I put ZR2 shocks on my Yukon - need advice

[stab6902]

@stab6902, I am curious about your first comment, about the lowering arms not helping the suspension compress… if the lower arm was 2” more level would it not be easier to compress the shock vs if they are at a steep angle like now?

Also I’m wondering if the lowering lower control arms move the lower shock mount position further towards the wheel/tire, which if it did I would imagine that would also help with having more leverage to compress the shock, no?

The angle of the arm doesn't really affect the wheel rate (aka stiffness) of the suspension - it's all about the motion ratio. See figure below. All of the lowering control arms I'm aware of maintain the same motion ratio as stock so the truck rides the same before and after being lowered.

To make your suspension "softer," you'd want to move the lower shock mount closer to your lower control arm bushings (reducing d1 according to the Suspension Worksheet). A little bit goes a long way, since you square [d1/d2]. This would give your tire more leverage on the coilover assembly.

I don't have any parts in front of me, so I had to guess based on pictures, but it appears as though the motion ratios for the K2XX and T1XX trucks are pretty similar. Therefore, it's kind of surprising to me that you find the shocks to be super stiff. If anyone could share actual measurements, we could be a lot more accurate.

If you're dedicated to making this work, it looks like you could buy some lowering control arms and drill some new lower mounting holes closer to the bushings (last figure). You'd need some precise lower control arm measurements, spring rates, and corner weights to guess how much to move the holes, but moving them as far towards the bushings as practical would probably be an OK starting point. You'd also have to be sure not to reduce the strength of the arms in doing this... welding in reinforcements where you remove material (if necessary) would be advisable.

 

[Favored]

@stab6902, think there is enough “meat on the bone” to move the mounting position far back enough? There’s probably a smaller mfg of control arms that would consider making a custom set.. wish I had a shop and a welder and I’d do it myself, wouldn’t be hard.

 

[Favored]

I’m also not sure how well moving the lower mount further inwards would work and here is why. The angle of the shock on the ZR2 is equal or more than the Yukon I think, I had to already force it to the current mounting position further inwards that what it seemed like it wanted to be. If I used maybe a 1-2” drop arm it may be a little less but at some point I’d start being concerned about forcing the shock to bend slightly inward. Although maybe you could make a spacer for the upper mount to correct the angle.

Not sure it’s all worth it to me though and I don’t have the place or tools for all this. I may just buy the Fox 2.0’s front and rear and post these ZR2’s.

 

[stab6902]

@stab6902, think there is enough “meat on the bone” to move the mounting position far back enough? There’s probably a smaller mfg of control arms that would consider making a custom set.. wish I had a shop and a welder and I’d do it myself, wouldn’t be hard.

Honestly I'd just be guessing if you had room to go back far enough having not seen firsthand or ridden in your truck. You'd need steel arms as a starting point for modification anyway, so you wouldn't have much to lose in that regard. Take it a step at a time... try drilling holes as far back as possible and see how it drives. If it's still too stiff, you can use the steel arms as a base to modify. You wouldn't really be able to modify the stock cast aluminum arms.

Are the external shock reservoirs too big to mount the crossbar underneath the arm, like this? https://www.tahoeyukonforum.com/threads/front-strut-“flip”-as-a-lowering-option.139425/ ?

If you could get away with doing that, at least temporarily to get your driveshaft angles etc in the ballpark, you could put some more miles on the truck to get a feel for how much of a change you need.

 

[stab6902]

I’m also not sure how well moving the lower mount further inwards would work and here is why. The angle of the shock on the ZR2 is equal or more than the Yukon I think, I had to already force it to the current mounting position further inwards that what it seemed like it wanted to be. If I used maybe a 1-2” drop arm it may be a little less but at some point I’d start being concerned about forcing the shock to bend slightly inward. Although maybe you could make a spacer for the upper mount to correct the angle.

Not sure it’s all worth it to me though and I don’t have the place or tools for all this. I may just buy the Fox 2.0’s front and rear and post these ZR2’s.

Yeah that's a fair point. I have another idea I just posted, but apparently a moderator needs to approve before you can see it, probably because there's a link in the post.

Anyway, did you have to drill new holes in the upper strut mount, or did the ZR2s bolt right in?

 

[Favored]

Yeah that's a fair point. I have another idea I just posted, but apparently a moderator needs to approve before you can see it, probably because there's a link in the post.

Anyway, did you have to drill new holes in the upper strut mount, or did the ZR2s bolt right in?

I used a step drill to open up the holes, they are maybe about 1/4” off, no big deal.

I got the rears on tonight, I wanted to see if I could atleast use them and just have to buy Fox fronts. So the external reservoir is too big to use them for the side they are labeled for but if you swap LH to RH then they fit just fine. I had to compress them about 2” more vs what the stock one last were. I drove it down the driveway and into the street, which have sizable bumps, and oh wow, now I’m motivated to get the fronts to work too! The back felt really really nice.

Very interesting on the strut mount flip.. I went outside to check, it would be really really close and not sure it would clear… I may have to try it although that would be hours wasted if it didn’t work.. also the bolts are not final on the lower mounts, don’t worry.

 

[Favored]

I’m thinking about calling these guys up on Monday, maybe they would be open to drilling a couple more sets of mounting holes for different locations, or modifying a set for me, worth an ask imo. Right now the rear is at 38”, the front is at 42”, so if I’d get 3-4” drop arms that should be nice, however if the angle gets fixed and the suspension compresses then probably wouldn’t want to go with 4”… 3” may even be abit much then. @stab6902 if I get you the measurements of the ZR2 vs Yukon geometry can you do the calcs pretty accurately to determine where the holes would need to be or is it still a pretty wild guess at that point? The strut angle still concerns me though… not sure if stacking washers between the top of the strut bolts and the strut tower to create more or less angle would work..?

 

[stab6902]

I used a step drill to open up the holes, they are maybe about 1/4” off, no big deal.

I got the rears on tonight, I wanted to see if I could atleast use them and just have to buy Fox fronts. So the external reservoir is too big to use them for the side they are labeled for but if you swap LH to RH then they fit just fine. I had to compress them about 2” more vs what the stock one last were. I drove it down the driveway and into the street, which have sizable bumps, and oh wow, now I’m motivated to get the fronts to work too! The back felt really really nice.

Very interesting on the strut mount flip.. I went outside to check, it would be really really close and not sure it would clear… I may have to try it although that would be hours wasted if it didn’t work.. also the bolts are not final on the lower mounts, don’t worry.

Doesn't seem like the flip would be too much trouble, I guess you might have to loosen the top bolts too if you really had to muscle them in there. You just need to get the lower shock mount around and below the mount on the A-arm. Based on your description, mounting them below would also put the struts in a more natural angle, which would reduce seal friction and improve the ride.

 

[stab6902]

I’m thinking about calling these guys up on Monday, maybe they would be open to drilling a couple more sets of mounting holes for different locations, or modifying a set for me, worth an ask imo. Right now the rear is at 38”, the front is at 42”, so if I’d get 3-4” drop arms that should be nice, however if the angle gets fixed and the suspension compresses then probably wouldn’t want to go with 4”… 3” may even be abit much then. @stab6902 if I get you the measurements of the ZR2 vs Yukon geometry can you do the calcs pretty accurately to determine where the holes would need to be or is it still a pretty wild guess at that point? The strut angle still concerns me though… not sure if stacking washers between the top of the strut bolts and the strut tower to create more or less angle would work..?

Yes, I if I knew the spring rate of your original springs (assuming you want the same wheel rate as when your truck was stock), the spring rate of the ZR2 springs, and the exact dimensions of your lower control arm, I could do the math.

There are 10+ front spring options for different Yukons, so I'd need your suspension RPO code (something like 7B4, 6SU, 7RC...) to hopefully be able to look up your rate on rockauto. Same story on a ZR2.

 

[Oh Kee Pah]

@Silverado4x4, perhaps I should have been more clear, I’m not driving around like this currently.

I’m trying to get advice on what parts I need or what I should do to make this work.

I was expecting about 2” of compression on the shocks once they were loaded with the Yukon on the ground and I only got 1/2”. I feel like if I got the expected 2” it may have been fine.

Any opinions on installing 2”-3” drop lower control arms, thoughts on if that could remedy this?

I understand that you were able to get the shocks at a fair price, but my primary question is, "Why?"
What is your goal with this Yukon build?
The ZR2 shocks are Chevy's answer to off-road racing. They are certainly a stiff ride. They already netted you 2-3" ride height increase. Don't forget, you're not really changing the suspension travel distance at all just by installing new shocks. You're still riding on the OE magneride coil up front and rear. I imagine it rides much harsher than it did with the OE magneride setup and 2" front spacer.
If you're installing off-road shocks, then why would you want to lower the LCAs? That's already your lowest point of ground clearance to begin with; assuming you've already taken care of the front air dam.

Before you spend any more time and $, I would heavily consider what the overall goals of the modifications are. You could get a respectable leveling kit with brand name coil-overs and UCAs for perhaps cheaper and installed faster than you could/will spend getting the ZR2 shocks to work. And, IMO, the ZR2s will never ride "comfortably" on the Yukon unless you're doing 45+ mph on a gravel, bumpy road...