Senton Center diff breaking / running hot

Zer0Fame

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Hi all,

First I want to say a huge hello, as this is my first post here.
I registered because I'm quite frustrated right now and could need some help :/

I'm having huge problems with my Senton since 2 days ago ... before that everything was more than smooth, best RC I ever had.

I've got the Senton since beginning of November and put well over 10 charges on it.
After 2 charges I swapped the center diff oil for 100k, front for 20k and rear for 15k.
Up until 2 days ago, it was nothing but a blast to drive, then the problems started.

The car suddenly didn't brake correctly anymore and lost acceleration, with the center diff screaming.
We opened the diff and saw a lot of wear (the clear oil was dark grey and metallic). We completely cleaned it and it worked again for 10 minutes, then same problems.
We swapped out all gears, filled with oil and went to drive again. After 10 minutes, same problems.
I ordered new gears again and we installed them today ... this time we put 20k oil in, which is a lot closer to factory default. We also did a maintenance on front and rear diff (oil also grey, but a lot brighter grey, means a lot less wear ... also after 10 charges, not after 1), checked all bearings (all still fine), greased all parts as necessary.
After 10 minutes, same problem ... cleaning diff again, driving, problems, rinse and repeat.
All worked well the first 10 or so charges, now we can't finish 1 battery charge without the center diff breaking. No changes to the car except for diff oil...
Diff seems to run pretty hot, temps are between 140-180F/60-85°C ... kind of makes me think the diff is getting too much load, but why? And why after 10 or more charges and not from day 1, as nothing changed?
All diffs seem to be smooth, all bearings are working, everything seems perfect when starting the drive, problems occur after about 10 minutes.

List of what we've done so far:
- Swapped gears in center diff twice
- Disassembled, cleaned, maintained whole drivetrain from rear to front differentrial
- Rebuild front and rear diff
- Greased where necessary
- Checked all bearings
- Different tires
- Checked pinion-to-spur position/mesh

We're all out of ideas :(

I ask for help as driving the Senton is more of a frustration than fun right now, as I have to expect braking (and breaking) issues every second ... also spending more time in the workshop than on the road.
 

Afro Samurai

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Hi all,

First I want to say a huge hello, as this is my first post here.
I registered because I'm quite frustrated right now and could need some help :/

I'm having huge problems with my Senton since 2 days ago ... before that everything was more than smooth, best RC I ever had.

I've got the Senton since beginning of November and put well over 10 charges on it.
After 2 charges I swapped the center diff oil for 100k, front for 20k and rear for 15k.
Up until 2 days ago, it was nothing but a blast to drive, then the problems started.

The car suddenly didn't brake correctly anymore and lost acceleration, with the center diff screaming.
We opened the diff and saw a lot of wear (the clear oil was dark grey and metallic). We completely cleaned it and it worked again for 10 minutes, then same problems.
We swapped out all gears, filled with oil and went to drive again. After 10 minutes, same problems.
I ordered new gears again and we installed them today ... this time we put 20k oil in, which is a lot closer to factory default. We also did a maintenance on front and rear diff (oil also grey, but a lot brighter grey, means a lot less wear ... also after 10 charges, not after 1), checked all bearings (all still fine), greased all parts as necessary.
After 10 minutes, same problem ... cleaning diff again, driving, problems, rinse and repeat.
All worked well the first 10 or so charges, now we can't finish 1 battery charge without the center diff breaking. No changes to the car except for diff oil...
Diff seems to run pretty hot, temps are between 140-180F/60-85°C ... kind of makes me think the diff is getting too much load, but why? And why after 10 or more charges and not from day 1, as nothing changed?
All diffs seem to be smooth, all bearings are working, everything seems perfect when starting the drive, problems occur after about 10 minutes.

List of what we've done so far:
- Swapped gears in center diff twice
- Disassembled, cleaned, maintained whole drivetrain from rear to front differentrial
- Rebuild front and rear diff
- Greased where necessary
- Checked all bearings
- Different tires
- Checked pinion-to-spur position/mesh

We're all out of ideas :(

I ask for help as driving the Senton is more of a frustration than fun right now, as I have to expect braking (and breaking) issues every second ... also spending more time in the workshop than on the road.

wow...few things...you got any pics?..I was going to say shimming but looks like you checked the clearances already...looks like you did everything....shimming on the internal spider gears?...

just to be thorough. ..you checked all the bearings...and you notice it after ten mins of running...and that's good info..all the air out of the diffs?..I am just reaching cause thus is really strange...

you are obviously well familiar with the diffs by now...have you tried any of the "bullet proofing" mods done by Tp-Parts Rc-Xtreme that he shows on his youtube channel?..
 

Zer0Fame

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Pictures unfortunately no...

Shimming on the planetary gears yes (tried with and without shims), on the spiders just the shims that come with it.
Am I supposed to get all air out of the diffs? I usually go for 1mm higher than the cross for the spiders...wouldn't completely filling them add even more pressure? (Just as a side note, I varied the level of oil, too ... from half full to almost full ... on almost full I had the oil pushing out from the diff after 10 minutes)
I'll have a look at the TP-Parts video ... the strange part is, that it worked for more than 10 charges and suddenly I'm having problems on every charge ... so I guessed if it worked for that long before it should also work now if everything is exactly the same? :/
 

Afro Samurai

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Pictures unfortunately no...

Shimming on the planetary gears yes (tried with and without shims), on the spiders just the shims that come with it.
Am I supposed to get all air out of the diffs? I usually go for 1mm higher than the cross for the spiders...wouldn't completely filling them add even more pressure? (Just as a side note, I varied the level of oil, too ... from half full to almost full ... on almost full I had the oil pushing out from the diff after 10 minutes)
I'll have a look at the TP-Parts video ... the strange part is, that it worked for more than 10 charges and suddenly I'm having problems on every charge ... so I guessed if it worked for that long before it should also work now if everything is exactly the same? :/

wow..yeah man...something is up and you hit it with all you got...wonder if arrma would send you a new center diff assembly..meaning is the something out of alignment. ..or out of specs with that diff or somehow something got out of spec...maybe a new center diff housing all together will get you closer since you already replaced all the guts...so is the problem on the outside somehow...hmmm...really strange...
 

Zer0Fame

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Tried the housing already, I took the housing from the front diff and used it for the center diff ... the only thing I didn't replace yet is the spur.
I assume something puts too much load on the diff and I have no idea what. I assumed some binding in the drivetrain, but every part I checked moves freely...
I would buy a new center diff if I would know that would fix the problem, but those are 65$ here ... I've already had 25$ go down the drain for the gears and now I'm nothing but frustrated :(
 

Afro Samurai

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Tried the housing already, I took the housing from the front diff and used it for the center diff ... the only thing I didn't replace yet is the spur.
I assume something puts too much load on the diff and I have no idea what. I assumed some binding in the drivetrain, but every part I checked moves freely...
I would buy a new center diff if I would know that would fix the problem, but those are 65$ here ... I've already had 25$ go down the drain for the gears and now I'm nothing but frustrated :(

well don't give up yet..cause the fun will soon make up for all this work...

I will keep thinking on this. ..but yeah...try the pinion..cause ..why not....
 

Zer0Fame

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Thanks alot for all your help man, I really appreciate it!
 

mrfurious40k

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Have you had any crashes? I'm wondering if you're looking at the inside of the diff and thinking something is wrong when it's actually being damaged because there's some outside force acting on it.

Check your chassis plate for trueness as the first step in the detective work.
 

Afro Samurai

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Have you had any crashes? I'm wondering if you're looking at the inside of the diff and thinking something is wrong when it's actually being damaged because there's some outside force acting on it.

Check your chassis plate for trueness as the first step in the detective work.
good point..something is wrong for sure...so you may be thinking the driveshafts are binding up possibly?..but ten mins then starts acting up...strange...maybe the diff oil just isn't up to par. ..maybe needs a different brand...not sure if maybe the diff oil he's using just isn't high enough quality. ..and breaking down early...just another guess...
 

mrfurious40k

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good point..something is wrong for sure...so you may be thinking the driveshafts are binding up possibly?..but ten mins then starts acting up...strange...maybe the diff oil just isn't up to par. ..maybe needs a different brand...not sure if maybe the diff oil he's using just isn't high enough quality. ..and breaking down early...just another guess...
I'm thinking something is binding and it's taking 10 minutes for it to heat up/grind up the parts to the point it fails. The powerplants in these rigs have so much power that they can overcome a lot of drive line drag without you even noticing until something goes boom. If he replaced all of the innards, something on the outside has got to be making it fail.
 

Zer0Fame

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I'm thinking something on the outside, too, as everything but the spur was swapped...spur looks good, no wear.
The diffoil I used is from Tamiya (also had this in when it worked for 10 charges, i think that means we can rule that out?)
No big crashes and the chassis plate looks good.
I went through all gears in the drivetrain and they look fine.

Is it possible that something minor, something that is hardly visible, can cause enough binding so the center diff heats up?
Or maybe something that binds only in special situations like cornering or full throttle?
Maybe I should look for binding in special situations like simulating the respective suspension situations and checking for bind with the motor deinstalled? (Like lifting the front and pushing the rear down to see if it binds then)
 

Afro Samurai

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I'm thinking something on the outside, too, as everything but the spur was swapped...spur looks good, no wear.
The diffoil I used is from Tamiya (also had this in when it worked for 10 charges, i think that means we can rule that out?)
No big crashes and the chassis plate looks good.
I went through all gears in the drivetrain and they look fine.

Is it possible that something minor, something that is hardly visible, can cause enough binding so the center diff heats up?
Or maybe something that binds only in special situations like cornering or full throttle?
Maybe I should look for binding in special situations like simulating the respective suspension situations and checking for bind with the motor deinstalled? (Like lifting the front and pushing the rear down to see if it binds then)

suspension binding...anything is possible...Why not...try it all...cause this is extremely interesting. ..and an important issue to resolve...
 

Zer0Fame

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Okay, so we experimented a bit and the front seems a bit tougher to turn than the rear... pretty minimal, but you can feel it.

Since it is very minimal, is it possible that this is causing the problem? Nothing grinding or something...but a bit tougher to move ... imagine it like the rear having a thin grease between differential and dogbone from the driveshaft and the front having a thick grease between differential and dogbone ... don't know the english word ... I mean the gear which connects the differential to the center driveshaft.

Another problem found:

One of the diffs is more difficult to install than the other diff... it's not the diff housing, but the diff itself ....I think I won't get around ordering new diffs.
I think that is the problem why the front is harder to turn.
However I don't know if that caused the center diff problem or if the center diff problem caused this.
I actually have to push the diff in ... while the other just needs a gentle nudge.
 
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Afro Samurai

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Okay, so we experimented a bit and the front seems a bit tougher to turn than the rear... pretty minimal, but you can feel it.

Since it is very minimal, is it possible that this is causing the problem? Nothing grinding or something...but a bit tougher to move ... imagine it like the rear having a thin grease between differential and dogbone from the driveshaft and the front having a thick grease between differential and dogbone ... don't know the english word ... I mean the gear which connects the differential to the center driveshaft.
ring gear ...big gear on outside of diff...spider gears on inside of diff some times called sun and planetary gear sets..pinion connects to ring gear...but terminology varies with age of the person speaking...

hmmm this is so very strange ..and sad that we are having trouble figuring it out. ...
dogbones allow for quite some degree of misalignment and if you were beyond that limit it would be easy to see...you got new gear sets..fresh diff oil...but still screws up after 10 mins...you got everything meshed and shimmed properly...you are simply feeling a little more drag...

one thing to check is the health of the bearings...meaning is that where the drag is coming from...I just recently melted the center hexes on my wheels on the nero twice...before I tracked back the problem to a bearing overheating...it was packed up...another reason to stay out of fine clay and to get sealed bearings...but even so I can imagine that any bearing can get packed up eventually...sooo..check all your bearings...which you have done..but just once more for sanity and make sure that they are seated and not cocked or anything...especially in locations where you are noticing more drag...but man...congrats. ..this is really a tough one...

I will keep thinking. ..we will get it fixed eventually. ..the answer may be "42"
 
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Zer0Fame

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one of the bearings creates little, very little drag.

Did you see my newest edit? The diff being difficult to install?
 

Afro Samurai

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one of the bearings creates little, very little drag.

Did you see my newest edit? The diff being difficult to install?
I spend so much time correcting my stupid posts cause my phones dumb autocorrect...but anyway...

wow..ok...now we are getting somewhere...how are the bearing saddles?..I wonder if there is an alignment problem there. ...I could see that causing some problems...

so difficult to install meaning...to get it into the diff housing where it is installed in the upper and lower housing...I am wondering if the bearing supports...the saddles on either side ...if they are out of alignment some how ..then as you tighten everything up ...things get worse....and get even worse as things heat up...you can get a bearing hot enough to eventually eat up all is internal clearance. ..making it a real power sapper...to the point it can lock on the shaft or in the housing...but just a thought...did you replace the diff mount housing already? pn ar310427?
 
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Zer0Fame

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That one isn't the problem, the problem is definitely the diff itself.

If I install the front diff in the front housing or the front diff in the rear housing I need to push pretty hard. After installing the diff doesn't spin very well.
If I install the rear diff in the front housing or the rear diff in the rear housing I just need a gentle nudge. After installing the diff spins freely.
It is not really "feelable" when the diff is installed and you spin the axles... but if you spin the diff itself inside the housing it is VERY feelable.

We also just swapped the bearings from rear to front, same problem, so it is definitely the diff itself, most likely the ring gear (thanks for that :) ). As said I don't know if this really is the cause or if the broken center diff caused this. But there is a very high possibility that this is causing the problems with the center diff, as the rear diff spins alot more freely than the front diff.
 

Afro Samurai

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That one isn't the problem, the problem is definitely the diff itself.

If I install the front diff in the front housing or the front diff in the rear housing I need to push pretty hard. After installing the diff doesn't spin very well.
If I install the rear diff in the front housing or the rear diff in the rear housing I just need a gentle nudge. After installing the diff spins freely.
It is not really "feelable" when the diff is installed and you spin the axles... but if you spin the diff itself inside the housing it is VERY feelable.

We also just swapped the bearings from rear to front, same problem, so it is definitely the diff itself, most likely the ring gear (thanks for that :) ). As said I don't know if this really is the cause or if the broken center diff caused this. But there is a very high possibility that this is causing the problems with the center diff, as the rear diff spins alot more freely than the front diff.

ok..I thought you were saying the front diff was hard to install. ..but I wonder if it's the same problem for the center diff...the mounts being off a bit or not aligned...or the mount holes in the chassis plate bing off a bit...causing the same effect..some bearing misalignment enough to the point of causing it to over heat...are you seeing any discoloration in the bearings?..yellowing?..turning blue?...
 

Zer0Fame

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Small update:
Spare parts will arrive either tomorrow or Friday ... I'll probably install them on Monday or Tuesday.

I ordered the following:

1x Diff
1x Center Diff
2x Diff housing
1x Plastic center diff mount (the one opposite to the red motor mount) as a set with the center diff cover
1x Shims for planetary gears (like recommended in the bulletproof video)
1x Shims for the spiders (like recommended in the bulletproof video)
New high temp diff oil (60k front, 200k center, 30k rear)
Fully sealed bearing set

I'm pretty sure it's the front diff causing the problems, some misalignment as Afro Samurai stated ... but I'm also pretty sure the center diff is killed due to this ... and the rest was rather cheap to buy.
I'm very positive that the issues will be fixed after the swaps.
 
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Afro Samurai

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Small update:
Spare parts will arrive either tomorrow or Friday ... I'll probably install them on Monday or Tuesday.

I ordered the following:

1x Diff
1x Center Diff
2x Diff housing
1x Plastic center diff mount (the one opposite to the red motor mount) as a set with the center diff cover
1x Shims for planetary gears (like recommended in the bulletproof video)
1x Shims for the spiders (like recommended in the bulletproof video)
New high temp diff oil (60k front, 200k center, 30k rear)
Fully sealed bearing set

I'm pretty sure it's the front diff causing the problems, some misalignment as Afro Samurai stated ... but I'm also pretty sure the center diff is killed due to this ... and the rest was rather cheap.
I'm very positive that the issues will be fixed after the swaps.

keep moving forward. ..
 

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