Early American "big nut" axle

updated 25 mar 2021

new ~ 2010

Even amongst AMCers there's a lot of rumor and fear about the driveshaft system on these early Americans, known as the "big nut" axle. "Modern" American cars have the rear U-joint yoke fixed to the rear axle pinion shaft; the big-nut rears instead have a splined slip joint with a compression sleeve tightened with a ... big nut, tightened to 300 foot-pounds. With big wrenches.

I was warned of the horrors of working on this thing, but it simply wasn't that bad. I bought a pair of 1-3/4" combo wrenches, Fuller brand, total cost for two including shipping: $50 (in 2009).

It did require different procedures but none of them were particularly difficult.

Since apparantly few people have seen these things I took some photos of the procedure to debunk the mystery.

Replacement seals do not exist as far as anyone knows. It is made by National and has an AMC part number of 3128171. It is Group number 9.064. The factory parts catalog shows that number superceded by 320 3580.

Not that this will help make parts appear, but as far as I know these were once replacement part numbers:

AMC 312 8171
AMC 320 3520
National 6855N
Timken 6855N
NAPA 49679
Sealed Power N-10180
Chrysler 2453144

25 March update: ... the pinion seal used on this rear was mysteriously used on 68-69 Javelin Sixes and is presently being reproduced by the vendors. It is available at american parts depot for $39 and bears the part number 990 6402B. I believe the other vendors have it as well. Also, Brent Havecost has an NOS 3128171 Seal at www.nashparts.com for $59 -- Sean Crane

This is the rear yoke, slip-joint coupler and the eponymous big nut, cleaned for inspection.

Ready to install.

This is the pinion end of the rear axle. I took these photos to later identify the seal, which are apparantly no longer available. It doesn't look like rocket science to adapt something to though.

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