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Old 07-01-2018, 02:34 AM   #1
BigRandy
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Set Up Steps For a 12 Bolt

Getting ready to do my first diff repair on an open rearend. Symptoms (whine under load but quiet when I back off) point to pinion bearings but not sure if that's all I'll find when I get it apart. So far the R&P look good but the spider gears are sloppy and worn.

Been reading the setup procedure and understand most of it except adjusting the pinion depth.

If I understand correctly the crush sleeve is used to set the pinion preload, seems simple enough, but but if the R&P don't mesh correctly the guide says (depending on the pattern) to adjust the carrier using shims, or move the pinion in or out which is where I'm stuck.

If pinion adjustment is needed, how can I move the pinion once the sleeve is crushed to the correct preload? Some guides say to adjust preload and then pull the pinion back out and install the sleeve and front seal. That sounds like a misprint or maybe a different rearend.

I thought once the preload was set the pinion was a done deal. Either I'm missing a step or not understanding the guide. Either is possible but the latter is more likely since most of the guides I've read cover rearends other than the truck 12 bolt.

I have the specs for preload (15-25 inch pounds) and backlash (.006-.0010) and torque. Also have a pattern chart which seems easy to read.

This is a 74 C10 with open 3.73's.

Any help getting me on track would be appreciated.
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Old 07-01-2018, 10:09 AM   #2
mongocanfly
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Re: Set Up Steps For a 12 Bolt

You can leave the crush washer out while setting the pinion depth....https://www.chevydiy.com/how-to-inst...-differential/
You may need to shim up or shim down your pinion to mesh with the ring gear.....if you've never setup a rear it can get frustrating....
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Old 07-01-2018, 11:52 AM   #3
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Re: Set Up Steps For a 12 Bolt

Theoretically, your pinion depth shim was setup correctly when the axle was built. That dimension doesn't change when you change parts. There's an old timer saying the pinion shim stays with the housing. (technically it's the carrier but that terminology is commonly misused)

In practice, the pinion shims are usually close enough and aftermarket gears sometimes produce gear patterns that need some correction or end up being a compromise setup between drive and coast side.

The link Mongo gave is decent. Their backlash setup leaves a LOT to be desired. It's important if your using gear patterns to make pinion depth adjustments to set the backlash every time the pinion shim is changed. It's a common lazy mistake to change the pinion shim and insert the same side bearing shims and take another pattern. The backlash must be in specification.
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Old 07-01-2018, 02:23 PM   #4
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Re: Set Up Steps For a 12 Bolt

Quote:
Originally Posted by Bigdav160 View Post
Theoretically, your pinion depth shim was setup correctly when the axle was built. That dimension doesn't change when you change parts. There's an old timer saying the pinion shim stays with the housing. (technically it's the carrier but that terminology is commonly misused)

In practice, the pinion shims are usually close enough and aftermarket gears sometimes produce gear patterns that need some correction or end up being a compromise setup between drive and coast side.

The link Mongo gave is decent. Their backlash setup leaves a LOT to be desired. It's important if your using gear patterns to make pinion depth adjustments to set the backlash every time the pinion shim is changed. It's a common lazy mistake to change the pinion shim and insert the same side bearing shims and take another pattern. The backlash must be in specification.
If I understand correctly, since the gears and shims were set up from the factory I should be okay with the depth if I'm only replacing the bearings. And if the backlash is off I can correct that with carrier shims?

If that is correct then this could be be as easy as pulling the carrier, pinion, replacing the bearings]races, reinstall the pinion and sleeve to the correct preload and reassemble? If it is then I've been overthinking this.

I understand that no stone should be left upturned if this was a 100% fresh build with parts that have never been together before. I'm hoping to get out easy with new bearings and spider gears.

Thanks for the advice.

Mongo, thanks for the link. It's one of the best I've seen.

Randy
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Old 07-01-2018, 04:02 PM   #5
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Re: Set Up Steps For a 12 Bolt

if using the org r&p ck your back-lash before taking it apart. Some say on used gears to set the b/L to what is was or close as the r&p have worn-in. some experts should chime in as i am not an expert. I'v had rear gears that had your symptoms and it was the r&p. good luck
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Old 07-08-2018, 11:24 PM   #6
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Re: Set Up Steps For a 12 Bolt

Okay.... pulled the cover to get a closer look but I'm not sure if this is normal or serviceable. I don't have a dial indicator at the moment but there is backlash - more movement than the 6-10 thou that I've seen in videos.

This is only a guess but wouldn't bad carrier bearings gooch the backlash? If so can someone take a look at these pics and tell me if this is worth a set of bearings or do I also need new gears? I didn't find any broken or chipped teeth. Thanks.
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Old 07-08-2018, 11:30 PM   #7
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Re: Set Up Steps For a 12 Bolt

Is there any movement of the carrier?....stick a pry bar under it and see if it'll move up and down any...
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Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563
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Old 07-08-2018, 11:46 PM   #8
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Re: Set Up Steps For a 12 Bolt

Quote:
Originally Posted by mongocanfly View Post
Is there any movement of the carrier?....stick a pry bar under it and see if it'll move up and down any...
I should have checked that. Will take a bar to it tomorrow.
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