hey all, ok here is the deal i have a 2007 base 350z i love the car so any man that loves his car is going to want to try and make it better, as i am sure you all can understand. i put in the spec stage 2 clutch with the clutch master aluminum flywheel, AEM intake,test pipes full exhaust. about a week ago my slave cylinder went so i figured if the trans is out and on the lift now would be the best time to put the 4.08 FD in. when i got the car back i started hearing a humming when decelerating faint at first then louder and louder. i have only driven the car about 20 miles and have not even got on it yet. i have seen one thread on here and he had the same problem after doing the same gear swap but the out come was never posted, i got all the parts from z1 and know that they are all Nissan parts install kits 1 and 2 where used in this install. anyone with any info please help.

 

Did you put solid aluminum bushings on the diff?

 

Who did the install? a 4.083 gear swap is not an easy install and is very easy to screw up. The gears must be positioned to an exact spacing from each other. Typically when new gears are installed, they will not replace the metal shims that are used to create a perfect gear mesh which could create a problem.

I would call and tell them about the issue, there should be no noise. The gears will wear slightly as they break in, but it should not create any humming at all.

 

i had the trans shop by my house do the work the same place that had installed my clutch and flywheel, i know they replaced the shims simply because thats the only part i did not have with the install kits. we had called Nissan and they had them sent over the next day. but you are right and i will be bring it back to them with the issue tomorrow afternoon i am just praying nothing was damaged in the short time i had it back. i would think no being driven only about 20 miles but you never know.

 

update. dropped my Z off at the shop to get that humming looked at. it was ripped apart and looked at and the shimming was perfect as was all other parts, we talked to smith town Nissan again still waiting on them to get back to us. any input on this matter is welcome. i would kinda understand if the gears where aftermarket however they are nissan parts i should not be hearing anything. another issue i was dumb founded on was the fact that the first time nissan was called when the shop was looking for new shims the parts guy had said you would not need them, he had said the Z should be drop in and go. could this be true? i never have seen fd gears that did not have to be shimmed however i could be wrong.

 

Did you have solid aluminum bushings installed, of you did, they will make your car hum, mine did, also, I am not sure if it would or not, but there is a rubber washer that goes between the diff ear bushings and the sub frame

 

no i didn't have the aluminum bushings installed, but as for the washer like i had said i took it to a shop so i was not there when the work was being done. but none the less i trust the mechanic and the shop so i would trust them to be doing the right thing.

 

 

Don't take this the wrong way but your trusted shop likely did not setup the gears correctly.

A 4.08 gear ratio is not that extreme of a reduction but with the increase in gear reduction comes louder gear whine.

If all the bearing preloads, pinion depth, and backlash are right in the middle of the allowable tolerances the gears will be very quiet.

I've got solid alum diff mounts, and stiffer urethane subframe bushings and theres just a little bit of gear whine that comes thru the cabin at speeds higher than 50 mph.

Maybe try a real transmission shop or find a 4X4 shop (they setup gears all day long) and ask them to take a look at it.

 

no offense taken. but they know what they are doing. now it is just a mater of time. however being checked and double checked givin the right gaping and tolerance i am eager to find out what the issue is and post what was wrong. i always am eager to find out the answer to a problem that i have never ran into. but thank-you for your input.