# Question on rear end size



## mrvandermey (Jun 15, 2011)

Hi guys, I know this sort of question has likely been asked a hundred times, but can some one tell me how close in size is a rear end from a '67 GTO compared to a rear end in '68 GTO is. If I recall, the rear end for my '68 was 55.25" for back plate to back plate. What is the size of a typical '67 rear end? if there is a size difference, will that affect the lower control arms or such?


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## Icefan71 (Apr 7, 2011)

I put a rear from a 66 Lemans in my 72. I was told the 64-66 rears are 2" narrower than the 67-72 rears. But, any A-body 64-72 rear can be swapped into any 64-72 A-body car. To answer your question, 67 and 68 should be the same size.


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## mrvandermey (Jun 15, 2011)

That is good to know. I discovered today that the rear end in question is actually a '66. I thought my internet search said it is 1" shorter over all. Anyone know for sure?


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## PontiacJim (Dec 29, 2012)

As usual, a web search provides all kinds of answers all different. Found this on the Hemmings web site.

Chevrolet used the division's own 8.2-inch 10-bolt and 12-bolt axles, while the other divisions used various other axle designs, including one 8.2-inch 10-bolt that saw use under certain Buicks, Oldsmobiles and Pontiacs, which led to its shorthand moniker, the "B-O-P" 10-bolt.

10-bolt 8.2-inch B-O-P axle usage:
• 1964-'66 Olds F-85, Cutlass, 4-4-2
• 1964-'72 Tempest/GTO
• 1967-'71 Firebird
• 1964-'71 Buick GS/Gran Sport 

hese 10-bolt axles were also offered in two different overall lengths: 1964-'65 assemblies were 56 1/2-inch, narrower than the 1966 and up units. This extra width was added between the brake backing plate and the lower suspension bracket--if your axle has 1 1/2-inches of space there, you have the later 58 1/2-inch wide axle. This can be important, as the axle-shaft lengths also differ between early and late and do not interchange.


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## mrvandermey (Jun 15, 2011)

oooh, I did not even think about the axel shafts. So if I were to us a '66 rear end in a '68 GTO, I should make sure I use '66 axel shafts. I was able to talk to owner of '66 rear end tonight, he said it measure 54 3/4" from side to side, and 55" from backing plate to backing plate.


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## geeteeohguy (Feb 2, 2008)

'66 is the same as a '68. '65 and earlier are 1" narrower. Bolt it in with no worries.


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## PontiacJim (Dec 29, 2012)

In a car magazine review of the 1968 GTO, it stated that the "new" 1968 GTO wide-track was 2" wider than the previous year. The track was 60" which makes the '67 at 58", and suspect the '66 as well. Now I don't know if some of this has anything to do with rim/tire size, which may add some. I also read a blog that stated that all lower control arms interchanged, but the top control arms were different, some early ones were shorter, so should not be a problem if you use the arms from the car you are installing it into. 

My Mitchell Interchange Manual stops at 1967 with regards to rear axle assemblies. The '66 & '67 axle shaft are the same, but cannot tell you about the '68. With regards to brakes, shoes and drums are the same up '64 to 1969. However, rear wheel cylinders seem to be a different part number. The '64 - '66 are the same and '67-'68 are listed as same. Don't know what the difference is. '64-'66 master cyl is the same for drum brakes while '67-'68 are the same (separated front & rear brake system I suspect). So, might want to use the '68 wheel cyl to match the '68 master cyl in your car?

That's about the best I can come up with. Hope it helps.


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## jetstang (Nov 5, 2008)

I heard 66 were 5/8" narrower per side than later. I put a 66 Chevelle 10 bolt in my 70 Lemans and tucked wider tires in, now I have a 66 12 bolt posi for the car. It bolted straight in without issue.


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