OK Axle Experts, what did in find inside?

[W_A_Watson_II]

I started the front differential on the Red 46 PW draining yesterday. Did you know the 46 drain plug is a small 1/4" pipe plug with the letters US stamped on the face? Since it was going to take a while I let it drip overnight.

When I got into the shop this afternoon, I found a small metal dowel like pin (lower piece in the picture) with angle sheered ends, and three groves cut the length of it laying on the top of the oil pan.

So I pulled the differential out (had planned on doing it anyway) and found two more large pieces, but nothing small and no shavings. One looks line the rest of the metal dowel, and the other might have been e piece that was smashed between the gears.

I've looked over the differential visually and found no issues problems or missing pieces. It turns great with a little back lash slop.

Have I found remnants of a previous broken deferential, or is there a part inside the carrier that I can see than might have come out?

[W_A_Watson_II]

Taper Grove Pins for Differential Case Cap?

Looking through M37 Power Train Manual (TM 9-8031-2/T019-75-1-100) I believe they may be the Taper Grove Pins for Differential Case Cap?

Mine has six holes (I'll take a picture later) and I don't recall seeing anything in them when I did the visual inspection.

[Charles Talbert]

Taper pins

Most likely it is the taper pins. You mentioned yours has 6 holes. This would indicate it has been gone into previously. Actually a new case and cap assembly has no pin holes, they must be drilled after the cap is tightened, very precisely and to exacting size.

Now getting back to the 6 hole issue; what happened is someone had the cap off, when they retorqued it, the holes did not line up at the same place when the cap hit bottom, thus a second set of holes in the case became necessary. This requires even more precise dilling because you must drill through the case with great precision so the hole aligns perfectly with the holes already in the cap. We have done it many times, requires extreme care be taken to prevent ruining the assembly. The fact that the pins have come out of yours indicates someone failed to drill precise enough leaving the taper pins in a loose fitted bore or they reused taper pins that should have been replaced with fresh ones, or very probably a combination of both factors. New taper pins can be had from McMaster-Carr if after close examination you determine a new pin would cure the issue and not just fall out again. You are indeed fortunate they were not picked up by the ring gear causing a massive explosion of the differential. My suggestion would be to disassemble the case and cap. Probably needs a new spider gear, thrust washer, and shaft kit anyway. This kit will include all the needed new pins for the gear shafts and the case cap. Closely examine the pin hole bores in the cap, if they are wallowed, the whole case/cap assembly is junk as these pin bores must be precise in order to hold new pins securely. If the holes measure up ok, hopefully you can warm up the case and retorque the cap bottoming out at yet still a different location. Get a precise set up of the case in a drill press and drill new pin holes in the case mating perfectly with the ones already in the cap. Install new pins with red lock-tite and peen the case well over the ends of the pins. Then cross your fingers and pray. My take is if you have any doubt at all about a TIGHT fit of the pins; do not run the risk, next time you may not be so fortunate. A complete diff overhaul is by far and away the most expensive gear box on your truck to rebuild.

[W_A_Watson_II]

Thanks Charles,

Yes it's the Taper Pins. As you can see in the attached photo, the holes are empty. One hole looks like the other half of the pin is still there, the other two seems completely gone, and the case cap has rotated 1/2 hole.

I'm going to clean up and use one of the carriers I pulled out of my M when I installed the ARB's rather than try and repair this one for now. With the exception of two teeth that have a little water pitting, the gears look good and the bearings all roll and sound good.

[Clint Dixon]

Confused here

Most likely it is the taper pins. You mentioned yours has 6 holes. This would indicate it has been gone into previously. Actually a new case and cap assembly has no pin holes, they must be drilled after the cap is tightened, very precisely and to exacting size.

Now getting back to the 6 hole issue; what happened is someone had the cap off, when they retorqued it, the holes did not line up at the same place when the cap hit bottom, thus a second set of holes in the case became necessary. This requires even more precise dilling because you must drill through the case with great precision so the hole aligns perfectly with the holes already in the cap. We have done it many times, requires extreme care be taken to prevent ruining the assembly. The fact that the pins have come out of yours indicates someone failed to drill precise enough leaving the taper pins in a loose fitted bore or they reused taper pins that should have been replaced with fresh ones, or very probably a combination of both factors. New taper pins can be had from McMaster-Carr if after close examination you determine a new pin would cure the issue and not just fall out again. You are indeed fortunate they were not picked up by the ring gear causing a massive explosion of the differential. My suggestion would be to disassemble the case and cap. Probably needs a new spider gear, thrust washer, and shaft kit anyway. This kit will include all the needed new pins for the gear shafts and the case cap. Closely examine the pin hole bores in the cap, if they are wallowed, the whole case/cap assembly is junk as these pin bores must be precise in order to hold new pins securely. If the holes measure up ok, hopefully you can warm up the case and retorque the cap bottoming out at yet still a different location. Get a precise set up of the case in a drill press and drill new pin holes in the case mating perfectly with the ones already in the cap. Install new pins with red lock-tite and peen the case well over the ends of the pins. Then cross your fingers and pray. My take is if you have any doubt at all about a TIGHT fit of the pins; do not run the risk, next time you may not be so fortunate. A complete diff overhaul is by far and away the most expensive gear box on your truck to rebuild.

My memory may be a little hazy, as it has been over 20 years, but when I installed the All-Trac in my WDX I followed John Zentmyers printed instructions to the "T". The differential I was working on had never been apart. I removed the pins using the stacked ball bearing method to push the pins out a little at a time. They were tight to the very end.

To reinstall, the instructions indicated to drill fresh holes in both the cap and case. No reaming to a taper, just drill to correct size and drive pins back in.

I remember these were grooved pins, but I don't remember them having a taper. Is there a difference in the pins between the WDX and the M37?

In any case, the differential has been in use for over 20 years, the carrier assembly has been removed several times for inspection, and no pins have ever backed out or sheared.

I spec out purchased componants from McMaster every day at work, but not grooved pins as they are not accurate enough for our designs. I am finding Taper Pins and Grooved Pins on their site, but not grooved pins having a taper.

http://www.mcmaster.com/#pins/=3bv7b7

[W_A_Watson_II]

In cleaning up the M37 front carrier, I found what I believe to be the side gear washer pieces inside of it. They are a plastic like material, is that what those washers were made of?

I'll now pull the M's rear carrier (both left over from the ARB installation) and inspect and install new bearings on it for use in the PW.

[Charles Talbert]

Pins are tapered

My memory may be a little hazy, as it has been over 20 years, but when I installed the All-Trac in my WDX I followed John Zentmyers printed instructions to the "T". The differential I was working on had never been apart. I removed the pins using the stacked ball bearing method to push the pins out a little at a time. They were tight to the very end.

To reinstall, the instructions indicated to drill fresh holes in both the cap and case. No reaming to a taper, just drill to correct size and drive pins back in.

I remember these were grooved pins, but I don't remember them having a taper. Is there a difference in the pins between the WDX and the M37?

In any case, the differential has been in use for over 20 years, the carrier assembly has been removed several times for inspection, and no pins have ever backed out or sheared.

I spec out purchased componants from McMaster every day at work, but not grooved pins as they are not accurate enough for our designs. I am finding Taper Pins and Grooved Pins on their site, but not grooved pins having a taper.

http://www.mcmaster.com/#pins/=3bv7b7

The pins in the M37 and PW are the same, they are tapered and have 3 equally spaced grooves around the circumference. I have a good stock and have not bought any in years, McMaster-Carr had the correct type at last purchase, that may have changed until now, have not checked recently. Holes are not tapered as pins get tighter as they are driven in. New holes are necessary in the case if the cap bottoms at a different location with pin holes not aligned after reinstalling in the case. There is not ample space for new holes in the cap cavities. If you drill precisely in the case, the same cap holes work great with new pins, never had an issue with that or with pins backing out. It is when new holes are drilled off center of the cap holes that you have a problem.

Where most wind up with problems is when they do not bottom out the cap, but back it off in order to line up the pin holes. This will not work. If the cap is not bottomed out tight, all the pressure rest on the pins, this is when breakage occurs. When the cap is bottomed tight, all the pins have to do is hold it from coming loose, the job for which they were intended in the beginning. They do that very well.

[Charles Talbert]

In cleaning up the M37 front carrier, I found what I believe to be the side gear washer pieces inside of it. They are a plastic like material, is that what those washers were made of?

I'll now pull the M's rear carrier (both left over from the ARB installation) and inspect and install new bearings on it for use in the PW.

Original side gear thrust washers are a fiber type material. It is typical for them to disintergrate with wear over time. New thickness is around .047" thick, this is actually slightly loose in most cases. We have been using bronze side gear thrust washers for years in rebuilds, .050" thick. These work great, you will experience fewer broken axle shafts also as a result. Loose motion anywhere in the diff set up, especially at the spider gears, thrust washers, side gears, and thrust washers contributes to slap and creates stress on the shafts everytime you let out on that clutch pedal. A good tight set up is much easier on shafts, that is a proven fact. This factor is of even greater importance if using an automatic type locker.

[W_A_Watson_II]

Charles,

Thanks, I have the 2nd carrier out of the M that still looks to have good side gear washers, so I'm installing a new carrier bearing and going to us it.

Should I need to get a carrier rebuilt, what would you charge?

[Charles Talbert]

Cost

Charles,

Thanks, I have the 2nd carrier out of the M that still looks to have good side gear washers, so I'm installing a new carrier bearing and going to us it.

Should I need to get a carrier rebuilt, what would you charge?

Cost are rising so rapidly on everything, I'll have to check and get back to you. Exactly what are you seeking in a rebuild, going back to the 5.83 stock gear ratio, etc? We generally go through the entire unit renewing everything to 100%. What is your take? I can then figure based on that.

[W_A_Watson_II]

Charles,

Was curious about the center section only, as when I pull the rear dif out I hope I don't find it having the same problem, as if it does I'll be out of good used carriers.

[Charles Talbert]

Charles,

Was curious about the center section only, as when I pull the rear dif out I hope I don't find it having the same problem, as if it does I'll be out of good used carriers.

That isn't a problem generally speaking. The spider gears, shafts, center block, shaft pins, thrust washers, side gears, bronze thrust washers, and taper pins will run $150. Time required to go through the center section is about 2 hours at $60 per hour. It is very wise to check the run-out of the ring gear flange before investing in the center rebuild. If the run-out is too much, say over a couple of thousandths, it will be impossible to get a real good gear set up. This is of extreme importance to a long life.

Just so you know, all the bearings to do a 100% rebuild of the entire unit is now over $600, our cost. If we include our pinion seal upgrade kit, that is $135, and it does not leak, drip, or seep oil if the installation is done right and the housing bore is in good shape.

[Clint Dixon]

Thanks Charles

The pins in the M37 and PW are the same, they are tapered and have 3 equally spaced grooves around the circumference. I have a good stock and have not bought any in years, McMaster-Carr had the correct type at last purchase, that may have changed until now, have not checked recently. Holes are not tapered as pins get tighter as they are driven in. New holes are necessary in the case if the cap bottoms at a different location with pin holes not aligned after reinstalling in the case. There is not ample space for new holes in the cap cavities. If you drill precisely in the case, the same cap holes work great with new pins, never had an issue with that or with pins backing out. It is when new holes are drilled off center of the cap holes that you have a problem.

Where most wind up with problems is when they do not bottom out the cap, but back it off in order to line up the pin holes. This will not work. If the cap is not bottomed out tight, all the pressure rest on the pins, this is when breakage occurs. When the cap is bottomed tight, all the pins have to do is hold it from coming loose, the job for which they were intended in the beginning. They do that very well.

I read more into your original post than I should have. I thought you were referring to true taper pins that require precision reamed holes having a matched and toleranced taper. Grooved pins have a lesser taper, created due to metal displacement during the forming of the grooves, as a result of being stamped deeper at one end than at the other. They, of course, do not require a reamed tapered hole but rely upon an interference fit within a drilled hole.

We are back on the same page.