X-Maxx Centre Differential critical design flaw... Possible solutions?

[Zash]

Preface: Engineer here. The following post is my humble opinions...

 

The centre differential has an aluminium housing which relies on sliding parts to work.

Inside the housing, the sun gears revolve freely against the aluminium housing, with a Stainless Steel washer in between.

In a traditional differential, the sun gear is lubricated by oil in the differential, however in the X-Maxx, there i no lubricant - only a 20 million weight putty.

 

1. The putty gums up the washer, causing it to bind against the sun gear.

2. The bound up stainless steel washer rubs against the small surface area of the aluminium housing, without lubrication, and wears it out. This in turn pushes the sun gears outwards, causing the teeth to lose full mesh, and strip.

 

In the end:

a. The aluminium housing is destroyed due to lubrication-less abrasion.

b. The silicone seal is destroyed due to abrasion (Silicone has very low abrasion resistance)

c. The Front Sun Gear is destroyed due to lack of mesh after the aluminium housing had become worn.

d. The aluminium filings get into the 20M putty and changes its characteristics.

All 4 items will need replaced often. Simply, the X-Maxx Centre Differential is poorly designed, and not fit for purpose.

Worst is the fact that the Centre Differential is the most difficult and awkward part to get at, requiring significant disassembly of the X-Maxx.

======================

Mitigating the issue:

 

20M weight putty is NOT a lubricant. From factory, the **Centre Differential is assembled without any lubrication***.

 

1. Dismantle the centre diff and clean all parts.

2. Lubricate the sliding areas with thin silicone lubricant: Traxxas 10k weight is decent. Shock oil is also a good alternative. Any lubricant is better than no lubricant.

Lubricate between:

 

a. Aluminium housing

b. Silicone seals - Silicone rubbing against a steel washer without lubrication is another huge oversight by Traxxas

c. Sun gear rear

d. *washer* - read on

e. Lubricate the reverse side of the spider gears.

 

The stainless steel washer is stronger, however the Teflon ('plastic' washers used in front and rear diffs) is one of the most frictionless materials known to man.

The down side is that Teflon is weaker than Stainless Steel.

 

So the choice:
1. Use steel washer and wear the Aluminium housing. (New housing = >$20)
2. Use Teflon washer and wear the Teflon instead. (New Teflon Washers = few cents)

 

I shall use Teflon washers on this build, and see how long they last. I do not have the forces data, so it will be all about intelligent guess-work. It may well be that the Teflon is not strong enough, and we shall have to go back to the Stainless washers - albeit with lubrication this time round.

 

Any more suggestions? Insights welcome 🙂

 

 

 

Edited August 12, 2021 by Zash

[mydoddy69]

1 hour ago, Zash said:

Preface: Engineer here. The following post is my humble opinions...

 

The centre differential has an aluminium housing which relies on sliding parts to work.

Inside the housing, the sun gears revolve freely against the aluminium housing, with a Stainless Steel washer in between.

In a traditional differential, the sun gear is lubricated by oil in the differential, however in the X-Maxx, there i no lubricant - only a 20 million weight putty.

 

1. The putty gums up the washer, causing it to bind against the sun gear.

2. The bound up stainless steel washer rubs against the small surface area of the aluminium housing, without lubrication, and wears it out. This in turn pushes the sun gears outwards, causing the teeth to lose full mesh, and strip.

 

In the end:

a. The aluminium housing is destroyed due to lubrication-less abrasion.

b. The silicone seal is destroyed due to abrasion (Silicone has very low abrasion resistance)

c. The Front Sun Gear is destroyed due to lack of mesh after the aluminium housing had become worn.

d. The aluminium filings get into the 20M putty and changes its characteristics.

All 4 items will need replaced often. Simply, the X-Maxx Centre Differential is poorly designed, and not fit for purpose.

Worst is the fact that the Centre Differential is the most difficult and awkward part to get at, requiring significant disassembly of the X-Maxx.

======================

Mitigating the issue:

 

20M weight putty is NOT a lubricant. From factory, the **Centre Differential is assembled without any lubrication***.

 

1. Dismantle the centre diff and clean all parts.

2. Lubricate the sliding areas with thin silicone lubricant: Traxxas 10k weight is decent. Shock oil is also a good alternative. Any lubricant is better than no lubricant.

Lubricate between:

 

a. Aluminium housing

b. Silicone seals - Silicone rubbing against a steel washer without lubrication is another huge oversight by Traxxas

c. Sun gear rear

d. *washer* - read on

e. Lubricate the reverse side of the spider gears.

 

The stainless steel washer is stronger, however the Teflon ('plastic' washers used in front and rear diffs) is one of the most frictionless materials known to man.

The down side is that Teflon is weaker than Stainless Steel.

 

So the choice:
1. Use steel washer and wear the Aluminium housing. (New housing = >$20)
2. Use Teflon washer and wear the Teflon instead. (New Teflon Washers = few cents)

 

I shall use Teflon washers on this build, and see how long they last. I do not have the forces data, so it will be all about intelligent guess-work. It may well be that the Teflon is not strong enough, and we shall have to go back to the Stainless washers - albeit with lubrication this time round.

 

Any more suggestions? Insights welcome 🙂

 

 

 

 Been using mine for over 2 years now ! Just cracked it all open for a full strip clean and re lube and the centre diff is fine and I added a silicone earplug as well a couple of years back !  So I’d say if it lasts over 2 years without the need of replacement there’s NO critical flaw at all. Maybe it’s just you over engineering it in your head 😂

[lorrylemming]

 

 

Have a look at this video. Use green slime or shock sealant for the outdrive orings, high pressure grease for the outdrive axles and the back of the sun gears, then use silicone oil for diff tuning. 

 

 

 

[Kpowell911]

Ive got/had five X-Maxx’s, never even looked in the centre diff, theyve all been fine?

[Zash]

Cheers for the replies chaps.

 

I'll take and share pics of what I found in mine - it's already disassembled, so it might be tricky. The thing was in such tatters that I just bought a brand-new centre diff assembly. New parts arrive tomorrow.

 

@mydoddy69, Glad to hear it's not a short term issue. However, I bet you didn't have a chance to inspect deep inside the housing where the Sun gear rubs, to inspect for wear. Was there any lubrication in there?

 

Regardless, when you earplug it, the earplug silicone is much thicker than the 20 million weight silicone from the factory - you effectively lock it so it doesn’t move unless it absolutely needs to. If there is no movement then there wouldn't be any wear.

 

@lorrylemming, Unfortunately the sun gear compresses against the silicone seals, so grease cannot be used. I'll be using silicone lubricant as that is silicone seal safe. I'm not sure how long it will last however - grease better tends to stick to metal.

 

@Kpowell911, Glad you haven't noticed much deterioration. Maybe it's a traxxas quality control issue. Certainly there were many a person complaining about the centre diff not being adequately filled with putty from the factory, whereas other people found it aptly filled. I hope it's just a quality control issue not affecting most parts, however, after opening a couple of aluminium diffs in the X-Maxx (I have replaced all diffs with aluminium ones), I can say that none of them had any lubrication on any of the sun-gear/housing sliding parts, which is a huge no-no.

 

 

 

[Juanmacine]

20 hours ago, Zash said:

Cheers for the replies chaps.

 

I'll take and share pics of what I found in mine - it's already disassembled, so it might be tricky. The thing was in such tatters that I just bought a brand-new centre diff assembly. New parts arrive tomorrow.

 

@mydoddy69, Glad to hear it's not a short term issue. However, I bet you didn't have a chance to inspect deep inside the housing where the Sun gear rubs, to inspect for wear. Was there any lubrication in there?

 

Regardless, when you earplug it, the earplug silicone is much thicker than the 20 million weight silicone from the factory - you effectively lock it so it doesn’t move unless it absolutely needs to. If there is no movement then there wouldn't be any wear.

 

@lorrylemming, Unfortunately the sun gear compresses against the silicone seals, so grease cannot be used. I'll be using silicone lubricant as that is silicone seal safe. I'm not sure how long it will last however - grease better tends to stick to metal.

 

@Kpowell911, Glad you haven't noticed much deterioration. Maybe it's a traxxas quality control issue. Certainly there were many a person complaining about the centre diff not being adequately filled with putty from the factory, whereas other people found it aptly filled. I hope it's just a quality control issue not affecting most parts, however, after opening a couple of aluminium diffs in the X-Maxx (I have replaced all diffs with aluminium ones), I can say that none of them had any lubrication on any of the sun-gear/housing sliding parts, which is a huge no-no.

 

 

 

I'm with you, always check the diffs on all of my rigs before run, the stocks lubricants are awfull.

[Zash]

Ahoy chaps!

 

I have taken some photos of the old diff and the new one.

 

===============

1. Old diff: The outer ring shows wear as a deeply scratched surface. I used vernier calipers to measure how much Aluminium had been destroyed - 0.4mm. For comparison, the diff washers are 0.5mm thick.

 

Note the amount of putty - there is hardly any - this was all that was inside. The aluminium shavings have mixed with the putty, turning it a sticky grey.

 

The destroyed silicone seal, and the scratched stainless washer, which was rubbing against the bare aluminium without lubrication:

 

The no-lube sun gear with destroyed teeth.

 

===============

 

2. The brand new, never been turned differential: The factory 20M weight putty is, at best, half filling the differential. With this little putty applied, what will almost immediately happen is that the vast majority will clear to the middle and sides of the spider gears, becoming useless, as most of it will never then come into contact with the teeth.

 

This picture shows a scratch free housing and the reverse of the sun gear. There is  no lubrication here except a bit of putty. Because of its extreme viscosity, it will quickly seep out from the sides leaving virtually nothing between the washer and the bare aluminium.

 

New sun gear from the new differential, showing no lubrication from factory.

 

I rebuilt the differential today, using a combination of the original 20M weight putty, silicone ear plugs, and 10k weight silicone:

 

a. Lube the aluminium housing in all its bare contact sections with 10k weight silicone, including spider gear brackets.

 

b. Lube and insert the silicone seal

 

c. Replace the Stainless steel washer with the Teflon washer on the Aluminium Housing side.

 

d. Lube reverse of both sun gears and between their washers.

 

e. Lube the internals of the Diff Ring gear - no lube was present.

 

f. Re-assemble the differential, filling all gaps with Silicone Ear Plugs, removing any excess.

 

===============

 

Notes:

i. The different viscosities will eventually mix to some degree but this ought to provide significantly better resilience against abrasion breakdown compared to the factory Differential.

 

ii. The ear plugs will make the differential stiffer, which will mean less movement. This will in turn intrinsically mean less wear.

 

iii. Aluminium is like the putty of metals - it is soft. It can't even be filed or ground well without it sticking into the grinding stone/file. Having a stainless steel washer rubbing up against it constantly, under pressure, without lubrication, is insanity. Replacing Stainless steel with Teflon - I would rather the Teflon wears against the aluminium housing, rather than the Aluminium housing wears against the stainless steel washer.

 

iv. On the  ring gear side, the ring and the sun gears are hardened so will not wear against the Stainless Steel washer - we can leave that as-is.

 

 

===============

All-in-all, these simple mods ought to vastly increase the lifespan of your X-Maxx centre differential. 

 

I took the X-Maxx out today after the rebuild. I have never seen it work so well.

 

P.S. Traxxas has censored my post on the Traxxas X-Maxx  forums, attempting to discuss this issue. ¯\_(ツ)_/¯

 

 

Edited August 13, 2021 by Zash

[Juanmacine]

15 hours ago, Zash said:

Ahoy chaps!

 

I have taken some photos of the old diff and the new one.

 

===============

1. Old diff: The outer ring shows wear as a deeply scratched surface. I used vernier calipers to measure how much Aluminium had been destroyed - 0.4mm. For comparison, the diff washers are 0.5mm thick.

 

Note the amount of putty - there is hardly any - this was all that was inside. The aluminium shavings have mixed with the putty, turning it a sticky grey.

 

The destroyed silicone seal, and the scratched stainless washer, which was rubbing against the bare aluminium without lubrication:

 

The no-lube sun gear with destroyed teeth.

 

===============

 

2. The brand new, never been turned differential: The factory 20M weight putty is, at best, half filling the differential. With this little putty applied, what will almost immediately happen is that the vast majority will clear to the middle and sides of the spider gears, becoming useless, as most of it will never then come into contact with the teeth.

 

This picture shows a scratch free housing and the reverse of the sun gear. There is  no lubrication here except a bit of putty. Because of its extreme viscosity, it will quickly seep out from the sides leaving virtually nothing between the washer and the bare aluminium.

 

New sun gear from the new differential, showing no lubrication from factory.

 

I rebuilt the differential today, using a combination of the original 20M weight putty, silicone ear plugs, and 10k weight silicone:

 

a. Lube the aluminium housing in all its bare contact sections with 10k weight silicone, including spider gear brackets.

 

b. Lube and insert the silicone seal

 

c. Replace the Stainless steel washer with the Teflon washer on the Aluminium Housing side.

 

d. Lube reverse of both sun gears and between their washers.

 

e. Lube the internals of the Diff Ring gear - no lube was present.

 

f. Re-assemble the differential, filling all gaps with Silicone Ear Plugs, removing any excess.

 

===============

 

Notes:

i. The different viscosities will eventually mix to some degree but this ought to provide significantly better resilience against abrasion breakdown compared to the factory Differential.

 

ii. The ear plugs will make the differential stiffer, which will mean less movement. This will in turn intrinsically mean less wear.

 

iii. Aluminium is like the putty of metals - it is soft. It can't even be filed or ground well without it sticking into the grinding stone/file. Having a stainless steel washer rubbing up against it constantly, under pressure, without lubrication, is insanity. Replacing Stainless steel with Teflon - I would rather the Teflon wears against the aluminium housing, rather than the Aluminium housing wears against the stainless steel washer.

 

iv. On the  ring gear side, the ring and the sun gears are hardened so will not wear against the Stainless Steel washer - we can leave that as-is.

 

 

===============

All-in-all, these simple mods ought to vastly increase the lifespan of your X-Maxx centre differential. 

 

I took the X-Maxx out today after the rebuild. I have never seen it work so well.

 

P.S. Traxxas has censored my post on the Traxxas X-Maxx  forums, attempting to discuss this issue. ¯\_(ツ)_/¯

 

 

Excellent post mate, very detailed and usefull.