Factory Spring Part Numbers & Associated Lift

[Trail X]

Based upon the below comparison, the BDS bushings appear much larger. That must be the cause of the difference between us in thickness of washer spacers.

Rough Country


BDS

[The Roadie]

But adding z71 springs to the rear will raise rear back up higher then front. Which after reading alot of the build threads is the way alot of people go.

I think I first explained my reasoning on the OS years ago. I used to get hung up on rocks on my frame rails a lot, due to the trails I was currently obsessed with getting up. And with my (then current) Silent Armor AT tires and previous to me being a convert to the airing down religion, traction was always limited. If you're higher in the back, rocks tend to get unwedged as you travel forward. It was purely functional. Appearance wasn't ever a factor. I use Z71, BDS spacers AND Airlift1000 bags in the rear now. Soon as I get my Icons back on, it will be time to do the C25 rear springs and choose new bags.

[Flying Monkey]

Thanks Roadie. Ok well to start then with marks lift and spacers ill be adding probably 87 springs to the front, if i can swing it at same time ill pick up Z71 springs and shocks for rear. if I have to wait a couple weeks for the z71 gear i should be ok running on stock for a short time. When I ran the numbers in the complete lift info thread on gm parts shop for the z71 springs it listed them as fronts...is that correct for the rear of our TB's?

[Trail X]

15234633 is what we've always told people. Buy them on ebay though.

[Flying Monkey]

15234633 is what we've always told people. Buy them on ebay though.

I always forget to check there for some reason. Found some that are new pretty cheap and found the z71 shocks at a good price too. Thanks.

[Gordinho80]

Z71 shocks are not worth it.... you'd be better off putting that money toward a BDS or Bilstein shock for the rear.

[NC_IslandRunner]

Looking to upgrade to 87's,

I have 7CC - 81's
6CD -???
Anyone have a CD RPO code too, I couldn't find anyone on this thread.
And yes I checked it three times it is CD and not CB.

Won't matter after I get the 87's

[Trail X]

6CD is actually associated with 15125884.

And for 2004, it appears 7CC is associated with 15125883.

So, hm... the RPO association might be more complex than I originally thought. Urg.

[Flying Monkey]

6CD is actually associated with 15125884.

And for 2004, it appears 7CC is associated with 15125883.

So, hm... the RPO association might be more complex than I originally thought. Urg.

So I may not have different springs after all since mine is a 2004 also.

[Nakashige]

Anyone know what springs are 6SJ and 7SJ

[Coloradolawdobe]

Hey, yeah mine are 6SJ and 7SJ too. It looks like they are 83 from what I found from another person on here that has 7SJ. However, a re-confirm would be great!

[Trail X]

Hey, yeah mine are 6SJ and 7SJ too. It looks like they are 83 from what I found from another person on here that has 7SJ. However, a re-confirm would be great!

Confirmed.

[Bay Wolf]

15234633 is what we've always told people. Buy them on ebay though.

25978750 is on sale for 8 more hrs for $45.04 ($13.74/pair + $31.30 S+H).

[RICHIET]

Lot of good information here. I have a couple of questions though. I have a 05' EXT which I'm sure will skewer the numbers some. I'm planning on lifting it, either BDS or Marks, and changing the shocks so I want to look into changing springs at the same time. According to my RPO, I have 85's up front. 88's should give .8" of lift and the 89's 1" though I figure with the EXT the numbers will be less. My concern is that since this is my daily driver and trip car, I am concerned about the ride. I hear complaints about how stiff the 89's are, mostly from SWB, and was wondering if the extra weight and length of the EXT would smooth it out some or should I drop to the 88's and forfeit the .2" difference in height.The only weight increase I'm planning for now is a brush bar and skid plates on the front. A little stiffer than stock is worth it but too much bounce for 6-700 miles could be torture ( especially coming from the passenger seat.) Same question for the rear. Z71's seem to be the choice though there is still the complaint about the stiff ride. Will the EXT help smooth the ride out enough as well as reduce the 1.5" lift and how do they compare with the stock EXT springs. I looked for the RPO's for the rear and I think 8NH and 9NF are for the rear, I couldn't find any reference to these in the threads and when I went to compnines site I found the site no longer exist. Any info on the rear would be appreciated. One final thought. With 120K+ miles I'm sure there is a bit of sag in the springs. What's the easiest way to figure the sag? I thought that since the clearance for the EXT is 8.1" I could measure the difference. I assume they measure from the diffs but if this is wrong could you tell be where to measure. Thanks.

[djthumper]

I would honestly have to say to do your lift and see how the ride is with what you have if you are really concerned about the ride because the pre-load on the springs will give you a slightly stiffer ride. As for the Z71 springs... Do you haul a lot of weight or a trailer much? If not several people do not like the stiff ride.

[navigator]

I have the Z71 springs in the rear on a SWB LS and I can tell it is a little firmer but not rough at all. It is hard to explain, I think it has less body roll is the biggest thing I notice if that makes any sense. More solid might be a better description.

Even on forest roads moving pretty fast they aren't rough at all.
My wife doesn't complain about them but she is usually easy to please.

As far as the 88's go, I don't think you can find those any more.

I guess Thumper has a great idea, lift it first and see how you like it and decide if you need more lift. The only downside to that is when you are adding the lift you already have the springs compressed, I can see the value in going ahead and getting the 89s installed at the same time.

[The Roadie]

... I assume they measure from the diffs but if this is wrong could you tell be where to measure. Thanks.

Ground clearance numbers from the factory are under the lowest part of the diff. Only thing that can raise that number up is larger tires. It's also the reason that when you're rock crawling over lumpy trails, you try to never take a tall rock down the centerline where it will hit the diff or the driveshaft. Try to take it under a frame rail, using the rail as a skid, or even better, put a tire on the tallest obstacle you can drive over. That will automatically raise the diff out of harm's way.

To measure the effectiveness of suspension or body lift, we usually measure from the ground to the top of the wheel well fender opening, through the center of the tire vertically. So if you see measurements in people's build or tire threads of 37, 38, 39", that's not tire diameter, but the wheel well opening.

[RICHIET]

I realize that questions about the ride are very subjective so I figure I'm looking more for opinions than hard facts. I know most of the comments about stiff rides with the 89's or the z71's are on the SWB TB's.I guess I'm trying to find out if the extra weight and length on my EXT would noticeably dampen the stiff ride or if that's immaterial. I do realize the ride will stiffen somewhat. I'm not really looking for much lift from the springs, leaving that to the lift and possibly spacers for now. I'm looking at the springs now for the reason Navigator said, everything's off now, do it all at once. Free weekends are at a premium. Roadie, yeah, stupid question about the`diffs, too many 12 hour shifts. What I was looking for is a way to measure how much sag at rest my springs have compared to when new. I did see in a lot of the threads about measuring before and after a lift thru the hub centerline to the top of the wheelwell fender but this would show the total gain in lift, not really what I was looking for. I will take pictures. As for not lining up the centerline with a rock, I'm new to Trailblazers, but I've had my share of K5's,S10's, and S15's going back to the 70's(including more than my fair share of where the heck did that rock come from???) Today it's careful, slow and easy.

[Trail X]

You'll probably be fine with 89s. If they top out, you can always cut a bit off the end of the spring.

[RICHIET]

Thanks James. I could also get a bumper like yours which looks like it would dampen the springs some. I will say, I went thru most of the build threads and your basic setup seems to be the closest to what I'm looking for. I need a daily driver that I also want reasonably trailworthy.