Scalloped Planetaries?
04-10-2006, 04:53 PM
#1
Registered User
Thread Starter
Scalloped Planetaries?
I was visiting a guy the other day who happened to have a 37RH transmission from behind a cummins apart. He was tearing it down because it was whining and had metal in the pan. The only thing he had found when I was there was this strange wavy pattern worn in the ridges of the planet gears on both planetaries. The edge of the profile at the ridge was kind of scalloped, or wavy, as well. The inside of the ring gears looked like they were brand new, and there was no debris of any kind in the ring gears.
I have never seen wear like that on a planetary assembly, but I have never worked much on automatic transmissions.
Is this common? I can't imagine how this wear would happen, unless the gear teath were flexing excessively under load. I have seen worn out planetaries, but they all had pretty even knife-edging and pitch lines at the root, nothing like this.
If anyone has experience with this, please share it. I'm curious now.
Thanks,
Alec
I have never seen wear like that on a planetary assembly, but I have never worked much on automatic transmissions.
Is this common? I can't imagine how this wear would happen, unless the gear teath were flexing excessively under load. I have seen worn out planetaries, but they all had pretty even knife-edging and pitch lines at the root, nothing like this.
If anyone has experience with this, please share it. I'm curious now.
Thanks,
Alec
04-10-2006, 05:04 PM
#4
Registered User
Thread Starter
Sorry, no pictures 
. It was both planetaries in the main case. Each assembly had four planets FWIW.
If you imagine that the planets started as a cylinder, with teeth cut into the side, instead of the cylinder having a smooth, square side, the side was wavy, as though the cylinder had rings worn into it, running around the cylinder. Also, instead of the ridge of the teeth having a smooth profile (round over, or acme shaped, etc.) they looked more like a flint arrow-head, with waves worn smoothly in at an angle to the pitch of the gears.
Does that make any better sense?
. It was both planetaries in the main case. Each assembly had four planets FWIW. If you imagine that the planets started as a cylinder, with teeth cut into the side, instead of the cylinder having a smooth, square side, the side was wavy, as though the cylinder had rings worn into it, running around the cylinder. Also, instead of the ridge of the teeth having a smooth profile (round over, or acme shaped, etc.) they looked more like a flint arrow-head, with waves worn smoothly in at an angle to the pitch of the gears.
Does that make any better sense?
04-10-2006, 09:26 PM
#5
Guest
Posts: n/a
The planet gears and the sun gear are hobbed to form the teeth, then the final finish is done by a gear shaver or roller. Some gears will show a scallop pattern along the edges and some won't. The scallop should not be down on the flank of the tooth where the wear takes place though, that part is supposed to be smooth as silk. You can finish hob gear teeth but it takes forever, for production parts they hob then let a roller or shaver take the last .005" or .006" off for a nice finish. Clear as mud? need pics to diagnose what you think is wrong.
04-10-2006, 09:37 PM
#6
Pretty common on the older 46/47 series transmissions. Not enough planetaries in an aluminum cage. Usually thats what happens when a lot of towing is done. It chews up the sun gear then starts on the planetaries. Lack of service, too much heat, running low rpm's too much will destroy the planetaries. The Cummins just hammers the internals out after a while. Toss 'em and use the steel carrier and 6 pinion gears and they last a lot longer, especially in the OD section. 
Trending Topics
04-12-2006, 07:34 AM
#9
Registered User
Originally Posted by no_6_oh_no
The Cummins just hammers the internals out after a while. Toss 'em and use the steel carrier and 6 pinion gears and they last a lot longer, especially in the OD section.
04-12-2006, 11:22 AM
#10
Registered User
Join Date: May 2005
Location: Galveston, IN (Kokomo)
Posts: 195
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Mcmopar
There is a little more than that involved, to put the 48RE stuff in the 47. I wish you could just throw a set of 6 pinion planetaries in there, but you need to change other parts too.
04-12-2006, 11:37 AM
#11
Originally Posted by Mcmopar
There is a little more than that involved, to put the 48RE stuff in the 47. I wish you could just throw a set of 6 pinion planetaries in there, but you need to change other parts too.
04-12-2006, 05:06 PM
#12
Registered User
Thread Starter
Okay -- I think that the "scallops" I saw must have been from the manufacturing process then. I still don't get how they are formed in the hobbing process, though?
Thanks,
Alec
Thanks,
Alec
04-12-2006, 07:08 PM
#13
Registered User
Durring the cyclindrical Hob process the blank (future gear) rotates on one axis (work head) and a cutter (Hob) rotates on another (Hob head) As the two axis spin at some determined speed based on many factors ( desired cycle times, material. diameter, dry or wet cutting, ect...) the work spindle speed and rotational position follows the hob head in a master - slave relationship at determined ratio.
If the spindle runouts open up (manufactured to <.00005) or The hob dulls. Tooling runout, positional errors (linier or rotational) occur, plus other posibilities it can leave the scallops you see in your pinions.
Often the scallops you see are .000030 or less in depth but depending on the application of the gear weather they are allowed or not.
Clear as mud?
http://www.gleason.com/cylindricalpr...machines/index.
snoop around here for more gear manufacturing info
If the spindle runouts open up (manufactured to <.00005) or The hob dulls. Tooling runout, positional errors (linier or rotational) occur, plus other posibilities it can leave the scallops you see in your pinions.
Often the scallops you see are .000030 or less in depth but depending on the application of the gear weather they are allowed or not.
Clear as mud?
http://www.gleason.com/cylindricalpr...machines/index.
snoop around here for more gear manufacturing info
04-12-2006, 09:35 PM
#14
Guest
Posts: n/a
I have put 48 re parts in an 84 727, the big stickler is the spline change on the output or intermediate shaft (depending on wether you have a 727 or 518) where the front carrier goes. The spline changed for the 94 model year so you have to respline the front carrier or get a newer shaft. You need to use everything within the planet assembly from a 48re or you'll be way too short or way too long for the ring grove at the end of the shaft, depending on which parts you are trying to mix and match. The 48re rear annulus gear has a machined surface for a thrust washer between it and the rear carrier. the older ones all used a stamped thrust washer of steel and let the rear carrier aluminum be the bearing material. The shell is thicker so they had to move the ring grooves on the sun gear farther apart. the front annulus support is thinner the same amount (more or less) that the shell is thicker. So then the lip on the front carrier had to be shortened to match the carrier support. Another gotcha is the number of splines on the OD of the front carrier was doubled, so then you need to use the 48re rear clutch fiber discs. There was a design change on the lugs on the front clutch retainer where it engages the drive shell, not sure if the older front clutch retainers would work without problems, didn't think to try one as I also used 48re front and rear clutch retainers and input shaft and reaction shaft support. 48re front clutch retainers are 5 plate clutches.
04-13-2006, 04:12 PM
#15
Registered User
Join Date: Dec 2005
Location: LOGAN OH NEXTEL ID #136*8015*1979
Posts: 12
Likes: 0
Received 0 Likes
on
0 Posts
if you want better planetareis call rick at A & A transmisson 317-831-3066, he also has a 6 pinon front planet for the 727's im currently running a 5 front and 4 rear along with some other goodies, and you cant beat his customer service.
Zach
Zach