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Old 11-21-2004, 05:35 PM
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How much side to side movement does a rear axle make

I narrowed a rear axle (just for mock up) and with the tire width I currently have I only have approximately 1/2 inch of clearance between the tire and frame and the same distance between the tire and fender. Is that enough clearance or would the rear axle move sideways more than that amount? It is a fat fender 50's pickup that I am Pro Streeting and I want to keep the 33/21.50/15 tires on it, but don't want them to rub anywhere on the fender or frame anywhere if the axle was to sache. I will be using a 4 link with a panhard bar, will this setup eliminate this problem?

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Old 11-21-2004, 05:42 PM
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Re: How much side to side movement does a rear axle make

Quote:
Originally posted by STATUTORY GRAPE
I narrowed a rear axle (just for mock up) and with the tire width I currently have I only have approximately 1/2 inch of clearance between the tire and frame and the same distance between the tire and fender. Is that enough clearance or would the rear axle move sideways more than that amount? It is a fat fender 50's pickup that I am Pro Streeting and I want to keep the 33/21.50/15 tires on it, but don't want them to rub anywhere on the fender or frame anywhere if the axle was to sache. I will be using a 4 link with a panhard bar, will this setup eliminate this problem?
It shouldn't move any more than the give in the panhard bar "Bushings" . there might be some body flex and or tire roll that could come into play. Make sure there is not sharp edges on the wheel opening lip.

I have the same size on my Camaro with about an inch clearance on the frame rail side and about that on the UPPER quarter panel 70 camaro qtrs. slant in at the top so my clearance issues are at the top of the quarter panel. I hope you don't have a problem or I might too.
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Old 11-21-2004, 05:56 PM
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The rear will move from side to side based on the total movement of the suspension (up and down) and the arc of the pan-hard bar. This could easily be a half inch either way especially in a pro-street situation with a somewhat short pan-hard bar. You would be better off in your case to use a watts link rather than a pan-hard bar.

The photo below shows a typical watts link. The gold pan-hard bars are connected to a swivel which would normally be mounted to the top of your differential. In this case it is mounted to a crossmember that mounts to a Mustang rear end. The article explains why and how a watts link allows full suspension travel without side to side movement. The video file shows how one works. You can see no side to side movement in the axle throughout it's entire range of movement.





Watts Link Explained

Watts Link Video

Centerline

Last edited by Centerline; 11-21-2004 at 06:02 PM.
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Old 11-21-2004, 06:02 PM
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I'm going to keep the tires one way or another, even if I have to widen the rear fenders (which has already been considered). I LOVE the look of the HUGE tires when veiwed from the rear of the truck,,,,AWESOME. I wanted it to set low to the ground also but I don't have enough clearance at the top of the fender when I factor in for suspension travel but after I put the roll pan on it will look lower anyway. I'm getting anxious because I have a seasonal job and it's time for me to be layed off so I will have approx. 4 months to work on my pro-street. Life couldn't be better
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Old 11-21-2004, 06:08 PM
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Quote:
Originally posted by STATUTORY GRAPE
I'm going to keep the tires one way or another, even if I have to widen the rear fenders (which has already been considered). I LOVE the look of the HUGE tires when veiwed from the rear of the truck,,,,AWESOME. I wanted it to set low to the ground also but I don't have enough clearance at the top of the fender when I factor in for suspension travel but after I put the roll pan on it will look lower anyway. I'm getting anxious because I have a seasonal job and it's time for me to be layed off so I will have approx. 4 months to work on my pro-street. Life couldn't be better
I have a wishbone track locater on mine. It has 0 movement side to side now. Under power may be a different story. Never considered the panhard bar movement. And that would most likely be a very short bar with 22.5" tires. My frame rails are only 15" apart. Yours can't be too much wider with those tires.

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Old 11-22-2004, 08:10 AM
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Statutory, you were probably a whiz at high school algebra and geometry, but, for those who had some trouble, let's look at how you can determine side-to-side axle movement by using the calculator function on your computer.

First, I'm assuming that the Panhard is horizontal at ride height. The roundy-round group like to play with Panhard angle, but, for a street and dragstrip car, there is no reason for the Panhard to be anything but horizontal at ride height.

Then, determine the maximum deviation from ride height, whether in jounce or rebound, and measure that total wheel travel. This is with BOTH tires going into either full jounce or full rebound. In other words, there is no rotation of the axle assembly relative to the rest of the car.

Go to the "scientific" version of the calculator on your computer. If you've never used the calculator function before, it will probably pop up in the standard version, so go to "view" and change it.

Enter the maximum wheel travel that you measured. Click on the "/" button. (On windows 98, it's right under the "CE" button.) Enter the length of the Panhard between pivot points and click on the "=" button. On the extreme left, there's a little box labeled "Inv." Click on it and an arrow should appear within the little box. Click on the "sin" button (below and to the right one column in windows 98). Click on the "cos" button. Click on the "*" button. (DO NOT confuse it with the "+" button. With my monitor, they look almost exactly alike.) Enter the Panhard length again. Click on the "=" button. Click on the "+/-" button. Click on the "+" button. Enter the Panhard length one last time. Click on the "=" button. What you see is the maximum side-to-side motion attributable to the Panhard bar ALONE.

Unfortunately, this isn't the full picture. Suppose the Panhard is mounted to the left frame rail and you're going through a left hand turn. The right tire is going into jounce, but the left is going into rebound. So, not only is the Panhard pulling the inside of the right tire into the frame rail, but the rotation of the axle assembly is making matters worse! Again, this can be calculated, after measuring angles and lengths corresponding to the mounting point of the Panhard to the axle housing and the fattest part of the tire section, but it's beyond the scope of this post.

And, finally, there's the matter of deflections, primarily of the tire carcass. I guess what I'm saying is that I'd almost guarantee interference with only half an inch of static clearance.
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Old 11-22-2004, 05:29 PM
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My frame width is 34" outside to outside but remember this is a 50's pickup with the wide rear fenders so my tires fit right under with no altercations except cutting out the inner wheel wells from the box. I can't use the lengthy equation since I haven't got my panhard bar and four link yet. I'm just getting some info before I begin "notching" my frame. I just purchased my tires a few weeks ago and I'm doing some measuring to make everything fits with as much room as possible so if anything has to be fabricated it can be done now before its to late. My fenders have a 1" "lip" rolled under from the outside so if I was to do some fabricating in that area, I would gain an extra inch on each side. Maybe I better plan on giving myself a good 1" of room on each side of the tire for good measure,,,,,, (SOMEHOW ). My only remaining option would be to move the frame rails inward when I notch the frame.
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Old 11-22-2004, 05:59 PM
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Quote:
Originally posted by STATUTORY GRAPE
My only remaining option would be to move the frame rails inward when I notch the frame.
That's the way most pro-street cars are built. It's really not that difficult to narrow the frame rails.

Here's an example of what I did on my pro-street 41 Chevy. I used a ladder bar setup but a 4 bar would be similar.



Centerline
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Old 11-22-2004, 06:33 PM
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I gave up on the panhard bar & went with the track locater. Panhard bar would have been only 14" long at most.
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Old 11-23-2004, 06:23 PM
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I like the looks of your set-up Centerline, that's basically what I have in mind for mine accept the narrowing of the frame rails. Narrowing is going to be a last resort. I guess if I have to, I could live with a tad bit narrower tires, just enough to compensate for side play of the axle but first I'm going to set mine up with as much clearance as I can and see what it does when I drive it. I plan on making EVERYTHING for mine right at home in my shop ( panhard bar, adjustable 4 link, brackets, braces, crossmembers, etc....) that way I can say I built it "literally". Last winter I chopped the top 5 1/2 inches and it turned out SUPER. It wasn't as much work as I was thinking it was going to be. This winter I'm going to "suicide" the doors utilizing the original hidden door hinges, SWEEEEEET
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