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Mustang II suspension issue

8K views 47 replies 12 participants last post by  mainstreetprod 
#1 ·
Returning to street rodding today after a 43 year absence! Just like riding a bike, except I missed out on the whole "drop in a Mustang II suspension" thing. My '41 Lincoln street rod, delivered today, has one and it rides like a buckboard. Looking at the springs, they appear to be extremely short, which would explain the lousy ride. So I ask of all those familiar with these installations- what's the cure? And if the answer is replace the spring with a full length one, how the heck do I figure out which spring to order to keep ride height the same?
 

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Discussion starter · #7 ·
That appears to be a stock MII unit right from the junkyard and has been converted to coil over shocks. It also appears to be a power rack, correct?

Correct.

Are the lower A arms parallel to the ground?

Yes

It also looks like the springs have been adjusted up to put more tension on them which would reduce travel and give a harsh(er) ride.

Probably adjusted this way to lower the car, but results in a harsher ride

Do you know the weight of the vehicle?

Probably around 4000 lbs. It's 4300 curb weight with the V-12 and estimate the 350 SBC knocks 300 lbs off. Not sure how the Mustang II vs transverse leaf affects the weight.

Take it down to the local truck stop or wherever and get the front, rear and total weight so that a proper spring can be ordered. What are you planning for upgrades?

None, just want to maintain ride height and improve the ride

What is the rear suspension?

Conventional leaf springs, transverse leaf is gone. 9" Ford rear.
 
Discussion starter · #8 ·
My Pontiac has an original 1974 MII suspension, still has the stock MII springs, shocks upgraded to KYB Gas shocks. The ride is smooth
Brakes upgraded to 11" rotors from Speedway.
PS rack replaced with '88 T-bird unit from Speedway.
As suggested, get your car weighed and get springs correct for the weight.

I probably need stock springs so there is sufficient suspension travel



Brakes upgraded to 11" rotors from Speedway.

Mine look like 9", I'm sure I need this upgrade


As suggested, get your car weighed and get springs correct for the weight.

I can probably do that at the county dump, where they weigh your vehicle before and after. Not sure if that alone will tell me the correct weight. From what I've read, the engine sets back much farther in a street rod than in a Mustang II, resulting in less weight on the suspension than you might think.


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Discussion starter · #10 ·
The springs shown with the coil over shocks appear to be shorter than stock. Then to get the ride height they are adjusted up what looks to be about 1 1/2 inches. These shocks do not compress the spring. They only provide ride height adjustment.

Mainstreet.. is probably right, you need a stock type spring. There are several rates available in the like by inspector. You would use a stock type shock too.

Would like to avoid having this done at a shop, but the job is a bit out of my wheelhouse- especially concerned about compressing the spring with a tool as described in multiple Youtube videos. Can the spring be installed by putting the front car frame on jack stands, removing the spindle, dropping the control arm with a jack, replacing the spring and jacking up to compress?
 
Discussion starter · #12 ·
The shock and spring are one unit that would be removed together. I think you are looking at the procedure for coil springs.


I was looking at the procedure for coils because I was considering replacing the coilovers with conventional springs. However, I don't see any reason why coilovers wouldn't work if the springs were not so short- most I see in internet photos are nearly the full length of the shock.
 
Discussion starter · #19 ·
mainstreetprod

Where are you located? I likely know someone near you with a spring smasher to figure the rate, then we can recommend something in about the same rate but 3-4" longer. I'd imagine that spring is coil binding or getting too close to coil bind and the rates will sometimes get way off when you're that close to coil bind.
I'm located just north of Nashville TN. I believe the springs for Mustang II front ends are generally 500, 600 and 700 pound. I would assume with this Lincoln I would need the heaviest capacity?

Also, my car still has the stock lower A arms - will the coilover drop through the bottom when unbolted?
 
Discussion starter · #28 ·
What you have is an early aftermarket cross member kit. A stock crossmember has a rolled edge to strengthen the spring tower. Also the tie rod ends have been lengthened to accommodate a longer spread distance from one side of the frame to the other. The lower control arm should be angled down from the pivot bolt. When it is level, you are 3/4 of the way through the stock travel.
Makes since that this is an early crossmember since the rod was built 15-20 years ago. I'll keep the control arm angle in mind when swapping the springs, not sure what the actual angle is since the car is so low and has been in my small garage since I bought it. All I have is the one picture to go by and the angle it was taken at could affect the perception.
 
Discussion starter · #30 ·
Start with the given. From the center of the spindle to the floor is about 12 inches, look at the car and see what the tire/ wheel clearance is to the fender opening. You can go with a longer spring/shock setup and then put a set of dropped spindles to bring the ride height down. Ideally the lower control arm pivot bolt should be 12in To put the control arm in the proper place.
From the picture, there’s a lot of work to be done. It is almost worth it to start over with a newer cross member setup. The first attempts at cross member kits were not that good. That’s why I stuck with the oem cross member. The first one I did was 1976. 1936 Plymouth sedan. 13 years And 147k miles. Sold it to a friend who is Still driving it.
Today I was able to drive the car a much longer distance. Rides much better than I thought- the roughness was flat spots in the tires that went away after a while. Did bottom out on a large speed bump, but does have some travel. Still a bit stiff and could use some improvement, but not bad and perfectly acceptable for a street rod. The lower A arms, looking under the front for the first time, are exactly parallel with the pavement. I believe it was you that posted they needed to go slightly downhill from inside to outside pivot?

Brakes are another story. The stock (I assume) Mustang II brakes with under floor power booster are very weak. They will bring the car to a stop, but can't skid a tire and are reminiscent of mechanical brakes. If anyone is using similar brakes on a car of similar weight with better results, let me know. Speaking of weight, I tried the Youtube "posterboard" method and came up with a whopping 5400 pounds. That can't be right- original curb weight was supposed to be 4300 and this car has a small block, not a V-12. Should be closer to 4000. I'll take it to the scale at the county landfill.
 
Discussion starter · #32 ·
So can someone tell me what would happen if I simply adjusted the coil over adjustment nuts downward, say an inch? Obviously suspension travel increases, but what happens to ride height and lower control arm position? Right now the bottom of the stock arms are exactly parallel with the pavement.
 
Discussion starter · #33 ·
I have a similar setup as yours in my 46 Ford Coupe (stock mustang II with coli over conversion). I'm sorry that I can't help you with spring rates since I can't remember the exact springs I used. It's been in service for over 20 years.

My car weighs about 3900 lbs with me and a half tank of fuel. I'm pretty sure I used the heaviest springs that I could get at the time. Seems to me that I started out with 500 lb springs, but they sagged pretty quick and started looking like yours. I think I went to 600 lb springs after that, but I notice that they might need to be replaced on the next freshening up I do on the car.

What I can tell you for sure is that removing the shocks and springs from mine is a more difficult than just unbolting them and dropping the control arm with a jack due to the deep construction of the stock stamped MII control arms. The strut rod rubber bushings will not flex enough to allow them to come out this way. I have to unbolt the struts from the lower control arm to get enough travel. I seem to remember having to break the lower ball joint loose, too, but it's been a loooong time since I had to pull them out.

You may have a tough time getting good suspension travel and keeping the ride height that you have now without going to dropped spindles. you can adjust the control arms for good travel and still get 2" lower ride height. Just a suggestion.

Also, I have looked at several stock MII's (the actual Ford car) and they all have the lower control arms running slightly downhill toward the tire when viewed from the front. This is because, on the stock stamped CA's, the center of the pivot bushing is not directly in line with the center of the ball joint ball when the CA is level. Having "level" control arms means having a line drawn though these pivot points level. Tubular CA's are not made like this and they will be level to the eye.
Very useful info. Theoretically the weight of my car should be very close to yours, but will find a scale to make sure. One my car, the bottom of the stamped steel arms is parallel to the ground.
 
Discussion starter · #35 ·
With the adjusting nut on the bottom, all that will do is lower the ride height....it won't change ride stiffness at all. To change ride quality, you've got to change the spring rate.
So adjusting the nut downward will lower the height? I assumed the reason they were adjusted so far upward was to get the car down on the ground. Also, it seems to me like the spring characteristics will change as the nut is adjusted down - coils will open up, suspension will have a lot more travel, and ride should improve. A compressed spring with little travel should have a rougher ride.
 
Discussion starter · #38 ·
So now you have to decide what your want. A softer or stiffer ride? The same ride quality but not bottoming out?
If it's just ride height and you're okay with the quality then you need 3-4inch longer spring in the same rate so the adjuster nut can have more upward travel to set the ride height where you want it.

As it turned out, my problem with the ride was mainly flat spots on the tires from 15 years storage. After driving a mile or so and getting used to the fact that it doesn't ride like a stock '48 Lincoln (a mobile sofa), I'm OK with the ride. And the ride height is perfect. So I guess what I have to decide is whether the suspension has adequate travel, and I'd say it's an inch or two short of that. And if I change the springs, I might as well soften the ride a notch or two. The trick is figuring out what spring to buy- I don't want to do three trial and error tear down and rebuilds of the suspension. While I'm at it I'll replace the pathetic 9" brakes with 11".
 
Discussion starter · #40 ·
This is the brake kit I used, it's a true bolt on. Only install tip is to sand the paint some from the outside of the replacement oil seals so they install easier and don't distort, read the reviews on the website. They also offer the kit with a Ford bolt pattern.
https://www.speedwaymotors.com/Must...ront-Disc-Brake-Kit-5-x-4-3-4-GM-BP,2007.html
Thanks for posting that, without a recommendation from someone buying a kit is just a shot in the dark. Price is great too!
 
Discussion starter · #42 ·
Keep in mind that any kit that uses Granada rotors will widen the track about 1" (1/2" per side). The Camaro rotors may do the same, but I have never used them.

There are some kits that use custom hubs and separate rotors that don't change the track as much. I have a Baer kit on my current project that only adds 1/4" to each side.

Check tire clearance to the fenders well to make sure you don't run into trouble.
Only had my car a couple of weeks and haven't had the wheels (5 lug 17" mags) off yet, but I assume if the 9" brakes are not aftermarket that I have wheel adapters to go from 4 to 5 lug, which should make the track similar to Granada rotors. Correct?
 
Discussion starter · #43 ·
Keep in mind that any kit that uses Granada rotors will widen the track about 1" (1/2" per side). The Camaro rotors may do the same, but I have never used them.

There are some kits that use custom hubs and separate rotors that don't change the track as much. I have a Baer kit on my current project that only adds 1/4" to each side.

Check tire clearance to the fenders well to make sure you don't run into trouble.
Only had my car a couple of weeks and haven't had the wheels (5 lug 17" mags) off yet, but I assume if the 9" brakes are not aftermarket that I have wheel adapters to go from 4 to 5 lug, which should make the track similar to Granada rotors. Correct?
 
Discussion starter · #46 · (Edited)
On my Pontiac the front track width was about 3 narrower than the Camaro rear track (some of that was the tires, 235 vs 215), and I had plenty of clearance inside the fenders for the wider front track. Mine had GM pattern 9" rotors when I got it, didn't have any worries about spacers/adapters.
Bob, I have a question for you or anyone else familiar with stock 9" brakes on large street rods (say 3500 lbs plus). I would expect lackluster performance since they were designed for a Pinto, but mine seem worse than that- stepping on them is very similar to a mechanical brake system, not remotely capable of a panic stop, "stomp and pray" . The only car I've owned with brakes this bad was a 1919 Chevy. I'm wondering if something else is wrong with mine. I have jacked up the wheels and confirmed they all are working. Also confirmed that my brake booster is operational.

As far as the track goes, checked today and found the rotors have 1" wheel adapters and front track is narrower than back, so any widening of the track by a new disc system, won't be an issue.
 
Discussion starter · #48 ·
My braking issue started with the booster that was on the car went bad. It was reputed to be from the same '74 donoor that the front clip came from. There is only one booster offered for '75-78 MII, and it didn't match up with what I had.

I went with an after market 7" dual diaphragm booster, dual MC with proportioning valve combo (brand new) I got from a friend. After mounting and making adjustments to get a straight push from the pedal to the booster, I had better brakes, but they still seemed a bit weak. That's when I went for the 11's. Better, but still not quite right!

Finally figured out the proportioning valve was for 4 wheel discs instead of disc front/drum rear. Changed that out and now have proper braking.

Might possibly been OK with the original 9" discs, but like cubic inches, you can't go wrong with more brake power!
Do you recognize this booster? I think it's working but not that well. Also, I could well have the same proportioning valve issue, will need to check mine and see what I have.
 

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