Thanks everybody for all the info about narrowing this 9' Ford rear I picked up to have installed in my roadster. I can't do this work myself so I'm sending it to a hot rod shop. I'm trying to do this right but as inexpensive as possible. It's a rat rod. We were going to keep the buggy spring ( Model A frame ) and maybe remove a few leaves because this car is so light. Install the narrowed rear with the "pumpkin" centered and probably use the aftermarket shocks that are on there now. What I don't understand is ladder bars and/or 4 link suspension. I understand their purpose but since they are rigid with a towards the front of the car pivot point how does the rear end manage to go straight up and down when you heat a bump. It would seem to me that the rear end would want to go up and down in an arc or part of a circle that has as its center or pivot point at the front of the ladder bar or other what ever set up you put on there? What am I not understanding?
It sounds like you understand it perfectly. Yes, everything moves in some sort of arc. Obviously, the longer the "link" in a ladder bar type suspension, the less pronounced this is during the couple inches of travel. Parallel 4- links can be shorter by virtue of their design but there's still some unavoidable arc. In a rear suspension, this results in a very slight fore and aft movement of the wheel as observed in the wheel well. I'm talking a fraction of an inch. Not a great big deal. Dealing with the arcs becomes much more important when the links run side to side, as in with panhard bar. Getting front and rear panhards equal length and swinging in the same arc goes a long way to avoiding bump steer and other handling gremlins.
Dutchmans Motor Sports http://www.dutchmanaxles.com/ packed up and moved from Portland to Idaho but there should still be a few shops in the Portland Area and Down I 5 that can narrow the axle.
I have used both types of suspension,4 bar and ladder bars and I have been pleased with both but in the future I will stick to the tried and true ladder bar set up. HRP
A 4-link suspension also holds the pinion angle while a ladder bar allows minor pinion angle change dave
If you use a model A rear crossmember, and eliminate leaves to make it ride better, you may have to cut up the removed leaves to make a spacer to fit on top or under the spring to make the U bolts fit tight.