Guys, Have done a search and a lot of reading and not seen any discussion on this. I know this isn't completely period correct but if your setting up a 1931 model A frame to use coil over rear suspension with ladder bars on a 9 inch rear, does it need to be with a flat rear crossmember or can the original model A rear crossmember be used? I thought if I could use the original crossmember and wanted to go back to a more traditional transverse leaf spring style of rear end at some point I wouldn't have to rework the rear crossmember. Also if doing coil overs do you need to do the rear frame step to get the rear of the car to come down or just do it with the adjustments in the coil overs? Thanks for any insight or help! Gordon
If you want to use the original X member I think you will need to Z the rear maybe 6" to use the coil overs. It's hard to know till you mock it up
Just a question, if your thinking you might go back to the transverse leaf why not use it now?. 9", ladder bars and an A spring look good. But to answer your question, yes you can use the stock cross member with coil overs maybe with some gussets. The stock cross member will give you a little more room to lower the rear, but if you want stupid low then Z'ing is in order.
Sure, just leave the stock rear crossmember there, it will give you some additional clearance for the middle of the axle to move up and down. No need to replace it. You will want to box the frame well and add a good center crossmember system to keep twist down because the coil overs will put pressure on the corners of the rear frame as opposed to the middle, like the original spring did. But no biggie there. Don
With the coil overs you will need a Panhard bar. Not so with the stock spring. Take a look at the after market Model A hot rod frames. They are designed to use coil overs and all have a step. Even so, they sit high. Good with stock fenders. Goofy without. If you want to go lower you will need to increase the step. Axle to frame clearance is another issue. Mock up what you want and build to it.
this worries me, I was talking to a frame guy down here and he says I must use a step up , even though I want to run the original rear crossmember/spring.I dont want to be super low...... would love to see some photos of options? step/no step
Look at the original Pete & Jakes setup and parts. Back then they didn't step the frame. The upper c/over mount was a bracket welded on top on the outer end of the rear crossmember. Jake's gold truck sat pretty good.
The frame will be for a fenderless roadster. Don't want to drop it too far so don't mind a small bit of Z'ing but not doing anything too radical. I want a useable trunk if possible. Plan to box it as well as add a full x member. Only installing a mildly built flathead and 4 speed. I am not planning on going back to the transverse leaf spring setup, just wanted to know if I could keep that option open while still building the frame for coil overs. Thanks for the info and help. Much appreciated. Gordon
Here's a couple of pics of one of my coupes. I originally used a model a spring with reversed eyes.but the spring settled and I had fender clearance issues. It was such a****** getting the spring out that I put coil overs on instead. I was able to fine tune the ride height easily after that. This car was built long before HAMB existed and that was a very common setup. Fender laws were in effect in PA also so I had to deal with them. This coupe has a modest 2 1/2 kick in the rear witch is a must have if you want your roadster to look like a hotrod. There's still 3 inches between the inner fender well and the axle for clearance. It's not crazy low but with no kick on a fenderless roadster, it might look a tad too high. Jim Jacobs 29 pickup looks great without a kick because it's a truck...a lot less clearance issues to deal with out back.
Jake now works at Waldon's Speed shop in California. He makes traditional parts under the name Jitney Parts. You might call out there and see if he could make a set of upper coil over mounts for you. They are very simple in design but if you've never seen them the cost and time getting him to fabricate a set might get your project moving sooner. I bought the whole rear setup they offered when Pete and Jakes first went into business and my '29 Model A sedan was the nicest riding hot rod I've ever owned. Frank
Awesome info guys! That A coupe has a beautiful stance flthd31! What can I say, the truck looks beautiful as well. Thanks Hot Rod Nut that shot of the shock mount is exactly what I needed. I borrowed a couple of upper shock mounts off a 1/2 ton truck that were riveted to the face of the rear crossmember. I can probably use those and either bolt or weld them in place on the rear cross member. Appreciate this info all! Another question. Anyone know the size of cage nuts I need to install for the body mount holes before boxing the rails? Gordon
here is one...channeled 4-1/2" with a 7" kick-up (Z) in rear with model A spring and reversed eyes...
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