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    Rear end interchange list?

    blacknred79
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    Post  blacknred79 on Thu Aug 30, 2018 6:15 pm

    It looks like I am not the only one searching this out here lately. My '79 coupe just puked the 7.5" rear for no apparent reason.......don't beat on it; it's full of oil, axle seals don't leak; yet it sounds like the ring and pinion crapped the bed. This is my only road worthy transportation right now; so I am really up a creek. I would just as soon put another 7.5" rear back in it with the same stupid lazy highway gears (2.41's?) that I think it's equipped with to keep everything as is and not throw off the speedometer. You'd think these rears would be given away for free since everyone wants the better 8.5" rears; but I am sure most of these have been scrapped by now. At this point I need to get the car back on the road; so if anyone has an interchange list for the rear ends I'd appreciate any help you can give me! Thanks, Ed
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    Post  rfoll on Fri Sep 14, 2018 10:31 am

    Many B bodies came with the 8.5. Cop cars and taxicabs. The bolt pattern is 5 on 5, and won't fit your wheels. The brakes are larger and will likely alter the front to rear braking balance. I was told the early 70s Malibu 8.5 will bolt in, and will have the smaller brakes and bolt pattern. I have to ask why you need the bigger rear end? If you don't put slicks on the car and add a bunch of horsepower, you don't need the 8.5. If the oil has been changed regularly, the 7.5 is good for about 200K before it needs axles and bearings. The spider gears start to flake at about the same time. If a previous owner had a habit of 1 wheel burnouts it will eat the pinion shaft, and everything goes downhill from there. I put 2.73 gears in mine and it makes a happy city/highway gear.
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    Post  blacknred79 on Fri Sep 14, 2018 11:12 am

    rfoll wrote:Many B bodies came with the 8.5. Cop cars and taxicabs. The bolt pattern is 5 on 5, and won't fit your wheels. The brakes are larger and will likely alter the front to rear braking balance. I was told the early 70s Malibu 8.5 will bolt in, and will have the smaller brakes and bolt pattern. I have to ask why you need the bigger rear end? If you don't put slicks on the car and add a bunch of horsepower, you don't need the 8.5. If the oil has been changed regularly, the 7.5 is good for about 200K before it needs axles and bearings. The spider gears start to flake at about the same time. If a previous owner had a habit of 1 wheel burnouts it will eat the pinion shaft, and everything goes downhill from there. I put 2.73 gears in mine and it makes a happy city/highway gear.

    Thanks for the information. That is what I had found out already from reading what I could find on the forum. I stated above that I would prefer another 7.5" rear; not the larger 8.5" one. The car does not appear to have been beat on ever; and it had 89,000 miles on it when I bought it 3 years ago. I've never even tried to do a burn out with it; and don't beat on it at all other than the few times I had to pass someone that was driving way too slow.

    If the ring and pinion from a first generation S10 7.5" rear will swap in place of the Caprice's 7.5's a family relative has a set of 3.42's, 3.73's, or 4.11's that I can choose from. Obviously, I would go for the 3.42's at this point to keep it as driver friendly as possible. Can anyone weigh in on this?
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    Post  rfoll on Fri Sep 14, 2018 11:35 am

    If you use the 3.42, you won't like it on the freeway. It will make you think you added 100 hp.
    blacknred79
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    Post  blacknred79 on Fri Sep 14, 2018 11:50 am

    rfoll wrote:If you use the 3.42, you won't like it on the freeway. It will make you think you added 100 hp.

    Perhaps not, but if it will get the car back on the road it is better than a kick in the teeth at this point. I do not do much or any highway driving with the car quite honestly; but do drive around 55-60mph on some stretches of country 2 lane roads.
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    Post  GLHS60 on Fri Sep 14, 2018 12:31 pm

    1973-1977 Chevelle, Monte Carlo, ElCamino, Buick Skylark, Olds Cutlass, Pontiac LeMans and G.P.

    Most had 8.5" rears, some are BOP, (non C clip), some are Chevy with C clips.

    All are 4.75 wheel bolt circle.

    Thanks
    Randy

    blacknred79 wrote:It looks like I am not the only one searching this out here lately. My '79 coupe just puked the 7.5" rear for no apparent reason.......don't beat on it; it's full of oil, axle seals don't leak; yet it sounds like the ring and pinion crapped the bed. This is my only road worthy transportation right now; so I am really up a creek. I would just as soon put another 7.5" rear back in it with the same stupid lazy highway gears (2.41's?) that I think it's equipped with to keep everything as is and not throw off the speedometer. You'd think these rears would be given away for free since everyone wants the better 8.5" rears; but I am sure most of these have been scrapped by now. At this point I need to get the car back on the road; so if anyone has an interchange list for the rear ends I'd appreciate any help you can give me! Thanks, Ed
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    Post  blacknred79 on Fri Sep 14, 2018 2:55 pm

    Thanks for the information Randy! That helps! What about the '84-'93 S10 rears? Will the 'innards' interchange? I am sure the housings/axles are not as wide; but think I was old that the ring and pinion are........between an Impala/Caprice 7.5" rear and the S10 7.5" rear.
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    Rear end interchange list? Empty Not helpful - I'm bragging

    Post  plepgeat on Fri Sep 14, 2018 10:52 pm

    I run a Moser 9" with 3.89s in my formerly diesel 1979 Delta 88 2-door, but I'm also putting down 315 horsepower at the wheels through a 4L80E so I need the beef.

    And I wouldn't run Moser again; I'd try to find a GM 12-bolt or use Currie for a Ford 9-inch if I couldn't find one.
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    Post  blacknred79 on Fri Sep 14, 2018 11:29 pm

    Like you said, we have two different 'types' of cars here. I just want mine back on the road for simple transportation and enjoyment before it gets parked in the garage for the winter. My Caprice has what I believe to be the original stock 305.....nothing special horsepower wise; so the 'wimpy' 7.5" stock GM rear will suffice. I am hoping that a family member can come through and help me rebuild the rear at this point.
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    Post  rfoll on Sat Sep 15, 2018 12:01 pm

    The 8.5 will require a shorter drive shaft. The carrier in your current rear, (assuming the common 2.41 ratio), won't work with any gears lower than 3.08. The S-10 gears will likely work, but the carrier might not have the same axle spline count. This might be a good time to pop the cover off for a good look and a real diagnosis.
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    Post  blacknred79 on Sat Sep 15, 2018 12:11 pm

    rfoll wrote:The 8.5 will require a shorter drive shaft. The carrier in your current rear, (assuming the common 2.41 ratio), won't  work with any gears lower than 3.08. The S-10 gears will likely work, but the carrier might not have the same axle spline count. This might be a good time to pop the cover off for a good look and a real diagnosis.

    Thanks! That is the most pertinent information I've heard so far. I have been reluctant to drop the diff cover at this point because I don't want to cripple the car in my garage if it has to go somewhere else to be fixed. I know that I will have a more solid answer on what is wrong with the rear by dropping the cover though.
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    Post  rfoll on Sat Sep 15, 2018 12:17 pm

    It's only going to cost oil and gasket to look. You can refill using a weed sprayer with a different hose attached. At this point we want pictures of the carnage. There is a tolerable chance the problem is a pinion bearing.
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    Post  blacknred79 on Sat Sep 15, 2018 12:29 pm

    rfoll wrote:It's only going to cost oil and gasket to look. You can refill using a weed sprayer with a different hose attached. At this point we want pictures of the carnage. There is a tolerable chance the problem is a pinion bearing.

    I thought about that; and really hope you are right! LOL! I would weirdly prefer to keep the long legged highway gears; despite the hot rodder in me wanting to see how the car would respond to a slightly steeper gear! LOL! I have to wait on a family member who mentioned possibly giving me a hand here with it. I have three crushed discs in my neck; so I am not too anxious to crawl under the car again.
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    Post  GLHS60 on Sat Sep 15, 2018 1:26 pm

    The 7.5 S-10 ring and pinion will fit but finding a suitable ratio could be an issue.

    3.08 -3.23 -3.42 -3.73 -4.10 were common ratios from 1983-1992, 26 spline.

    Some 1988 and newer(7.625) were 28 spline but your 1979 Impala should be 26 spline.

    Your 2:41 carrier would be a "2" series and should work with ratios up to 3:08

    3:23 and steeper gears require a "3" series carrier or a ring gear spacer.

    If junkyard shopping grabbing the complete "innards" might be the way to go including the side spacers.

    Thanks
    Randy






    blacknred79 wrote:Thanks for the information Randy! That helps! What about the '84-'93 S10 rears? Will the 'innards' interchange? I am sure the housings/axles are not as wide; but think I was old that the ring and pinion are........between an Impala/Caprice 7.5" rear and the S10 7.5" rear.


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    blacknred79
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    Post  blacknred79 on Sat Sep 15, 2018 1:58 pm

    GLHS60 wrote:The 7.5 S-10 ring and pinion will fit but finding a suitable ratio could be an issue.

    3.08 -3.23 -3.42 -3.73 -4.10 were common ratios from 1983-1992, 26 spline.

    Some 1988 and newer(7.625) were 28 spline but your 1979 Impala should be 26 spline.

    Your 2:41 carrier would be a "2" series and should work with ratios up to 3:08

    3:23 and steeper gears require a "3" series carrier or a ring gear spacer.

    If junkyard shopping grabbing the complete "innards" might be the way to go including the side spacers.

    Thanks
    Randy

    You've been very helpful Randy! My wife's cousin should have the complete 'innards' from what he was saying; so that basically answers my other question.




    blacknred79 wrote:Thanks for the information Randy! That helps! What about the '84-'93 S10 rears? Will the 'innards' interchange? I am sure the housings/axles are not as wide; but think I was old that the ring and pinion are........between an Impala/Caprice 7.5" rear and the S10 7.5" rear.
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    Post  GLHS60 on Sat Sep 15, 2018 3:37 pm

    blacknred79 wrote:
    GLHS60 wrote:The 7.5 S-10 ring and pinion will fit but finding a suitable ratio could be an issue.

    3.08 -3.23 -3.42 -3.73 -4.10 were common ratios from 1983-1992, 26 spline.

    Some 1988 and newer(7.625) were 28 spline but your 1979 Impala should be 26 spline.

    Your 2:41 carrier would be a "2" series and should work with ratios up to 3:08

    3:23 and steeper gears require a "3" series carrier or a ring gear spacer.

    If junkyard shopping grabbing the complete "innards" might be the way to go including the side spacers.

    Thanks
    Randy

    You've been very helpful Randy! My wife's cousin should have the complete 'innards' from what he was saying; so that basically answers my other question.

    Right on my friend, happy to help!!

    Thanks
    Randy


    blacknred79 wrote:Thanks for the information Randy! That helps! What about the '84-'93 S10 rears? Will the 'innards' interchange? I am sure the housings/axles are not as wide; but think I was old that the ring and pinion are........between an Impala/Caprice 7.5" rear and the S10 7.5" rear.


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    Post  blacknred79 on Sun Aug 11, 2019 6:13 pm

    rfoll wrote:It's only going to cost oil and gasket to look. You can refill using a weed sprayer with a different hose attached. At this point we want pictures of the carnage. There is a tolerable chance the problem is a pinion bearing.

    I'm afraid you might have been right all along. This past fall I replaced the outer wheel bearings and seals since at least one side was bad; and it appeared that the center pin for the spider gears had excessive play. I now believe that the play in the old pin was normal but at the time we put another used one in that fit a hair more snug, dumped fresh oil in it, and buttoned it back up. The noise still persisted. The car was then parked for the winter and come spring time I pulled it out and started driving it again. At some point (don't recall exactly when) it appeared that the noise went away or at least got much quieter. Then several weeks ago I noticed the noise came back and started increasing over the 3 week span. The family member who helped me tear the rear apart the first time believed that the spider gears were the culprit. I now know that was unlikely; but not before I ordered new ones from Summit and swapped them out a week ago. The noise obviously did not go away. Another close car buddy of mine that I've known for 20+ years came up from North Carolina and helped me swap out the starter and tear the rear apart again. He checked the carrier bearings and couldn't find anything wrong with them. After inspecting the axles were they ride on the outer bearings he was sure that the passenger side axle was bad.....having gone through the exact same thing years ago with an S10 Blazer he had. I just got a new axle in from Summit this past week and swapped it out along with a new bearing and seal. Needless to say that was still not the problem! The rear is not leaking from the front or anywhere else, u-joints feel tight, and I don't think there's too much play at the back of the trans either. So, am I screwed now that I have more than $300.00 tied up into this turd? I could have likely bought a used rear (if I could find one) for less than $300.00; or paid someone to fix it if we knew up front it was the carrier bearing for example. Now I'm tapped out and our daily driver is down for the count too.......and we need the Caprice for transportation. If anyone has any suggestions or more information let me know please.....Ed

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