GMC AT4 4" BDS Lift Issue

[TheElementalCashew]

*Disclaimer* - Yes, I know these sort of things happen when modifying vehicles, and I'm not complaining. 

 

I have a 2019 GMC AT4, and added the 4" BDS lift last year for a total of 6" of lift. After the initial install, I took the truck back to the installer to check all of the bolts for tightness, and mentioned to them that I was experiencing a front end clunk fairly regularly, especially at low speeds while turning. At the time they brushed it off as new suspension noises. 

 

Recently, the clunking has become more regular and is easily reproduced so I brought the truck back to the installer again for a more in-depth look. After some investigation they concluded that the CV axles are not fully seated in the differential anymore. I understand this is a fairly common problem with some lift kits, but I figured with the AT4 axles and a BDS lift touted for what it was, I should be ok. The installer said these new T1 axles do not allow for a spacer like older axles used to, so they have reached out to BDS for possible solutions. 

 

While we wait to hear back, I wanted to hear if anyone else with a BDS 4" or 6" lift has experienced anything similar and what, if any, were the solutions. I thought that if this was a common issue, I probably would have heard about it by now, especially with non-AT4 Sierras with different axles not designed for lift. 

 

The installer seems to think that at this point there are really two options going forward: BDS provides a solution or I have to get custom length RCV axles made. 

[topgear1224]

*Disclaimer* - Yes, I know these sort of things happen when modifying vehicles, and I'm not complaining. 
 
I have a 2019 GMC AT4, and added the 4" BDS lift last year for a total of 6" of lift. After the initial install, I took the truck back to the installer to check all of the bolts for tightness, and mentioned to them that I was experiencing a front end clunk fairly regularly, especially at low speeds while turning. At the time they brushed it off as new suspension noises. 
 
Recently, the clunking has become more regular and is easily reproduced so I brought the truck back to the installer again for a more in-depth look. After some investigation they concluded that the CV axles are not fully seated in the differential anymore. I understand this is a fairly common problem with some lift kits, but I figured with the AT4 axles and a BDS lift touted for what it was, I should be ok. The installer said these new T1 axles do not allow for a spacer like older axles used to, so they have reached out to BDS for possible solutions. 
 
While we wait to hear back, I wanted to hear if anyone else with a BDS 4" or 6" lift has experienced anything similar and what, if any, were the solutions. I thought that if this was a common issue, I probably would have heard about it by now, especially with non-AT4 Sierras with different axles not designed for lift. 
 
The installer seems to think that at this point there are really two options going forward: BDS provides a solution or I have to get custom length RCV axles made. 

What did BDS tell you? Did you install only their kit components? Or did you do UCA too?

What exactly does your installer mean that the CVs aren't fully seated in the axle?? If they're being pulled out of the axle it should be ripping a boot not pulling the CV end out. Is he sure he got them fully seated in the differential? There should be an internal snap ring that stops them from coming out easily.

I'm struggling to think of anything outside of an accident that would give a strong enough sudden EVEN outward jolt to the CV for it to hop over that snap ring. (Think slide hammer)

Is it possible that since that kit is designed for non at4 trucks that the kit favors the shorter non At4 axles. Where exactly is the clunk coming from is it because under certain conditions the CV is compressing and reaching the end of its travel so it's actually hitting internally?

I'm pretty sure if it was the opposite, actually being pulled out, there would be a ton of complaints about it especially form people with the shorter axles.

I wouldn't go custom axles it just makes it a massive pain in the butt if you ever have an issue.

Something smells fishy here.

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[TheElementalCashew]

What did BDS tell you? Did you install only their kit components? Or did you do UCA too?

What exactly does your installer mean that the CVs aren't fully seated in the axle?? If they're being pulled out of the axle it should be ripping a boot not pulling the CV end out. Is he sure he got them fully seated in the differential? There should be an internal snap ring that stops them from coming out easily.

I'm struggling to think of anything outside of an accident that would give a strong enough sudden EVEN outward jolt to the CV for it to hop over that snap ring. (Think slide hammer)

Is it possible that since that kit is designed for non at4 trucks that the kit favors the shorter non At4 axles. Where exactly is the clunk coming from is it because under certain conditions the CV is compressing and reaching the end of its travel so it's actually hitting internally?

I'm pretty sure if it was the opposite, actually being pulled out, there would be a ton of complaints about it especially form people with the shorter axles.

I wouldn't go custom axles it just makes it a massive pain in the butt if you ever have an issue.

Something smells fishy here.

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The installer has reached out to BDS, I haven’t heard back from them yet. All the suspension components installed are BDS. I’m using the stock Ranchos, not coilovers.

I may have been unclear in my terminology, but what they told me is that the splines of the axles are not fully seated in the differential itself. This is causing movement of the axles, especially when turning sharply from a stop or at low speeds.

This kit should be designed for the AT4, that is how it is marketed.

I really don’t want to do custom axles either. While I realize that every vehicle install is a bit different, this significant of an issue should not be occurring.

At this point I am not wary of the installer. They have been very upfront and have done lots of these installs. They are actually an official BDS installer too, which should hopefully make this process easier.

[Ryguy]

The CV boot would pop off or tear if the axle came loose. The sway bar and UCAs’s should prevent suspension from articulating enough to cause the axle from popping out. Have you checked if there’s any play in the axle? If you’re getting a clunk I would guess one of the suspension bolts is not fully tightened. The sway bar is a good place to check first, then just go down the line. If you have the tools I would check these things yourself, don’t rely on the shop. 

[topgear1224]

The installer has reached out to BDS, I haven’t heard back from them yet. All the suspension components installed are BDS. I’m using the stock Ranchos, not coilovers.

I may have been unclear in my terminology, but what they told me is that the splines of the axles are not fully seated in the differential itself. This is causing movement of the axles, especially when turning sharply from a stop or at low speeds.

This kit should be designed for the AT4, that is how it is marketed.

I really don’t want to do custom axles either. While I realize that every vehicle install is a bit different, this significant of an issue should not be occurring.

At this point I am not wary of the installer. They have been very upfront and have done lots of these installs. They are actually an official BDS installer too, which should hopefully make this process easier.

We know the at4 has slightly longer axes than the non At4 modles likely the kit splits the difference.


EDIT: forgot this is a bracket drop kit. Kit isn't the issue.

Either the installer messed it up, or you have become super sensitive from the clunking (unlikely to be the axle.) All CV move in and out in their snap ring grove. I wonder if he got the CV fully seated in the knuckle before tightening the axle but. If he didn't (or didn't torque to spec) that would make the axle compress leading to binding.

it is very unlikely unless you're purposely driving with the windows down and 5 mph that you would hear anything in the front differential area.

I also want to point out if he removed the shocks it's possible he over tightened the bushings which would lead to binding which would lead to sudden release his which would lead to a sensation of clunking or movement in the front end.

When your truck automatically starting with the start-stop system are you noticing any roughness? it's possible that the powertrain mounts themselves are allowing the movement which is resulting in the sound/feeling.


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[TheElementalCashew]

The CV boot would pop off or tear if the axle came loose. The sway bar and UCAs’s should prevent suspension from articulating enough to cause the axle from popping out. Have you checked if there’s any play in the axle? If you’re getting a clunk I would guess one of the suspension bolts is not fully tightened. The sway bar is a good place to check first, then just go down the line. If you have the tools I would check these things yourself, don’t rely on the shop. 

There is no obvious damage to the CV when looking underneath. It doesn’t really budge when I try and move it.

It is on my list of things to do to get the wheels off and go over everything, I had just been hoping the shop would have it taken care of. [emoji17]

[TheElementalCashew]

We know the at4 has slightly longer axes than the non At4 modles likely the kit splits the difference.


EDIT: forgot this is a bracket drop kit. Kit isn't the issue.

Either the installer messed it up, or you have become super sensitive from the clunking (unlikely to be the axle.) All CV move in and out in their snap ring grove. I wonder if he got the CV fully seated in the knuckle before tightening the axle but. If he didn't (or didn't torque to spec) that would make the axle compress leading to binding.

it is very unlikely unless you're purposely driving with the windows down and 5 mph that you would hear anything in the front differential area.

I also want to point out if he removed the shocks it's possible he over tightened the bushings which would lead to binding which would lead to sudden release his which would lead to a sensation of clunking or movement in the front end.

When your truck automatically starting with the start-stop system are you noticing any roughness? it's possible that the powertrain mounts themselves are allowing the movement which is resulting in the sound/feeling.


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I don’t think I’m sensitive to it. It is a loud, solid, metal on metal clunk that is audible with windows up and music playing. And it can be felt in the floorboard. It wasn’t this bad initially.

I will definitely be taking the wheels off and poking around myself here soon. I’d hope the shop is intelligent enough to have checked all these things already. I’m hoping they aren’t just trying to cover something up, but they’ve never given me reason to doubt.

I have the start/stop disabled. The powertrain feels as smooth as day one otherwise.

[TheElementalCashew]

I just went out and took a look, it actually looks really bad. First pic is driver side, second is passenger.

[Jav_eee]

I just went out and took a look, it actually looks really bad. First pic is driver side, second is passenger.

Well that proves that it came out.

Clips were supposed to hold it in according to an earlier post. Wonder if that’s true.


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[topgear1224]

The gap is normal looking at the kit installed though yours seams excessive. How did the installer not see that????

 

 

Wonder if he actually followed the instructions. Maybe he missed the spacer.

 

Screenshot is from this video from BDS

 

I personally would call BDS tech line... Shouldn't make A clunk if it's "floating". When I get hole I'll crawl under my stock truck to see how far it hangs out from factory

 

 

 

[ullose272]

Makes me womder if they never seated the axle after the lift install.

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[TheElementalCashew]

The gap is normal looking at the kit installed though yours seams excessive. How did the installer not see that????
 
 
Wonder if he actually followed the instructions. Maybe he missed the spacer.
 
Screenshot is from this video from BDS
 
I personally would call BDS tech line... Shouldn't make A clunk if it's "floating". When I get hole I'll crawl under my stock truck to see how far it hangs out from factory
 
 

 

If I don’t hear back from the installer in a reasonable time, I’ll probably reach out to BDS directly as well.

Here’s a shot of my part, looks like the spacer is in place.

[topgear1224]

If I don’t hear back from the installer in a reasonable time, I’ll probably reach out to BDS directly as well.

Here’s a shot of my part, looks like the spacer is in place.

when I get home I'll put the truck up on ramps and I'll start yanking at my CV axles I'll be able to tell if GM used a c-clip design or not it's been a long time since I've seen somebody not use a c clip design since you run the risk of during an accident it becoming a projectile but I suppose it's possible.

to be honest though I still don't see how that could cause a clunk..... maybe from the rust on the splines. But it's not like the exposed splines corroded away. it appears to just be surface rust so it should be able to slide in and out smoothly you shouldn't feel anything.

The only thing I could see is when you turn your putting a side load on the CV itself then if you were to say cycle the suspension while turned I could maybe see it binding and then releasing but I don't see how that would be as noticeable as you described. I'm still betting something was over torqued or under torqued.

To give you a visual of the situation I'm thinking of, it would be like if you turned full lock and then tried to climb up on a rock like a Jeep.

Regardless I'm sure you'll let us know what you find out.

I want more travel but don't want to trim anything I am looking at either GM's kit (shitty shocks though) or BDS 4 inch. I have a GMC so it appears 33" is a large as I can fully tuck up front. Icon had my eye but I don't like the level look as I tend to carry things in my bed. Fility Motorsports looks good too. I like the idea of rebuildable shocks. I REALLY like Fox's dual adjustment. So many choices!!

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[TheElementalCashew]

9 hours ago, topgear1224 said:

when I get home I'll put the truck up on ramps and I'll start yanking at my CV axles I'll be able to tell if GM used a c-clip design or not it's been a long time since I've seen somebody not use a c clip design since you run the risk of during an accident it becoming a projectile but I suppose it's possible.

to be honest though I still don't see how that could cause a clunk..... maybe from the rust on the splines. But it's not like the exposed splines corroded away. it appears to just be surface rust so it should be able to slide in and out smoothly you shouldn't feel anything.

The only thing I could see is when you turn your putting a side load on the CV itself then if you were to say cycle the suspension while turned I could maybe see it binding and then releasing but I don't see how that would be as noticeable as you described. I'm still betting something was over torqued or under torqued.

To give you a visual of the situation I'm thinking of, it would be like if you turned full lock and then tried to climb up on a rock like a Jeep.

Regardless I'm sure you'll let us know what you find out.

I want more travel but don't want to trim anything I am looking at either GM's kit (shitty shocks though) or BDS 4 inch. I have a GMC so it appears 33" is a large as I can fully tuck up front. Icon had my eye but I don't like the level look as I tend to carry things in my bed. Fility Motorsports looks good too. I like the idea of rebuildable shocks. I REALLY like Fox's dual adjustment. So many choices!!

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I'll be interested to hear what you find on yours. Mine don't seem to move much at all even yanking on them pretty hard, but I don't have great leverage without the wheel off. 

 

Looking at the pictures I also don't see a clunk happening with that axle. The axle splines would really have to be slamming hard, and the rusty area just doesn't look worn like it's been moving or rubbing. 

 

On the bright side, stock axles don't look too expensive, if they do end up being the problem. I'm going to see if I can get a video of it occurring here at some point. It is easily recreated. 

 

I think BDS also has a 2.5 inch coilover lift available now. You might be able to squeeze 33s with that, but it would probably be tight. I have 35s on my 4 inch lift and there was still a lot of trimming to be done. I think my truck looks perfect the way it is set up, but it truly is massive now. If I did it all over again, I'd probably go with the 2.5 inch and some smaller tires. 

 

Props to BDS though, when it isn't clunking, the truck drive so smoothly. Doesn't feel like there are 6 inches of lift and 35s for sure. 

[topgear1224]

I'll be interested to hear what you find on yours. Mine don't seem to move much at all even yanking on them pretty hard, but I don't have great leverage without the wheel off. 
 
Looking at the pictures I also don't see a clunk happening with that axle. The axle splines would really have to be slamming hard, and the rusty area just doesn't look worn like it's been moving or rubbing. 
 
On the bright side, stock axles don't look too expensive, if they do end up being the problem. I'm going to see if I can get a video of it occurring here at some point. It is easily recreated. 
 
I think BDS also has a 2.5 inch coilover lift available now. You might be able to squeeze 33s with that, but it would probably be tight. I have 35s on my 4 inch lift and there was still a lot of trimming to be done. I think my truck looks perfect the way it is set up, but it truly is massive now. If I did it all over again, I'd probably go with the 2.5 inch and some smaller tires. 
 
Props to BDS though, when it isn't clunking, the truck drive so smoothly. Doesn't feel like there are 6 inches of lift and 35s for sure. 

That's the thing I'm running into, stock size is 33 on my truck. It's a 275/60R20.

I'll have to do it today after work, I forgot that I had my freshly clayed crown Vic in the garage so I'll throw some wax on it this evening and then I'll pull the truck in.

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