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View Full Version : J30 LSD Question Again(kinda)..



**DONOTDELETE**
04-15-2002, 07:30 AM
I used the serch function, but I couldn't really find a definate answer to my question. I know about the fitment issues involved. I just want to know a definate answer on which model year has the proper gear ratio. I've read that the '95+ does, but noone seemed really sure. Does anyone have a definate answer to this? Thanks for your time http://www.freshalloy.com/

jdzumwalt
04-15-2002, 08:44 AM
get the 95 to 96 model and you will be fine

orion
04-15-2002, 10:41 AM
I hate to say it, but I'm starting to believe all the J30 diffs are the 3.92 ratio...

I know for a fact the '97 diffs are, but I thought that could just be the Touring models...

We've all speculated that the '95-96 are the same, but I think it's just wishful thinking...

Case in point: We went on a highway trip this past weekend and 95 S14's speedo (which has a J30 diff) read about 9% off...5% b/c of tire size (we previously did the math after measuring the tires), but the other 4% seems to be from the diff. But I will point out: It's not even noticeable in driving...

I put on my LSD web page that I wasn't sure of the ratio, but with this evidence, and the few people that have said they called Infiniti dealerships and were told it was 3.92, etc...it all points to a different ratio. That, and besides speculation (and my hoping it wasn't true) I don't think I've seen any evidence of it being a 4.083...

But as for what fits, if you still need answers, see here: http://plaza.ufl.edu/briand/lsd.htm

Later - Brian

04-15-2002, 10:59 AM
So...has anyone pulled the rear cover off the the diff and actually LOOKED at the ring gear of their J30 diff? If I'm not mistaken, the ring gear actually has the ring and pinion tooth #'s stamped into it, i.e. 48/11 (or whatever it has to be).

BTW, 48/11 = 4.3636363... (which is avl. from Nissan Motorsports), and 49/12 = 4.0833333... (OEM 240sx ratio). I wonder if the J30 diff is 47/12, which is 3.916666....

I realize it's a pain to do with the diff installed, but if anyone has one sitting around, check!

Please http://www.freshalloy.com/

Asad

[ 04-15-2002, 12:06 PM: Message edited by: asad137 ]

orion
04-15-2002, 12:44 PM
Originally posted by d240t2:
I hardly think that the 9% mistake in your speedo can remotely be attributed to a different gear ratio...<font size="2" face="Verdana, Arial[/img]I agree (unless you have the 4.6:1 rear end)...but I didn't say the diff was the only contributor. I only think the diff contributes the percentage it is different from the stock rear end - 4%. We measured and did the math on Britts tires and found they are 5% off...

4% from the diff, 5% from the tires, and the speed reads about 9% off...makes sense to me assuming we're getting good reading from both speedos.


My speedo reads about 6% higher than what the Techtom reads off the ECU. The speedo can't even display what the ECU reads...<font size="2" face="Verdana, Arial[/img]

If that's so then the tires could be the whole reason his is off. The speedo we were using for comparison was in a GTI...dunno how accurate those are, but I would assume pretty good considering the Germans propensity for quality sh!t. And if his speedo is 6% off like yours, and you factor in the difference in tire size by the numbers (3%), then we have our 9% difference again.


Different tire brands of the same "size" have been known to be different sizes. Besides the fact that tires do wear, and the OD changes slightly with tire pressure...<font size="2" face="Verdana, Arial[/img]

That's exactly what I'm talking about...his tires are off, about 3% by the size/width, but 5% as measured by us when installed and inflated properly. He runs 225/40-18's (NT-555's), BTW...


So the Infiniti dealership says that the gear ratio is 3.92? Anyone who has ever talked to a dealership knows that they don't know anything...A dealership's info isn't reliable IMO.<font size="2" face="Verdana, Arial[/img]I agree, but if all the indicators point to one thing, and we have no info otherwise, how can we dispute it...?

Also - I'm not making a case for or against anything here...I'm just throwing this info out there...hopefully someone will take off the cover of their J30 diff and get the numbers. Until then, I'm lead to believe it's the 3.92 ratio.

Later - Brian

240zx
04-15-2002, 02:51 PM
asad, i am currently in the process of putting in my J30 diff in my s14. you are correct, the amount of teeth on the ring for the J30 is 47 and on the 240 it's 49. both pinions have 12 teeth so if you do the math. 49 divided by 12 is roughyl 4.08 and 47 divided by 12 is about 3.92

04-15-2002, 02:53 PM
Originally posted by 240zx:
you are correct, the amount of teeth on the ring for the J30 is 47 and on the 240 it's 49. both pinions have 12 teeth so if you do the math. 49 divided by 12 is roughyl 4.08 and 47 divided by 12 is about 3.92<font size="2" face="Verdana, Arial[/img]Sweet, thanks for the info!

What year is your J30 diff?

Asad

knate
04-15-2002, 03:02 PM
Originally posted by orion:

</font><blockquote><font size="1" face="Verdana, Arial[/img]quote:</font><hr /><font size="2" face="Verdana, Arial[/img]The speedo we were using for comparison was in a GTI...dunno how accurate those are, but I would assume pretty good considering the Germans propensity for quality sh!t.<font size="2" face="Verdana, Arial[/img]

</font><hr /></blockquote><font size="2" face="Verdana, Arial[/img]They may make really quality cars, but that doesn't lend to speedometer accuracy. BMWs have been known to have very high readings, and I read in a car magazine that it has to do with European (or just German) laws. They have to be a certain percentage high, and American cars sold over there are actually adjusted for it. However, odometers are required to be accurate within 1-2% or something, so that would be a better test (if you have stock tires..)

johnathan_berlin
04-15-2002, 03:08 PM
hey 240zx...what year j30 is you diff from...i have a 94 J30 VLSD....

hssaini
04-15-2002, 11:08 PM
When i did my swap

My research came up to match 95 and 96 LSD of the J30

BTW, i found the 95 one and it was a piece of cake after that.....also, due to the ABS sensor people say to shorten the shafts, you don't have to worry about as there is enough play in the 240 to compensate for it and my car is the witness to this as well.

RINKU

PS. i was asking these silly questions myself not too long ago. BTW peeps here are very helpful...just have to have patience. SO THANKS ALL

d240t2
04-15-2002, 11:17 PM
I hardly think that the 9% mistake in your speedo can remotely be attributed to a different gear ratio...here it goes...the long list of reasons a speedo can be off.

My speedo reads about 6% higher than what the Techtom reads off the ECU. The speedo can't even display what the ECU reads.

The speed sensor and speedo aren't the most accurate devices. The speed sensor doesn't have an infinite resolution. How many teeth does it have on it? That can give you an idea of how close it can be.

Different tire brands of the same "size" have been known to be different sizes. Besides the fact that tires do wear, and the OD changes slightly with tire pressure.

So the Infiniti dealership says that the gear ratio is 3.92? Anyone who has ever talked to a dealership knows that they don't know anything. According to info from a dealership that Paul got, the Q45 and M30 diffs will fit the 240. Anyone who has ever looked under the M30 knows the diff won't fit in a J30, S13, NA Z32, etc. A dealership's info isn't reliable IMO.

Dennis