ignorant 12 bolt question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Rust_never_sleeps** · 06-02-2024, 04:59 PM

While adjusting rear drums, one wheel in the air, tranny in neutral...
Rotating the rear hub by hand ~1/2 turn each way, I noticed different resistance going forward vs backward. Same with the drum off, so brakes not involved
Is that unusual?

**'68OrangeSunshine** · 06-02-2024, 05:46 PM

Quote:

Originally Posted by Rust_never_sleeps

While adjusting rear drums, one wheel in the air, tranny in neutral...
Rotating the rear hub by hand ~1/2 turn each way, I noticed different resistance going forward vs backward. Same with the drum off, so brakes not involved
Is that unusual?

Do you have POSI?

**Rust_never_sleeps** · 06-03-2024, 12:54 AM

No limited slip on the SPID

**Richard** · 06-03-2024, 01:39 AM

I would run it. But if you are worried about the axle maybe disconnect the driveshaft and try the test again with the drums off. Would bet what you are thinking is a problem goes away.

weq92f · 06-03-2024, 02:03 PM

.

Recently I noticed the same thing on my 12 bolt posi equipped '67 while adjusting the rear drums. In neutral, it was way easier to turn the wheels one way vs the other way...don't remember which was which though. I used the easy turn to finish what I was doing and didn't think about it again until reading this post!

-Kevin

**Rust_never_sleeps** · 06-03-2024, 04:58 PM

It felt the same without the drums. It wasn't alarming, but I couldn't think of a reason it'd be different.

I need to swap the diff gasket and pinion anyway, so if there's anything wonky in there, I'll know soon enough.

Thanks

**HO455** · 06-03-2024, 05:39 PM

The difference is the resistance caused by turning the pinon shaft. If the ring and pinion were straight cut gears the torque to turn would be the same in both directions. With hypoid cut gears there is more drag induced when turning. The amount of drag differs depending on the direction turned. The amount of torque to turn is magnified by using the axle to turn the pinion or in other words driving the gears backwards.

weq92f · 06-03-2024, 06:04 PM

Quote:

Originally Posted by HO455

The difference is the resistance caused by turning the pinon shaft. If the ring and pinion were straight cut gears the torque to turn would be the same in both directions. With hypoid cut gears there is more drag induced when turning. The amount of drag differs depending on the direction turned. The amount of torque to turn is magnified by using the axle to turn the pinion or in other words driving the gears backwards.

.

Science!

-Kevin

**Rust_never_sleeps** · 06-03-2024, 06:30 PM

Quote:

Originally Posted by HO455

The difference is the resistance caused by turning the pinon shaft.

Oh yeah, wouldjalookithat. Makes sense now, thanks

06-02-2024, 04:59 PM	#1
Rust_never_sleeps Senior Member Join Date: Jun 2022 Location: San Ramon,CA Posts: 589	ignorant 12 bolt question While adjusting rear drums, one wheel in the air, tranny in neutral... Rotating the rear hub by hand ~1/2 turn each way, I noticed different resistance going forward vs backward. Same with the drum off, so brakes not involved Is that unusual? __________________ 1970 C10 Custom longbed 350/350

06-03-2024, 12:54 AM	#3
Rust_never_sleeps Senior Member Join Date: Jun 2022 Location: San Ramon,CA Posts: 589	Re: ignorant 12 bolt question No limited slip on the SPID __________________ 1970 C10 Custom longbed 350/350

06-03-2024, 01:39 AM	#4
Richard Senior Member Join Date: Dec 1999 Location: Southern California Posts: 2,880	Re: ignorant 12 bolt question I would run it. But if you are worried about the axle maybe disconnect the driveshaft and try the test again with the drums off. Would bet what you are thinking is a problem goes away. __________________ Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 Last edited by Richard; 06-03-2024 at 01:45 AM.

06-03-2024, 02:03 PM	#5
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,217	Re: ignorant 12 bolt question . Recently I noticed the same thing on my 12 bolt posi equipped '67 while adjusting the rear drums. In neutral, it was way easier to turn the wheels one way vs the other way...don't remember which was which though. I used the easy turn to finish what I was doing and didn't think about it again until reading this post! -Kevin __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

06-03-2024, 04:58 PM	#6
Rust_never_sleeps Senior Member Join Date: Jun 2022 Location: San Ramon,CA Posts: 589	Re: ignorant 12 bolt question It felt the same without the drums. It wasn't alarming, but I couldn't think of a reason it'd be different. I need to swap the diff gasket and pinion anyway, so if there's anything wonky in there, I'll know soon enough. Thanks __________________ 1970 C10 Custom longbed 350/350

06-03-2024, 05:39 PM	#7
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,350	Re: ignorant 12 bolt question The difference is the resistance caused by turning the pinon shaft. If the ring and pinion were straight cut gears the torque to turn would be the same in both directions. With hypoid cut gears there is more drag induced when turning. The amount of drag differs depending on the direction turned. The amount of torque to turn is magnified by using the axle to turn the pinion or in other words driving the gears backwards. Attached Images __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377



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