Left vs. Right Coil Springs

[DanD]

I have a question that's bugging me. It's not really important but I'm just curious. I put new rear Bilstein shocks on my 03 Trailblazer today. Since I was there I also replaced the rubber coil spring insulators on the top ends of the springs since they were getting old and crushed. Very easy job all around. Anyway, when I got the springs removed, I noticed that the left and right springs were different part numbers. One side is 15174231 while other side is 1517432. Both come up as coil spring part numbers online ( have been superceded though). I looked at both springs side by side and can see no difference. Why are there different numbers for left and right? I can tell you that the coil springs were replaced when the vehicle was fairly new. I took it in to the dealer because at certain engine speeds and conditions (like going up a small hill at 55 mph) there was a VERY loud resonance in the passenger compartment. There was a TSB about this problem caused by vibrations from the engine passing through the drivetrain up through the springs into the body. The remedy was to install redesigned coil springs. Afer they were replaced, this didn't happen any more. Anyway, back to the present...I reinstalled both springs on their original sides with the new insulators and everything went well. Just can't figure out what the difference is. Anyone know? Like I said, not important, just a curiosity. Looks like most aftermarket springs are just two of the same part number.

 

[Mounce]

All four springs are likely different.

I feel like I either read something about it or saw it when I defined my rpo codes that they put different springs in to compensate and make all four act the same. I think my rpo codes even told what spring was put where.

Can't remember for sure though.

 

[djthumper]

Each corner likely is different due to the sag to one side or the other. Each 360/370 had that done to keep them looking level and provide a smother ride for the soccer moms.

 

[kickass audio]

They are different to compensate for changes in height in all 4 wheels of the vehicle. It is GM's way to make the ride level on our platform. Nothing else.

 

[HARDTRAILZ]

They are different to compensate for changes in height in all 4 wheels of the vehicle. It is GM's way to make the ride level on our platform. Nothing else.

How is the height of the wheels different?

 

[kickass audio]

Sorry, that is a typo. I meant it as in the height of the vehicle being different at the 4 corners of the truck. For example, front left, front right, left rear, right rear. It is not the wheel that is causing the difference. sorry, that is my fault.

 

[HARDTRAILZ]

Makes sense. Thought I missed something.

I know they do it for fuel tank weight, different option packages, some say driver weight, and all kinds of variables.

 

[kickass audio]

I can't agree with the driver weight part though. Who is to say that the person buying the vehicle will be 100 pounds or 300 pounds? I honestly have no idea what differences there could be when my truck is assembled vs the next envoy of the same exact trim coming off the line where the springs would be different part numbers. The only thing I can think of would be maybe if during the casting process there is a slight variation in the size of the part, but if that was the case, I would think the part would be rejected as something like that where it can cause a difference in ride height has got to be way out of the tolerance specs.

Maybe it is something weird like when the frame gets welded together where the little ledges that the springs set inside of when installed are at a slightly different height and as a result the height of the truck varies. I really am not too sure the exact difference in one truck vs the next for the need in spring differences to compensate for it.

 

[HARDTRAILZ]

Driver weight is the one I don't get but some say that they figure "x" for average driver and figure that in w other variables to pick springs.

I think its more about we got a bunch of these springs: run them this week/day/shift.

 

[Sparky]

Probably more the options and left/right weight bias of the vehicle than anything.

 

[HARDTRAILZ]

Curious what options y'all think might affect left to right bias.

Fuel tanks for given year were same. Most other options would not be side specific that I am thinking of.

I know v8 vs i6 and swb vs lwb changes springs but dont see that as side to side.

 

[Wooluf1952]

I can see the side to side. Especially in those with the 22 or 25 gallon tank. My '03 only has an 18 gallon tank.

 

[HARDTRAILZ]

But the tanks were not options. They would be the same in all for a given model or year.

 

[Wooluf1952]

IIRC,there was bigger tank as an option in the later 2003 model. I ordered mine in July 2002 and the bigger tank wasn't available at that time.

 

[coolasice]

Look in the glove box at the rpo codes, any codes for
6##
7##
8##
9##

where ##= two letters is the code for the springs

6=Left Front
7=Right Front
8=Left Rear
9=Right Rear

mine is such:
Right Rear 15948009 9UY
Left Rear 15948010 8UZ
Left Front 15125883 6UT MAX LOAD 7576N/1703LBS
Right Front 15125883 7UT MAX LOAD 7576N/1703LBS

notice the left rear is always a number higher = stiffer spring. More then likely due to location of fuel tank.

 

[The_Roadie]

4WD option makes a large difference because the front differential is on the driver's side of the oil pan, and the front driveshaft and transfer case contribute to the asymmetry. EXT makes a difference because of overall weight, and the gas tank versus the rear HVAC system. For all I know the designers also made allowance for the fact that a SWB might only be driven by the driver, at some average weight, and the soccer-Mom EXT would often have kids. I'm very sure they didn't choose the springs based on slight fabrication differences in the spring perches or frames.

When offroaders replace our springs (I need to change them every 3-4 years due to sag) we never care about side to side variation. Just give us stiff.

 

[coolasice]

I dont know about differentials... i would think if that caused a problem they would have put different rate springs in the front left vs right. im gonna stick with my gas tank location theory. i bet anyone with a 2wd will also have different springs in the rear left to right.

 

[Sparky]

They do use different springs left vs right in the front on some trucks. We've seen that before.

 

[coolasice]

anyone care to take a gander at their rpo codes for springs?

edit mine were 6NT 7NT for the front. i mistyped that

 

[coolasice]

did a bit more digging, seems some trucks have different front springs but same rears and some have dofferent rears and same fronts like mine... saw a post somewhere that gm determined spring rate per wheel when on production line based on weight bias?

 

[Denali n DOO]

mine are 6FU and 7FU, and 8JN and 9JN, 6&7 front, 8&9 maybe rear bags

 

[DanD]

anyone care to take a gander at their rpo codes for springs?

edit mine were 6NT 7NT for the front. i mistyped that

Since I started this topic, here are codes for my Trailblazer. I had no idea they were so intricate with the springs. Figured they'd be like aftermarket springs. Two for the back and two for the front and call it good. They must have decided it was worth all of this effort!
[sharedmedia=gallery:images:1135]

 

[The_Roadie]

The insane design team for this platform used as many as 12 different springs for the computer to choose from on the assembly line. 12 for the front and another 12 for the rear. Aftermarket vendors offer 2 or 3 max choices. If I ever meet the suspension designer at a party I'll piss in his drink.

 

[BC backroader]

Interesting quirk in our design! I just checked mine, the fronts are the same, but the backs are different side to side. No matter, my Z71s are in a box waiting for installation soon.

 

[Bow_Tied]

mine are 6FU and 7FU, and 8JN and 9JN, 6&7 front, 8&9 maybe rear bags

X2 which makes sense since we have essentially the same model.

 

[coolasice]

Since I started this topic, here are codes for my Trailblazer. I had no idea they were so intricate with the springs. Figured they'd be like aftermarket springs. Two for the back and two for the front and call it good. They must have decided it was worth all of this effort!

Ha all 4 of yours are different... That's way weird

 

[Denali n DOO]

I wonder why so many 360's I see have passenger side rear sitting lower than driver side rear?

 

[EarlsTB]

Mine say 1 and 2