Hey guys,

I just supposedly install a 2009 g37 6MT rear different with 3.7FD into my 2005 g35 6MT and instead of feeling more punch. The car feels slower instead and the ABS keep slipping at WOT. So I am not sure if I get ripped off in receiving a differential that is not from a g37 but maybe a g35 with 3.3FD? So how can you tell if i receive a g37 3.7 pumpkin instead of a g35 3.3? And Is it possible that I got sold an automatic g37 rear diff with 7 speed? Please help, thank you in advance

 

Jack up one side of the the rear of the car and put a piece of tape on your jacked up rear wheel and also a piece on the driveshaft. With the car in neutral, rotate the tire with the tape on it (the one that's in the air) 10x, and count how many times the driveshaft rotated during those 10 tire rotations. Divide the number of driveshaft rotations by the number of wheel rotations, and you should have a fairly accurate depiction of your differential gearing ratio.

 

Double post.

 

How would the diff affect the ABS? Unless u took apart the brakes and messed with the sensors then it shouldnt be affected.The lag can be attributed to taller gearing.

 

g37 has 3.3 gears for the auto version could b that

 

damn, I guess I will try to do the method mention above, i will come back with update

 

I just attempted the method you told me and i got 20 driveshaft spins, that does not sound right, correct? That means its 2.0 gearing? I don't think there is a differential with 2.0 right?

 

there are 2 differential ABS sensor connected to the differential, here its what it looks like, maybe i disconnect it and its faulty now?

 

If you take the diff cover off, the gear ratio is stamped on the ring gear.

But yea if its on that car thats not so easy, What is your RPMs at 80mph?

 

^
ok let me go for a drive and cruise at 80 and will come back with my finding.

 

That's not really going to matter since the speed is determined by the transmission output shaft. If he has a different rear end ratio in has car, his speedometer will be off.. so it will still say 80 MPH at the same engine RPM that it did before the rear-end differential change.

He will have to drive side-by-side with another car, and have the other car hold a steady 80 MPH and then check the RPM's in his G35 at 80 MPH.

Use this site to figure out your ratios based on your engine RPMs by tinkering with the rear end ratios in the calculator until it seems about right for your engine RPM at 80 MPH (according to the pace car's speed).

http://www.car-videos.net/tools/spee...B1=Recalculate

 

^ False, rpm does change,We also have a thread with RPM ranges per FD Ratios, so it will be very simple for him to hit 80 and tell us what his tach says.

3.3 you should be at 2.9-3k
3.5 3.1-3.2k

https://g35driver.com/forums/drivetr...ms-80-mph.html

 

ok just did a cruise at 80mph on 6th gears, i am at 3K. so i guess I got ripped off on a 3.3 differential?

 

The speedometer becomes inaccurate on the 06+ coupes with different FD gearing.

 

I would take a handheld navigation unit with you or use a pace car to verify that your indicated 80 MPH is actually a real 80 MPH. I'm not at all sold that the speedometer would still be accurate after a final drive gearing change. I've swapped gears before on pickup trucks and in buddies track cars, and it always resulted in an inaccurate speedometer... because (at least in the cases of those cars) the actual speed was determined by the rotational speed of the transmission output shaft, which usually drives a speedometer gear. Unless you change that speedo gear or your transmission gearing itself, the indicated speed and engine RPM in each gear are always the same, regardless of how fast you're actually going.