Gears and Pinions

[Nacho-RT74]

Has been told that Gears and pinions are not interchangeable between different cases, 741, 742, 489 becase the large stem size of each one... Is just the pinion or also the gear ?

Why I say or ask this ? I found 5 NOS pinion and gears kits. Well some of them only did have the gear and pinions and not the rest of the kit ( spacer and flange/yoke ) and here is what I found on stamped PN:

1 3/8 pinion stem to 741 case:
3:23
Pinion: 3507318
Gear: 2800270--- Notice is small pinion stem and the gear mounted on the 489 I'm trying to rebuilt with same ratio has stamped the same PN.

3:55
Pinion: 3507319
Gear: 2070898

3:91
Pinion: 3507320
Gear: 2070225

1 7/8  pinion stem to 489

3:55
Pinion: 3507397
Gear: 2070898

Notice both Italic gears PN... same Gear PN but matched to diferent pinion stem sizes. Same to the 3:23 exposed above.

So, or I'm crazy when I thought both were different between cases or really is JUST THE PINION the difference on cases, being the gears also interchangeable.

With all this variety of options in my hands, I don't know what to choose to my car , having also a 741 unit. Actually my REAL problem is damaged spider gears shaft, is really worn what still haven't found 

[John_Kunkel]

Ring and pinion gears are mated for life at the time of manufacture.

Just because the same numbered ring gear is used with different ratios in different pinion sized assemblies doesn't mean that any numbered ring gear will mate with its numbered pinion.

[Nacho-RT74]

Ring and pinion gears are mated for life at the time of manufacture.

Just because the same numbered ring gear is used with different ratios in different pinion sized assemblies doesn't mean that any numbered ring gear will mate with its numbered pinion.

what ?

[Ghoste]

No interchange.

[Nacho-RT74]

ok, my assembly with large pinion stem and the one I got NOS with small pinion stem says the oposite... I already compared both side by side.

Same about the large and small stem pinions 3:55 kits I got NOS.

[tecmopar]

What John and Ghoste are saying that Ring and Pinion gears come in sets and are machined to stay together. You can't take a pinion gear from one box and a ring gear from a different box and expect them to work correctly, good luck.