I'm a suspension fool...Had some questions on my Model A. 1930, aftermarket frame looks like a bunch of Pete and Jakes stuff, so possibly that. It's got a Dana 41 rear, (guessing a Jeeep of some kind), ladder bars, a panhard bar that utilized the top 2 bolts of the rear diff cover...See photos below. To say it has a stiff ride is an understatement. Expansion joints and general areas with chewed up New Engalnd asphalt pockets (not potholes, per se, but non-smooth surfaces) can be violent. It'll bounce me off of the seat, in some cases. It's no fun to be cooking along at 65-70 and having to slow down to 40-50 when you see an unsavory surface up ahead...even worse in the dark when the lights don't allow you to see the unsavory surface at all...normal surfaces that our late model Honda and Toyota glide over without any drama. I have no idea what the spring rate is, but it's a much flatter spring than what I'm seeing in my Rodders' Journal collection that most of the rear transverse leaf springs are more the buggy style with the high arch. I don't have room for that, for sure. I've been tossing around the idea of doing a coil-over setup. Would this setup allow a simple removal of the leaf and bolt-on of a couple of, say 130 lb adjustable QA1s or something? Would the Panhard bar (not pictured) need to be relocated away from the bolts? Is this just wrong all the way around? I don't think I really NEED to do anything here, just wondering if it's easy enough to make it better. Thanks in advance.
Take some leaves out. Start at the top and take every other one. Will take some trial and error to get where you want it. Dave
From what I can see your Model A is a highboy without fenders which makes it fairly light, it appears to have an eight leaf spring with a spacer on top to raise the ride height. The angle on your shocks is pretty steep and the bump stops look like they've been hitting the rearend. The closer your shocks are to 90 degrees the better they work, I was always told 15 degrees max but have read that 5 degrees is better. I'd have someone bounce it up and down while I watched and see if it's hitting the bump stops and see if the shocks are binding up. Coil overs would give you more adjustment but not at that angle.
I count 9 leaves but I don't know if the top one is must more of a spacer than an effective leaf. I was pondering the leaf removal route but I was both worried about the finished ride height (clearance more than aesthetics) and also a local builder said "you can do that...but it won't make much of a difference...A's just ride hard." That bump stop looks off because I had to trim a stock one...as it sits I only have 1.25" from top of axle to the bottom of the trimmed bump stop. I don't think they've been hitting. For lack of a helper...I just duct taped a Sharpie to the bottom of the body and set a slat on top of the axle and bounced my 235lb arse on the trunk about 7 times...spun the slat around and did it again and on both cases the line was 3/4" long.
I would agree that you have way too much spring (rate) and that is the reason for the harsh ride. How much does the suspension drop out when you lift the car up by the frame? The reason I ask is the shock in the 2nd image looks like it is nearly fully extended, and if that is the case with the car sitting on it's wheels, it would indicate that the rear spring is much too stiff. Pull a few leaves, and see where it gets you. You can always add a thicker spacer to get the ride height back to where you want it.
I agree with everyone who said to remove leaves. I would leave in the one next to the main leaf and remove every other one going up. TECH TIP: If you remove the shock absorbers and start bouncing up and down on the rear bumper you can get the car bouncing in "symathetic resonance" and keep bouncing while you count how many times per minute it bounces. A rule of thumb is a sports car will be rather stiff and resonate about 120 times per minute. A luxury sedan cruiser will resonate only about 60 times per minute. Adjust spring rate to suit taste. I like the fact your spring leaves have slider pads under each leaf too. Add an additional spacer above the spring pack to get the ride height and snubber clearance correct. Good luck with your project.
I agree the you have way too much spring. Also, remove the shocks and drive it to make sure the shocks aren't too stiff or too long.
I honestly don't think the shocks are doing much. When I bought the car they were one hole up on that bracket. It'll be winter before I get around to messing with this, but if I don't want these tensioned springs blowing up in my face...would my plan then be???? 1. Measure the current thickness of the spring pack plus the spacer (for ride height purposes) 2. Lift and support frame rails on jack stands 3. Support third member with a jack and remove those 4 bolts holding it to the cross member 4. Lower axle to ground 5. Remove center bolt and spring clamp/holder things 6. Remove a few leaves and put back together... 7. Measure, bounce, and otherwise test out.
After you put the weaker spring back together, it will sit even lower. If you have a little over an inch of travel now, you might have zero with less leaves.
That is my fear/ obsession at this point. I would either need to put in a much thicker spacer or get into frame modification… What is a reasonable distance to have between axle and bump stop?
Once you determine the ride height with spring leaves removed you can add a spacer on top to raise the chassis. You've been given good info about reducing the number in the spring pack.
My 31 Tudor sits on an aftermarket chasis. It has qa1 soft ride coilovers with #250 springs. I would describe the quality of my ride the same way you did. Normal highway, back roads all is good. But when I hit a transition on a bridge or a series of pothole patches, it will break your spine. For what it's worth, I would remove your rear shocks and see what that does. If it's a shock or a spring problem that will tell you at an easy cost. I have been told that a model a with such limited axle travel can only do so much.
We are all freaked out about the spring, but there is too much we don't yet know to be able to make a judgement. Are your shocks bottoming? Are they any good? Is your bump stop too close to the rear end? Is something on your suspension bottoming on the frame or the floorboard or something else? Are your spring shackles doing something they are not supposed to? Is there anything else you might have going on? My advice is to spend some time under there with a flashlight and make SURE none of the above is happening, then we'll take a look at the spring. Keep us posted. -Abone.
Be VERY CAREFUL with step 5. There can be tremendous energy stored in those spring leaves and removing the centering bolt can be dangerous. Use a press or spring clamps designed for the job.
I went through a lot of this when I got the car...the Panhard bar hit a tubular part of the frame...that got sorted out and it was much better. I don't think there's anything else under there...and I REALLY don't think that the bump stops have ever hit. There's no evidence (rubbing or scuffing) on the axle or the bump stop. I'll have a look at the shocks, but I think I compressed and extended them all the way when I moved the mounting hole and had plenty of room. Was thinking maybe now is the time for a 9" and noted something interesting here... https://www.roadstersupply.com/Buggy-Spring-Rear-Housing-p/rsc-52010.htm It says that the spring perch width is 44". Mine are 48. I suppose another option would be to get a pack with a longer spring... Again...nothing will happen with this until winter time. That 9" setup looks like a bolt in for me. Ladder bar connections are the same.
Frenchtown...The last time I messed with a spring pack I used big C clamps and slowly backed them off as I backed off the center bolt. My PLAN was to keep the mainspring bolted to the axle and just do this in the car. Is that a bad idea?
Your methodology is sound to me. My guess is that you'll fix this with the only cost being some spanner time, and maybe some flat bar to make up spacers. I like aluminium, easier to work with and doesn't rust if you skip the painting stage. A pic of the shackle end of the spring would be handy though, if only to eliminate any issues there. And what tires are you running and at what pressure? Chris
Silvertown wide white radials at 35 psi. Here is a profile and the shackle. Doing more searching…looks like a true highboy could stand to come up 3 inches or so….
Well, if everything looks normal under there, it is probably time to peel two leafs out of the spring pack and see what happens. You can do it in an afternoon, and it doesn't cost anything. Be careful with that sucker and make sure losing two leafs doesn't change anything else like shock travel. -Abone.
Maybe it's the angle of the one picture; but are the shock eyes in different planes. If in fact they are, won't that also cause a bind in suspension movement?
Your rear spring setup is pretty common with the flat rear cross member and a '40 Ford front spring used on the rear. Your spring looks like a Posies super slide. If the car is lite you may, as suggested, need to remove a leaf or two. The suspension does look like it could benefit from some fine tuning, but nothing that needs to be thrown away. You certainly could install a 9" Ford rear and coil overs if you don't mind the fab work and think you might like it better. Probably will add some unsprung weight. Ride quality in a lite roadster can be problematic, especially here in NE.
Looking back at the pics, I noticed a few things that might be a concern. But not necessarily to the rough ride problem. As Rich said, having the shock eyelets on different angles is just lazy. They will probably work, but not like they are supposed to. There will be bind. Is the steel brake line far enough away from the contact point of rubber bumper to axle? Don’t want to smash it. Is the exhaust running through the middle of the ladder bar? Might just be an optical delusion. But if it is, then WTF? Move it.
10psi out of the tires is a free fix in the right direction. Experiment with the pressure, a few psi a time. Shackles look fine. I'd be shelving the idea of a 9" and putting the funds to a better exhaust! Chris
I was worried about exhaust when I got the car. That’s how little the suspension moves. It’s never made contact. Good point though… if I start taking out leaves, I’m going to want to address the exhaust. Maybe dump it out the side in front of the rear tire. as far as the shock goes. I put an angle finder on it yesterday and it’s at 15°.
The load rating on each of your rear tires likely is close to the weight of your entire car. Like @Happydaze said, Drop 10psi and see what that does. I run about 22psi in my pickup (700-16)
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