Rear Axle Swap - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 01-25-2012, 04:44 PM Thread Starter
 
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Rear Axle Swap

I finally found a rear end for my car, it's a ZH code Nodular 4 pinion 3:55 gear out of a 68 GTO. I currently have what I think is a Chevy 8.5 peg leg? Will this be a straight forward bolt in or is there alignment procedurers that need to be followed to get the drive shaft angle and square with the car? I would appreciate if someone could give me a dissasembly and reassembly order. I am hoping that the driveshaft length doesn't have to be altered. Thanks in advance.
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post #2 of 6 (permalink) Old 01-25-2012, 07:41 PM
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If you have an 8.5 rear end in there now, changes were made to get it there. If your arms were left alone, your new rear will bolt right in and be "in spec" from the get-go. Are you sure it's not an 8.2 already in there???
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post #3 of 6 (permalink) Old 01-25-2012, 07:43 PM
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It should be a bolt in, unless your car was modified to install the rear that's in it now. If you've got factory upper and lower control arms then there's not really any adjustment possible - you'll just get what you get. However it's still good to double check it to see where you're at. Any front end alignment shop that can do "4-wheel" alignments should be able to tell you if the axle is square in the car (actually square with the front axle). There are lots of reference sites on the internet that describe how to check your drive shaft angle. Here's one: DRIVE LINE PHASING

Generally, the procedure is to get the car high up in the air and support the frame with jack stands, support the rear axle at normal ride height with a good floor jack.
Disconnect the shocks from the rear axle.
Disconnect the drive shaft
Disconnect (and plug) the brake lines at the T fitting on the axle.
Disconnect the parking brake cables at the connectors just in front of the lower control arm frame mounts.
Use the floor jack to position the axle up or down so that the control arm bushings aren't in a bind.
Remove ONE of the upper control arm bolts on just one side (which end doesn't matter - do the easiest to get to)
Thread a piece of rope, chain, wire, etc through the center of each rear spring top to bottom (or bottom to top) and around the axle tube. Leave the loop "loose" enough so that when the spring expands fully it won't be in a bind, but only just. This is a safety precaution.
Tie a rope or something from the unbolted upper control arm mount on the axle to the frame. The intent here is to have something in place to keep the axle from flopping over backwards when you lower it later.
Remove one of the other upper control arm bolts on the other side.

At this point, the only things keeping the axle from flopping over forwards or backwards are the lower control arms and the springs and what you tied to the upper control arm mount, so be careful.

Slowly lower the floor jack to relase the tension on the springs. When they get loose enough they may pop out. That's why you tied them through the center - so that they can't throw themselves at your head when they come loose. If they don't come out on their own, pull them out by hand but again - be careful.

Push the axle forward so that it sort of "lays over" onto the lower control arms.
Unbolt the lower control arms (usually at the frame end) and use the jack to lower and remove the axle. You'll probably want some help to keep it balanced on the jack while someone else is operating the jack.

Installation is pretty much the reverse sequence. Don't forget to reconnect and bleed the brakes. Sometimes it takes some finagling with the jack, moving the axle up or down, to be able to get all the control arm bolts in. There is a correct orientation for the springs - how they're "clocked" and seated into the upper spring perches - so pay attention to how they're oriented before you relase the tension on them so you can reinstall them in the same positions.

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post #4 of 6 (permalink) Old 01-26-2012, 12:51 PM Thread Starter
 
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Ok I did some research and I found that the casting #3969277NF is for a 70 to 72 Chevelle and it's an 8.2, but the cover must be from something else because it doesn't match any 8.2 pic that I have seen. That's why it has been so hard to figure out what this is. So this should bolt right in?
Thanks Bear for the proceedure.
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post #5 of 6 (permalink) Old 01-26-2012, 03:36 PM
 
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I agree with the guys in that the rear will be an absolute bolt-in, just follow the steps Bear outlined earlier. There is , however, one very important item not yet mentioned, and that is the rear U-joint. In some years (I think all years... '64-72) the pinion yoke on a Chevy rear-end takes a smaller diameter U-joint cup than do the Pontiac, Olds, and Buick yokes (BOP). The BOP U-joint is pn 2-3011 and all 4 cups are the same (larger) diameter. To to do a Chevy rear into a GTO swap using the GTO driveshaft a 'crossover' u-joint, pn 3-3130, is used. The 3-3130 u-joint has 2 opposing cups in the diameter required for BOP and the other two are the correct diameter for the Chevy rear. Assuming your '68 GTO still has its original driveshaft AND believing the Chevy rear-end has the small cup yoke, you must replace the u-joint with the BOP unit at the same time you swap the rears. Otherwise, though the small cup will drop into the yoke on your new GTO rear-end, it will not be fully supported and will distort when cinched down and will certainly fail. But to confirm what you have, just take a cup from your U-joint and place it in the yoke of the new rear and see if it fits snugly or not. Good luck. And congratulations on locating a now hard to find Nodular 4-spider rear. Gary
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post #6 of 6 (permalink) Old 01-26-2012, 09:33 PM
 
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Agree with AZ. I put a Chevy rear in mine and had to get the conversion U joint. They may have put a Chevelle driveshaft in instead of the U joint. In that case, you'll need the reverse U joint to keep the Chevelle driveshaft, you'll have to measure the caps to find out what you have. If it's the Pontiac driveshaft, then just get a stock U joint.

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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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