Outcast Help me bulletproof my diffs

[ross_jsy]

Hi guys

Another half a battery pack in, another sheered diff pin I've thrown in the towel on the standard BLX diffs. Only been sticking with them because I have such a parts graveyard, but the 4985 is just shredding them.

So what do I need to build decent EXB diffs? Going to order a pair of diffs from a kit breaker and the shims to convert them to open. Is there any additional shimming they would benefit from or any other while I am there upgrades you would do?

Cheers!

 

[Greengaunja]

Hi guys

Another half a battery pack in, another sheered diff pin I've thrown in the towel on the standard BLX diffs. Only been sticking with them because I have such a parts graveyard, but the 4985 is just shredding them.

So what do I need to build decent EXB diffs? Going to order a pair of diffs from a kit breaker and the shims to convert them to open. Is there any additional shimming they would benefit from or any other while I am there upgrades you would do?

Cheers!

Youtube and the bulletproofing thread here that a quick search brings up.

 

[RCbuzz]

There are a few posts on the forum about this. One in particular caught my eye saying the stock pins are weaker and slightly thinner than they should be.

This was a recommended fix (for BLX the 2.25mm): https://www.aliexpress.us/item/2255800798163755.html

I have not tried them yet but plan to.

If you want to go EXB there really isn't much to it. I believe the gear ratio is the same so if you grab a take off (the entire unit with diff, diff input, and case) you should just be able to swap and play. Note, the BLX and EXB diff's and Inputs are different enough that they really don't mix.

 

[djrahbee]

Zero issues with my 6s exb diffs and the arrma shim kits

 

[HZRDOS]

My way of doing a bullet proof EXB diff

Thread 'Building a stronger 29mm diff' https://www.arrmaforum.com/threads/building-a-stronger-29mm-diff.43971/

 

[pomplemus]

^ I can vouch for excellent results with the open setup with fully supported output gears in that thread!

I recently upgraded to a Castle MMX8S and 1717 motor, shredded 3 sets of V4/RTR crown gears within the first three packs, and that was shimmed with aluminum bulkheads, but not diff covers.

I went all out for bulletproofing the diffs, going for EXB diffs, open front and rear, with the fully supported output gears. I also upgraded to aluminum diff covers to match the bulkheads, and really took my time shimming.

Results have been perfect, I must have have put over 30 packs through them so far, with some very full bash days and huge jumps with I'm sure some partial on throttle landings. They look immaculate, not a single chipped tooth every time I look in there when I'm doing other maintenance!

I used a TRB RC shim kit to make up the space behind the output gears in the diff. With hot racing bulkheads and diff covers, I ended up putting three 0.2 mm shims on the crown gear side in front, and two shims in rear. Both front and rear have two 0.2 mm shims behind the input gear, but of course your mileage may vary. I also added a shim or two under each pin on the output cups.

Take your time shimming and play around with different setups. A set of calipers comes in really handy.

I'm really happy I finally got my diffs being a pretty close to bulletproof setup!

 

[djsarma]

To really bulletproof the diffs ive found for my use cases i needed to remove all slop inside the bulkhead and minimize gear backlash. I use aluminum bulkheads and diff cases in all my EXB trucks to lock everything in and remove flex or stretching due to plastic. My outcast exb probably has over 150 standing backflips running a max 6 and 4092, multiple on power landings, self righting etc and the diffs are still ok. My Kraton EXB runs a 4985 and mmx8s with similar abuse too. Only failure has been the original 2.5mm pin for the outdrive cup which snapped, replaced with a 2.55mm tool steel blank from mcmaster cut to spec.

Inside the bulkhead i shim the diff assembly for 0 side to side axial play using an assortment of 13x16 shims in thickness of 0.1mm, 0.15mm, and 0.2mm to really fine tune. I usually like this to be slightly tight as it will break in. This prevents the assembly from moving into or away from the pinion and changing mesh. An additional benefit of this is it'll prevent the diff case from opening due to the screws loosening up over time. Having an aluminum bulkhead will eliminate any stretching or flex the stock one has but you may be fine with plastic depending on your use case. Behind the pinion i found the the stock 0.2mm arrma shim to be enough.

Now for the ring and pinion mesh try to minimize backlash using the 13x16 shims mentioned above as much as you can without binding during a full rotation. I always place and tighten the bulkhead cover for each trial as it will affect the mesh. It'll take a few trial and error assemblies until you find the perfect shim combo. If there is slight tightness at 1 spot in the rotation its probably due to manufacturing tolerances & parts not being 100% straight and true, for me these broke in fairly quickly so it should be ok.

Moving on to shimming internally in the diff case. You mentioned you're interested in EXB diffs but ill quickly say that for regular RTR diffs there is a mugen shim kit (MUGE0206) which is perfect and all youll need. EXB diffs are more complicated to shim due to the LSD plates. Converting EXB diffs to open using the optional arrma shims is not ideal because the replacement shim will not key into the back of the sun gear and support the outdrive pin load. Many have snapped the sun gear once converting to open. The original circular LSD plate keys into the sun gear, you can fit 2 of these on the back for extra support and then either complete it with a squared LSD plate or shims that sum up to the thickness of 1 LSD plate. Theres a image below so you can see what im talking about. Finally for EXB diffs i highly recommend a metal case with lots of Loctite applied on the screws. EXB diffs run hot due to the LSD friction which can melt the stock plastic case, and then big power systems loosen/pull the clamping screws out the plastic threads because they are a flat head type.

This is a basic overview of what i did, let me know if you need more detail as there's too much to include in 1 post lol.

Edit - just saw HAZRDOS's thread which perfectly illustrates what i mentioned above in detail

 

[ross_jsy]

My way of doing a bullet proof EXB diff

Thread 'Building a stronger 29mm diff' https://www.arrmaforum.com/threads/building-a-stronger-29mm-diff.43971/

You legend, this is exactly the sort of thing I was looking for. Time to order some bits

^ I can vouch for excellent results with the open setup with fully supported output gears in that thread!

I recently upgraded to a Castle MMX8S and 1717 motor, shredded 3 sets of V4/RTR crown gears within the first three packs, and that was shimmed with aluminum bulkheads, but not diff covers.

I went all out for bulletproofing the diffs, going for EXB diffs, open front and rear, with the fully supported output gears. I also upgraded to aluminum diff covers to match the bulkheads, and really took my time shimming.

Results have been perfect, I must have have put over 30 packs through them so far, with some very full bash days and huge jumps with I'm sure some partial on throttle landings. They look immaculate, not a single chipped tooth every time I look in there when I'm doing other maintenance!

I used a TRB RC shim kit to make up the space behind the output gears in the diff. With hot racing bulkheads and diff covers, I ended up putting three 0.2 mm shims on the crown gear side in front, and two shims in rear. Both front and rear have two 0.2 mm shims behind the input gear, but of course your mileage may vary. I also added a shim or two under each pin on the output cups.

Take your time shimming and play around with different setups. A set of calipers comes in really handy.

I'm really happy I finally got my diffs being a pretty close to bulletproof setup!

That's what I want to hear. I am pretty good at building an EXB diff now and already have Scorched bulkheads so it is time to just bite the bullet.

To really bulletproof the diffs ive found for my use cases i needed to remove all slop inside the bulkhead and minimize gear backlash. I use aluminum bulkheads and diff cases in all my EXB trucks to lock everything in and remove flex or stretching due to plastic. My outcast exb probably has over 150 standing backflips running a max 6 and 4092, multiple on power landings, self righting etc and the diffs are still ok. My Kraton EXB runs a 4985 and mmx8s with similar abuse too. Only failure has been the original 2.5mm pin for the outdrive cup which snapped, replaced with a 2.55mm tool steel blank from mcmaster cut to spec.

Inside the bulkhead i shim the diff assembly for 0 side to side axial play using an assortment of 13x16 shims in thickness of 0.1mm, 0.15mm, and 0.2mm to really fine tune. I usually like this to be slightly tight as it will break in. This prevents the assembly from moving into or away from the pinion and changing mesh. An additional benefit of this is it'll prevent the diff case from opening due to the screws loosening up over time. Having an aluminum bulkhead will eliminate any stretching or flex the stock one has but you may be fine with plastic depending on your use case. Behind the pinion i found the the stock 0.2mm arrma shim to be enough.

Now for the ring and pinion mesh try to minimize backlash using the 13x16 shims mentioned above as much as you can without binding during a full rotation. I always place and tighten the bulkhead cover for each trial as it will affect the mesh. It'll take a few trial and error assemblies until you find the perfect shim combo. If there is slight tightness at 1 spot in the rotation its probably due to manufacturing tolerances & parts not being 100% straight and true, for me these broke in fairly quickly so it should be ok.

Moving on to shimming internally in the diff case. You mentioned you're interested in EXB diffs but ill quickly say that for regular RTR diffs there is a mugen shim kit (MUGE0206) which is perfect and all youll need. EXB diffs are more complicated to shim due to the LSD plates. Converting EXB diffs to open using the optional arrma shims is not ideal because the replacement shim will not key into the back of the sun gear and support the outdrive pin load. Many have snapped the sun gear once converting to open. The original circular LSD plate keys into the sun gear, you can fit 2 of these on the back for extra support and then either complete it with a squared LSD plate or shims that sum up to the thickness of 1 LSD plate. Theres a image below so you can see what im talking about. Finally for EXB diffs i highly recommend a metal case with lots of Loctite applied on the screws. EXB diffs run hot due to the LSD friction which can melt the stock plastic case, and then big power systems loosen/pull the clamping screws out the plastic threads because they are a flat head type.

This is a basic overview of what i did, let me know if you need more detail as there's too much to include in 1 post lol.

Edit - just saw HAZRDOS's thread which perfectly illustrates what i mentioned above in detail

View attachment 303096

I've gone as far as I can go with the stock RTR diffs. Whilst I don't have the Mugen kit, I have amassed all the shims to fully shim a diff (input gear, main gear, plus internals) and got pretty good at building them. But no matter how good you shim a diff, it won't prevent the planetary gear from chipping, the pin from sheering or the output drive from splitting, which are the three things that have cut my last 3 bashes short with the Outcast, and one of the three will be the reason for this failure.

Guys thank you all for your input, I'm going to get some shims and diffs ordered up and hope for the best

 

[pomplemus]

Cool, glad to help! Credit to @HZRDOS for developing/posting the method, has saved me much frustration.