Your rear diff bushing is toast. Should probably look at getting a set of solid bushings (SPL makes some). This could be causing additional movement/resonance that is not normal.

 

Yep, Sharif and I looked at it this morning. New bushings on the way.

 

Car is an 04 Enthusiast. Definitely like the gears, great mod. There is a bunch of posts in the 4.083 gear thread (think its a sticky) and they are all pretty dead on. The good feeling is a little bitter sweet for me since there is definitely something not right about the install and its going to be more money to fix it (bye bye headers from the budget this year).

The car pulls much more strongly throughout the range and the gears go by real quick. First gear is still somewhat usable; I had heard people before say that they just started in 2nd after the gear upgrade since 1st was so quick and that's true it does go by real fast, but if you're just driving normal it's not such a big deal. I'm really hoping Sharif & Co. can get it fixed before the 30th so I can make my track day @ TGP.

 

What does second top out at, 55 or so? I can't imagine having such low gears on the original DE.

 

https://my350z.com/forum/engine-and-...installed.html

 

Just ordered the SPL kit.

 

Acceleration in each gear after a diff ratio change is roughly the cube root of the gear pecentage change. For example a 15% ratio change will increase acceleration by ~~ 2.5%.

Based on a few such 15% gear changes observed, it appears to decrease highway steady state MPG by at least 10% depending on normal cruise speed above 55 mph.

 

Are you sure? 2.5% sounds like you wouldn't even feel it.

 

Oh you feel it. I have an open diff (3.3FD) on my 05 DE G35 coupe.
I had the chance to run the VLSD 3.5FD diff in my car for a while. For me it gave about 6% faster acceleration per gear.

I ended up selling the pumpkin a week and a half ago when I couldn't figure out what was going on with my diff. My installer and I encountered a similar situation only my diff sound was quieter and had a different sounding pitch in it's hum around 60MPH or so.

After changing the fluids, the sound lessened but was there somewhat. I got tired of driving back and fourth a long way to try and figure out what was going on so I decided to let my diff go. I really enjoyed the faster driving dynamics the shorter gears bring IMO.

As for the geddyup, its enough to feel throughout the entire range. You're definitely quicker off the line. I can only imagine how much faster my acceleration would be if I were using the 4.083 FD gears.

Not only that, but most of you are already running FI which makes the acceleration even more ridiculous.

Under these conditions, I have no idea how someone would be able to use 1st gear at all.

 

Was theorizing with a friend of mine at work today - would working on a diff in any way cause something to change/break in the tranny? As far as I know the only thing that would be touched remotely close to the tranny would be the driveshaft as it was unbolted/rebolted to the diff? Other wise tranny shouldn't be touched correct?

 

Hey, I just had mine installed today. I have the exact same noise issue. Used both install kits. Im calling the installer tomorrow. I will suggest the bearings to them too as the source. Please keep this thread updated! Thanks

 

I talked about it with my friend who is a mechanical engineer, and he was positive its the bearings making noise. New bearings, which both the OP and myself have do make a loud noise, I also noticed that after driving for a bit, they heat up and the noise goes down slightly. I guess the only way to see if something is truly wrong is to open her up again. But for now, I will wait and see if the bearings do break in and the noise disappears.
Any others on here that used install kit #2 on their cars??

 

Did your rear pumpkin make noise when the car was brand new and you first drove it off the dealer lot? No - and neither should it make any noise when you install any of these gears. All the pieces we supply are factory Nissan parts - nothing is aftermarket. Something is either off with your install, or you have other issues (rear diff bushing, etc). Either way, it needs to be looked at by whomever installed it for you.

 

Quick update on mine - I picked it up this morning from Forged and it checked out ok. The noise is still there, but the measurements and settings for the diff were all correct. They opened the pumpkin, checked everything, dropped everything off the car, and replaced the rear subframe bushing with the SPL aluminum bushing as well; my annoying wheel hop issue is fixed too. The car drives much better.

Regul8or - do you have a lightweight fly by any chance?

 

Frizille, I do not have a lightweight flywheel. Glad to hear that all the measurements and specs were good and that the bushing were replaced. I checked under mine, and I see no sign of the black marks that run alongside the diff.

So the noise is still there huh? Maybe it is just the "break-in" period. Driven about 100 miles thus far, and have run it hard a few times, but am now easing up a little bit. What did the guys at Forged suggest??
Thanks

 

Said it's probably just whine from the gears being as high strung as they are. I've had the measurements checked by 2 shops and both said it's in spec so at this point I've got to believe everything is setup right. I put about 100 miles on it today and it *seems* a little quiter. Either that or I've just become accustomed to it. I'll be driving to and from work in the Z Mon-Wed so should have another few hundred miles on it by mid week.

I've got a track day on Thursday so I'll find out one way or another if it's ok ...

 

Bump from the dead. Same issue as yours frizille. Shop even took it apart a second time and reshimmed it and it did not improve very much at all. Same decel noise just like yours but I also notice a pretty pronounced clunk when shifting 1-2. Shop blames it on the solid bushings. Did this issue ever get resolved??

4.08/Quaife/SPL bushings

 

Hey guys. Ive been communicating with frizille. We have the same issue. Both 4.08 with install kits 1 and 2. I dont know if they over tightened my crush sleeve, but if they have to take it apart again to loosen it, then maybe its not worth it. I feel that the noise has decreased slightly, but still apparent. Can you point me out to a pic of the crush sleeve that could be overtightened. Once again, I did not install my gears, so I dont know too much about it.

 

let me dig up a photo of it

 

You could try using a thinker weight gear oil. With 4.88 gears and lockers in my truck I have to use a 140w oil. I think I have 80-90 in the z. A little noise might be heard in the break in period. You should change the gear oil at 100 miles and again at 500 miles.