I have not had occasion to get into a 12K axle rebuild yet, so I have not previously looked for any alternative boots to the 57K3515 kit called out in the parts manual. One thing to note if you do use the 57K3515 kit is that it does not include the tulip, part 5715542, as noted on the HPG listing (
57K3515C / 01-457-1337 2530-01-457-1337 - KIT, HALFSHAFT BOOT (12.1 GVW) {PAIR} | Hummer Parts Guy (HPG) ) and discussed here:
(157) Half Shaft Rubber Insert... Can't find a part number that works. | SteelSoldiers . AMG has a good picture of it here:
SPACER HALFSHAFT BOOT TULIP 12K (5715542) - Chassis | Genuine Humvee Parts
I took a look at the boots on a M1152 I have here. The tulip has number 239-0076 on it as mentioned in the thread linked above. Here are a couple of pics:
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In 2018, I posted the EMPI catalog for CV boots and described how to convert the EMPI numbers to NAPA numbers (add a "6" at the beginning and remove the dash), post #16 here:
(157) CV boot on HMMWV | SteelSoldiers
The inner and outer 12K boots are the same, but the inner boot uses the tulip to adapt it to the trilobe CV joint cup. The outer cup measures close to 4.00" diameter, shaft is 1.200" diameter and the overall length of the boot is about 4.5". Looking at the EMPI catalog, it looks like the best matches (looking only at the round boots) are 86-2326 on page 16 of the 2017 catalog, or 86-2352 on page 17. The length of 86-2326 is about an inch longer than the stock boot, but maybe would compress or could be clamped further out on the shaft than the stock boot; 86-2352 is for a 0.980" diameter shaft but would probably stretch OK. These are NAPA part numbers 6862326 and 6862352 respectively. If these will work, the nice thing then is that you can buy just one rather than the two that the 57K3515 kit comes with.