Rear End ID help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

68C10HotRod · 09-22-2010, 01:01 AM

About a year ago, I got a 72 Burb with 400ci/TH400/posi SPID options. Well, I finally got around to working on it this last month. Have been noticing some odd things on the rear end lately.
1) the brake shoes are worn on the outer 1.5" of the 2" shoe - drum also doesn't encapsulate the backing plate either & matching odd wear.
2) DS drum was real gunky so figured the wheel cylinder needs replaced.
3) jacked up & spun 1 wheel forward to see the other side reverse.

Decided to remove the cover to confirm the G80 has been stolen in it's previous life.

It only got worse, the gears were marked 3817778 11:41 GM 11-68 3. Think this means it's a 3:73 set from Nov 68 in a 3 series carrier. The 400 should have been 3.07 std I believe. Can anyone confirm this?

PS housing tube says HA 1202 W. Not sure how to decode this. Think the gears & housing are from a 1968 & they just swapped the 6 & 5 lug axles - explains the odd brake pad/drum wear. Same with the drum & it doesn't sit all the way down around the backing plate. Also measured 55.25" from back-to-back plate on the rounded outer edge. Wheel mount surface with drums on was 63.75".

Any info would be appreciated & might help others.

raycow · 09-22-2010, 04:43 AM

I think you nailed it. Your PO did a complete rear end swap and then put the 72 shafts in the earlier housing to keep it 5 lug. He wasn't worried. No buyer was ever going to look.

Ray

**425HP409** · 09-22-2010, 10:27 AM

I did the exact thing your PO did before I was "Enlightened" in this forum. I put 72 5 lug axles in my 68 6 lug diff not knowing that they were different widths. My brake drums stuck out too far not engaging the shoes properly causing a soft pedal and poor stopping as the brake shoes were flexing upon application. A quick fix to keep your existing differential and axles is to install brake drums for 2.5" shoes. The NAPA part number is ND4401234 for the drums. You will then have full contact of the shoes to the drums, with a little left over.

68C10HotRod · 09-22-2010, 11:19 AM

Charles,

Thanks for that insight. That would allow them to function normally & could get me by without doing an entire rear end swap. My local NAPA sells those for $66.49/ea so I'll keep it in mind. Great info!!

On the other hand, if I can find a correct 3.07 posi rear in my neck of the woods for a reasonable price, I'd probably jump on that since the gears would help mileage a little & restore it to OEM.

Here's an extra question: What should the STD ratio be in a 1-leg 71 truck rear end?

capev86 · 09-22-2010, 02:45 PM

i personally like the 3.42-3.73 range gears (with an overdrive) but if you go hi-po and stroke out that 400 big block some day the 3.07 will be a reasonable on the highway. i'd also suggest you run the wider rear axle for better stability and looks.

09-22-2010, 01:01 AM	#1
68C10HotRod Registered User Join Date: Feb 2008 Location: Omaha, NE 68144 Posts: 333	Rear End ID help About a year ago, I got a 72 Burb with 400ci/TH400/posi SPID options. Well, I finally got around to working on it this last month. Have been noticing some odd things on the rear end lately. 1) the brake shoes are worn on the outer 1.5" of the 2" shoe - drum also doesn't encapsulate the backing plate either & matching odd wear. 2) DS drum was real gunky so figured the wheel cylinder needs replaced. 3) jacked up & spun 1 wheel forward to see the other side reverse. Decided to remove the cover to confirm the G80 has been stolen in it's previous life. It only got worse, the gears were marked 3817778 11:41 GM 11-68 3. Think this means it's a 3:73 set from Nov 68 in a 3 series carrier. The 400 should have been 3.07 std I believe. Can anyone confirm this? PS housing tube says HA 1202 W. Not sure how to decode this. Think the gears & housing are from a 1968 & they just swapped the 6 & 5 lug axles - explains the odd brake pad/drum wear. Same with the drum & it doesn't sit all the way down around the backing plate. Also measured 55.25" from back-to-back plate on the rounded outer edge. Wheel mount surface with drums on was 63.75". Any info would be appreciated & might help others. __________________ Bryan '52 Bel Air 2dr HT - in pieces '68 C10 - 6cyl/4spd REMOVED, LT1/T56 to be installed “Any society that would give up a little liberty to gain a little security will deserve neither and lose both.” - Benjamin Franklin "And those who know what's best for us, Must rise and save us from ourselves" - RUSH lyric (mockery)

09-22-2010, 04:43 AM	#2
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Rear End ID help I think you nailed it. Your PO did a complete rear end swap and then put the 72 shafts in the earlier housing to keep it 5 lug. He wasn't worried. No buyer was ever going to look. Ray

09-22-2010, 10:27 AM	#3
425HP409 425hp409 Join Date: Oct 2008 Location: Prosper Texas Posts: 841	Re: Rear End ID help I did the exact thing your PO did before I was "Enlightened" in this forum. I put 72 5 lug axles in my 68 6 lug diff not knowing that they were different widths. My brake drums stuck out too far not engaging the shoes properly causing a soft pedal and poor stopping as the brake shoes were flexing upon application. A quick fix to keep your existing differential and axles is to install brake drums for 2.5" shoes. The NAPA part number is ND4401234 for the drums. You will then have full contact of the shoes to the drums, with a little left over. __________________ Charles 68 SWB, Dad bought new, now 396 & factory ac 64 Impala SS, 409 425HP, 4 speed AC 64 Bel Air Wagon, 400 Small Block 57 Bel Air all original 283 w/Factory Air 77 GMC Sprint, 454/425HP 67 Olds 442, all original 90 ZR1 Corvette

09-22-2010, 11:19 AM	#4
68C10HotRod Registered User Join Date: Feb 2008 Location: Omaha, NE 68144 Posts: 333	Re: Rear End ID help Charles, Thanks for that insight. That would allow them to function normally & could get me by without doing an entire rear end swap. My local NAPA sells those for $66.49/ea so I'll keep it in mind. Great info!! On the other hand, if I can find a correct 3.07 posi rear in my neck of the woods for a reasonable price, I'd probably jump on that since the gears would help mileage a little & restore it to OEM. Here's an extra question: What should the STD ratio be in a 1-leg 71 truck rear end? __________________ Bryan '52 Bel Air 2dr HT - in pieces '68 C10 - 6cyl/4spd REMOVED, LT1/T56 to be installed “Any society that would give up a little liberty to gain a little security will deserve neither and lose both.” - Benjamin Franklin "And those who know what's best for us, Must rise and save us from ourselves" - RUSH lyric (mockery) Last edited by 68C10HotRod; 09-22-2010 at 11:21 AM. Reason: ratio

09-22-2010, 02:45 PM	#5
capev86 Registered User Join Date: May 2009 Location: Eliot, Maine Posts: 1,314	Re: Rear End ID help i personally like the 3.42-3.73 range gears (with an overdrive) but if you go hi-po and stroke out that 400 big block some day the 3.07 will be a reasonable on the highway. i'd also suggest you run the wider rear axle for better stability and looks. Last edited by capev86; 09-22-2010 at 02:46 PM.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.