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rear gear /diff change?


Guest zfan

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I have a 1971 240Z with a sbc 355 roller set up.

Tranny is a vette 700r4, gears are r200 with 3.54's. Tires are 25.5 inches tall.

 

I ran 13 flat at 111 mph with a best 60 ft. of 2.08 launching at idle. I now have better tires and can use my stall to launch at 2k.

 

I have been told by several people to go to 3.90's for diff. gears and that would get my times lower. I may have a lead on a LSD 3.70 rear end so it may not matter about the 3.90's.

 

Other question is it worth spending the money to go to the 3.70 lsd, are they worth the money or am I just as well of going to a 3.90 open diff.

 

I mainly cruise the car and do some drag racing.

 

Any imput or personal experiences would be appreciated. I'm calling on the lsd unit tomorrow.

 

Mike

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I hate having a car without LSD. I like how they drive/handle under power. I think it is a must have for autocross or drag racing and I like my street cars to have them as well. In a nutshell, yes, it's worth it. There is a 5% gain in gear goinng from 3.5 to 3.7 or 10% from 3.5 to 3.9. I would do the 3.7's from a $ perspective as adding an LSD to another case seems to be cost prohibitive relative to my wallet... :rolleyes:

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Well the 3.70 LSD fell thru so I guess I will keep hunting for the ever elusive pain in the a--!

 

Man they are hard to find and not cheap! This the second one I thought I had nabbed.

 

Mike

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I feel your pain. I have found a guy in Oregon who is going to send me his OEM front diff from his Xterra (he put an ARB in it) and I am going to pull apart the 85 300zx turbo diff I have and try to find out if these things are the same. You can buy the Xterra front LSD diff for $450 brand new. I am willing to spend that, but not the $750 that Nismo wants or that most of the used ones seem to go for. I've got my fingers crossed...

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Guest Anonymous

the 3:7 LSD is a lot of $$$ but the 3:9 is cheep i pay $75 at a junk yard down my way

FYI you can take the LSD out of the 3:7 and put it in the 3;9

if you can't do it your self the dealer should have someone that can

(i hear they had a bad batch in 87 and any one that worked at the dealer in 87 or 88 should know how to do it)

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Swapping the LSD is not hard. IF you keep pinion depth where it is at. Just measure the backlash of the 3.90 before removing the open diff using a dial indicator. Then when reinstalling the ring gear on the LSD, just set it so the backlash is the same as it was to begin with. You can get universal carrier shim sets at a local driveline shop. Check your pattern and good to go. Once again, PAYING for the LSD, whether it is from the boneyard, NIssan or wherevver is the hard part!

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