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1993 Buick Roadmaster Estate Wagon
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Discussion Starter #1
I want to refresh all the springs on my 93 RMW. I love spirited driving, especially in a big car, but it has to ride at least somewhat cushy to keep my wife and 6yo daughter happy on long drives.

I've looked into some of the available options, but I'm confused. I read up on all the factory options (FE1, FE2, 9C1), and I assume my RMW with tow package came from the factory with FE2. But I can't figure out what that corresponds to in part numbers from various manufacturers. I want to mostly retain OEM ride height, though a slight increase in ride height at the rear would be nice.

What I see from different manufacturers seems to boil down to variable rate vs single rate, which I assume corresponds to FE1 vs FE2 (in my experience, single rate is usually the firmer option). But you know what happens when you assume... your ass gets burned half the time :LOL: What I see on my car now LOOKS like single-rate springs, though it's harder to tell when they're installed, and they're rusty as hell.

So here's a setup I was considering:
  • Moog 5402 straight rate springs up front (or equivalent from other manufacturer)
  • Moog CC623 variable rate springs out back (or equivalent from other manufacturer)
  • Air Lift 1000 spring helpers for the rear
  • Bilstein sport shocks all around (in place of the current air-adjustable shocks)
This way, I can adjust the rear spring rate to match the front for spirited driving, bring it up for towing/hauling, or bring it down for cushy cruising.

Do I have my assumptions right? Any constructive criticism on this plan?

One other wrinkle: at some point in the next year or so, I plan to drop a L65 6.5TD in place of the L05. I'm not sure how to accommodate this with front springs while retaining OEM ride height. I'll happily change the front coils at that point, but I'm not sure where to find appropriate ones.
 

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My experience with Moog variable rate was on a crown vic. Height too high if the car was totally empty and prone to wheel hop. The same model car with factory air suspention (bags only) handles much better and is always at the right height.
This way, I can adjust the rear spring rate to match the front for spirited driving, bring it up for towing/hauling, or bring it down for cushy cruising.
It can be very hard to get what you want when you have three very different objectives and a moving target. I would wait until the motor is in. You could do the crown vic rear sway while you are waiting.
 

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Z09B4U is on the money. Start with swaybars (front and rear, and bushings), and I'd add shocks. Bilsteins will make a huge difference. The KYBs should be nice too, for much less money--I've liked them in other cars. Some folks like Monroes, but the ones I've tried were harsh. As someone on the forum pointed out to me, the GM rear air shocks don't do much to limit body roll and understeer.

If your car is FE1, then swaybars should be very high on the list. Better cornering with soft ride.

I have your set-up on my FWB, minus the front springs: stock FE1 front coils (soon to go away since one is sagging), Moog CC623 coils in the rear (a bit too high for my taste, and quickly become stiffer than I'd like, even with 225/75 or 235/70-15 tires), Bilsteins all around. I go back and forth on the Airlift 1000 bags, in and out of the car, can't make up my mind. I keep them at a bare minimum pressure (several psi) under most conditions. Heavy load I bump it up a little. The bags might too much given the CC623 coils. Looking back, I'd probably go for a softer spring while keeping the airbags for added loads or twisty-road driving.
 
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I've a set of front springs I'll send you for the 6.5 - you pay the shipping and they're yours. I was within 1/4" of factory ride height with them with a Duramax in the engine compartment. The 6.5 is likely just a bit heavier since it's iron heads vs aluminum, but will otherwise be in the same ballpark on weight.

I measured the rate on them and they came out in the low 700 lb/in range - Springs are new from the front of a F450/550. I can send a couple sets of un cut ones if you want to trial/error.

Springs with double the rate and 20+% more load on them require shocks with more damping to control the higher forces involved. I ran the above springs on worn out OEM shocks with the Duramax and the ride was soft and squishy.

In the rear - variable rate springs are not something you can actually vary. You can't make them stiffer one day, and softer the next. The spring rate is soft in the initial stages of compression and gets stiffer as you compress it further. The only control you have over this is the load on them - you can't change it unless you put 500 lb in the back, which will be stiffer, but not what you want for handling. Airbags inside the springs just add friction and hysteresis to the suspension (exactly what you're trying to eliminate in the other thread about bushings and control arms). While functional for preventing sag with extra load, really put a wet blanket on the suspension.

At some point you need to make the decision to go with adjustable coil overs or try to piece together various springs/shocks/etc. Coilovers are expensive initially, but when building a unique setup like we're doing, most of the "standard" setups that people reference are not going to be relevant, so there will be some trial/error involved if you piece it together on your own. I chose the coil over route so I can adjust ride height with a few turns of a wrench, adjust both compression and rebound damping independently with a twist of a knob, change springs without a spring compressor (and all the fun/danger involved with that).

In some ways it's a time vs money vs effort balance. In the end it's your preference - a good setup can be had either way.
 

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1993 Buick Roadmaster Estate Wagon
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Discussion Starter #5
I didn't consider the coilover option because I was skeptical about the load-carrying capacity of the shock mounts. Seems like coilovers put all the vehicle weight onto those mounts rather than spreading them out onto the wide spring perches. Is that not the case?

My other wagons have coilovers, but they don't weigh 4000+ pounds (well, my allroad V8 does, but it's built for coilovers).
 

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Yes, coilovers put the weight of the vehicle on the shock mounts, however those are arguably stronger than the coil perches since the load is closer to the wheel (less bending moment on the axle housing) and it is spread out over more of the axle tube with the bracket that also holds the control arm vs the couple points on top with the spring perch. The upper shock mount is also one of the more reinforced parts of the rear frame/crossmember. I did put a washer between the shock mount and the frame as well as used M10 bolts instead of 5/16 or M8 that the factory uses. The coil (if it was there) takes all this load right next to it and is farther from the frame/crossmember so has more leverage than at the upper shock mount.

If you just put coilovers on the stock lower shock mounts without any additional brackets/bracing and use a 1/2" bolt in single shear - it's going to fail as others have found. If you get a good kit with 1/4" thick brackets that attach at multiple points and use Grade 8 5/8" bolts - I'm confident it won't be an issue. Same on top.

FYI - the SpeedTech rear coil over bracket (shown below - welded to the factory shock/control arm bracket where the paint is missing) doesn't fit particularly well - hence the welding. I'm guessing that it's a Wagon vs Sedan thing, but don't know the particulars. I lined up the shock square with the upper mount and got the lower mount square with the shock so the pivots were straight and no bending as it articulated, clamped it where it wanted to be and welded it in. It's tilted and angled such that the bolt in method just isn't viable. A bit frustrating for the $ spent, but it is not the specific car that it's designed for so they were not too interested in fixing it - this is the world of custom car building. The parts are high quality and well made, this one just isn't quite right for a wagon.

Just for an additional thought - You could put coilovers in with a lighter spring and put in airbags in place of the coil springs. This will give you some of the variable rate/adjustability you're looking for. I'm planning to do something similar but use the onboard compressor and height sensor to retain the level control system. Should only need 30-40 psi max and only when loaded (will be low pressure when empty) so hopefully the system will be simple/robust with the OEM compressor.

I think these drop in (not sure yet, but the tape measure says they will)

These are what they spec, but they'd be designed to carry 100% of the load and are more than necessary as a "helper" in my opinion

 

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If you want to improve handling, wouldn't you want stiffer springs front and rear? Previous threads indicate the wagons got 440 lb/in front and 211 lb/in rear springs. Your CC623 choice for the rear is just a little less at 206 lb/in, but it also has a taller free height. So it is likely going to sit higher. The 5402 is a 338 lb/in spring. It just seems like you're going the wrong way.

I put used Global West springs (760 lb/in) on the front of my wagon with Koni shocks. The Koni's are fairly soft in compression with an adjustable rebound. My wife didn't notice a difference in the ride, but she did notice that the tendency to roll over in a corner was drastically reduced.

I'm still deciding what spring to use in the rear. The CC625 is a possibility since it is a little stiffer and a little shorter. This should allow me to install bags bring it up to the correct height and stiffen it up a little further. Not sure that will get me where I want to be. I think they should be stiffer yet in order to match the front. My guess is that I want to be over 300 lb/in to come close to matching my front springs.

Since air bags can transfer air from one side to the other, they don't offer as much roll resistance as standard springs. I plan to combat that by installing a valve between them to isolate them. I'll wire it to open any time the compressor runs or the system vents.
 

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Jim, if you are using the bags to just trim, as in not holding the car up, if you seperate 1/8th od nylon lines all the way to the front and t them there will be pretty much no transfer.

This is how my car is.
If you block one line and jack a corner up with the other, it takes a long time to equalize once you connect them back up.
Also, you may know, you must disable the check valve in the drier when using air bags.
If you dont, the residual 8-10 pounds will not allow the car to drop when empty and the exhaust valve will burn out from trying.
 

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Since air bags can transfer air from one side to the other, they don't offer as much roll resistance as standard springs. I plan to combat that by installing a valve between them to isolate them. I'll wire it to open any time the compressor runs or the system vents.
The factory ford air spring(air bag) system used two electric air valves one on each bag. More money up front but it is easier to diagnose a problem since each air bag is it's own system and that makes it easy to spot a one side leak. The 1/8 line that 95Wagon suggests is "tried and true" and has less electrics and moving parts.

Also, you may know, you must disable the check valve in the drier when using air bags.
If you dont, the residual 8-10 pounds will not allow the car to drop when empty and the exhaust valve will burn out from trying.
The factory ford compressor is designed for air bags and will let them empty without modification. They were not designed to ride under the car they live in the front fender.

For that mater a complete junk yard ford air ride control system would perk up a car that may have obsolete parts in the factory GM system.
 

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Discussion Starter #10
I think these drop in (not sure yet, but the tape measure says they will)
I love the idea of having full air springs in the rear (not just air assist springs), but my concern is that the spring rate changes with increased pressure while the shock valving does not. So if I raise/stiffen up the rear for more aggressive handling or towing, the shocks won't manage the bouncing adequately if I'm running "comfortable" shocks, or vice versa if I'm running aggressive shocks and try to run low spring pressure for comfort, the shocks will overly dampen and make the ride rough. My allroad deals with this by having shocks that adjust valving based on the air pressure in the spring, but I've never seen such a thing for other cars. This isn't the same thing at all as the air-lift shocks typically used in B-bodies
 

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Jim, if you are using the bags to just trim, as in not holding the car up, if you seperate 1/8th od nylon lines all the way to the front and t them there will be pretty much no transfer.

This is how my car is.
If you block one line and jack a corner up with the other, it takes a long time to equalize once you connect them back up.
Thanks for the info. I had just noticed how it did not take long to lower the rear when the factory system vented. But bags have a lot more volume than the shocks. I suppose air transfer while cornering may be less detrimental than I had originally thought.

Also, you may know, you must disable the check valve in the drier when using air bags.
If you dont, the residual 8-10 pounds will not allow the car to drop when empty and the exhaust valve will burn out from trying.
Yep. Read threads on it. But thanks for the heads up anyway! I might actually piece together my own system and scrap most of the factory stuff. Or look into the Ford parts as Z09B4U recommended. I have a big list of projects to get to before this anyway.
 

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That and the very low pressure the helps bags run at if they are only trimming and adding anything with added load .
If I pull the hose off when there is no cargo in the back of my wagon , the hoses just breath out, barely hissing at all.
Whether not not it really helps, I disconnect my LR bag at the drags.
When my susp adjusts, there is still only about 20 pounds in the right bag.

No experience with real air susp and achieving the desired rate at a given height
Seems to me if you run one ride height and rate , as soon as you try and increase rate , the ride height goes up, the sup goes out of its correct working position, Geometry goes to crap.
To change either rate or height without changing the other, air bag dia would have to change, wouldnt it ?
 

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If you wanted to completely separate the two bags on the factory system, you could put a normally closed solenoid valve between the two.
Wired to two diodes , one to exhaust, one to compressor.
This so when ever the system adjusts, the bags would be interconnected, all other times not
 

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Regarding the complicated ford system. Found in vics/marquis/TC.
The forums say that the 2011 height sensor is available new and works with the older systems. The controller is behind the glove box until the PCM took over this function in the mid 2000(?). Features of the controller are it controls a air valve at the compressor(pump and vent) and the two valves for the air bags directly. The compressor uses a relay. It has on board diagnostics and a tester is easy to build to read the diagnostic codes. It will not vent with a door open and has a sleep mode.

From a personal sample of three cars there have been zero control problems with cars that have 125-150 thousand miles.

Fresh from a junkyard crawl are the controller and sensor. Ignore one of the electrical plugs. It is for variable force steering. This control is a very rare TC part(2years) that allows the driver to pick the amount of steering assist at driving speeds.
SuspCtrl.JPG
SuspHeight.JPG

Seems to me if you run one ride height and rate , as soon as you try and increase rate , the ride height goes up, the sup goes out of its correct working position, Geometry goes to crap.
To change either rate or height without changing the other, air bag dia would have to change, wouldnt it ?
Can not have it all with air suspension. It maintains height and the "spring rate varies" other forums claim the frequency is twice that of a normal metal spring. Seems to work with the factory shocks that are specific to the air system.
My allroad deals with this by having shocks that adjust valving based on the air pressure in the spring,
Good idea but complicated. Someone get out a slide rule to see if the damping rate would change enough to need this.

Check the load sticker on the car. It's load capacity can be overloaded by fat passengers and some luggage. If you are going over a few hundred pounds at the hitch, a load leveler system on the hitch does wonders. Again suspension is designed for a goal and when you chose several there will be compromises or complicated and expensive solutions.
 
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