The Stovebolt Site Forums The Shop Area Engine Shop Drive & Pinion Gear Chipped

I'm in the process of rebuilding a 57 1/2 ton NAPCO front differential. I found some metal in the bottom of the differential case. It appears that it came from a chipped drive gear tooth and a chip in the pinion gear. On the drive gear, about 1/3 of the tooth is missing. On the pinion gear, about 1/5 of the tooth is distorted
somewhat. All other teeth of both gears seem fine. When I turn the pinion gear by hand everthing appears to mesh fairly smoothly in
both directions. However, I am worried that under load it may be a problem. Will this be a problem or can I leave it as is? If the prevailing opinion is that I need to replace both, are there any recommendations for sources? I bought the differntial from someone else, I know he never installed it. Tanks for any advice.

This is not your lucky day. You could grind the breaks to smooth them and extend the life, but sooner or later the gears will fatigue under load and fail. Since you are rebuilding it, now is the time to fix it, not when you're stranded on the side of the road. You could try posting an ad in the swap meet, or try one of the 4x4 boards for another gear set. Hopefully someone who knows more about where to get replacements will chime in.

Well, he won't be stranded since it is his front diff.

I guess it depends how much meat there is left. Finding replacements is probably dreaming.

Are you going to drive this truck hard?

Would randy's ring and pinion or other sources still have parts? Is this a GM or Dana or what kind of axle?

chip

Try calling Randy's Ring and Pinion
Randy\'s Ring and Pinion They can get you new gears and an install kit. But have you ever set up gears before? They do require some careful assembly and setup.

You probably wont get stranded by that gear set unless you are in a location that requires 4x4 to get out.

Thanks everyone for the advice. I think I will replace the gears at this point. I will try Randy's. I 've never done this before, but I do have the NAPCO manual that has the procedure. Is it a reasonable thing to do for an average hobby-mechanic, or should I seek out a transmission shop for this particular set-up?

With a good dial indicator and a good set of instructions, it isn't that hard to do. Randy will give you good advice on it, too. He's a really good guy for the business.

Just to provide closure on this, first of all, thanks again for all the advice. I did call Randy's but they did't have the gear-sets. Although I have come to find that the 1/2 ton Napco gear sets are the same as the 2wd versions. On the Napco set-up the front & rear differentials ratios need to match. I called Patrick's & he said that you can find the existing ration by the two numbers etched into the back of the pinion gear. However, he only carries 3.38 gear sets, I know my existing gearsets are not 3.38. Therefore I am going to bite the bullet and get two 3.38 gearsets from Patricks. I have a lot invested in rebuilding the front & rear differentials and the transfer case already. Also I picked up another newer 3 speed overdrive. So from a long term perspective it should be a reliable set-uop and a good highway cruiser. Again tthanks for the feedback and pointing me in the right direction.

Being the furthest thing from an expert on this, it does strike me that you may over gear the motor. Perhaps a nice SM420 with granny low might work a little better. To go from at least a 4.11 or even a 5.(16?) to a 3.38 is a huge jump. And then to go to a 3 speed w OD may just be too much. The SM420 may or may not be the answer, but I just wanted you to think about the question some more.

Good thought K10, I'll mull that over. My logic is that I have a 261 with 2x2 Holleys, Fenton exhaust, HEI ignition, mild cam & 60 thou. overbore. Plus I don't have to shift into O.D. except in advantageous situations. However, I didn't think it through from the perspective you bring. Thanks. I still have plenty of time to change my mind about the O.D.

The interchangeability brings another solution.

You could search for a used gearset to match what you have. If you buy the pumpkin, you wouldn't have to reset the gears, provided they show a good wear pattern. One place to try is Tom Myers Truck Parts in Miami Oklahoma 918 542 3871. This all depends on how happy you are with your existing ratio combined with the overdrive ratio.

The 3.38 is a good ratio for driving, and adding an od behind the 261 will work good for road use, but if you plan on 4 wheeling, you will want more gears. Also consider using a 4 speed SM420 with these gears, it will give you a granny if you need it. It would also let you sell the od trannys and raise some cash to pay Patrick for his gears.

Decisions, decisions. No one said owning an old truck would be easy!