Kraton All Diff Pins Broken but Kraton was Driving Fine? Should I get the Harder M2C Outdrives?

[pomplemus]

Hi all!

While doing my usual inspection after a bash and getting ready for the next, one thing lead to another (dirt in bulkhead, found dead bearings, open diffs...) and now I have my front and rear diffs open for the first time.

My intention was just to replace the bearings, shim them up while I was in there, and replace the fluid. However, when taking them apart, I found the pins behind each sun gear were each broken into three pieces! I've found this so far on the front and rear, and haven't gotten into the center yet. I'm not super surprised (I may have gotten a bit overzealous during my past session saving a backflip and landed on power for a split second once or twice), but I do find it odd that it was driving just fine when I packed it up before the tear down.

Is it normal for the sun gear pins to break in a way that is not immediately apparent until you get in there?

Anyway, another issue I found was that the outdrives would not come cleanly out of the cup and bevel gear, I had to tap them out with a hammer. I figure this was because of deformation of the pin holes making the ends a bit bigger and no longer sliding through, due to the broken pins. Hopefully the cup and bevel holes weren't damaged by the removal, they seem fine to me.

Anyway, I have several spare diff components on the way, including some 2.25 mm drill blanks from McMaster to make my own (hopefully stronger?) pins.

I figure I should also replace all the outdrives as well due to the hole deformation- would M2C hardened outdrives be a good idea here to reduce slop and hopefully reduce the chances of this hole deformation happening again? I'm taking this as an opportunity to do a full overhaul after the 20 or so packs I've run through it so far, and I have plenty of new goodies on the way, including an M2C chassis and towers.

I welcome any other tips to toughen up my diffs while I'm at it! Shim, drill blank pins, new fluid, and rubber shielded bearings plus maybe the M2C outdrives if they are recommended is my plan.

Thanks!

 

[Kingleo619]

Add shims...my typhon 6s is fully upgraded shims do make a difference, center front reaf diff has 2 shims behind sun gear and 2 out drive shaft cup

 

[Yas]

Shims will help for a longer gear life, but it will still be common for these pins to break. The diff is still very tough so yes you'll still be able to drive it normally, although eventually it can result in a planetary gear to split down the centre

There's no point checking these after every bash because the chances are one of these pins somewhere will have become broken, but will be unnoticeable. Keep spares of these pins or fabricate some stronger ones for whenever you will do another diff rebuild

The new EXB diffs have larger pins and outdrive shafts which may help

 

[jondilly1974]

If you just want to replace the pins, buy some drill bits of the same diameter and cut them to length. Tool steel is much more durable.

 

[pomplemus]

Sounds good- yup, I have shims and 2.25 mm drill blanks on the way.

I did not realize the pins breaking and causing no issue, at least for while, was common. As long as I don't open the diffs I guess its fine!

Between the drill blank pins, shims, M2C outdrives, and some TLC looks like I'm on the right track to get the diffs as tough as possible short of an EXB. I'm throwing in a Hot Racing aluminum bulkhead for the rear as well, a bit of additional stiffness may at least help reduce the amount of grit getting in there.

I thought about the EXB diffs, but they're not really available anywhere yet AFAIK. Hopefully, by the time another diff inspection/rebuild is necessary, the complete EXB diffs will be available at Jenny's for a reasonable price, and I'll be able to drop those in with some additional tweaks.

The EXB pins appear to be 2.50 mm in diameter (same as Savage pins), about 23% more area than the regular 2.25 mm pins. Sounds like that could make a difference.

 

[jondilly1974]

Sounds good- yup, I have shims and 2.25 mm drill blanks on the way.

I did not realize the pins breaking and causing no issue, at least for while, was common. As long as I don't open the diffs I guess its fine!

Between the drill blank pins, shims, M2C outdrives, and some TLC looks like I'm on the right track to get the diffs as tough as possible short of an EXB. I'm throwing in a Hot Racing aluminum bulkhead for the rear as well, a bit of additional stiffness may at least help reduce the amount of grit getting in there.

I thought about the EXB diffs, but they're not really available anywhere yet AFAIK. Hopefully, by the time another diff inspection/rebuild is necessary, the complete EXB diffs will be available at Jenny's for a reasonable price, and I'll be able to drop those in with some additional tweaks.

The EXB pins appear to be 2.50 mm in diameter (same as Savage pins), about 23% more area than the regular 2.25 mm pins. Sounds like that could make a difference.

You can also grab some Tekjo gaskets from eBay to help seal the bottom of the diff housing against the chassis. ??

 

[pomplemus]

Right, I forgot about those! Just got a set of Tekjo gaskets on the way, and am leaving the HR aluminum bulkhead for another day if that is ever necessary.

 

[RCBro80]

For anyone having trouble finding 2.25mm drill bits, I discovered that #43 drill bits are 2.26mm and fit in both the outdrive and sun gears just fine.

 

[pomplemus]

Figured I would follow up here regarding the drill blanks and M2C hardened outdrives-

This was my first diff rebuild and shim adventure, so I took my time and played around with various combinations until I got something that felt best to me- I must have taken apart and put together the diffs about 10 times (dry).

Anyway, all of the combinations I tested in order of most to least slop:

- Stock pins and outdrives (lots of slop, about half a sun gear tooth pitch distance)
- 2.25 mm drill blanks (Mcmaster 2900A239) and stock outdrives (noticeably better but still a fair bit of slop)
- Stock pins and M2C outdrives (slightly better than the previous combination)
- 2.25 mm drill blanks and M2C outdrives (NO perceptible slop at all across the three diff sets I assembled. Feels absolutely perfect)

We have a clear winner! Its very satisfying to see how much better the drill blanks and M2C outdrives are than stock. With the drill blanks, its very close to an interference fit in the M2C outdrive holes, but still easy to assemble and take apart. Before I cut down the drill blanks, I slid the whole piece in and out of the outdrive holes a few times to knock down any tiny burrs or imperfections, which definitely helped with final installation.

At only $2 more per set than the stock units, I personally feel the M2C outdrives are money well spent to help make the diffs as solid as possible. In combination with the drill blanks and shimming, my diffs feel pretty perfect and will hopefully last longer than usual.

 

[Paul777]

@pomplemus Any update on how has this worked out in use?

 

[Dscracing1320]

I 100% recommend the m2c outdrives. But you have to make sure your droop is set properly or they will break. As for the pins I also highly recommend them. But it you do you the hardened drill blanks you have to do a heat cycle on them to bring the hardened level down or they will break almost as easy as the stock pins.

I now stand behind my "bulletproof" setup on 6s and exb diffs both using m2c cups and heat cycleed drill blanks as a must from extreme sends.

 

[Paul777]

But it you do you the hardened drill blanks you have to do a heat cycle on them to bring the hardened level down or they will break almost as easy as the stock pins.

When you say a heat cycle - how hot do you get them and how do you cool them?

 

[Dscracing1320]

When you say a heat cycle - how hot do you get them and how do you cool them?

Turn them red then let them air cool