Going to build a model A style frame with model A rear crossmember and spring. Want the spring to be behind the rear end so I can get it to sit as low as I can. How much would the crossmember have to be extended behind the axle. Ideas and pics would be appreciated.
That is purely a question based on where the crossmember is today (in relation to the spring hangers) and how the new spring hangers are setup. So - if your new spring hangers (off the axle ) are 3" back from where they were before, then the cross-member needs to move that far back (assuming you're using the same spring). You want the wheel location to remain in the correct spot - so, depending on your spring hangers, you'll need to determine where to move the crossmember (or make a new one). Hopefully this makes some sense . . . just simple math.
'32,'33 and '34 used a bent spring to clear the center section, if you use one of those rears you will need a bent spring... but from '35 to ' 48 the spring was straightened out... plenty of guys here that will go out and measure how far from their housing center to the shackle bracket center for you... you will need to add that much to your wheelbase...
Also to have the car set low I recommend putting a Z or a step in the rear of the frame when you extend it... figuring 4" of travel, try lowering your body and frame till there is 4" between the axle and frame... that is as low as you can get without a Z... then go ahead and Z it... good posts here on the subject... I think 2.5" to 4" are most common...
I think you would find that the 32 up rear springs always give a better ride than you would ever get with an A or T spring. The earlier springs have a lot more friction because of the double bend. A 40 front spring sits low and gives a great ride.
if you ever want a "quickie" you will wish you had run the A stuff... increased resale $ having the quick change option .
The dimension for 35-48 Ford rear axles is, 7-1/2" from the axle center line, to the center of the spring. If you go with the A spring, you will give up trunk space, but the quick change option will be there. This is one I did , sorry I didn't have a better picture. I would use the standard 7-1/2" set-back, regardless of the spring or rear axle you choose.
Also, it depends on the rear end, the cross member you're using and the type of spring. As some noted, the 32-34 spring is curved - and needs a cross-member that is designed for it. Give us some more information to go on . . . D
Run the model a spring in front of the axle and then z the height of the frame rail. You won't have to add to the frame. You basically cut a 45 degree cut through the side of the frame. Long point of the frame so you can stack the pieces weld them together and box it all. Same wheelbase as stock . been done a million times
This approach works well - and is easy to do. You should think about finding a later V8 banjo, then you flip the bells around for the spring to run in the front. As he noted - very common stuff. What I can't remember is whether or not you can use the Model A spring with the perch widths of a later rear? Anybody know off hand? Or - just build/buy new spring hangers and weld them to your axle tubes (I've built plenty of them - not a big deal). With this said, obviously there are implications for how you finish the metal work and trunk area - but nothing new to the hotrod world by any means. Also, you can run a quick change with this setup - as you'll not have spring/banjo clearance issues to think about behind the rear (if you had been thinking of a later type spring -- 32-34, 40, etc).
I lengthened a frame once on a model A for spring behind, and later wished I hadn't. If I ever get the chance again, I'm going to flip the bells, and run the spring in front of the rear end. The challenge is coming up with a traditional looking cross member that's cool, and not a piece of square tubing.
I extended my A frame to accomadate a Posie 35-40 spring hanger kit to put the spring (a speedway Medium arch spring A type) behind the axle ( a 9" early Bronco, approx 52" from Backing plate flange to flange) It was tight but I made it fit and made my own rear radius rods that wer angled to the center line of the frame (I gusss about 10-12" spacing) I would have "Z"ed the frame if I had thought about it a little longer to gain an additional 3 + inches of drop. See photos
From your picture it appears that your spring hangers are way too close together, spring should be under a fair amount of tension with no weight on it. Sent from my Nexus 5X using The H.A.M.B. mobile app
car & frame went down the road 4 years ago, the narrow Bronco rear forced me to mount the hangers like that, I believe the radius rods/"traction" bars are pretty close to being parellel also Had I finished the A coupe a shorter main leave could be fitted and with full weight on the frame I would have had a better handle on it. The guy who bought the car has it almost on the road but has not e=mailed me since completion
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