Leaky differential

[PKMSM]

Drained two 6000mah on the wrong tires on pavement and has a blast the whole time:

This was my first run with the ET48, and I noticed a leak in the differential:

The black trail could be the grease on the shaft, but the diff itself is leaking as seen on the casing, the is a small amount of “wet” on top as well, under the spur gear. Is a little leak expected/normal or do I need to fix something?

 

[Billl DeLong]

not uncommon to have a small amount of residual fluid around the spur when you fasten it... after 15 battery packs, I would change the fluid and inspect to make sure it's still full, if you had a significant leak, it would be obvious with a large mess all over the place, what I see above after 2 packs is nominal.

 

[PKMSM]

not uncommon to have a small amount of residual fluid around the spur when you fasten it... after 15 battery packs, I would change the fluid and inspect to make sure it's still full, if you had a significant leak, it would be obvious with a large mess all over the place, what I see above after 2 packs is nominal.

Thanks. I did remove it and what you are saying seems to be the case. There was very little silicone oil there, and the back grease is what was slinging around.

Also thanks for the tip to change after 15 batteries. I trust this should be done on all three diffs?

 

[Billl DeLong]

Yes all 3 diffs, wipe all the bearings clean and check for crunchy bearings, fresh grease all rubber seals in diffs and shocks, etc.

15 packs is a good benchmark to inspect your cleaning interval... if the fluid is still a bright grey milky shade then you can probably go longer between rebuilds... if it's starting to turn brown then that's the limit where fluid is breaking down and no longer functioning at it's peak... if it's black then you've gone way too long between rebuilds and risk premature wear of parts.

Casual speed runs on the street can probably go longer between rebuilds... harsh driving on a dirt track with lots of sandy loam will probably need to be rebuilt sooner.

I recently did some races at tracks on the east coast where they spray calcium on the track and everyone does a rebuild after every single race day there to prevent corrosion from the calcium.

 

[PKMSM]

Yes all 3 diffs, wipe all the bearings clean and check for crunchy bearings, fresh grease all rubber seals in diffs and shocks, etc.

15 packs is a good benchmark to inspect your cleaning interval... if the fluid is still a bright grey milky shade then you can probably go longer between rebuilds... if it's starting to turn brown then that's the limit where fluid is breaking down and no longer functioning at it's peak... if it's black then you've gone way too long between rebuilds and risk premature wear of parts.

Casual speed runs on the street can probably go longer between rebuilds... harsh driving on a dirt track with lots of sandy loam will probably need to be rebuilt sooner.

I recently did some races at tracks on the east coast where they spray calcium on the track and everyone does a rebuild after every single race day there to prevent corrosion from the calcium.

Thanks for the tip. I didn’t realize these things needed fluid changes this frequently. By “rebuild” I’m assuming you mean o-rings as well?

 

[Billl DeLong]

Yes, a complete rebuild means you pull every bearing, wipe clean with a rag, roll the bearing and if it's not butter smooth, then carefully pry the rubber seals with a hobby knife being careful not to bend the seal. Flush the bearings with WD40 or an ultrasonic cleaner, then blow dry with an air compressor and pack fresh grease, snap the rubber seals back in place.

Pull all rubber seals in the diffs and shocks, inspect for tears, replace if necessary, I've never had to replace a rubber seal in any of my cars over the past 12+ years I've been racing.

Fresh fluids in diffs and shocks, inspecting all the pins in the arms and shafts... replace any worn parts, look for hairline cracks, etc.

I use furniture polish and air compressor for a final cleaning to rejuvenate all the plastic to make it look like new again.

Racers tend to take better care of their cars to ensure they don't get a DNF (Did Not Finish) due to poor maintenance.... Bashers on the other hand tend to let their cars go until something breaks, they often complain that their car doesn't drive as good as when it was new and that simple due to poor maintenance. A seized bearing can damage a lot of parts which trickle down to having to replace a damaged ESC, motor or both!

If you want to save money, do yourself a favor and put in the work on the maintenance.

Your first rebuild might take 2-4 hours, but with a cordless drill, I can do it an about an hour if have a fresh pack of bearings. I always keep a spare pack and alternate the process of cleaning my bearings after a rebuild, sometimes it takes make longer to clean the bearings than rebuilding the whole car! Many people with deep pockets will opt to replace their bearings than clean them just for convenience. I'm a cheap bastard and don't mind killing the time with a favorite TV show in the background.

Some of my tools here:

• Tools for the Pit Table

A list of my bookmarks here:
https://www.rcgroups.com/forums/showthread.php?3003342-Bill-s-Bookmarks

 

[PKMSM]

Yes, a complete rebuild means you pull every bearing, wipe clean with a rag, roll the bearing and if it's not butter smooth, then carefully pry the rubber seals with a hobby knife being careful not to bend the seal. Flush the bearings with WD40 or an ultrasonic cleaner, then blow dry with an air compressor and pack fresh grease, snap the rubber seals back in place.

Pull all rubber seals in the diffs and shocks, inspect for tears, replace if necessary, I've never had to replace a rubber seal in any of my cars over the past 12+ years I've been racing.

Fresh fluids in diffs and shocks, inspecting all the pins in the arms and shafts... replace any worn parts, look for hairline cracks, etc.

I use furniture polish and air compressor for a final cleaning to rejuvenate all the plastic to make it look like new again.

Racers tend to take better care of their cars to ensure they don't get a DNF (Did Not Finish) due to poor maintenance.... Bashers on the other hand tend to let their cars go until something breaks, they often complain that their car doesn't drive as good as when it was new and that simple due to poor maintenance. A seized bearing can damage a lot of parts which trickle down to having to replace a damaged ESC, motor or both!

If you want to save money, do yourself a favor and put in the work on the maintenance.

Your first rebuild might take 2-4 hours, but with a cordless drill, I can do it an about an hour if have a fresh pack of bearings. I always keep a spare pack and alternate the process of cleaning my bearings after a rebuild, sometimes it takes make longer to clean the bearings than rebuilding the whole car! Many people with deep pockets will opt to replace their bearings than clean them just for convenience. I'm a cheap bastard and don't mind killing the time with a favorite TV show in the background.

Some of my tools here:

• Tools for the Pit Table

A list of my bookmarks here:
https://www.rcgroups.com/forums/showthread.php?3003342-Bill-s-Bookmarks

Wow!

Had no idea of the maintenance needs lol! I both printed and saved this page with the links as I'll be referencing it, thanks for taking the time to provide all the details. Looking at your tool list, good news is that I already have the majority of them.

Speaking of bearings, I am just curious as to what a replacement set will cost. Is there a good place to buy a full set for each car/truck?

 

[Billl DeLong]

Everyone's gonna have their favorite source for bearings, but I just buy them in bulk off Amazon from any random seller. It's a little more work because you need to select all the bearing sizes yourself but like I said earlier, I'm a cheap bastard so it saves money this way.

If you like the convenience of selecting a pre-packed kit, there are tons of suppliers out there, one of my favorites is AVID and it's fairly reasonable pricing going this route:
https://www.avidrc.com/flexkit/?kit=3244&kitname=EB48+2.0

I don't believe quality is significant when it comes to steel rubber sealed bearings, I'm sure someone will claim otherwise, but I haven't found any difference between the dozen or so brands I've used over the years.

 

[Nicochau]

@Billl DeLong , there was a time when I was clearing my mind with maintenance and I was cleaning and greasing bearings with Mobil 28 aviation grease. Man, this grease is good! They would last forever!

I do that once in a while, but I get full kits from aliexpress for $14... that is like $0.5 per bearing... Not even worth the cost of the degreaser, grease and equipment I use to do it myself.

@PKMSM , don't put too much pressure on yourself. Buy a kit of bearings or two from ebay or aliexpress and keep them ready. Maintenance is what make a lot of people quit RC, you have to be smart about it and manage your appetite for it. The good thing with Tekno, is you have the right tech to manage it efficiently.

I do exactly what Billl mentioned: wait for a failure. The one thing though is to immediately stop using the truck when any issue is detected. I always have more than one truck with me, so that is not an issue. Not to mention that a two minutes inspection before and after you run your truck can save you a lot of money and effort. Hub inside bearings are visible and are the one who fail most, check them. Turn wheels to measure diff's resistance to movement (too little resistance = no more diff fluid). The center one is the most sensitive. Rear diff pinion bearings are a bitch too, but again, you can see a failure coming. If I ever open the diff case, I will do a full maintenance on it though.

One other thing you should do is to keep a maintenance log up to date. After a while, there is no way you'll remember when was stuff done on the different trucks. By doing so, I also notice that I more or less do the whole truck rebuild after 20 to 30 packs, which isn't that bad, I just never do it one shot.

One exception to the above: maintenance before track days. The other thing that makes people quit RC is the need to wrench at the track while your buddies are having fun. My race stuff get's better treatment (it is also the stuff I buy new).

 

[Billl DeLong]

+1 on the maintenance log

I actually keep a race log (using Google Sheets) with all my stats which are reset every time the track makes a new layout, then I have new PR (personal records) to beat, hot consistency, hot lap, hot qual, hot main and stack rank, plus I also track any broken parts, tuning changes as well as the maintenance where I do a rebuild after every 3 race days where I average 5 packs per race day.

 

[PKMSM]

What surprised me was the frequency of rebuilds. 15 batteries (or 20-30) doesn’t seem like a lot of run time between full rebuilds, but then again, these things are exposed to all kinds of dirt and abuse.

I had actually found the $14 kit you’re talking about while searching last night. I ordered a couple of sets to keep on hand (assuming the ET and EB48 2.0 all use the same bearings. I agree that for the price it’s not worth rebuilding them, other than maybe a therapeutic activity to tune out, or while watching TV as Bill mentioned!

I enjoy building things. Years ago I was into airplane RC (and then helicopters) and realized that I was spending a lot more time building them than flying them! After a crash, however, the rebuilding process wasn’t as enjoyable for me. Knowing this about myself, I’ll need to find the right balance.

In the meanwhile, I received my MT410 and a bunch of M2C goodies, and I’m looking forward to starting that build!

 

[PKMSM]

+1 on the maintenance log

I actually keep a race log (using Google Sheets) with all my stats which are reset every time the track makes a new layout, then I have new PR (personal records) to beat, hot consistency, hot lap, hot qual, hot main and stack rank, plus I also track any broken parts, tuning changes as well as the maintenance where I do a rebuild after every 3 race days where I average 5 packs per race day.

Yes, forgot to mention I already started the log when you mentioned 15 batteries between rebuilds!

 

[Nicochau]

What surprised me was the frequency of rebuilds. 15 batteries (or 20-30) doesn’t seem like a lot of run time between full rebuilds, but then again, these things are exposed to all kinds of dirt and abuse.

I had actually found the $14 kit you’re talking about while searching last night. I ordered a couple of sets to keep on hand (assuming the ET and EB48 2.0 all use the same bearings. I agree that for the price it’s not worth rebuilding them, other than maybe a therapeutic activity to tune out, or while watching TV as Bill mentioned!

I enjoy building things. Years ago I was into airplane RC (and then helicopters) and realized that I was spending a lot more time building them than flying them! After a crash, however, the rebuilding process wasn’t as enjoyable for me. Knowing this about myself, I’ll need to find the right balance.

In the meanwhile, I received my MT410 and a bunch of M2C goodies, and I’m looking forward to starting that build!

Regards to frequency of rebuilds, it can seem like not that much fun between rebuilds but it is actually not that bad.

With time, i also learned to break a lot less. I don’t bash hard and stick more and more to track driving / racing.

I also don’t spend too much time cleaning my stuff. Push some compressed air on them to get rid of the dust and thats it (and not too close to the bearings). No wd40 on plastic or washing non-sense. I rather have a loose dusty truck than a shiny crunchy driveline.

Congrats on the MT410!!

 

[Billl DeLong]

Not sure if the bearings are the same between the ET48 2.0 and the EB48 2.0 but I guarantee the bearings are not the same for the MT410 which is based on the .3 platform so try looking for a EB48.3 kit which may work for the MT410.

 

[PrimaRC]

What surprised me was the frequency of rebuilds. 15 batteries (or 20-30) doesn’t seem like a lot of run time between full rebuilds, but then again, these things are exposed to all kinds of dirt and abuse.

I had actually found the $14 kit you’re talking about while searching last night. I ordered a couple of sets to keep on hand (assuming the ET and EB48 2.0 all use the same bearings. I agree that for the price it’s not worth rebuilding them, other than maybe a therapeutic activity to tune out, or while watching TV as Bill mentioned!

I enjoy building things. Years ago I was into airplane RC (and then helicopters) and realized that I was spending a lot more time building them than flying them! After a crash, however, the rebuilding process wasn’t as enjoyable for me. Knowing this about myself, I’ll need to find the right balance.

In the meanwhile, I received my MT410 and a bunch of M2C goodies, and I’m looking forward to starting that build!

The bearings aren't all the same, it depends which version diffs you got, ET48 2.0 has a different rear diff bearing to when it was first released.

 

[PKMSM]

Thank you both. I know the ET/EB have different bearings than the MT, but I had assumed the ET/EB use the same bearings. Given the price I didn’t look into it too hard. I’ll go through the list and see if there are any differences, thanks for pointing it out