[nadmik]

Hello,

Broke an upper control arm ear on my original '66 LeMans rear end (ouch). Going to have to swap another one in and would like to stay with a '66, but might have to purchase a different year.

Would like to know what will work and what will not work? I understand...I think..that the '65 rear is an inch shorter?..maybe thats just the axles? And the '67 has a different coil spring perch...can I make my '66 spring work with this rear? Am I correct thinking that the '68 and above is an inch wider and will not work?.

I'm trying to stay away from as much modifications as possible and I don't mind too much the 2.78's that are in there now...so performance is not that big of a deal. I only say this because I have the stock 326, 2bbl and going to a 3.55 posi will not change things much.

Any help and suggestions would be appreciated.

Thanks, Dan

[nadmik]

And...I already have a follow up question.

If I buy a '67 rear housing, can I use the gears and axles from my '66 rear? Is it a straight swap?

Thanks again..

[nadmik]

Found this link on an older post...guess I'm answering my own question:-)

http://442.com/oldsfaq/ofdif.htm#DIF...ial%20Swapping

Swapping
Gears are available for most every differential. But buying and installing a bunch of parts can get expensive - fast. It would probably be a bunch cheaper in the long run to find the rear with the gears and anti-spin that you want.

Interchange Guide

From 64-66 to 64-66 Model(s) GM A-body - Cutlass, Chevelle, LeMans, Skylark = bolt in.

From 67 to 64-66 GM A-body Lower spring perch is different, requiring the use of the 67 springs.

From 68-72 to 64-66 GM A-body Axles are about an inch wider than the earlier ones and also have the control arm mounting locations in a slightly different place; the axle will physically bolt up to the early car but the pinion angle will be wrong.

This table works in the opposite direction ("year to" to "year from") as well.


[ Thanks to Joe Padavano for this information ]

[getmygoat]

Wow, does this mean a Jan 67 dated rear doesn't work well in a 1970 GTO?

I just invested a bunch of $$$$ in such a situation... about to install it.

Fred

p.s. - I hate it when I screw up.

[copper128]

Originally Posted by getmygoat

Wow, does this mean a Jan 67 dated rear doesn't work well in a 1970 GTO?

I just invested a bunch of $$$$ in such a situation... about to install it.

Fred

p.s. - I hate it when I screw up.

That shouldn't be a problem unless you have big tires and a lot of backspacing in your wheels. The '67 rear is a little narrower and will probably pull the wheels in a 1/2" or so per side, so if yout tire/wheel combo was close on the inside before, you might get interference.

[getmygoat]

Originally Posted by copper128

That shouldn't be a problem unless you have big tires and a lot of backspacing in your wheels. The '67 rear is a little narrower and will probably pull the wheels in a 1/2" or so per side, so if yout tire/wheel combo was close on the inside before, you might get interference.

I have the stock 14" rally II's on there... But how about the pinion angle? Are the "ears" in the right spot?

[Shadowjack]

According to conventional wisdom, '67 was a transition year for that width change, but nobody can show proof exactly when the change occurred. It may have been early in the '67 model year, it may have been late. In any case, the spring perch DID change right at the '66-'67 model year, so if you have a '67 rear, no matter the width, it will fit a '70 with no issues. The springs are the same.

[getmygoat]

Originally Posted by Shadowjack

According to conventional wisdom, '67 was a transition year for that width change, but nobody can show proof exactly when the change occurred. It may have been early in the '67 model year, it may have been late. In any case, the spring perch DID change right at the '66-'67 model year, so if you have a '67 rear, no matter the width, it will fit a '70 with no issues. The springs are the same.

Thanks, but I don't think "springs are the same" = "no issues".. i.e. I'm worried about the pinion angle. Well, I'll probably pick it up tomorrow, and I can compare it side by side with the Chevy rear I pulled out.... at least..

Not sure what that will tell me exactly.

Sorry to hijack the thread.

[Shadowjack]

"No issues" means "no issues". '67-'70 rear axle center castings are all the same. '67-'70 control arms are all the same. And the pinion angle varies more with the changes in ride height caused by different-length rear springs than any other factor.

[Pontirag]

Not for nothing but I always thought that the rear tread width increased by 1 inch in the '68 model year. but checking Zazarine/Roberts "Pontiac Restoration Guide '64-70" '85 edition states that "the rear axle design was unchanged for 66-67 although the '67 rear tread was widened one inch". pg. 307. Yet several rear end catalogs indicate as I suspected and as was stated the axle width change occured between 67 and 68.

While Zazarine/Roberts book identifies several and various changes in the 66-70 rear end designs such as spring perch changes, tread width changes differential information stamp locations, new ring gear, bolts and differential case changes and the intro of pontiacs 12 bolt rear plus two types of axle bearings available in '70 10 bolt rears. no mention is made of upper control arm mounting location changes. That does not mean it didn't happen. And this aint the bible but with so much info on other changes.....?

If that does not confuse you enough.... Parts catalogs indicate that although lower trailing arms are the same between 64-72, uppers are different between 64-67 and 68-72. Further more the rear crossmember reinforcing braces available on manual trans models was also different between 64-67 and 68-72. But the no-hop/ anti hop bars manufactured by Edelbrock and others designed to decrease pinion angle, mounted to the upper control arm mounting points on A-body rears fit all A-bodies 64-72. so I think the difference is it the frame, not the rear upper control arm mounts on the housing.

I think the upper trailing arm mounts are all in the same location on each rear but pinion angle will change if you accidently use the wrong year upper control arms. Stick with the ones that go with your frame.

i'm just as confused now as you were befor reading this. Go deep into left field and buy a moser rear and all new arms from Hotchkis, what the hey! Kids diapers dont fill up if you stop buying them food and if you put peanut butter in thier mouth they stop cryin too. Its win win all around! Unless wifey wises up to it and sneaks off to buy shoes or a hand bag.

[getmygoat]

Well, I picked up my 1967 GTO differential today... Its been fully rebuilt and detailed..

I took some measurements of the length, trying to sort out if its the pre 67 "narrow" version or the 68-72 compatible "wide" version. (Measure is without backing plates, as I need to paint those first :-)

Not sure if anyone knows these well enough to tell if the "ears" are setup correctly for a 70 GTO (i.e. no pinion angle problems).

Thanks for any insights.

[6T5 Cat]

You have a 67 housing. The date code indicates the housing was cast on Jan 25,1967. Pontiac went to a 1 inch wider rear for the 67 A Body cars, Chev didn't change to the wider housing untill 68. There's no problem with the ears on the housings, there were some minor differences in the spring perch angles between the GM divisions, but nothing to cause any major problems if exchanging rears. The lower control arms are the same, but begining in 68 the upper control arms are not the same length because of the change to a different frame design . So, use the correct upper control arms and there's no problem. I went through this issue when changing rears in my 65 and 67 GTOs.

[68Ragtopp]

I just had a posi carrier put in my 68 GTO and I measured it like your picture. The measurment I got was 55 1/2" (however, it depends on how you run the tape across the center of the rear end). By the way what gear do you have and how much did you pay? Just curious what they are going for it cost me $900 to have a new auburn posi carrier and 2 new axle bearings put into my rear.

[Shadowjack]

This is out of a '69. Is it 1" narrower, 1" wider, or the same as you guys'?

[6T5 Cat]

SJ, that's the wide housing.

[lust4speed]

Just a little more proof. The original Pontiac 10 bolt in my '67 is 55.5" flange to flange as is the Chevy 10 bolt out of a 1969 El Camino I have sitting on the garage floor at the moment.

So this would mean that the earlier rears were only 54.5" flange to flange?

[getmygoat]

Originally Posted by 68Ragtopp

I just had a posi carrier put in my 68 GTO and I measured it like your picture. The measurment I got was 55 1/2" (however, it depends on how you run the tape across the center of the rear end). By the way what gear do you have and how much did you pay? Just curious what they are going for it cost me $900 to have a new auburn posi carrier and 2 new axle bearings put into my rear.

68Ragtop - Is your rear original to your car? What is the date code? Perhaps all this variability is just measurement error?

Fred

p.s. - I paid $1100 to rebuild and detail the rear, including a new eaton posi carrier. (not including brake stuff)

[copper128]

Originally Posted by getmygoat

p.s. - I paid $1100 to rebuild and detail the rear, including a new eaton posi carrier. (not including brake stuff)

I think I did pretty well then. I paid $675 to have my 67 Olds 12-bolt disassembled, housing blasted & painted, a new Eaton posi and 3.90 R&P installed with new bearings and seals.