I've been working on my dad's model A coupe he put together years ago. The car is really stiff in the rear. It's got a 40 rear with spring perches welded on top. They measure about 47 inches eye to eye, which I'm thinking might be a little tighter than stock. The original spring has leaves removed and spring liner installed. The shackles are almost pointing straight down, which I know isn't right. I know a model A spring not installed is probably only about 44 inches wide, so I'm not sure why it's bowed so far out, but I'm thinking this might all be contributing to the harsh ride. I see some paint chipping indicating that the spring deflects and bottoms out on the axle perch. What's my best option to fix this and hopefully get a better ride out of the car? I see posies makes a narrower spring but I don't really want a reversed eye.
The harshness of ride will be the spring bottoming out on the mount, and there doesn't look to be much travel before that occurs. Heck, it might be locked up just by the drivers weight! Why no love for the reversed eye spring? Might make it lower, but that could be counteracted by spacing the top of the spring. A new spring has to be the quickest solution, but spendy. New main leaf? Bit more messy and possibly needing shortening of other leaves too ( which isn't without complication given the shaping of the last couple of inches or so). Or change the mounts on the axle? Cutting, welding painting. No quick, easy, cheap way, as is usually the case! Shackle angles are fine imo, as long as there's enough roof for them to operate and something to control sideways movement of the axle. Some will disagree with this, quoting the 45 degree thing. Chris
As you have already identified, there is not enough room! I would normally suggest diconnecting the shock and doing a bounce test to see how stiff the spring actually is, but in this case it looks like it will just bottom the shackles on the perches. Do the test anyway and get someone to observe.
Just in case its of any use, I've just checked some dimensions from my 32 3w project thats approaching final ***embly. I have a narrow SoCal model a rear spring. The main leaf on its own in a relaxed state measures 41" eye to eye, c to c. Clamped up with its 7 friends it's at 38 1/2". The axle brackets are just about 46" (hard to measure accurately, axle dis***embled). Its not seen the road yet but it has a nice feel to it with me bouncing around on the rails! I forgot to measure the clamped up pack of 8 leaves, but each is about 1/4" which would compute to about 2" in total). Chris
The main leaf is too long, the shackles are almost completely vertical, instead of the preferred 45*.
I had a Model A spring modified by a spring shop in St. Louis. I wanted it narrowed and the eyes reversed. They un-rolled the ends, cut both sides off about 1" if I recall correctly, and then re-rolled the ends and heat treated it. Lynn
Model A rear perch width should be at 49.5". Your setup is 2.5" too narrow if you are using a Model A spring. The following Posies spring should work, and it is standard eye (not reversed). Posies 1928-31, Model A SuperSlide Rear Spring For Narrow Width Model A Spring- 46.5" Perch Centers POSIES SKU: POS 29-31S-C
My bro had a spring custom made for his coupe at St. Louis Spring http://www.saintlouisspring.com/ They can make whatever arch and length you want. If you could send them your main leaf, and tell them you want it 2.5" shorter I bet they can do it. Or better yet make you a fresh one without 95 years of wear on it.
Yes, the perches are too close together, stock is 49.5 like stated above, those 2.5" really do matter. I had the same issue. A narrow Posies spring for 47" perch centers are available in standard or reverse eye the last time I checked.
When we pull leafs to soften the ride the main leaf spreads. It's a balancing act to get it right. Were the leafs pulled to soften the ride or lower it or both? I'd be tempted to try a T spring.
As stated earlier in the post you spring shackles need to be at a 45% angle most of your ride will be corrected with a narrowed spring allowing the shackles to move up and down
Had the exact same problem. My spring was to long and it rode rough. I ordered a extra narrow reverse eye spring from Posie. took out a couple of leaf's and it fixed most of the problem. Angled the rear shocks steeper at 40-45 degrees and that helped a lot to soften the rest of the ride.
Would you gain enough room with going to a model A perch bolted on to the backing plate? https://www.jalopyjournal.com/forum/threads/spring-over-mounts.947166/
You need clearance between the spring eyes and perches. A '40 spring should have 48 1/2" between perches. A 35-36 rear spring needs 46 1/2 between the perch centers. That would probably work better and you could get one without reversed eyes, but it will raise the rear up. Also the 35-36 spring will put you closer to 45 degrees on your shackle angle. also the lesser angle the shocks are at, the more effective they are.
This true and why Some Guy angled them more so they will work less. The gas charged (even cheap weak ones) are to strong (same with non gas) and actually added to the problem. Worked and rode great without rear shocks but need some rebound help. Looking into manual tune shocks with separate adjustment for compression and rebound.
I see one problem right off the bat. The spring perches are nowhere near deep enough and the spring eyes will hit them (bottom out if you will) with even a little bump. That will make the spring essentially a solid member with no give. They aren't tall enough, either. Although it's a nice, neat installation, it won't work like that. I would use a little shorter spring and move the perches in a bit with deeper eye to vertical depth so the spring, when it flexes down has ample room to expand in length. You can use the mount height to alter the height of the rear to give more room over the rear center section. If you move the perches in be sure to use gussets to eliminate breakage. A model A roadster spring has less leaves and would be a good choice for ride comfort. Also, a Model A spring has a higher arch for more up/down travel, also. I don't see anything wrong with the shock position.
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