Ok, time to tame my rear end (2001 P74 HPP Crown Victoria LX)

[OzBloke]

I recently purchased a 2001 Crown Victoria HPP equipped LX (P74) but it does not still have the rear air suspension system. Currently it wants to step out at the back severly on bumpy or broken, rough pavement mid corner. Hell even in a straight line you can feel the rear end (which is very harsh) want to walk around if there's big potholes and bumps. It has those "cargo coil" conversion kit springs in the back, and they are just way too hard. Harder than my old P71 CVPI.

I have confirmed that it is a "converted" HPP car ... with the 28.5mm front sway bar (almost a CVPI which is 29.5mm) and a 21mm rear sway bar ... I am left with a couple of options. The car already has KYB CVPI rate shocks (almost new) on all 4 corners, and ride height needs no alteration really. It's not sagging or anything. Due to spending the past year battling cancer, I have zero dollars and even less health to do anything major to fix this, so I have to take the cheapest and easiest path to handling heaven that I can find.

My options are two basically 1 of three choices I have figured out after some research into the HPP and civilian P74 cars. I knew all about the P71 CVPI's but I don't have one of those anymore, so I have to start all over again.

1. Keep the sway bars as is (rebush them of course) and find some softer springs for the rear. I'd like the 130 lb. rating of stock coils but you can't find them new anymore, even "old stock" that some places still have lying around is hard to get confirmed ... they list part numbers and color tag codes that never seem to match the records of all the great research some have put up on this site and the P71 forum site. Maybe I can find a wrecked base model P74 civilian car and pull the rear coils out of that. That would be the absolute cheapest and probably what I really want.

2. Or I could put the 160 pound P71 coils under there, but I feel like that might be too much with a 21mm rear sway bar, the cops had the stiffer coils yes ... but the softer 17mm rear bar. I liked that set-up on my old P71 CVPI. It wasn't harsh like my HPP currently is.

BigMerc96 assures me the ride was "ok" with P71 coils and a 21mm rear bar and that the back end was tamed compared to what we're describing with these "conversion" or "cargo" coils I currently have. So it's an option.

However ... given my poverty and health status (meaning do the cheapest and simplest fix possible) I'm going to continue searching for the "old obsolete" 130 lb. base coils and keep everything else as is.

3. If I eventually give up on that fruitless quest, I'll whack some P71 160 lb. coils under it ... and if the rear end is not to my liking, exchange my 21mm rear sway bar for a 17mm P71 CVPI item. So basically a stock P71 set-up with a 28.5mm front HPP sway bar (instead of P71 29.5mm) and slightly softer front HPP springs (540 instead of P71 600) ... that would work although it might push the front a little. My old P71 never suffered from understeer and you could slide the back if you wanted to without trying really hard, so a *tiny* bit more understeer probably wouldn't be a disaster.

PS: I was wondering tonite if some of the harshness was the KYB heavy duty shocks, I don't think it is because it's mainly the back end that is harsh. Also my old P71 had the same shocks and it wasn't harsh at all, just firm. Would worn out bushes make the pothole performance really crash bang hard like I'm experiencing ? They are being exchanged anyway, as part of this spring fix ... if that's the case.

[bgreywolf]

I would definitely start by checking out the bushings in both front and rear. I've had front end jostling "feel" like rear end wandering on rough roads. I would do this before any hard parts, even if replacing worn out items. No shocks or springs can fix bad bushings, loose/broken bolts, worn ball joints...

I've had mixed results with the KYBs on daily drivers. I didn't care for the KYB/Cargo Coil combo on my '86, but it was more of a float through cornering and an unsettled feeling after rough road patches (of which there are many in back woods Maine). Part of the problem was front and rear control arm bushings and some wear in the steering idler arm. Some of the problem was fixed (to my personal preference) with Bilstein shocks and heavier (non-progressive) springs. I'm still looking for a rear sway bar so I definitely don't consider all of the handling sorted out yet.

I'm an aggressive driver with an older Panther, so while the standard YMMV applies, the control arm and sway bar bushings would still be the first place to look.

[OzBloke]

Oh I'm getting the bushings done first thing. We'll look at the ball joints when it's up in the air. I am broker than the roads around here so I'm going to have to live with the KYB's as they are virtually brand new. If it were my choice I'd have fitted Bilsteins. The ride is very harsh at the rear and the back axle wants to STEP OUT BIG TIME on broken tarmac mid corner. That seems to tell me those "conversion coils" (the progressive rate conversion springs that usually come with air ride conversion kits) ... sometimes referred to as "cargo coils" (I believe they are one and the same) are just simply too hard. The car is very flat so body roll is NOT an issue ... as it does have HPP bars front and rear in addition to HPP front coils. It doesn't wander on roads it just wants to step out at the back on rough or badly bumpy stretches, and if that is in the middle of a corner, then it REALLY wants to step out. Plus the ride is harsh. Like, jarring.

I have the advice of another guy who went through all of this taming an air-ride equipped car that had been converted to coils and his experience was exactly as I am theorizing here with mine. He went with option 1 and 2 (from my post) on his vehicle, and liked them both ... but he liked option 1 a little better because he preferred the softer ride while still having good control over the "slightly more control but firmer ride" of option number 2.

I guess I know what all my options are in the cheap and easy circumstances I am forced to pursue and I'm really just looking for the knowledge of those who have gone to the same place as I am headed to confirm I'm on the right track, given my fiscal abilities right now are close to non existent.

[sly]

Shocks make a big difference. If you got stiff shocks, ride will be harsh. I know this first hand from putting the F150 4" drop shocks on the back of the 88 MGM I had. Much smoother ride with the civi shocks and even the KYB Gas-a-justs were smoother than the truck shocks. But with the trunk full of 200-300 pounds of whatever, it rode great.

[OzBloke]

I have KYB Gas-a-justs on all 4 corners.
28.5 mm front sway bay and 540 lb. springs (P71 CVPI is 29.5 mm and 600 lb springs)
21 mm rear sway bar and "god awful" 180+ lb. cargo springs (P71 CVPI is 17 mm and 160 lb. springs)

I have decided after 2 days of learning more about spring load rates and check-in load height and check-in load value than I thought I'd know in an entire lifetime, and how much it costs to have that duplicated if the spec's you want are not available "over the counter" .... that I will just go and pick up the 130 lb. rear coils out of as low a mileage P74 base model as I can find in a salvage yard. If I can't find those I'll just use a pair of P71 CVPI 160 lb. coils and if the 21 mm rear sway bar proves too stiff with those on, go and grab a 17 mm P71 CVPI rear sway bar.

I really think I'll get the most neutral handling out of 130 lb. rear springs matched to my HPP 21 mm rear sway bar, and a decent ride as well. Interestingly I spoke to one custom spring builder with binders full of data for about 2 hours ... who told me that while the original air-ride springs don't use the same rating as static coils do (because they are dynamic not static) ... if you wanted to gauge an "average" value to compare an unloaded air-ride HPP to a static coil car ... you'd probably get a value of about 140 lb. Ideally, that's what I'd want. Being almost bankrupt from my year long dance with cancer, that's not an option. So I'll make do by other means.

[IPreferDIY]

Something simple you can do as part of your diagnostics with the car parked is try giving the ass end a big push sideways. If your car starts shaking its booty, then there's a bushing issue. The original Watts link and rear control arms/trailing arms have rubber bushings, and they don't last forever. What's your mileage at? If you're well past 100,000 miles, you probably need to replace them.

BTW, the 28.5mm bar is essentially equivalent to the 29.5mm bar, since the size increase compensates for the different shape.

[OzBloke]

It seems pretty solid on a push test, I actually did that when I came home last night before I posted here. Weird huh ? My mileage is just on 85,000 miles. Of course, it's also 18 years old.

[IPreferDIY]

Congrats for your successful cancer dance BTW. Maybe one way to put the car on the back burner for now would be to drive like a geezer until your health and finances improve.

[sly]

junk yard rear springs from a civi model would probably fit the bill as well and save on $$. Even with all my suspension changes on the old 88, there's a few asphalt clover style highway crossovers in town that have severe asphalt migration bumps. Softer (civi - original) spring and performance shocks seemed to hold it the best. The cargo coils and truck shocks would take speed bumps at speed the best though. I think you're definitely on the right track thinking that HPP springs would help with the rear skipping issue.

+1 on drive like an old fart for a while and save up. Bushings should be good enough for a few more years that way.

[OzBloke]

Current plan is drive like a 90 year old in fast corners while I replace the entire bushing set, front and rear. That might include some hardware like tie rod ends and idler arm, maybe even ball joints. I'm still debating with myself the better directional stability of poly over the nicer ride of elastomer bushes. It's pretty damn flat in the corners thanks to the KYB HD shocks and large sway bars. When that's all done we'll see if it's step out behavior has been tamed somewhat before I start into spring replacement and tuning. I like my current ride height and don't want to do any more than I have to, for obvious reasons.

I think poly, while tighter handling .. also lasts longer than rubber bushes ? I might mix it up little and use rubber on bushes that insulate vertical shocks (like shock absorber bushes for example, and sway bar frame mount bushes) and use poly for the torsional (twisting) isolation, like sway bar end links and also for the steering links (idler arm, tie rod ends) that you want to be nice and precise.

[Mainemantom]

I am sorry to hear about your journey with cancer. Hopefully it is gone for good. I do not know how people get through cancer and the financial devastation it causes for those without great insurance. I am a survivor as of today. Working on cars is mostly done forever.
You are blessed that you can work on your cars !! I am sure you get tired fast though. I wish you the best. This site has many good people who have plenty of knowledge to help you. Include pictures when you can.

[OzBloke]

I'm not currently doing a lot of the actual physical work on it because I'm still pretty screwed up from the treatment I received over the past 12 months. I will get there slowly however.

My old CVPI (2004) P71 that got wrecked by a friend while I was in hospital. It was a nice car. Some mods, very tidy.



The 2001 HPP P74 they bought me to replace it. 85,000 miles. Modified a little. Super nice car.

[IPreferDIY]

Is there any particular reason why going back to air springs isn't on the table? I can see why some people wouldn't bother, but I doubt you would find too many people saying the ride quality is inferior.

[OzBloke]

Cost and complexity. I'm still sick and I can't afford to take on anything bigger than it has to be. A previous owner threw away all the air-ride stuff, compressor, springs ... some of the lines. If it were as simple as just replacing air bags or compressor I probably would stick with the air-ride. Not an option for this cancer victim at this time.