Wanted: 3.9 "pumpkin"

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mikeb
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Wanted: 3.9 "pumpkin"

Post by mikeb » Sun Apr 14, 2019 1:44 pm

Hi all,

Getting tired of the 4.37 and am looking for a low mileage 3.9 pumpkin to pull the ring and pinion from and install in the limited slip unit.

Thanks!

Mike

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Re: Wanted: 3.9 "pumpkin"

Post by david premo » Sun Apr 14, 2019 3:36 pm

I don't think that will be compatible as 4:37 used a different limited slip spool than the 3:9 unit.

mikeb
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Re: Wanted: 3.9 "pumpkin"

Post by mikeb » Sun Apr 14, 2019 4:25 pm

David - Is the issue related to the ring gear spacer noted here in the comp catalog or is it something else? I previously had a 4.625 in the car.
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2mAn
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Re: Wanted: 3.9 "pumpkin"

Post by 2mAn » Sun Apr 14, 2019 6:28 pm

If you can swap over the LSD without the spacer, Im definitely a buyer for that as I will likely need one. PM sent
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spyder
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Re: Wanted: 3.9 "pumpkin"

Post by spyder » Mon Apr 15, 2019 1:11 am


david premo
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Re: Wanted: 3.9 "pumpkin"

Post by david premo » Mon Apr 15, 2019 6:22 am

The 4:37 gear was designed for a different size housing as were a few other ratios. The off set was different and made them not compatible with the other differential housings. A 4mm spacer was made so one of the housings would work the one way, but the other housing would never go the other way. I think if I remember correctly the one you have will only go the housings it is designed for.

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cktrap
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Re: Wanted: 3.9 "pumpkin"

Post by cktrap » Mon Apr 15, 2019 8:45 am

So I picked up that 4:11 from Brian and wanted to swap out my 4:37 pumpkin with it. So I need to change out the complete rear end hub to hub? I thought the housing were all the same. Is it just the carrier that's different?
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mikeb
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Re: Wanted: 3.9 "pumpkin"

Post by mikeb » Mon Apr 15, 2019 8:31 pm

So this is pretty confusing...but according to the Gordon's Garage link that spyder posted above, I think I understand:

1. Nissan LSD part 38420-16330 can only be used with: 4.375, 4.625, and 5.125.

2. Nissan LSD part 38420-A9980 can be used with all, but requires the shim to be used with the 4.375, 4.625 and 5.125 noted above.

I won't know until I pull the unit out, but if mine is the 38420-A9980 unit with the 4.0mm shim installed, I should be able to remove the shim and install the 3.89 ring and pinion. Is that correct?

Mike

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Re: Wanted: 3.9 "pumpkin"

Post by david premo » Mon Apr 15, 2019 8:44 pm

That would be correct. The “shim” is a 4mm spacer that was inserted between the ring gear and LSD spool. Motorsports had it made back in the day as a solution for one diff fitting all the ring gears.

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2mAn
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Re: Wanted: 3.9 "pumpkin"

Post by 2mAn » Mon Apr 15, 2019 11:22 pm

Fingers crossed it works out. Sorry I forgot to call you today Mike. I will call you tomorrow
Simon
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-1968 Datsun Roadster 2000 - happiness of pursuit

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Re: Wanted: 3.9 "pumpkin"

Post by mikeb » Mon Apr 22, 2019 3:18 pm

Here's some more information from the Bob Sharp manual, page 3-7:

"On the above 1600 and 2000cc units, the 3.70, 3.89 and the 4.11 carrier assemblies are aluminum. The 4.38 and 4.62 are steel.

"If you wish to use either the 4.38, 4.62 or 5.13 ring and pinion gears in an aluminum carrier to reduce the unsprung weight, it will be necessary to place a .150" thick spacer behind the ring gear to gain the proper tooth mesh."

So the early carriers for the 4.38 and 4.62 were made of steel - has anyone ever seen one? I thought they were all made of aluminum.

Mike

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Re: Wanted: 3.9 "pumpkin"

Post by JT68 » Mon Apr 22, 2019 5:47 pm

Yep, definitely seen them..back in the day.
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