I recently bought a '48 pickup with some updates, including a Mustang II front end which needs a little work. Yesterday I tried to install the front shocks and realized the lower control is at a sharp downward angle from the frame and makes it impossible to connect the shock at the bottom. Doing a little research online, I learned the lower control arm should be close to parallel to the ground when the truck is sitting on the wheels. I can, presumably, make that happen with a shorter spring, but that will lower the truck way too much. I'm told it has drop spindles, so I'm thinking stock, non-drop spindles will get it back up where it belongs. I'm sure lots of people have been through this and I'm wondering if someone can give me a ballpark spec on springs; free length and rate. Also, if I'm headed in the right direction.
Welcome Craig. Unfortunately you likely have a few issues.
The "standard" MII front end kit is installed such that the lower control arm is basically right at the bottom of the frame. What the vendors call a "standard height" spindle is standard height for a mustang 2, not for the truck. Depending on spring rate/length and adjustment that results in about a 2"-4" drop compared to stock.
The solution that I have seen a few times is to install the MII kit with spacers to offset it below the frame and make up that height difference. If you do a search for user Coilover, he had a post 18 months ago with pictures showing how to do that.
With yours already installed, the initial 2"-4" drop in likely the best you can do without major changes.
Can you post up some pictures of your setup? If so, we might be able to see another solution.
Side note: I would *strongly* caution against just cranking the adjustments to get the height you want by angling the lower control arm down. That does a lot of bad things to your suspension and steering geometry and will give you problems down the road.
Ditto to the above comments! A lot of people who install the M-II suspension kit have little to no understanding of suspension geometry and end up with a job that's less than pleasing to look at in the best case scenario, and possibly deadly dangerous in anything but straight line driving at worst. You'll need to find someone with the fabrication skills and general suspension knowledge to correct the installation errors first, then deal with the ride height and handling concerns with spindle position and spring rate adjustments.
When I was involved with building round track race car frames from a pile of square steel tubing a few decades ago, we would sort out the steering and front and rear suspension with no springs installed, with the frame supported on screw-adjustable height jack stands and chained down to a level floor, before choosing the proper weight carrying capacity of the springs. That process still works today on street machines. Good luck! Jerry
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Thanks guys, good information. I like the idea of getting it on a flat surface, maybe with the lower control arm pretty much parallel to the floor, then working from there. As you can see in the pictures, it's canted down way too far, which makes it impossible for the spring to seat where it should. If I get rid of the presumably 2" drop spindles and replace with stock, that should allow me to have about the same ride height I have and allow me to get the lower control arm closer to 90 degrees plus get the springs pointed in the correct direction. This would require either a shorter spring and/or relocating the top bracket to get the upper control arm correctly oriented. I'm thinking the top bracket is going to need to move up as bringing the lower control arm up a couple of inches would make for a very short spring. With the suspension loaded, the current springs are compressed to about 10 inches. Finally, I'm not sure what limits suspension travel at full extension, the shock?
I think you have something else wrong as well. Look at the angles on your ball joints. Maybe it is just due to the springs, but they are really off-axis.
I would recommend you doo like HRL was talking about and remove the spring and use the jack to position your parts and see how everything lines up.
It kind of looks like you have a mismatched upper/lower arm set.
Yep, definitely the place to start. I'm hoping when I get the lower control arm all nice and perpendicular to the frame it will improve the angle of the lower ball joint. As to the upper, I'm thinking the pivot points are going to need to be changed. Would be nice if I could find a picture of one that's already done right, but no luck yet.
Pay particular attention to how far out the upper arm mounts are compared to the lower arm mounts. I am not sure how similar a 52 frame is to your 48, but it is closer than any of the other ones I have seen. The kits appear to be for 48-54, so I think it should match?
If so, it looks like either your upper mounts are installed too far in or your lower mount is too far out.
TCI has a nice kit that is well regarded, maybe you could get some dimensions off theirs to compare to yours and get at least a WAG on what you need to do.
That huge notch in the frame rail for the tie rod is a BIG red flag to me. By the time the lower control arm approaches parallel with the ground, the tie rod will almost touch the frame, even with the notch. Something needs to be done to move both upper and lower control arms lower on the frame rails, to allow approximately equal up and down travel of the control arms, with weight on the wheels and the springs compressed. I believe some major structural modifications are going to b required before the geometry gets right. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The notched frame is fairly typical on installations that are intended to be slammed. They generally use airbags instead of springs between the control arms and do not handle rough terrain well.
You honestly might be better off taking this setup off and getting a crossmember to install (and reuse the rest of your parts) than trying to manipulate this into something that you are happy with.
I finally found some dimensions I can check, assuming, per Fibonachu, the geometry of most Mustang II systems should be the same. Upper control arm pivot points are 29-1/2 side to side, and lowers are 22-1/4. So, splitting the difference of 7-1/4 is 3-5/8, thus my upper should be 3-5/8 farther out than the lower. Also, with the lower parallel to the ground, I'm looking for 9-1/2 inches between the lower and upper control arm at the mid point of the upper. Hopefully, that will get my ball joints better oriented. It will no doubt require shorter springs and getting rid of the drop spindles. Fingers crossed! Now to figure out if any of my spring compressors will work or if I have to cobble something together.
The critical thing you will see is that both control arms should be parallel to the ground at the same time. As you go up and down from center the camber will change, so you do want to check it when the lower arm is level.
I will add a caveat that the geometry should be the same for any proper MII installation assumes stock length control arms and spindles.
The greatest majority of parts you can buy are the stock lengths, but if you find that things don't line up reasonably be aware.
Are your springs indexed properly into the control arms? It doesn’t seem so judging by the second picture. This might gain you an inch or more. You can see where the spring tail isn’t locked into its notch. Or am I not seeing this correctly?
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Good find on the Fatman raised spindles??? That is a fabulous, earthshaking, life changing find! The guy I got my truck from told me they had installed drop spindles, so I ordered a pair of stock height ones that arrived yesterday and finally dismantled one side, thinking I'd be able to reduce the spring length a couple of inches, moving the lower control arm more parallel to the ground. The good news, once the extra long spring is out and the ball joints re-attached I can raise the suspension up to where the ball joints are correctly positioned and the geometry of the control arms looks a lot better. The bad news is I didn't have dropped spindles; mine are the same as the stock height ones I ordered. Poop! The other aggravating factor in making the truck too low is the extremely low profile tires it came with. They are only about 24 inches tall. The 6.50 16's the truck came with were 27.5" tall, so there's another 1.75 drop I don't need. So the plan today is to get the truck the height I want it on jackstands, wheels and spring off, ball joints attached, figure out what size tires I need, then raise the lower control arms to a couple of inches above 1/2 tire height and see what the suspension looks like.
Any suggestions for tire size? The truck is kind of a hot rod and I was thinking of 15" torq thrusts or even steel wheels. I definitely want to ditch the low profile tires and 19" rims I have.
Thanks very much for the guidance here. I'm not out of the woods yet, but you guys have given me some solid advice and options.
Those would be ~28.4" tall, so that gives you a starting point.
Depending on your brakes, you probably need to go with a 16" rim to clear them. Given that 16" was the stock rim size, that should look good too.
What I did for my 58 was decide on the rim diameter, find a tire size for that rim diameter that gave me the height I wanted, then looked at rims available in the diameter/width that would fit that tire size until I found something I liked.
In your case, 215/75R16 is 28.7" tall and a fairly common size. If you were to pick that size, your rims would need to be between 5.5" and 7" wide. With that info, you can go to Summit, or Tire Rack, or any number of places and just look for rims in that size range with the bolt pattern you need.
(Please note: that tire size is given as an example, you can go wider or narrower with appropriate profile changes to get whatever height you want)
One more thing that I would recommend is going to someplace like Discount Tire and putting in the tire size you are thinking about using to make sure there are options available. If there is only one or two models available now, you run the risk of the size going obsolete and being unable to replace them later.
Edit: it is really hard to go wrong with Torq Thrusts. If you have 11" rotors, a set of 15s will probably fit. If you have a Discount Tire nearby, you can order one rim and test fit it on the truck before putting a tire on it. If it won't clear the brakes and you have not mounted it, they will give you a full refund.
Fatman raised spindles are ordered. Wheels off again this morning for more measuring. Current 19 X 8 wheels with no or very little offset have the tires well centered side to side in the wheel opening. Yesterday, I cut my #375 springs off a bit. Well, a bit too much as the lower control arm is now going uphill toward the tire and the truck is even lower. No big deal, live and learn and springs are relatively cheap. Looks like my rotors are 11" and it's 6-1/2" from the outside of the caliper to the center of the spindle, so 15" wheels should work. Fatman says I may have to do something with calipers to accommodate lift, but mine look like they will be OK, maybe with a little nip on an outside corner, but looks like plenty of room. I'm pretty set on Torq Thrust D 15X7 5X4.75 wheels with a tiny bit of negative offset, so I need to figure out tires. Also, replacement springs. Looks like anything I get I'll have to trim to length, a little more cautiously this time around. #350 springs can be had for about $70 for the pair, where #375's like I had or #400's go for $120 or so. Any recommendations?
Again, thanks for all the guidance here. Can't imagine doing this in the old "pre-internet days"
Oh, and to get back to Fox. No, they were not properly indexed. One was actually upside down. I should have tried them in correct position before cutting. Hindsight! Although one was already cut some... I think the upside down one. There was so much wrong here and so many loose or incorrectly installed things, I'm glad I got into it before something came apart; like finger tight nut on ball joint.
Another thing that looks suspicious is the castle nuts on the spindles. With the washer between the nut and the bearing, they only thread on about 1/4". I'm thinking this isn't enough, BUT, the hole in the spindle for the cotter pin lines up perfectly. Thoughts?
If the castle nut is threaded the full depth of the uncut threads plus enough for the cotter pin, there is plenty of thread engagement.
What tire height do you want? I can help you find a size that will fit those rims.
Are you looking for a highway tire? A knobby truck tire? Something inexpensive?
Do you need high speed of high weight rating tires?
Edit: to clarify, the castle nut has enough thread engagement assuming it is properly torqued. Given what else you have found, I would be real tempted to pull the cotter pins and retorque everything.
I would also recommend inspecting the welding job on the crossmember/sping hats real close to make sure that wasn't phoned in. A bad job on that is the kind of failure that kills people.
Well, my #350 springs arrived and, even installed full length, the lower control arm is still down lower than parallel with the ground. So, I obviously need a stiffer spring. I'm thinking of going to #400's to try and get another inch, maybe 1-1/2 higher where control arm looks better, but does anyone here know what spring I should be starting with? It's a '48 short bed 3100 Thriftmaster with a 235 6 cylinder engine and what I'd describe as generic Mustang II suspension. I think I need to get this right before I move on to spindles and wheels/tire height.
The spring rate is how many pounds of force it takes to compress the spring one inch.
The "right" way to calculate the necessary spring rate is to measure:
1. Spring length when the lower control arm is level 2. Unsprung weight of front end 3. Distance from lower control arm bushings to center of spring mount 4. Distance from lower control arm bushings to center of tire
With me so far?
#2 is how much weight the suspension needs to lift. If you have a way to measure that, use that number. Otherwise we can estimate. The 1948 GM Heritage Center vehicle information kit says the front curb weight of a 3100 pickup is 1835lbs. Technicallly your wheels/tires should be subtracted from that and the IFS added. For now, lets just use that number to get a starting point. If this number is a bit high, we will calculate a heavier spring than needed and make it ride too high (fixable by trimming the spring a bit).
Divide that by 2 to get ~917lbs. Hold onto that number.
Now divide number 4 by number 3 to get the mechanical advantage that the control arm has relatove to the spring. I don't know the actual numbers, so I will make something up to finish the math. Lets say that 4 is 12" and 3 is 4". That gives an advantage of 3x (12/4).
Multiply that by your weight (3*917lbs=2751lbs) to get how much force the spring needs to have to hold the vehicle.
Now you can look at springs online to get the fully extended length (or measure what you have since I believe they are standard) and compare it to measurement #1. Multiply the difference by the spring rate of the spring to see how much force it will excert installed.
Look for a spring that matches the force (2751lbs) above. More force -> higher ride, so I would be inclined to go a bit high so you can trim to get exactly the height you want.
Clear as mud?
If you post up the 4 measurements above, I can walk through some real numbers with you.
Well, my #350 springs arrived and, even installed full length, the lower control arm is still down lower than parallel with the ground. So, I obviously need a stiffer spring.
A stiffer spring will just make the situation worse, as they will push the lower control arm farther down. If anything, you need a shorter spring, or at least shorter when the chassis is sitting on the wheels. Or the upper spring seat needs to be higher. That's just from looking at your pics. I'm no suspension expert.
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Can you post a picture of how everything sits with the 350lb spring? I am not sure if you mean that the lower control arm is pointed down or up right now.
If it is pointed down (the ball joint is lower than the bushing) you can probably fix it by carefully cutting it down. If you don't want to cut it, you can get a softer spring but be aware that will make the whole front end softer. Whether or not that is a good thing is up to your personal preference.
If it is pointed up (the ball joint is higher than the bushing) then you need either a longer or stiffer spring.
Your originals were 375lb, but you noted that they were installed incorrectly so it is hard to say what it would have looked like with that spring rate.
I don't think I was clear when I said the lower control arm is down lower than parallel to the ground. I should have said the ball joint is pointed up; it needs a longer or stiffer spring to lower it, thus raising the truck. I'll post pictures below showing where it (the ball joint is now and where it would be with the truck at the height I want it to be. I want the truck to be higher. My three step plan is moving it up about 1-1/2" with the springs, another 1-1/2 with the raised spindles I ordered from Fatman, and another inch or so with 26" or 27" tall tires (current tires are just over 24") So, it's ideal to have the lower control arm parallel to the ground, but if I fudge just a little I can get my 1-1/2". First picture below is where it is now with my #350 springs, and the control arm is going downhill a little to the pivot point. Second one is with the spindle and body where I would like them to be. So, the question is what spring will make that happen. I'll get the front end weight and distances from lower control arm pivot to spring and tire centers tomorrow. Also, length of spring at the height I want.
Speedway has a guide that says a ~1800lb front end should use 425lb springs: https://www.speedwaymotors.com/Mustang-II-Suspension-Front-Springs,45731.html
Not sure if that is 100% right for your application, but if you run the numbers and come up with something in that ballpark, it is probably correct.
They also say the standard length is 13.5".
Eaton sell a whole variety of lengths.
I see a number of places that list 8.5"+/- as the correct compressed height with the lower control arm parallel to the ground, so that gives a ballpark of 5" of compression.
Looks like the Speedway site would call for #425 springs although, at this point, I'm very tempted to order #450's and trim until I get it just where I want it.
The great thing about Speedway is they are racers, Flat track yes, but racers. The Tech Reps at speedway have helped me with several different projects, they are very knowledgeable and more than willing to help. Give them a call and talk them through what is going on, I am sure your situation is not the only MII style to have this problem.
Last edited by TUTS 59; 10/25/20235:53 PM.
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Trimming a spring shortens the length of the coiled spring wire- - - -effectively stiffening it. If you had a straight torsion bar instead of a coil made of the same piece of spring wire and cut three inches off the length, it would make the shortened piece harder to twist. Taking a coil off a spring wire wound into a circle has the same effect. Think about what you're doing before you start whittling on a spring. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Depending on how much play there is in your +/-, I come up with 450-490lbs rate.
Hyperco's online calculator gives the same values as my math above.
Ridetech recommends a 475lb spring with your numbers.
Eaton recommends a 367lb spring (13-3/4" long) for a 50s truck or a 383lb (14-15/16" long) for "heavy engine".
Honestly, calling Speedway like Tuts 59 suggested is not a bad idea. They can give you some feedback and you can see if they will do exchanges if the one you order isn't quite right.
Bear in mind that a heavier spring will make the front end stiffer. So you might be better off with a longer, lighter spring. The length will make it ride the correct height, but the lighter will soften the ride a bit.
Running 15" rims with 28"-ish tires will also soften things a bit from sidewall flex.
Thanks guys, #450's are on their way as I pretty much got there with Fibanachu's formula too, before I saw the suggestion to call Speedway. The supplier of the #350's was nice enough to take them back. I am definitely going with 15 inch wheels, probably 6 or 7 wide (need 5 on 4-3/4 lug pattern and not a lot of offset, although maybe a tiny bit as I like the deep look they used to call punched or reversed. Used to be steel wheels like that everywhere, but not anymore. Your help here is much appreciated. Stay tuned, I'll report my further adventures.
Progress: I trimmed my new #450 springs down to get lower control arms parallel to the deck and put on some 15" steel rims with approx 28" tall tires and things are looking a lot better height wise. The spindles I ordered, still a month out, will give me another 1-1/2" up, so I might even be able to run a little lower profile tire. Close to pulling the trigger on a new set of Torq Thrust D's as the steel wheels don't look as good as I thought they would. So many, many variables here.
No pictures since the early ones. I've been looking at different wheel/tire options but can't really make a decision until I get the raised spindles installed and parts are probably another 3-4 weeks out. One thing I need to get for the final assembly is dust boots for the ball joints. Searching eBay, there are a lot of different ones for Mustang II. I guess it depends on which ball joints I have. Can anyone shed some light on this?
I think you are just going to have to measure your ball joints and find boots on spec. Unless you can find part numbers on them, that is the only way I know to get new boots.
When I was about 20. I bought a really sweet Austin Healey powered by a 289 that was said to be from a GT350. I broke the clutch, which I removed and took the pieces to a local Ford dealer. When I couldn't provide year, model, etc, the parts guy said "Son, your problem is you don't know what you have" It's been pretty much the same way ever since, but the internet and forums like this one make it a lot easier to deal with. And, it's been a long, long time since I've bought a part for anything from a dealership. OK, maybe the CA catalytic converter for my kid's Camry, but that was from a southern CA dealer who sold it to me on eBay for half the price the local guys were asking.
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That reminds me of a story from when I was in grad school. I was putting new control arm bushings on my car and buggered up one of the pinch nuts that held the upper control arm on. I took it to the dealership with me because the local hardware store only had nylocks in that size.
I gave the guy (mid 20s?) working the counter all the info on the vehicle and he spent 20 minutes farting around with his computer and decided that part didn't exist. One of the older guys came over as I was explaining that I know it exists because they made a million of these cars and did not just glue to control arms on.
The old guy wanders into the back and comes out with a handful of the nuts about 90 seconds later, hands them to me, then tells me that these don't exist so he can't sell them to me but maybe I can figure out what they fit.
The look on the younger guy's face was pure gold.
Edit: One thing I would recommend is keeping a notebook (or similar record) of all the parts that you identify for the build. Someday you or a future owner will want to replace parts and it will be a lot easier if you have dimensions, part numbers, specs, etc recorded.
I like to write down both part numbers and the relevant specs both in case that part number/vendor is gone when I need parts next.
