I have been driving my old straight axle this week and it rides pretty harshly. I decided to put a M2 in my next project and I would like to soften the ride as much as possible. If you run a spring rate that is too low, what will happen, ride wise? Too low? Too bouncy?
It bottoms out all the time. Spring rate, and spring height, are both important. It needs to sit up enough to have decent travel, and also have stiff enough springs that it doesn't go further than full travel. If the springs are too stiff, you'll get a rough ride because the suspension won't deflect over bumps.
My 35 just jars your teeth when you hit the expansion joints. With this next build I want to avoid that. I wonder about tire size also. I have the VW tire size up front 165/15. I was thinking a guy might go with a little more surface area to cushion. The wife's Lincoln has those little rubber band tires from the factory and it rides better than mine. Of course, it's the latest technology vs horse drawn wagon technology. I was looking at a 275-300 lb spring. The weight of the truck is about 2600# Figure 60/40 weight split =1560# divide that by 2 wheels=780# divided by 2=390#. Is my thinking right here?
the control arm gives some leverage on the spring, so the load on the spring is not exactly the amount on the tire. It's complicated.
When I installed the MII in my 38 I tried to use stock four banger springs from the Mustang I "relieved" of it's components They were way to long/stiff whatever. I couldn't even get the shocks to bolt up. That was when the bolt on style was made in eastern Iowa (twenty years ago), I called their tech guy, he told me what I needed and in a few days I got 'em and installed them, rides fine now. Short answer, call the tech line, good luck!!
There 's a rear spring thread going which is trying to gather data points for guidelines. https://www.jalopyjournal.com/forum/threads/post-rear-coil-over-lb-rate-for-your-car.1330859/ As @squirrel said, you rarely have a spring vertical acting directly at a 1:1 relationship to tire movement. There are formulas and charts, opinions and back to back testing, but the best source is going to be the people on the front line every day, trying to sell the right part the first time. Just like cams, it has to fit the combo and usage. EXAMPLE https://www.eatondetroitspring.com/mustang-ii-coil-springs/ 275 to 450! I remember an old article that compared 2 different schools of thought on road race springing. One liked a softer spring with a very strong shock. The other liked a stiffer spring with less firm shocks. Both were respected, professional team owners. If they couldn't agree, what chance do us regular folk have? EDIT, didn't find the article, but remembered one of the names. Here's a discussion about Herb Adams and his stance. Not MII but you get the idea, that even in this modern age with computer simulations, and F1 drivers doing laps in simulations, it isn't an exact science. https://www.camaros.net/threads/herb-adams-advice-for-springs.29493/
I figured if I could get close, I could experiment. The good thing is the springs are fairly cheap, so I wouldn't be saddled with a life long regret.
Eaton Detroit has never steered me wrong. Call them. The lady who answers the phone (Sandy?) has been doing it for years and has a great database. I buy all my springs from these folks.
I'll also vouch for Eaton Detroit. Swapped my old cut springs for new drop springs in my 50 and it made all the difference in the world for ride quality.
I am a fan of the softer spring theory. For road racing I feel the spring balance is more important than other applications might require. I know that on my 51 with a big block I have opted for a slightly softer springs to allow the front end to come up and transfer weight to the rear. Heidt's had multiple spring options for the 51. I went with the heavier small block springs which were 50 lbs lighter than the heavy small block springs. I plan to use shocks with adjustable extension and compression to control the front end lift and rebound compression. As long as the springs don't reach coil bind they should be the right choice. If the shocks can't keep the spring extension from hitting the stops on them, I might have to put a full extension limiting strap on them. If the shocks bottom out and over extend the shocks then I'll have to go to a heavier spring. Spring rates and how to control the ride quality is considered by many to be a science that most will never fully understand. For those of us that fall into the category of not fully understanding, we need to rely on trial and error to a large degree. The OP would be ahead to contact one of the suspension companies and use their experience to minimize the potential for error based on the trials made by their customers.
Why not take a few leafs out of your straight axle ride to improve the ride ? As far as the mustang ll spring thing it reminded me of a thread here a long time ago of good riding springs. I ordered the springs that many had recommended as being "the ones to get" what arrived was a spring that was much taller but slightly smaller coil diameter. It took all I could do to get them in, I'm lucky I didn't decapitate myself, look at the banana bow in these cocksuckers Old springs New banana springs, this is sitting on the ground too ! I don't remember what springs I used afterwards but I did cut a coil off of them to dial it in and it rides great
also you can't compare springs until EVERY part is on the car...and you've driven it around a while... Cutting springs works OK if you understand how it affects things. But if you don't, you'll be in for a surprise.
Are you sure the springs are not bottoming out now, or that something else might be bottoming out? Maybe the shocks are bottoming out? How much air pressure do you have in your tires? You may already have too soft of a spring! Larger diameter radial tires tend to ride better then short wall bias ply tires do. Modern gas filled shocks give a harsher ride then the old oil filled shocks did.
If the cross spring in your pickup is too stiff, why not remove a leaf or 2 to soften it and simply put a block on top of the spring to get the ride height back?
I will be the odd man out but I would not use a mustang 2 suspension. The lack of travel under normal driving conditions is a severe downside. I owned an original mustang 2. I can tell every car I have ridden in with a mII front in about 50 feet. It has filled a place in our world. Affordable, adaptable, many positives. But I would look for something with more travel. I spent years with a straight axle 32. The lowered springs are stiffer which gives far worse ride quality. When you drive them every day under adverse conditions you are well aware of this. Compromises aren't something you may want to deal with every day with age. IMHO.
Getting any lowered car to have sufficient suspension travel for a smooth ride, is difficult. The whole point of lowering a car is to reduce the available travel, and there's just no way to have soft enough springs for a smooth ride, if they can't have the travel needed. I gave up on lowered cars years ago...
If the MII suspension is limiting the car’s wheel travel, the car isn’t set up properly. Control arms, springs and ball joints limit travel range. The kit I bought has the same length control arms as the stock car so the travel will be about the same. I don’t see any design issues that will restrict the wheel travel. The harsh ride is from improper spring rates or possibly mechanical binding due to improper setup. Steering geometry can adversely affect the handling if it is setup wrong. Edit: As Squirrel pointed out, lowering the car with shorter springs normally reduces the amount of control arms travel thus limiting suspension function. Suspension is more than just the pieces. They have to be designed to work together. Other than being inexpensive cars, MIIs didn’t drive badly and some were tweaked to handle fairly well.
I had ElPolacko (Steve) build me a crossmember and a set of tubular control arms with the heavier duty Dodge Dakota ball joints.
I dunno. I bought the high dollar shocks. It helped, but still...man it drives a man to drink. For 30 years I used the stock axle and it wasnt any better.
My 37 has an M2 from a ‘74 donor. When I got it, it had what were probably stock springs, with cut coils, and “oops we went to far” rubber coil lift biscuits. Rode pretty hard, with little spring travel because of the lift biscuits. Called Eaton, talked to their support guy, went over what I had and what I wanted, and he recommended a spring. Got them, put them in, and with some new shocks I’m happy with the ride and ride height. It doesn’t ride like my old ‘73 LeSabre with the “driving your living room” suspension, but it wasn’t supposed to.
Here's an old thread with some spring info, I can't find any other photos suggesting I changed springs again after I cut that coil off the tall springs. My truck does ride really good even though it has 90/10 shocks up front. https://www.jalopyjournal.com/forum/threads/what-mustang-ll-spring-rate.500183/ Here's my trucks weight with a full 15 gallon fuel cell in back and a blown big block up front
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