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Old 10-17-2005, 08:52 PM
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Half inch offset on frame

I bought a 34 ford project that was being built as a pro street. The frame was built at a professional frame shop, so I was told. I'm about to weld in a ladder bar rear suspension to the rear axle.
Here's my question. A neighbor of mine says that if the frame was built correctly there would be a half inch offset in the rear section of the frame. There appears to be one. Why would a frame be built with a half inch offset only to weld in the rear to correct the offset? Why not just have everything centered all the way from front to rear. None of my friends seem to have a clue. They all thought that everything is always centered.
Why the offset ????????

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Last edited by jaxhome; 10-17-2005 at 08:54 PM. Reason: Used a word twice in a row
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Old 10-17-2005, 09:23 PM
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Could be wrong but I suspect it was set up for a 9" or similar rear end where the pinion isn't centered. It's possible that the offset built into the frame was designed to center the pinion.
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Old 10-17-2005, 09:50 PM
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offset

Centerline, i think you are right. When i put the s10 rear in my 48 chevy the pinion was not centered. I never thought of offseting the frame. So i agree with you.
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Old 10-18-2005, 07:12 AM
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If it is for the 9" rear, then why a 1/2" offset? I thought all 9" rears had a 2" offset. I know that is what mine has. Seems to me a 1/2" frame offset is a lot of work to go to when you would still end up with the pinion offset well over an inch. Plus, I'm having trouble figuring out how the geometry of an offset rear frame rail would even work. Yes, you could center the pinion, but then your drivers side axle is going to stick out 2" from the center line of the car, and your passenger side is going to be inset 2". Maybe somebody could do one of those nifty photoshop drawings to help my slow brain visualize how a frame offset would solve more problems than it would cause.

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Old 10-18-2005, 07:57 AM
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Quote:
Originally Posted by cboy
If it is for the 9" rear, then why a 1/2" offset? I thought all 9" rears had a 2" offset. I know that is what mine has. Seems to me a 1/2" frame offset is a lot of work to go to when you would still end up with the pinion offset well over an inch. Plus, I'm having trouble figuring out how the geometry of an offset rear frame rail would even work. Yes, you could center the pinion, but then your drivers side axle is going to stick out 2" from the center line of the car, and your passenger side is going to be inset 2". Maybe somebody could do one of those nifty photoshop drawings to help my slow brain visualize how a frame offset would solve more problems than it would cause.

Dewey
There are other rears that have less offset than the 9" but when I first read the post I had the same thoughts you did but couldn't figure out any other explanation. Other than to center the pinion the only thing I can think of would be if it's the main crossmember or "X" section that's offset in order to allow engine and trans to be mounted a little off center for steering clearance or something. You're right that a drawing or pic might help to explain this.
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Old 10-18-2005, 09:10 AM
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Quote:
Originally Posted by Centerline
There are other rears that have less offset than the 9" ... Other than to center the pinion the only thing I can think of would be if it's the main crossmember or "X" section that's offset in order to allow engine and trans to be mounted a little off center for steering clearance or something.
I think moving the engine/trans mounts, as you suggest, is a far more traditional way of aligning with the pinion than some sort of jog in the rear frame section. You are absolutely right that there are rears with less offset then the Ford 9", but then I start to wonder why anyone would go to the effort at all. Back when I put a 307/350 in a Mazda RX-7, the rear end shop I went to said it was advantageous to retain the offset between the trans tail shaft and the pinion. I never did quite understand his reasoning, but he claimed a pinion in direct left/right alignment with the tail shaft would cause more potential problems than if the two were offset (but parallel). I'm with you...I don't quite understand what jaxhome's neighbor had in mind regarding the frame offset but now I'm sure curious.
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Old 10-18-2005, 04:02 PM
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Offset

My neighbor, who also designs and builds drag racing cars for people, looked over the frame again today. He claims the engine and tranny are centered, but the rear frame rails are 1/2 inch off. His fix it plan is to move the engine mounts over 1/2 inch. Thus an offset of 1/2 inch all the way down the car.
After he left I called in another guy with frame building skills and he said the 1/2 inch offset, which works out to be 1/4 inch each way is no big deal. He feels lots of cars come off the assembly line with a 1/4 inch off. plus, 9 inch rears are 2 inches off and guys run them He says weld it up and be happy. Some dilemma. Who's right? Got me!!!!
Also, does anyone know if there is a offset on the body of a 1934 ford? I'm wondering if the rear frame rails are offset becuse the body in 1934 was offset, and this frame was supposedly built for this car.
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Old 10-18-2005, 05:43 PM
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Quote:
Originally Posted by jaxhome
My neighbor, who also designs and builds drag racing cars for people, looked over the frame again today. He claims the engine and tranny are centered, but the rear frame rails are 1/2 inch off. His fix it plan is to move the engine mounts over 1/2 inch. Thus an offset of 1/2 inch all the way down the car.
After he left I called in another guy with frame building skills and he said the 1/2 inch offset, which works out to be 1/4 inch each way is no big deal. He feels lots of cars come off the assembly line with a 1/4 inch off. plus, 9 inch rears are 2 inches off and guys run them He says weld it up and be happy. Some dilemma. Who's right? Got me!!!!
Also, does anyone know if there is a offset on the body of a 1934 ford? I'm wondering if the rear frame rails are offset becuse the body in 1934 was offset, and this frame was supposedly built for this car.
the critical demention for drive angle is the face of trans to face of pinion must be withe in 5 degrees I
I offset or up and down not critical for smoth vibration fre operation, or offset side wAys ok aslong as face angles ar with in the magec 5 degrees. cliff
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Old 10-18-2005, 06:05 PM
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offset

Dont worry about the offset, just install it and it will work fine. Thats what i did with my 48 chevy, and i dont feel or notice any problem when driving it. I was told by a frame shop that it was such a small offset that it would not affect anything.
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Old 10-20-2005, 11:14 AM
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Quote:
Originally Posted by cboy
...the rear end shop I went to said it was advantageous to retain the offset between the trans tail shaft and the pinion. I never did quite understand his reasoning, but he claimed a pinion in direct left/right alignment with the tail shaft would cause more potential problems than if the two were offset (but parallel).
I dealt with this recently installing a Ford 9" in my 71 C-10. I thought I was hosed when I realized the offset pinion, but after research on here and talking to different people I found that it is common to have some offset. Now as to why it is actually better, I had one experienced street rod builder tell me that with some offset you are "exercising" the U-joint in two directions [or radii or planes, if you prefer], rather than just one, so all the U-joint bearing surfaces are getting spun.
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