I need help decoding my rear eand - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 07-30-2017, 08:17 AM Thread Starter
 
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I need help decoding my rear eand

I have a 1971 lemans sport. I cant find any info on the rear end in it. Here is what is stamped on the axle tube. Any help would be greatly appreciated
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post #2 of 10 (permalink) Old 07-30-2017, 08:36 AM Thread Starter
 
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Here is what is on the pinion housing
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post #3 of 10 (permalink) Old 07-30-2017, 11:52 AM
 
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Mike, don't recognize the tube stamping. The K at the end of the stamp string stands for McKinnon industries in Canada. McKinnon had a rearend plant for GM for various applications. About to head out to my hsg racks to double ck the casting number. The pic you have provided of the front lwr area of the center hsg, almost convincing enough to say by the looks of the lugs back by the rear cover, that's its the most common style of 8.5 A-body hsg, but I'm begiing to think its a 7.5. Something about that axle tube stamping, though, that and even the hsg tube looks thin. Are the axle tubes 3" in diameter?

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post #4 of 10 (permalink) Old 07-30-2017, 03:44 PM Thread Starter
 
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here are two more of the pinion housing.
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post #5 of 10 (permalink) Old 07-30-2017, 04:03 PM Thread Starter
 
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here is a pic of the back of it
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post #6 of 10 (permalink) Old 07-30-2017, 05:14 PM
 
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Does this rear end have bolt in axles?

If so, are there 4 access holes in the axle flange (where the drum seats). If you haven't pulled the drums, feel free & shoot a pic of the back of the backing plates where they bolt to the rearend hsg, & I will respond. If it is what I think it might be, have two of the same hsgs still to move & put in the racks.
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post #7 of 10 (permalink) Old 07-31-2017, 05:31 AM Thread Starter
 
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here are the pics of the backing plates
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post #8 of 10 (permalink) Old 07-31-2017, 01:18 PM
 
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Mike, your latest pics confirm a c-clip axle GM rear. I'm betting if you look closely at the upper control arms, the upper control are not perfectly straight, or the upper arms are in a bind with the wider spaced upper control arms. If the upper control arms are perfectly normal (not chop sawed & rewelded) angled upper control arms or some type of fabricated tubular upper control arm, then the rear is some sort of '68-72 c-clip axle low performance Chevy 8.2 10 bolt rear, & the axle code Is not listed in my Hollander interchange books.

Over the years, I've also built quite a few '73-77 bolt-in axle 8.5 A-body rears, as well as '78-87 A/G series 7.5 rears & about a dozen '84-87 8.5 G-body (Grand National) rears. All the '73 up style rear ends with upper control arm mounts, they all have a wider spread & slightly different angle between the upper control arm perches than the earlier '64 & '65-72 A-body rears, the '73-77's are also nearly an 1" wider than the stock '72 A-body rears. The pic you have of the axle tube with the LZ, maybe it's an optical illusion, but that axle tube sure look small. All the different stock '64-72 GM A & '67-81 F-body rears have 3" OD axle tubes. 3 " diam tubes were also continued on 8.5 & 8.875 MP series B-body rears up through the 80's. On B -bodys, 3" diam 8.5's continued up through the 90's on Caprices & Roadmasters.

The 7.5 light duty 10 bolts started showing up in '77 models under small engine leaf spring Venturas, Omegas, Novas. Believe they were also avail in '77 Pontiac & Buick B series with wimpy engines. All '78-83 A-G series rearends are 7.5's, they are narrow, aprox 52 3/4" inside of backing plate to inside backing plate. These 7.5 A/G series rears I've actually had two that came in rigged under '70 & 72 LeMans parts cars. The 7.5' B series rear was first avail in '77 & continued up into the mid 80's in lowest powered GM B series. These c-clip axle B series rears are same width as '73-77 A body rearends. Both will have same spot perches as the '73-77 A-body rears & will have 4 3/4 boltpattern axles. I would measure the axle tubes, are they 3" in diameter or closer to 2.5" in diameter??? Either way, if you have one of these later rears up under your '72 LeMans Sport, there is going to be control arm geometry problems. In the 90's, I built numerous '71-72 8.5 A body rears & one narrowed 12 bolt Malibu rear to go in heavily modded '78-87 ElCaminos & '78 Malibus. In order to get the control arm geometry right, my customers bought special rear swap control arms.... trying to remember who fabbed them. WIthout the fabricated upper control arms, the swapped in earlier A-body rears, the pinion pointed up a bunch & it was a real fight to get next to worn out bushing stock upper control arms to bolt on. As mentioned earlier, ive seen later rears made to qto under '64-72 A-body's, but this was just a temporary thing to make the project car a roller as there was all kinds of binding going on.

Last, I'd look at the stock pinion flange. U bolts, lock washers, & nuts, the rear is a c clip axle 8.2 Chevy. 7/16" headed bolts & stamped steel straps to retain the ujoint, you have a later rearend, one def need to ck the axle tube diameter to tellif a 7.5. I do have a listing in my latest Hollander Edition (the 47th) for an LZ coded 8.5 10 bolt, one with 2.41 gearing & an S spring posi. That c-clip rear was used in an '81 Chevy Impalla. Having tore down well over 1500 GM rears, many many from the early to mid 80's harvesting gear sets, the stamping of the LZ sure looks '80's to me. unfortunately, I do not have 55th edition Hollander to ck mid to late 80's axle codes.
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post #9 of 10 (permalink) Old 07-31-2017, 01:29 PM Thread Starter
 
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Thank you so much. Yes, the control arms are straight so it is some kind of 10 bolt posi out of a 68-72 a body. I am going to take it to a shop to have them replace the pinion seal and tell me what kind of gears are in it.
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post #10 of 10 (permalink) Old 07-31-2017, 01:46 PM
 
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Good to hear the stamped steel upper control arms are straight, def a Chebby 8.2. The Chebby 8.2 rears used a splash lip style rear cover. As there is also a splash lip type rear cover that's used on certain '71-74 8.5 A-body rears & since all the round style 8.5 & Chevy 8.2 rears covers can be swapped backe and forth, i hate to ID 10 bolts by cover style alone.
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