Warm Frog Gearbox

[Kowalski86]

So...more Frog issues. When I apply throttle forward the diff will engage for a moment, then the pinion/spur gears will spin but the rear wheels will struggle to rotate, and it'll make a terrible sound.

Before this it had been making that noise and the gearbox would warm up, so I'm thinking that there's some friction going on in there.

If need be I'll post a video later if necessary, strangely everything works fine with I apply throttle in reverse.

It's all stock other than an aftermarket brace from a member on here.

[Snappy1]

Unfortunately that is normal for the ORV chassis, it either needs a trans brace or a MIP ball diff or a rebuild of the diff gears.

[El Gecko]

The gearbox getting warm is supposed to happen, because the metal side plates also function as heatsinks for the motor.

The clicking/slipping is probably the diff gears, which wasn't supposed to happen with the brace.

The only way to find out for sure is to pull it apart and see what's going on in there.

[Kowalski86]

2 hours ago, Snappy1 said:

Unfortunately that is normal for the ORV chassis, it either needs a trans brace or a MIP ball diff or a rebuild of the diff gears.

I have a brace on it, I can only guess it'll need new gears given the age of the ones in it.

[El Gecko]

20 minutes ago, Kowalski86 said:

I have a brace on it, I can only guess it'll need new gears given the age of the ones in it.

Oh wait, it's a vintage one? Probably the hex driveshafts have rounded out, then. Especially if it's worse in one direction.

[Frog Jumper]

Sounds like a loose pinion.

Terry

 

[Kowalski86]

3 hours ago, El Gecko said:

Oh wait, it's a vintage one? Probably the hex driveshafts have rounded out, then. Especially if it's worse in one direction.

Could be, the boots look torn in a few places. 

2 hours ago, Frog Jumper said:

Sounds like a loose pinion.

Terry

I want to say that, but for testing I kept the gear cover off (the thing the two screws go into), and I watched the pinion and spur gears rotate.

[Juggular]

It could be the droop in the swing arm.

I would run it at slow speed, and lift one arm or both arms to see if the noise gets reduced.  If it's the cause, usually only a few millimeters of upward swing would relieve it. 

As for the heat, the plate on the motor side should get warm because of the motor.  But I don't know if the other side should warm up.  Even if the drive cup is getting heated because of the friction with the dog bone, the bearing is insulated by a plastic piece.  

Several of Tamiya chassis do allow more droop than the dog bone and the drive cup are comfortable with.  They tend to make click-clack sound.  

 

[Kowalski86]

23 minutes ago, Juggular said:

It could be the droop in the swing arm.

I would run it at slow speed, and lift one arm or both arms to see if the noise gets reduced.  If it's the cause, usually only a few millimeters of upward swing would relieve it. 

Several of Tamiya chassis do allow more droop than the dog bone and the drive cup are comfortable with.  They tend to make click-clack sound.  

I'll give that a shot later on as well as post a video of the problem. I have an original so it still has hex drives.

[Kowalski86]

Tamiya Frog ORV Transmission Issue - YouTube

Probably is the hex drives if anything, I wish that the axle hop-up was a bit cheaper!

[Frog Jumper]

17 hours ago, Kowalski86 said:

 

And you’re watching through the window while the car is being lifted off the table, ie there is no load on the gears???

[Kowalski86]

2 hours ago, Frog Jumper said:

And you’re watching through the window while the car is being lifted off the table, ie there is no load on the gears???

I had it sitting on a stack of batteries, does the same thing when the wheels are on the ground.

EDIT: While I will probably try to diagnose the issue on my own, I will be selling the Frog to fund future projects.

[Pablo68]

As much as I might be called a heretic because this is a vintage Frog, the first thing to go would be the hex drive system, replaced with dogbones. I know that system worked well enough for some, but I hate them with a passion, nothing but problems.
To be fair, this was on an MB, I'm perhaps selling this point a bit hard.
And I hear ya on the price of replacement. Prices for most things RC are currently ridiculous.

[Kowalski86]

5 hours ago, Pablo68 said:

As much as I might be called a heretic because this is a vintage Frog, the first thing to go would be the hex drive system, replaced with dogbones. I know that system worked well enough for some, but I hate them with a passion, nothing but problems.
To be fair, this was on an MB, I'm perhaps selling this point a bit hard.
And I hear ya on the price of replacement. Prices for most things RC are currently ridiculous.

I've replaced the hex drive system, but the real culprit ended up being the 30-something year old spider gears being chewed up.

The hex shafts were actually okay, I just figured that dogbones would be good insurance.

The Frog is for sale...but I could go either way. I don't mean to knock Tamiya, but as antiquated as the ORV chassis is it felt more "hobby grade" than some of the other Tamiyas I've owned.

[Pablo68]

3 hours ago, Kowalski86 said:

I've replaced the hex drive system, but the real culprit ended up being the 30-something year old spider gears being chewed up.

The hex shafts were actually okay, I just figured that dogbones would be good insurance.

The Frog is for sale...but I could go either way. I don't mean to knock Tamiya, but as antiquated as the ORV chassis is it felt more "hobby grade" than some of the other Tamiyas I've owned.

Hmmm, can't say I'd go as far as to say 'Toy Grade' about the Frog. I mean I've seen some truly poopful toy grade chassis that are designed to look the part, I guess to fool people into buying them. The Frog aint that.
As much as I love the Hornet, I reckon it's the one closest of the first ~100 to being toy grade.
Glad to hear you found the issue btw.

[DavidJH]

I always wanted the Frog but it was a little too pricey so I got the Hornet instead.  If my wife ever divorces me I'll get one

[Kowalski86]

22 minutes ago, Pablo68 said:

Hmmm, can't say I'd go as far as to say 'Toy Grade' about the Frog. I mean I've seen some truly poopful toy grade chassis that are designed to look the part, I guess to fool people into buying them. The Frog aint that.

I think you misread my post, to me the ORV very  "hobby grade", more hobby grade than some modern offerings.

20 minutes ago, DavidJH said:

I always wanted the Frog but it was a little too pricey so I got the Hornet instead.  If my wife ever divorces me I'll get one

You can always buy mine for half the price of a NIB kit and drop a shell on it!

[DavidJH]

Sorry the build is all part of it!!

[Pablo68]

20 minutes ago, Kowalski86 said:

I think you misread my post, to me the ORV very  "hobby grade", more hobby grade than some modern offerings.

You can always buy mine for half the price of a NIB kit and drop a shell on it!

Oops, looks like I don't read good. My bad there mate.

[Kowalski86]

47 minutes ago, Pablo68 said:

Oops, looks like I don't read good. My bad there mate.

No problemo! It does come with aluminum oil filled shocks, ball bearings (for the transmission),  metal motor mount, aluminum front bits, metal axles... it's just a bit spendy NIB.

[Saito2]

I like my Frog gearboxes warm, nicely toasted to a golden brown. Too hot and they get burnt and charred. Ruins the flavor. Too cold and they're like a 2 day old pizza slice sitting in the fridge, congealed with grease.

Seriously, glad you found the problem and good luck with the sale.

[Kowalski86]

1 hour ago, Saito2 said:

Seriously, glad you found the problem and good luck with the sale.

Thanks, whoever gets it will be getting something a little nicer than the usual filthy flea market flips.

[Juggular]

On 6/7/2023 at 9:58 PM, Kowalski86 said:

Tamiya Frog ORV Transmission Issue - YouTube

Probably is the hex drives if anything, I wish that the axle hop-up was a bit cheaper!

I just saw that clip and thought, "that sounds like worn diff gears."  Then you confirmed it.  

Pot-metal ORV bevel gears in the diff might be the same things in the FAV and Wild One, etc.  They wear out as easily as copper pinions.  

I was lucky enough to come across really thick diff grease in 2001 or so.  So thick, it would burn out the motor if used on regular gears.  But you want diff gears to have a lot of resistance.  And it made the bevel gears nearly impossible to wear out.  Perhaps because of that, ORV happened to be one of my favorites.  But ORV isn't everybody's cup of tea.  There are dozens and dozens of other chassis.  I hope you find something more to your liking.  

 

[Kowalski86]

41 minutes ago, Juggular said:

I was lucky enough to come across really thick diff grease in 2001 or so.  So thick, it would burn out the motor if used on regular gears.  But you want diff gears to have a lot of resistance.  And it made the bevel gears nearly impossible to wear out.  Perhaps because of that, ORV happened to be one of my favorites.  But ORV isn't everybody's cup of tea.  There are dozens and dozens of other chassis.  I hope you find something more to your liking.  

Thank you, the ORV is close to what I'd want from Tamiya, some parts are just a bit too expensive imo. 

I ran fairly stiff grease in mine on the first re-build when I installed the brace. The current re-build was done to the instructions, so just Tamiyas ceramic grease.

I will say that I enjoyed restoring and driving this more than trying to assemble an M05 kit, so much easier to get to the transmission.

Do the dogbones usually stay put in the Frogs/Brats?

[Juggular]

57 minutes ago, Kowalski86 said:

Do the dogbones usually stay put in the Frogs/Brats?

I feel uncomfortable using ceramic grease on pot-metal gears... It's basically microscopic sand.  It's fine on plastic gears. But I fear it's not so good on pot-metal or copper gears.  

When I ran hex-bones, they did run away once or twice in a year (fortunately, I found them easily on both occasions).  Usually from overextending the swing arm when running on very rough broken concrete pavement.  I haven't ran the newer Blackfoot much, so I couldn't tell you about the dog bones.