Hi guys a fairly simple one here. I've noticed the back of my 87 trans am sagging pretty noticably. Its definetely time for new shocks, which I have. Would you bother with new springs as well? I don't think there is anything wrong with the springs, and I feel the sagging is the old shocks. I'd rather put the money into something else. I don't think springs really wear out do they? If you do think springs, is oem good enough or would I gain anything with aftermarket? Thanks guys!

 

It depends. If all you want to do is get rid of the sag, slap your new shocks in there. If you want some more handling, add springs as well.

Springs don't really "wear out". They will be springy until they rust apart. Now, springs will fatigue and not be as springy as they were new as they get more load cycles on them. If your new shocks don't solve the sag, throw in some new stock height MOOGS:

http://www.summitracing.com/search/D...?Ns=Rank%7cAsc

Theres two different choices there, a progressive & non progressive spring. They'd do just fine with aftermarket shocks.

 

to add to 89-RS, the springs can be worn out faster if they rear shocks are bad, since they will be moving a lot more without the shock controlling them.

New springs will not hurt, i would recommend them if the car is sagging. And springs are cheap

 

does your car sit lower in the rear? if so shocks alone will not help this.
when i hear the word sag, i think of ride height. if your springs are sagging there worn out. chances are you need both springs and shocks. aftermarket springs are just a little more money. imo i would go with eibach pro kit. now if your just interested in changing the rear, oem moog would be my choice.

 

I would change the springs. You're looking at $50-60. The new Moogs will increase your ride height back to stock. And most importantly, the rear springs fall out when you change rear shocks anyways. So there is essentially no extra labor charge to put them in.

Go for it. My rear end height went up 1" on the driver side and 0.5" on the passenger side when I traded my original springs for new Moog springs. That's how much the old springs had sagged over the years. The differences in height are due to the driver side having sagged more over time than the passenger side. (99% of the time, it's just me in the car)

 

While the Moogs (5662 and 5665) are supposed to be IROC replacement springs, the fronts lowered the nose of my car and the rears jacked it up to nose bleed height. I was forced to do some cutting in the rear. If I had the choice again, I might well purchase some lowering springs.

JamesC

 

Hey DM. Worn shocks will cause all kinds of trouble but really won't have anything to do with rear ride height. As mentioned above, new springs are in order.

Give us a call if you are planning to upgrade anything else on your car. Good luck!

Ramey

 

Thanks as always for setting me straight. I didn't realize springs were so cheap, and you're all right, common sense would dictate I replace the springs as well while I'm in there. Just 2 more questions.

I'm not at all interested in lowering my car, and will only be doing the rear shocks/springs at the moment due to limited funds. So I believe that means I need to go with 5665 moogs, probably the progressive ones, since I think I read ei-bach and others sell just the lowering springs. Is this correct?

Also, if a new spring gives the car the same ride height, I fail to see the performance benefit between springs. I get the difference between progressive and standard, and why a lowered car should handle better, but not the 'performance difference' a few of you spoke of between springs that give the same ride height....

 

Hey D-man.

Manufacturers can tune their spring height and rate to yield a stock ride height upon replacement even though the rates may be different brand-to-brand.

The performance difference happens when you change spring rates. Let's say you have a stock ride height and a 200 lb rate rear spring. Change that to a 250 lb rate rear spring and the car will be "looser" or oversteer more.

Hope this helps.

ramey

 

Ahhh right that makes perfect sense. Would you guys recommend a stiffer spring than the Moog 5665 or its progressive partner? I really don't want a lowering spring, the the eibach pro kit is tempting.... Its not a daily driver and I'd prefer performance over comfort on this one....I think

 

If budget is the driving factor, get the MOOGS. They will feel so much better than the saggy springs you have now. If performance is the driving factor, determine the spring rate, then find that spring or have it made.

 

Shocks have nothing to do with it sagging, it needs springs if it is sagging. Shocks don't support the weight of the vehicle, the springs do. I'm surprised no one above mentioned it, unless I skimmed over it. But as cheap as both components are you may as well just replace both while you are in there.

 

Hey D-man. Ride height has very little to do with spring rate from a performance standpoint. As you increase spring rate the manufacturer can adjust free height so ride height remains the same. If you autocross your car, or take an exit ramp too fast for that matter, it probably will slide the front tires before the rears. This is called understeer, or "pushing". With nothing else changed, you can go from a 200lb set of rear springs to a 250lb set of rear springs and the car will become "loose" or will oversteer. The car could look the same ride height-wise.

Spring rate is rated in lbs/inch deflection. A "200lb" spring will compress one inch if a 200lb guy stands on it. If the same guy stands on a 250lb spring it'll only move 0.8 inches (200 divided by 250).

To summarize, if you stiffen an end of the car, that end will slide. If your car is always loose you stiffen the front, either with spring or sway bar. If your car is always tight, you stiffen the rear.

have a good weekend

ramey

 

Holy god UMI-sales part of my brain just exploded there!!! Great explination, I totally get it. I'm going to try to find some balance for both the front and back ramey. I think my problem is I haven't had much experience (actually lets call it zero experience!) with changing springs on my TA. What my main focus is with the springs and any mod/improvement is to try to do it right the first time, without overspending based on my amateur driving habits. That being said, and after all the advice from everyone, I might just go with all around eibach pro kit springs. Unfortunately, it'll be an added cost to put them on the front where they don't seem to be needed, but I don't know if the 5665 moogs will 'match up' with these unknown springs that've been on there for god knows how long...maybe the originals...

Or maybe I'm just over thinking it since I'm not an auto cross guy...anyone want to venture a guess if the moog progressive springs will work for my ride height and normal driving habits?

 

They sure will. If all you need is new springs for daily driving, the moogs will do just fine.

 

I thought you had the CC635 springs in the back of your car? Do you remember what the height was before you changed springs?


DufussMan, I wouldn't worry too much about spring choices. The overwhelming performance improvement will come from struts/shocks. However, if you're going to replace the rear springs, you might as well do rear shocks at the same time.

Moog 5665 (linear)
Moog cc635 (progressive)

Those are the stock replacement rear spring choices. Stock height (for the most part, some members have differing results) Both are in the 105 lb/inch range area. That sounds like not much. But there really isn't much weight in the back of the car. Of the two, I'd recommend the 5665 since it's a tiny bit more performance oriented due to it's linear rate. And members here seem to have higher ride heights with the cc635 than they do with the 5665.

Now if funds are limited and you don't want to lower the car, I see no point in going with Eibach Pro Kit springs ($250) and then going cheap on rear shocks ($50)......I did it the other way around. Went for the Koni yellow rear shocks ($250) and Moog 5665 springs ($50). That way I got the massive performance increase from the high quality shocks while still retaining a nice ride due to not having lowering springs.

The (rear) Pro Kit springs are listed as 109-177 lb/in progressive, 1 inch lower. This is going to be a rougher ride than the 5665 with their 107 lb/in linear spring rate. The Pro Kits need to have a higher lb/in figure in order to keep them from hitting the bump stops on a pothole. The Moogs are already an inch taller, so they're less likely to hit the bump stops. (When you hit the bump stops, that's what gives you that jarring hit when you go over a bump)

Don't worry about oversteer and understeer for now. ANYthing you put on the car at the moment will improve handling in all situations. The people with 1000 lb front springs and 250 lb rear springs get into tinkering with their suspension and getting the over or understeer balance just right. But for people like you and me. We just want something better.

As far as matching the front and rear springs. If the Moog rear springs raise it up a bit too much for you, it will just give your car a slight raked look. For what it's worth, my car with Moog 5665 rear springs is 28.5" tall from ground through the center of the wheel to the fender lip. Pro Kit should be aprox 27.5". If you measure what you currently have, you'll get a rough idea of what your results will be. Just keep in mind that these numbers are different for everybody. A Pro Kit might be 27.0" for somebody else while the Moog 5665 could be 28.8" for somebody else.

The 1" lowering spring advertising is for the most part accurate, but not precise.

 

No, I've always had the 5665's. I don't recall what the ride height was before, but afterward, 28.5 is about right. My dislike was such that I cut (and used radiator hose for the insulator) until I was down to approx. 27.5.

JamesC

 

89 rs thanks man really appreciate the help as I'm ordering these soon. I'm going with the moog 5665

Reid Best post yet. I was just out measuring and I think the moogs will work great for my needs. Believe it or not, I think my current rear springs are stock, with 104,000. Anything will be an improvement. Got an aluminum driveshaft and control arms and new shocks going in at the same time too. I'm pretty excitied. Thanks bud!

Think we should close this thread out, no point in rambling on. I learned a lot, and its insightful to a searcher. Thanks a bunch guys

 

Don't close it out yet because I would like a update as to how things worked out for you. Id like to do the same with my DD, the 5665s and KYB-Gas-a-Just shocks rear leaving the front springs for now but changing the front struts to KYB-GR2s.Just waning to restore to basically stock fronts with a slight up grade for the rear.

 

This thread makes me want to totally re-vamp the suspension on my GTA. Probably lower it and put some performance shocks on it. It's lowered about an inch now but there's still that stupid gap between the wheel and the fenders. I bought it with Monroe shocks on them. Any opinion on them?

 

i installed monroes in the rear about 50,000km ago and were useless within 40,000km. The only time i would use them again if they were almost free and i were selling the car.

now running everything moog, pro-kit, koni yellow.

theres lots of good quality shocks out there, dont cheap out on shocks.

 

Question ??? Are Koni yellows just for corner handling ? How will they perform for the occasional rip down the 1/4 mile ?

 

Koni yellows start with higher initial valving as per their website, as compared to the reds which are a high performance stock replacement. They will work fine for the occasional drag race but of course don't offer the specific features found in a drag shock.