M998 12k Axle Conv. Issues

[NateTheGreat]

Hi guys I've been lurking on the forum a while. Finally found the courage to field a couple questions.

I'm rebuilding a 93 M998 and moving from a new cooling system onto 12k axles/brakes/ball joints/steering. Have a few concerns:

1) Buying axles I didn't distinguish between ECV axles (for solid rotors) and the A2 axles (vented rotors). I bought vented rotors, but I'd like to run the ECV axles on some corners. But since the ridge on the flange of the halfshaft is a smaller diameter it won't be a tight "centered" fit. I was thinking of installing them using 3 countersunk bolts, tighten the other 3 bolts and then replace w the real bolts where the CS bolts were (to center everything). It's that or have some spacers made on a lathe and mount to the flange but that sounds like a big $ hassle. I just worry that the torque involved could cause them to shift if I don't go the spacer route. Maybe just the 6 bolts alone holds them center? Thoughts?

2) I notice quite a bit of play / lash in the front diff after pulling my first axle. The diff flange can be turned quite a lot before the driveshaft starts turning. It seemed to run OK when I was driving it. Is this normal for these? I really don't want to find out later I should have yanked it and gone through it after I put it all back together. I was going to change the diff flange seals and inspect the flanges for grooving but that was it. Should I yank the cover?

3) The first geared hub I removed had quite a bit of metal on the drain plug. A good glob on the end of your finger. Is this typical? I haven't torn it down yet but wonder if the adjustment on the bearings was a bit tight on the spindle or spur gear? I'd expect to see that on a transmission due to bands wearing blah blah etc... But this seemed to be a lot of metal for just a hub w 2 gears.

Thanks,
Nate

 

[Action]

You want to run ECV axles on SOME corners? What?
If your axle doesn't fit the brakes, buy the correct rotors. If your rotors don't fit the output flange, get the correct rotors.
Your output flanges, rotors, and halfshafts all fit together.

When the halfshaft fits properly to the rotor / flange, the 6 bolts hold them together. If you use a halfshaft with a smaller center than the rotor, those bolts are now holding the pieces together and holding them frommoving sideways.
If you lose control of halfshafts, you lose the abilty to stop.

 

[Retiredwarhorses]

What "Action" said....and let me add, you also need 12k geared hubs and new 12k caliper brkts.the spline count is not the same for 10.3k and 12k halfshafts. You can change out the upper spur gear when you tear down you geared hubs.
The 12k HS's are cheap, that's for sure..at least the small flange type anyway, there is also a large flange 12k as used on my M1097A2 and they are much more rare and they are full price most of the time. This truck uses vented 12k rotors that are large flange. I just installed 12k solids on a truck in the shop, changed the flanges over to the smaller ones, these can be had on flea bay for about $50ea....so if you do it, change the 4 flanges, rotors, upper spur gears, caliper brkts....I would also change over to the flexible brake line kit...as there is Even less room after adding all the above.

 

[Retiredwarhorses]

Oh....your diffs, you would,need to check it per the TM. But these days, not worth sending out. New 2:73's are about $350.00ea....you need 2. But I would just drive it till it Grenades.

 

[NateTheGreat]

Thanks for the speedy replies and comments. I have all the parts for the conversion otherwise so I am 90% good-to-go. Let me better explain myself on the 12k halfshaft predicament...

For all the reasons mentioned (availability/price) I picked up mostly ECV axles instead of the RCSK17028-x axles. But I already had bought a set of vented rotors. So rather than buy extra parts and move over to solid rotors, I'm suggesting running the ECV axles with the vented rotors / original larger diameter diff flanges.

Given that the 6 bolt pattern matches for both axles there is nothing to really keep you from bolting ECV axles to a vented rotor. (This doesn't work the other way around, you cannot bolt an RCSK 12k axle on solid rotors).

The down side is the ridge on the end of the axle is a precision tight fit and centers it exactly on the rotor.

So if I were to cut some small spacer rings on a lathe that I affixed to the ECV axle flange, it can be made into a RCSK axle for all functional purposes and run on the vented rotors.

My question was whether the 6 bolts are a tight enough tolerance and could center it sufficiently. If so I could just bolt it up and run it and not deal with making spacer rings at all. Edit: On closer read it seems you guys frown on the idea of doing this...

This could be done with spacers if nothing else. Apparently no one has been fanatical enough to try it lol. I really don't want to wheel and deal all my 12k parts if I don't have to.

 

[86humv]

12K frames also have different X members .[ all 4 ].
And different diff. brackets...[ all 10 ].
Might be a clearance issue with the bigger rotors and the X members.

 

[Action]

Your diffs will need to move forward or backwards to make room for the bigger rotors.
12k halfshafts are available with large and small ends. My m1114 ECV came with solid rotors, and my m1152 REV came with vented rotors.
You can hook it up without those spacers you speak of, but you will be adding more stress to those 6 bolts.

 

[NateTheGreat]

Your diffs will need to move forward for backwards to make room for the bigger rotors.
12k halfshafts are available with large and small ends. My m1114 ECV came with solid rotors, and my m1152 REV came with vented rotors.
You can hook it up without those spacers you speak of, but you will be adding more stress to those 6 bolts.

Thanks for the follow up. RE moving the diff's, So new X-members and brackets like 86humv mentioned? Do the diff's need to move far enough that driveshafts need shortening?

 

[Action]

The drive shafts have slip yokes. Do you atill have a 218 T/C and a 3 speed trans?
The correct diff brackets put them in the correct location.

I would have just bought a2 10k shafts and been done with it. The originals were like 7.7k. If you are worried about breaking them, learn how to properly drive the HMMWV. When you upgrade shafts, you will break the next week item in the line. (which may cost more to replace)

 

[NateTheGreat]

Ya 218 and a 3 speed. I understand, but I want to swap drivetrains eventually so getting the 12k out of the way now.

 

[NateTheGreat]

Finally got around to finishing this up and felt to post a follow up. Scrounged large flange 12K axles and finished up the front end last year. I wanted to have a spares kit anyway and could buy 12K fronts all day for super cheap.

I then had a local machine shop cut some spacers so I can use the smaller flange solid rotor axles with vented rotors. They are drilled with holes for 4-40 countersunk screws and drilled and tapped the flange to match.

Instead of buying complete rear axles ( $$$ ) I found some 12K axle rebuild kits that only have the shaft and hub side of the CV assembled for a lot cheaper than complete rears. So I swapped the inner flanges off my small flange axles, install the spacers and built up the rears.

So I ended up with 12K large flange axles all around and a kit of parts to have a complete set of spares to field assemble any 12K axle.

Here are the spacers.

 

[NateTheGreat]

Finally got around to finishing this up. With the help of a local machine shop here are the spacers I came up with.

Since rear axles have been a bit expensive and hard to find surplus NOS, I bought a couple more fronts and some rear axle rebuild kits for a lot cheaper. Ended up with just enough parts to create a complete assemble-any-12K-axle spare kit.