Need help. Setting up new gear set 742 case

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737jetdr

737jetdr

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Hey everyone. I'm attempting to change the ring and pinion set in a 742 case. Everything was looking good until I went to torque pinion nut to 240lbs and it all locks up. I reused the shims from the gear set I removed hoping it would get me close. The shim in between the pinion gear and aft bearing and a smaller shim on the top of the pinion. Do I need another smaller shim up top? Can someone tell me what I did wrong? Thanks
 
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It has been years since I did one but I remember you have to do the math between the pinion being removed to the pinion being installed. The pinion will be stamped .
 
You need more shim between the pinion bearings. I wouldnt change the shim between the pinion and inner bearing yet, untill you run a pattern.

It has been a few years since i set one up but from recollection I would not torque the pinion nut untill you have finished setting the pattern up with shim between the pinion and inner bearing. After this you shim between the bearings and torque the nut, adding or removing shim till you get the right drag torque for the pinion rotation. After all this do a final check of backlash and pattern.
 
When I put it together I used my impact and just snugged the pinion nut. I had my backlash set at .008 and my pattern looked good. That's when I went to torque the pinion nut and realized the pinion preload was wrong. I will add shims and try again tomorrow, This is my first one. Big learning curve. You can read all of the articles you want. Only really makes sense when you pull one apart yourself. I'll update tomorrow. Thanks for the replies.
 
Just an update. Took it back apart, added 5 shims on the front, pinion too loose. Removed 2, pinion too tight. 4 shims is the magic number for this pinion. All back together just in time to go to work.
 
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737jetdr said:
Just an update. Took it back apart, added 5 shims on the front, pinion too loose. Removed 2, pinion too tight. 4 shims is the magic number for this pinion. All back together just in time to go to work.
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No offense intended but just so someone doesn't read this and think this is gospel on how to set pinion bearing preload I want to point that out that shims come in a variety of thicknesses. The thickness of the shim(s) you need isn't always the same. It varies from differential to differential and gears to gears. Even changing one pinion bearing can throw off the pinion preload
 
None taken. This is true. Every pinion set is probably a little different. My rebuild kit from Dr.Diff came with a small bag of shims that were all the same thickness. My old pinion only used 1 shim. The 4 shims was the magic number for this particular pinion.
 
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