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Planetary gear cooling

AgitatedPancake

AgitatedPancake

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So I've been thinking about planetaries lately, and have some stuff to learn. Is there anything that makes the planetaries of a transfer case low range (like the ultra common 2.72:1 NP/NV set) different than the planetaries in a transmission from a duty cycle perspective?There's obviously a sheer size difference due to the amount of upstream reduction, but anything else? Is there any reason transfer case planetaries can't be run at 100% duty cycle with stock-like reliability, or would you toast the bronze bushings in the planets?

I know the TeraLow 4:1s had issues, and I think that led me to believe that transfer case planetaries in general were kinda "part time" from a duty cycle persepctive. But then in automatic transmissions, you've got planetaries engaged in any gear but 1:1. Are they fed pressurized oil into the bushings, or just splash lubricated? From the few google pics I've looked at, they almost seem just splash lubricated like the transfer case gears.

Turbo 400:

s-l1600.jpg


2.72:1 NP/NV transfer case planetaries

807-74527.jpg
 
total newb said:
In both trans and oe tcase they are dirrect feed with low psi flowing atf.
In crawl boxes and axle drives they are splash lubed in sealed cavities.

tcases are fed with gerotor pump through the output shaft to the pocket bearing and flows back over the gears, and back down to the sump.
Click to expand...

For the gear mesh itself I'd agree they get a good amount of oil, in heavy splash (nearly bath), and the feed from the pump.. Do you think that's where most of the heat is? Is there any oil flow through the planetary case, planetary shafts, into the bronze bushings? As far as I recall, that doesn't happen. Which if true there's only cooling for the gear mesh itself, and not the bushings. Making sure the gear meshes stay lubricated shouldn't be a biggie, but the bushings make me a little more wary
 
I only know the tcase stuff, idk about trans.

No, they dont but they are not like trans radial bushings either. They are trust washers because the in/out put shafts are supported by 3 brg's.

Slip yoke bushings tend to have some sort of oil grooving and typicaly have at least a splash catch that will redirrect oil to the bushing.
 
I think a second oil pump for low range transfer case planetaries would be great. Or a squirter directed at the planetary. I have a TerraLow 4:1 on the shelf that likes to eat thrust washers. It spins too fast for the little bit of atf that travels from the opposite end of the input shaft.
 
The place that I worked at that built planetary gear box's for industrial use ran needle bearings instead of bushings. These were splash lubricated and rated for continuous duty. This seems like a way better option for a T-case. No pump needed.
 
Hmmm needles seem like they would be great, that makes sense. Does anyone happen to know if the planetaries in transmissions run on needles vs bushings? That would be pretty interesting, I just don't know enough to know

And the thrust factor of transfer case gears also makes sense due to them being helical vs straight cut.

Does anyone have examples of running planetary reduction transfer cases in low range at high RPM for super extended periods of time? Like I'm not sure if anyone runs the whole of KOH in 2.72:1 low range (but I do know some do similar in geared cases with less reduction)
 
AgitatedPancake said:
Hmmm needles seem like they would be great, that makes sense. Does anyone happen to know if the planetaries in transmissions run on needles vs bushings? That would be pretty interesting, I just don't know enough to know

And the thrust factor of transfer case gears also makes sense due to them being helical vs straight cut.

Does anyone have examples of running planetary reduction transfer cases in low range at high RPM for super extended periods of time? Like I'm not sure if anyone runs the whole of KOH in 2.72:1 low range (but I do know some do similar in geared cases with less reduction)
Click to expand...
Tilton makes gear oil pumps specificaly for racing diffs pumping gear oil like nascar and circle track. Circle car run deep gears for as fast as they do run. 6.50 is common and 30 tires at 65-110mph.


A pump to a cooler and back into the top of the box with a sealed 1/2g res would be a massive improvment over as is.
 
AgitatedPancake said:
Hmmm needles seem like they would be great, that makes sense. Does anyone happen to know if the planetaries in transmissions run on needles vs bushings? That would be pretty interesting, I just don't know enough to know

And the thrust factor of transfer case gears also makes sense due to them being helical vs straight cut.

Does anyone have examples of running planetary reduction transfer cases in low range at high RPM for super extended periods of time? Like I'm not sure if anyone runs the whole of KOH in 2.72:1 low range (but I do know some do similar in geared cases with less reduction)
Click to expand...
One of my broncos got stuck in low range, a 1350 running in low going 60mph gets pretty fucking hot. Drove from Glamis to Brawley that way. It was puking oil by the time I stopped at the autoparts store.
 
Take the support bearings out of the equation my guess is there metallurgy is pretty similar. One is splash/poorly pump lubed with what 2 quarts of oil. The other is pump lubed in a system that has a cooler and a few gallons of total oil capacity.

So yeah the quantity and heat capacity isn't even close.

Just look at a 242 in a Jeep vs. an H1. The H1 which the front and rear planetary is under load 100% of the time on the street and also in a vehicle with a higher GVW has an auxiliary cooler system.

You probably could run a t case in low non stop with no issue if you could increase the capacity and cooling to accommodate that usage.
 
total newb said:
Tilton makes gear oil pumps specificaly for racing diffs pumping gear oil like nascar and circle track. Circle car run deep gears for as fast as they do run. 6.50 is common and 30 tires at 65-110mph.
Click to expand...

Back before the pumps circle track cars mounted a hydraulic ram on the rear axle with two check valves and used that to pump fluid. Not gonna work on the highway but in the desert that'll move plenty of fluid.

total newb said:
A pump to a cooler and back into the top of the box with a sealed 1/2g res would be a massive improvment over as is.
Click to expand...
It would be stupid easy to make a bracket that sticks a P/S pump on the back of the case and belt drives it off of the t-case output. No need to run a fancy gear pump as long as your oil level in the transfer case is higher than the bottom of the rotor in the power steering pump.

Someone who's super fancy could design a NP205 bearing retainer that holds the bearing and on one side and fits over a ford C-whatever pump or a canned ham the way the normal reservoir does on the other.
 
AgitatedPancake said:
So I've been thinking about planetaries lately, and have some stuff to learn. Is there anything that makes the planetaries of a transfer case low range (like the ultra common 2.72:1 NP/NV set) different than the planetaries in a transmission from a duty cycle perspective?There's obviously a sheer size difference due to the amount of upstream reduction, but anything else? Is there any reason transfer case planetaries can't be run at 100% duty cycle with stock-like reliability, or would you toast the bronze bushings in the planets?

I know the TeraLow 4:1s had issues, and I think that led me to believe that transfer case planetaries in general were kinda "part time" from a duty cycle persepctive. But then in automatic transmissions, you've got planetaries engaged in any gear but 1:1. Are they fed pressurized oil into the bushings, or just splash lubricated? From the few google pics I've looked at, they almost seem just splash lubricated like the transfer case gears.

Turbo 400:



2.72:1 NP/NV transfer case planetaries
Click to expand...
Hey there, gearhead! Planetary gears are fascinating things, aren't they? I'm not a professional mechanic by any means, but I've been tinkering with cars for years and love learning about how things work. Here's what I've picked up on your question about transfer case vs. transmission planetaries:

You're definitely right about the size difference. Transfer cases need that extra grunt for low-range situations, so the gears are gonna be beefier. But beyond size, there might be some other key differences.

Here's my thinking: transfer cases are built for those short bursts of intense off-roading, whereas transmissions are dealing with the constant wear and tear of everyday driving. That might mean the materials used in the planetaries are a bit tougher in a transmission to handle that continuous load.

Now, on the lubrication question, that's a good one. From what I've read, transfer cases tend to rely more on splash lubrication, which makes sense since they're not engaged all the time. Automatic transmissions, on the other hand, often have pressurized oil circulating through the planetaries for better cooling and wear protection. Those fancy transmission coolers you see on some cars? They help keep that oil nice and cool for those hardworking planetaries.

The TeraLow 4:1 situation is interesting. Maybe their higher gear reduction put extra stress on the components, leading to those reliability issues. It just goes to show that pushing things to the limit can have consequences.
 
Teralow is a piece of design trash. The gears are sling fed but the slinger directs the oil away from the gears. The gears are also only partially supported along the length of the gear. Lastly they're cutoff from any oil supply by solid brass top and bottom.
Factory oil slinger spits right onto the gear shaft washer which has channels for oil to creep inside. Even if you did run a factory planet dry I believe the plastic bushing inside is impregnated with graphite to buy you some time.
The oil pump is used to deliver oil volume to the slinger inside the planet, bearing and shift bushings.
 
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