Axle Position Firebird
 

On our '68 Firebird, I've measured the distance from the centerlines of the front wheels to the rears. The passenger side is 1/2" further forward than the driver's side. The OD of the tire touches the fender well on the passenger side.

As you can see in the photos, the difference is noticeable. The second picture is of the side that's close (Tire not centered in wheel well).

What locates the axle position on these cars? I thought there was a locating pin or slot to position the axle on the leaf springs.

Your talking about the tires rubbing the rear 1/4?

Is it possible to have one leaf turned around?

There is little to no adjustment that I'm aware of.


Here is a pic of the Hotchkis springs I put in next to some unknown leaf that was in it.
http://i1305.photobucket.com/albums/...psxrua4f80.jpg

There should be a pin on the leaf springs like in the pic above to center the axle. If the spring pad is missing or really worn it might cause what you're talking about. When I put the axle under my '67 without the pads so I could roll it around, there was about a 1/2" slop.

IIRC, the wheelbase should be 108" center of rear hub to center of front hub.

http://artmorrison.com/instructions/...Front-Clip.pdf

We checked to see if one of the springs was reversed. Not possible, since the front to center vs. rear to center is over 2" different. I think we're going to ignore the difference and use smaller OD tires.

Real problem is the 255-70r15 Goodrich T/A's being too big OD--29.1" will not fit the wheelwell no matter the rim offset. They rub at about the 10:00 position on the passenger side and 2:00 on the driver's side. The 235-70r15 is 28", which would work. Or, we could use 255-60r15's, which are only 27" OD. With the 4.11 gears this car has, the 235's would be better.

Again , if the pin is worn or even missing you can have the problem your having right now. I would take the u-bolts off on the side to close & make sure the spring in on the pin or if it missing or someone put a bolt instead of the pin in it can be to far away or to close to either the front or back of the wheel well. If there is no pin in the spring pack you can move the axle back & forth to put it where it needs to be to. Also if the hole in the bottom of the axle mount is bad or worn out it can move in the spring to. Don't change the tires until you find out the reason the axle isn't where it should be as that will throw off the way the car drives if it's off that much too. Fix the problem don't just put a band-aid on the problem .

There's 2 different ways the rear is centered on those cars (to my knowledge), and it's a matter if it's a multi-leaf or mono-leaf car. Really, the only thing that's different is the mount pad on the rear housing, and the isolator that's used with one or the other. (multi-leaf is thinner)

The locating pin on the leaf(s) don't pass thru the mount pad on the rear, it gets 'captured' in the isolator, which has a ridge or 'nub', and that is in a groove/hole in the mount pad. That portion of the isolator can wear, deteriorate, or can allow the rear to slip forward from hard launches, etc.

If you mix the isolators between the multi and mono leaf setups, all it takes is one launch and that thing moves. I've seen this happen when folks swap rears.

So, long story short, check your leaf isolators, and make sure you have the right ones for the pads you have. If the pads on the rear are for a mono leaf setup, and you have multi-leafs, you may have to make something to ensure it works/locates/retains the housing.

If by chance in the future, you order a new housing, like from Moser, use the 'hybrid' mono leaf mounting pad with multi-leafs, which properly locates the housing by the pin passing thru it, and eliminate the isolators all together. That's the ticket not only for ensuring proper location, but for high horsepower apps.

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A 29.1 is a big @ss tire for our birds. My tires are 25.5 tall. I think 26" is more of the norm.

I'm sure a smaller tire will give you the clearance but I would still be concerned with the 1/2" difference.

^^^^ This. Except measuring to the front wheel is nearly useless to judge the rear axle location. The difference could easily be the mounting of the sub frame and/or the front end alignment. If you adjust the camber you are moving the front wheel forwards/backwards slightly. Same thing with the toe as you are turning the wheel slightly.
Instead, I would measure to somewhere on the unibody and that would be after I measured the pin location on the leaf springs themselves.

In any case, it's not likely we can change it unless the error is in the springs and we buy different ones.

Yes, the 29.1" tire OD is big, but we were hoping to avoid changing rearend gears from the 4.11's. If the 8.5" Posi breaks, a 9" Ford will go in its place with a ratio in the mid 3's. That would be the logical time to fix the misalignment problem. Measuring from the front wheels to the rear would be the way to "adjust" the problem regardless of spring perch location, etc.

I have seen the "pins" on the leafs get bent or sheard off from slicks or hard use, perhaps the pin is sheared or bent allowing one spring to mis-align ? Tim john---

Here's the difference (pics) between mono and multi-leaf perches and a set of isolators. The isolator that has a 'nub' is for the leaf pin, and on mono-leaf perches, there are nubs on both the top and bottom isolators.

Like I mentioned, the pin doesn't actually mount positively in the perch, it 'floats' in the isolator, which makes it susceptible to slipping out or moving.

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I was thinking the same thing too. I'm just not sure what would be good reference points to use to determine if things are square.

Edit: I have never tried to measure from these. Maybe next for me.


http://www.pozziracing.com/Media/F_gen_Firebird_sub.jpg

You would use plumb bobs on strings to measure the distances.

I think you mean caster not camber...

It would be easier to measure the location of the housing between spring eyes.

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That smw thing is funny. Those are my initials. Put a piece of masking tape on the floor and make a X right under the plumb bob. That is how we measured the race car to see if it was bent after a big wreck.

Body shops use a "tram gauge" when checking/measuring for straightness on a frame machine.