagger to be more in line to the OEM stagger. Whether this issue is resolved before I do that or not, I will go ahead with my plans for better on-track performance and, there is always this,.....I can shut off TC :--).

Thanks again for your input and have a Happy New Year!

Any new developments?

No, nothing new but the only thing left is the stagger of front to rear tires, which is @ 0.8 inches. That should not be an issue either but it is, as I said, the only thing left to look into by replacement. Everything else suggested and tried has not solved the issue.

I would like to go to 18s but at the moment, I still have quite a lot of rubber on the 19/35 71Rs that are on the car and I've decided to hold off until the end of the 2017 tracking season to replace those tires with 18s with a smaller stagger. Although the 19s were never an issue before, the change in ratio may have been just enough to trigger the problem. IDK, it's only a guess at this point .

I rarely drive the car on the street so I can ignore the random flashing slip light and RPM cut by not getting overly enthusiastic when I do drive it on the road .

When I do replace the tires I will update this thread.

Thanks to all who have responded to this thread with their ideas. I appreciate the involvement especially without the flaming that seems to occur regularly on some of the other 350Z sites

Well, my PDX season is over and now would be the time to buy 18 inch wheels and tires and get back to the original stagger to see if that change has any effect on the irregular slip light issue that I have been having. I promised to update my earlier post with the results.

Well, ........Irma has destroyed my wheel and tire stash sooooo, it will be awhile before I can update this thread with any results. Sorry folks but I will be back .

Could be wheel bearing. I've seen cars with very minimal almost undetectable amounts of wear and play in a sealed unit bearing allow enough movement under load to disrupt the wheel speed sensors.

Interesting comment. I haven't physically checked the bearings but I have run the car on a lift and listened very carefully. Nothing. But that doesn't mean there isn't a slight variance as you mentioned even if no noise was evident.

After I change the wheels and tires(which has been pre-planned for awhile anyway, issue or not) and the issue still isn't resolved, wheel bearings will be one of the next things to be checked much, much closer. Thanks for the post.

Ok, I guess it is time for an UPDATE and closure.

As I said earlier, my quest for light 18 inch wheels to reduce stagger, get closer to OEM and hopefully solve my "slip" issue had to be put on hold due to the financial cost of last year's hurricane. Well, it has been long enough and although I couldn't find an 18 inch wheel that would fit over my BBK that I liked and would also reduced unsprung weight, I finally found a wheel that fit my needs...... although the wheels were again 19 inch :--). 9/10 lbs. per corner reduction was not something I could ignor. So, back to my 0.8 stagger with the same size tires I had before, but this time new ones. What the hell, just decided I'd live with the issue on the road. Oh well!

But, as It turned out, and trying to induce slip every chance I got for the lst 2 months, I have not been able to light up the slip light nor have I been able to see a RPM drop as before when "slip" was noted. Huh? What changed? The only change was the tires. Same brand, same sizes, .....only new compared to 2 year old rubber. So I checked the old rubber again and although they were 2 years old and aging, there was plenty of life left in the tires. The front thread depth read about 7 on the gauge and the rears were at 5. I can't believe that small difference in depth was enough to induce "slip" on occasion but there were no other changes to my setup.

At this point, the only thing that makes any type of sense is a combination of things led to my issue. Maybe the perfect storm. Old tires, close to the dreaded 1.0 stagger, and a small difference in thread depth front to rear caused the slip issue on the road.

YMMV, but that is the only thing that I can point to and report.The slip light and the RPM drop has not happened since the installation of the new tires. I'll take it!